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ant, (family Formicidae), any of approximately 10,000 species of insects (order Hymenoptera) that are social in habit and live together in organized colonies. Ants occur worldwide but are especially common in hot climates. They range in size from about 2 to 25 mm (about 0.08 to 1 inch). Their colour is usually yellow, brown, red, or black. A few genera (e.g., Pheidole of North America) have a metallic lustre.

Typically, an ant has a large head and a slender, oval abdomen joined to the thorax, or midsection, by a small waist. In all ants there are either one or two finlike extensions running across the thin waist region. The antennae are always elbowed. There are two sets of jaws: the outer pair is used for carrying objects such as food and for digging, and the inner pair is used for chewing. Some species have a powerful sting at the tip of the abdomen.

There are generally three castes, or classes, within a colony: queens, males, and workers. Some species live in the nests of other species as parasites. In these species the parasite larvae are given food and nourishment by the host workers. Wheeleriella santschii is a parasite in the nests of Monomorium salomonis, the most common ant of northern Africa.

Most ants live in nests, which may be located in the ground or under a rock or built above ground and made of twigs, sand, or gravel. Carpenter ants ( Camponotus) are large black ants common in North America that live in old logs and timbers. Some species live in trees or in the hollow stems of weeds. Tailor, or weaver, ants, found in the tropics of Africa (e.g., Tetramorium), make nests of leaves and similar materials held together with silk secreted by the larvae. Dolichoderus, a genus of ants that are found worldwide, glues together bits of animal feces for its nest. The widely distributed pharaoh ant ( Monomarium pharaonis), a small yellowish insect, builds its nest either in houses, when found in cool climates, or outdoors, when it occurs in warm climates.

Army ants, of the subfamily Dorylinae, are nomadic and notorious for the destruction of plant and animal life in their path. The army ants of tropical America ( Eciton), for example, travel in columns, eating insects and other invertebrates along the way. Periodically, the colony rests for several days while the queen lays her eggs. As the colony travels, the growing larvae are carried along by the workers. Habits of the African driver ant ( Dorylus) are similar.

The red imported fire ant ( Solenopsis invicta), introduced into Alabama from South America, had spread throughout the southern United States by the mid-1970s. It inflicts a painful sting and is considered a pest because of the large soil mounds associated with its nests. In some areas the red imported fire ant has been displaced by the invasive tawny crazy ant (also called hairy crazy ant, Nylanderia fulva), a species known in South America that was first detected in the United States (in Texas) in 2002. The hairy crazy ant is extremely difficult to control and is considered to be a major pest and threat to native species and ecosystems.

The life cycle of the ant has four stages, including egg, larva, pupa, and adult, and spans a period of 8 to 10 weeks. The queen spends her life laying eggs. The workers are females and do the work of the colony, with larger individuals functioning as soldiers who defend the colony. At certain times of the year, many species produce winged males and queens that fly into the air, where they mate. The male dies soon afterward, and the fertilized queen establishes a new nest.

The food of ants consists of both plant and animal substances. Certain species, including those of the genus Formica, often eat the eggs and larvae of other ants or those of their own species. Some species eat the liquid secretions of plants. The honey ants (Camponotinae, Dolichoderinae) eat honeydew, a by-product of digestion secreted by certain aphids. The ant usually obtains the liquid by gently stroking the aphid's abdomen with its antennae. Some genera ( Leptothorax) eat the honeydew that has fallen onto the surface of a leaf. The so-called Argentine ant ( Iridomyrmex humilis) and the fire ant also eat honeydew. Harvester ants ( Messor, Pogonomyrmex) store grass, seeds, or berries in the nest, whereas ants of the genus Trachymyrmex of South America eat only fungi, which they cultivate in their nests. The Texas leafcutter ant ( Atta texana) is a pest that often strips the leaves from plants to provide nourishment for its fungus gardens.

The social behaviour of the ants, along with that of the honeybees, is the most complex in the insect world. Slave-making ants, of which there are many species, have a variety of methods for "enslaving" the ants of other species. The queen of Bothriomyrmex decapitans of Africa, for example, allows herself to be dragged by Tapinoma ants into their nest. She then bites off the head of the Tapinoma queen and begins laying her own eggs, which are cared for by the "enslaved" Tapinoma workers. Workers of the slave-making ant Protomognathus americanus raid nests of Temnothorax ants, stealing the latter's pupae. The pupae are raised by P. americanus to serve as slaves, and, because the Temnothorax pupae become imprinted on the chemical odour of the slave-making ants, the captive ants forage and routinely return to the slave-making ant nest.

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Ant, any of approximately 10,000 species of insects (order Hymenoptera) that are social in habit and live together in organized colonies.

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It is often challenging to recognize ants from a picture. Because different species may be treated differently, be sure an ant problem is correctly identified before attempting control.

Many ants enter homes from outside nests as they look for food. To find their nest, follow the ants. You can encourage foraging by setting out attractive food.

Ants usually take regular routes to and from their nest by making a chemical (pheromone) trail. The nest may be found by watching where the ants go. For some ants, such as carpenter ants, this works best at night, just after sunset. When the nest is found, it can be treated. In some cases, ants may need to be observed for 30 minutes or longer to locate a nest. Diligent observations can pay off as locating and treating the nest directly is often the most effective way of controlling ants.

Ants can also be a nuisance in lawns because of the mounds they produce, especially if they are abundant. Tolerate ant nests in lawns when possible.

Using insecticides

Outdoor nests can be very difficult to get rid of without applying an insecticide. Be sure to select a product that has directions for treating lawns.

Granules and dusts are most effective, these products contain active ingredients such as permethrin or deltamethrin.

Liquid insecticides can work if they are soaked into the nest. You may need 1/2 gallon or more of mixed material to treat large nests. Common examples of active ingredients include bifenthrin, cypermethrin, gamma cyhalothrin, and lambda cyhalothrin.

Retreatment of nest sites may be necessary if above-ground activity resumes after the initial application.

If the nest cannot be found, in some cases ants can be kept out of the house by applying an insecticide barrier around the exterior of the building.

If ants are entering only through one area of the house, you can spot-treat that area. If it is not clear where the ants are entering, then treat a 2- to 4-foot wide area around the entire building. This control method is temporary and is not a long term solution.

Insecticides used for treating the exterior of a building may be a liquid or granules. Common examples of available insecticides have active ingredients such as:

bifenthrin

cypermethrin

deltamethrin

gamma cyhalothrin

These methods are NOT effective to get rid of ants:

Flooding nests with water

Pouring gasoline in a nest (it is dangerous and causes environmental pollution)

Using spearmint gum, red pepper, orange peels, cinnamon, or other herbs

Lavender and other essential oils

Drenching a nest many times with an insecticidal soap solution is sometimes effective in forcing an ant colony to relocate.

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It is often challenging to recognize ants from a picture. Because different species may be treated differently, be sure an ant problem is correctly identified before attempting control. Many ants enter homes from outside nests as they look for food. To find their nest, follow the ants.

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The Respiratory System. 2010 : 11-28.

Andrew Davies, MA PhD DSc

Carl Moores, BA BSc MB ChB FRCA

Introduction

Just as each part of the respiratory system has its particular function, so each part has its particular pathologies. Respiratory structures are disrupted by disease, and the oft-repeated aphorism 'structure is related to function' is never more applicable than in the respiratory system in health and disease. Study of its structure considerably eases understanding of how the respiratory system works.

We will first describe the airways of the lung and then the tissues that surround them.

The upper airways

The neck is the part between the face and the trunk. The front part is of gristle and through it speech and respiration take place; it is known as the windpipe. Aristotle, Historia animolium. 4th century bc

The 'gristle' (cartilage) that Aristotle describes is important in preventing the collapse of the upper airways, which in turn is vital to lung function because although the gas exchange of respiration takes place deep within the lungs, those parts of the respiratory system outside the chest, which are referred to as the upper airways, allow and effect the process, and are of such clinical importance that they must be considered.

The structures of the upper airways are clearly seen in a paramedial sagittal section of the head and neck ( Fig. 2.1 ).

Mouth and nose - rhinitis, the common cold and obstructive sleep apnoea

It is unlikely that any of our readers have escaped the unpleasant obstruction to breathing associated with the common cold. The major discomfort of this condition is the result of an inflammation of the nose (rhinitis) and, if more severe, the paranasal sinuses. In about 50% of cases this rhinosinusitis is initially caused by rhinoviruses, 25% by corona viruses and the remainder by other viruses. A transient vasoconstriction of the mucous membrane (see below) is followed by vasodilatation, oedema and mucus production. With secondary bacterial infection the secretions become viscid, contain pus cells and bacteria, and contribute to the obstruction of breathing.

Rhinosinusitis may also be allergic in aetiology or idiopathic (i.e. intrinsic, of no external cause). Idiopathic rhinitis is thought to be a result of an imbalance of the activity of the sympathetic and parasympathetic nerves serving the mucosal blood vessels, and in this type of rhinitis anticholinergic medication often relieves symptoms.

Allergic rhinitis may be seasonal in response to allergens such as pollen, or perennial, where a major cause is the allergen Der pl in the faeces of the house-dust mite Dermatophagoides pteronyssinus.

The mite is just invisible to the unaided eye and lives on shed skin scales, particularly in human bedding. The allergen from this creature is also responsible for much asthma, but the rhinitis it provokes demonstrates the filtering action of the upper airways in trapping it in the nose.

Much more sinister and life-threatening than rhinitis is obstructive sleep apnoea (OSA; apnoea = absence of breathing). This should not be confused with central sleep apnoea, where the patient ceases to make respiratory efforts while they are sleeping. In OSA the patient's attempts to breathe are physically obstructed by anatomical and physiological peculiarities of the upper airways.

In Figure 2.1 the subject is breathing through his nose because the lips are closed and the tongue lies against the palate. When you breathe through the mouth - for example when you blow out a candle or suck through a straw - the soft palate is arched upward to form a seal against Passavant's ridge at the top of the pharynx. This form of airways obstruction is a normal function. Similarly, under normal circumstances, the genioglossus muscle of the tongue has a high resting tone in conscious subjects, and this holds the tongue forward, preventing it from obstructing the airway. During sleep, and particularly in those suffering from the dangerous condition of obstructive sleep apnoea, the tongue falls against the back wall of the pharynx and obstructs breathing. The muscle tone of the pharynx itself becomes reduced, particularly during REM (rapid eye movement) sleep and in OSA the pharynx collapses under the negative pressure of inspiration. Blocking of the airways by the tongue also and almost inevitably occurs during general anaesthesia and requires immediate attention from the anaesthetist.

Most, but not all, healthy persons breathe through the nose unless exercising. The resistance to breathing of the nose is about twice that of the mouth and nearly half the total resistance of the airways. The disadvantage of this is offset by the advantage obtained by the air-conditioning and filtering activities of the nose, which warm, moisten and filter the air before it comes in contact with the delicate respiratory regions of the lungs. Newborn babies have great difficulty breathing through their mouths: they are almost obligate nose breathers and become very distressed when their nose is blocked. Their predominantly nose breathing may be associated with their ability to suckle and breathe at the same time. On the other hand, many animal species, such as rabbits, manage to eat and breathe at the same time by having lateral food channels on either side of the larynx (see below) that bypass the airway. Marine mammals such as whales have completely separate air and food channels, with the airway ending at the back of the head.

In humans the nose extends from the nostrils (external nares) to the choanae (internal nares), which empty into the nasal part of the pharynx. Each nostril narrows to form its nasal valve, and at this level the total cross-sectional area of the airways is narrower (3 mm ²) than anywhere else in the system. This narrowing imposes the majority of the high resistance to airflow found in the nose (see Chapter 5) and, combined with the sharp turn the inspiratory air must make as it enters the wide (140 mm ²) lumen of the cavum of the nose, causes turbulence. The walls of the nasal cavum are rigid bone projecting out into the airway from the lateral walls as the turbinates. These have a large surface area (150 cm ²) covered by vascular mucosal erectile tissue important in the 'air-conditioning' activities of the nose. This mucosal tissue can swell considerably in conditions such as rhinitis (described above), and it is here that nasal decongestants such as oxymetazoline, an agonist of α adrenergic receptors on vascular smooth muscle, act to clear a blocked nose by causing the vascular smooth muscle to contract.

Case 2.1

Obstructive sleep apnoea

Mr Sinclair is 50 years old. He is rather overweight for his height: he is 168 cm tall but weighs 102 kg. He also drinks rather heavily and is a smoker.

For the past 2 years, Mrs Sinclair has slept in a different room from Mr Sinclair because of his very loud snoring and restlessness at night. Recently, Mr Sinclair has been feeling more and more tired during the day. For some time, he has been regularly falling asleep when he arrives home from work. Over the past month or so, he has found it increasingly difficult to concentrate at work and on one occasion recently, he was caught sleeping at his desk by his manager and he is facing disciplinary action. Mrs Sinclair eventually persuaded her husband to visit his doctor.

Mr Sinclair's doctor referred him to a specialist in sleep medicine. The doctor suggested that he may be suffering from obstructive sleep apnoea (OSA). He explained that during periods of deep sleep, Mr Sinclair's airway was becoming obstructed. During an episode of obstruction, Mr Sinclair's sleep becomes lighter until the obstruction is overcome. These episodes of obstruction and sleep interruption are responsible for Mr Sinclair's daytime sleepiness. The doctor went on to suggest that Mr Sinclair might be treated with a nasal continuous positive airway pressure device.

In this section we will consider:

1.

What causes obstructive sleep apnoea?

2.

What are the signs, symptoms and treatment of obstructive sleep apnoea?

Normal physiological swelling of the mucosa and consequent restriction of airflow takes place asymmetrically over a period of time, so that one nasal passage is more constricted than the other. Thus both nasal passages are not uniformly constricted, with the major constriction, and therefore airflow, alternating between nostrils over a period of hours. This oscillation of airflow may help to sustain the nose in its air-conditioning activities by allowing one channel to rest while the other carries out most of the work.

The major function of the upper airway is to air-condition the inspirate. It is not essential to breathe through the nose to do this, and the mouth will make a fairly good job of warming and humidifying inhaled air before it reaches the larynx. However, the mouth has not evolved for that purpose and the unpleasant consequences of using it are well known to anyone who has had to breathe through their mouth because a cold has obstructed their nasal airways.

The larynx - intubation of the airways

A common cause of accidental airway obstruction is the inhalation of food into the trachea. Normally, to prevent this during swallowing, the larynx, a box-like structure at the upper end of the trachea, is elevated (moved towards the head) by the muscles attached to it and the epiglottis folds backward, forming a very effective seal, like the 'trapdoor' over the entrance to the larynx. Because the 'trapdoor' can only open outwards, increased pressure in the pharynx makes the seal of the epiglottis on the larynx tighter and it can withstand considerable inward pressures of up to 100 kPa.

If this system of preventing solids entering the airways fails, powerful cough reflexes can be provoked by nerves in the lining of the larynx and trachea.

The larynx (see Fig. 2.1 ) is in fact a rather complicated box made up of plates of cartilage. It can be closed off by drawing together the two curtains of muscle which make up the vocal folds across the lumen of the larynx. Effective coughs depend on the closure and rapid opening of these 'curtains', which under less extreme circumstances are used to produce and modify the sounds that make up speech. The vocal folds can be drawn together so strongly that they are airtight against the greatest efforts to breathe the subject can make. This is clearly a 'bad thing' and can occur accidentally when an anaesthetist is trying to get an endotracheal tube into a patient's trachea. This dangerous closing of the larynx is called laryngospasm. A picture of what an anaesthetist would see when approaching the larynx is shown in Fig. 2.2 .

Bronchoscopy

It is frequently useful to inspect the airways below the larynx. First the trachea (part of which is extrathoracic), and then the intrathoracic airways. The instrument used for this is called a bronchoscope and may be of the rigid 'open tube' type through which the airways are inspected, or the flexible fibreoptic variety ( Fig. 2.3 ) which, as well as providing a view of the inside of the airways through its fibreoptic system, contains channels through which a variety of sampling and surgical instruments may be passed. Each type of bronchoscope has its advantages, but 95% of bronchoscopic procedures carried out these days are fibreoptic. Biopsy forceps, brushes and needles, balloon catheters and laser fibres can all now be passed through flexible bronchoscopes to carry out procedures after an initial inspection of even very small intrathoracic airways.

The intrathoracic airways

The trachea is a single tube leading from the extrathoracic environment of the neck, where it is anchored at one end at the larynx, into the intrathoracic environment containing the lungs. It is the first of the conducting airways of the lungs. The conducting airways, as their name implies, conduct air to the respiratory airways, where the exchange of gas that makes up respiration takes place. The structure of these conducting airways differs from that of the respiratory region, mainly in having cartilage and smooth muscle in their relatively thick walls. This cartilage is particularly prominent in the trachea, where it forms horseshoe-shaped incomplete rings, with the two free ends facing backward and closed with a layer of smooth muscle (trachealis) with the oesophagus lying against it.

The functional consequences of this increase are profound because it causes the velocity of the air to fall rapidly as it moves into the lung. This effect is discussed in more detail in Chapter 5. The dimensions of some of the airways that make up the bronchial tree are given in Table 2.1 .

Table 2.1

Generation

Name

Diameter (cm)

Total cross-section (cm²)

Cumulative volume (%)

Number

0

Trachea

1.80

2.5

1.7

1

10

Small bronchi

0.13

13.0

4.0

10 ³

14

Bronchioles

0.08

45.0

7.0

10 ⁴

18

Respiratory bronchioles

0.05

540.0

31.0

3 × 10 ⁵

24

Alveoli

0.04

8 × 10 ⁵

100.0

3 × 10 ⁸

As you go deeper into the lung the transitional and respiratory generations of the airways bear more and more alveoli until the alveolar sacs are totally made up of them. Alveoli do not look like the bunches of grapes or balloons stylistically represented in many textbooks, but rather pock-marked cavities with holes (pores of Kohn, K in Fig. 2.7C ) between many adjacent alveoli and with macrophages wandering over their surface ready to engulf and digest foreign particles (see Fig. 2.6 , Fig. 2.17 ).

It is a testament to the remarkable power of evolution that computer models which can analyse a branching system of tubes tell us that the branching angles and the changes in diameter of the airways of the human lungs are just right to cram the maximum alveolar surface into the minimum volume.

Histological structure of the airways

The microscopic structure of the wall of the airways changes as you go deeper into the lungs. Three 'snapshots' of airway wall structure are shown in Figure 2.7 but of course the structure changes gradually from generation to generation.

The conducting airways consist of three general layers which vary in proportion depending on airway type:

The inner mucosal surface consists of ciliated epithelium and underlying mucus-secreting goblet cells. The activity of the cilia and the secretions of the globlet cells make up the mucociliary escalator (see Air-conditioning, below), which is important in removing inhaled particles in the lungs.

Outside the mucosal layer comes a smooth muscle layer in which the fibres are in continuous bundles. This smooth muscle is found in decreasing amounts from the largest airways right down to the entrances to the alveoli.

The outermost layer is of connective tissue, which in the large bronchi contains supporting cartilage. As the airways penetrate the lung they first lose their cartilage support and smooth muscle occupies a greater percentage of the airway wall. Then the ciliated epithelium becomes the squamous type, finally forming the respiratory region of the lung.

Bronchitis and the Reid Index

The arrangement representing bronchial structure illustrated in Figure 2.7 and described above is modified in chronic bronchitis in a way that provides a histopathological quantitative diagnosis of the disease. The Reid Index provides a measure of proportion of bronchial glands to total wall thickness ( Fig. 2.8 ). In normal lungs mucous glands occupy less than 40% of total wall thickness. In chronic bronchitis this proportion is altered by hyperplasia of the glands. A characteristic of chronic bronchitis is an increase in the products of these glands.

The respiratory region

The respiratory regions of the lungs show a wonderful degree of adaptation. They carry out the functions of a respiratory surface while withstanding the assaults of a polluted atmosphere and the mechanical trauma of being stretched and then relaxed about 12 times a minute for the whole of your life as a result of the movements of breathing.

One of the characteristics of the respiratory surface of any animal is that it should be thin, offering minimal separation between the outside medium (air or water) and the blood. This is beautifully demonstrated in the lungs, which are the only place in our body where blood capillaries come into direct contact with the outside air, as a result of the fusion of the type I epithelial cells (which make up about 95% of the lining of the respiratory zone; Fig. 2.6 ) with the pulmonary capillary endothelium. This fusion results in an ultrathin layer ideal for the diffusion of gas but not much good for support. Evolution has resulted in this thinning occurring on only one side of the pulmonary capillaries, whereas the cells on the other side remain separate and more robust, supporting the capillary in its place ( Fig. 2.9 ).

The junctions between the endothelial cells of the capillaries are 'leaky' and allow an easy flux of water and solutes between the plasma and the interstitial space. The junctions between the epithelial cells, however, are sufficiently 'tight' to prevent the escape of large molecules such as albumen into the alveoli, which would result in pulmonary oedema. Macrophages can easily push their way through the epithelial junctions to carry out their scavenging activities on the air side of the alveolus.

The rounded type II cells, much less numerous than type I and found at the junctions of alveolar septa, are the stem cells from which type II epithelial cells are formed. They are also important in producing lung surfactant (see Chapter 3).

Blood vessels

The pulmonary circulation only offers one-sixth of the resistance to blood flow that the systemic circulation offers. It is therefore a low-pressure system and this is reflected in the thin walls of its arteries. These arteries follow the airways through the lungs in connective tissue sheaths. The pulmonary arterioles are also very different from systemic arterioles, having very little smooth muscle in their walls. This absence of smooth muscle in the arterioles, and of course the capillaries and venules, persuades many scientists to consider the microcirculation of the lungs as a whole, rather than making a special case of the capillaries, which snake along several alveolar walls, one after the other, before reaching the venules. Venules join to form veins which, unlike the arteries, do not travel with the airways but make their own way along the septa that separate the segments of the lung. The airways and pulmonary blood vessels down as far as the terminal bronchioles receive their nutrition from the bronchial circulation which, as part of the systemic circulation, is distinct from the pulmonary circulation of the lungs. Part of the bronchial circulation returns to the systemic venous system in the normal way, but part drains into the pulmonary veins, 'contaminating' their oxygenated blood with deoxygenated blood. This situation constitutes a ' shunt ' (see Chapter 7, p. 97Chapter 7p. 97).

Pulmonary hypertension

Hypertension (high blood pressure) can occur in the pulmonary circulation as well as in the systemic circulation. Pulmonary mean arterial pressure is normally about 15 mm Hg. This means that the limited smooth muscle in the pulmonary system is normally quite adequate to control flow. Pulmonary hypertension can arise for extrapulmonary reasons, such as mitral stenosis or left ventricular failure, both of which prevent the heart pumping away blood returning from the lungs. Congenital defects which allow blood to pass from the left (high-pressure) side of the heart to the pulmonary circulation also produce pulmonary hypertension.

By far the most common causes of pulmonary hypertension are changes in the pulmonary vessels themselves. They may be blocked by emboli, circulating fat, amniotic fluid or cancer cells. They may be obliterated by destruction of the architecture of the capillary beds by emphysema, or the smooth muscle in their walls may be provoked to contract by low oxygen tension, resulting from high altitude or diseases such as bronchitis and emphysema.

The clinical features of pulmonary hypertension are mainly the result of the increased pressure, producing oedema in the lung and imposing a pumping load on the right heart which it has not evolved to cope with. The patient complains of chest pain, dyspnoea and fatigue. Heart sounds are modified and the ECG demonstrates right ventricular hypertrophy.

The lymphatics

The perivascular spaces of the alveolar wall are drained by lymph vessels. The lymph system of the lungs begins as tiny blind-ended vessels just above the alveoli. These join to form lymphatics in close approximation to the blood vessels and airways. They are an important feature in the control of fluid balance in the lung and can contain considerable amounts of lymph, particularly during pulmonary oedema, when they produce the characteristic 'butterfly shadow' on the chest X-ray ( Fig. 2.10 ).

As in other tissue the lymph system plays a key role in immune defence in the lungs. These reactions are more the province of a textbook of immunology, but can be classified in outline as:

immediate hypersensitivity

antibody-dependent cytotoxicity

cell-mediated immune reactions.

Many immune disorders have the characteristics of asthma, whereas those causing interstitial lung disease are characterized by restrictive patterns (see Chapter 4).

The nerves

The sympathetic nervous system, which is anatomically represented, has yet to be proved to have functional importance. The NANC (non-adrenergic non-cholinergic) system, which runs in the vagus nerve, secretes a variety substances that contract and relax bronchial smooth muscle, depending on circumstances.

Afferent nerves from receptors near the alveoli (J receptors), in the smooth muscle of airways (stretch receptors), and free nerve endings between the epithelial cells of airways (rapidly adapting, irritant, receptors) conduct sensation and sensory reflex information from the lungs to the brain, where it influences patterns of breathing (see Chapter 11) and bronchomotor tone.

The pulmonary circulation is innervated by sympathetic and parasympathetic nerves, but unlike the situation in the airways the sympathetic supply is of greater functional importance than the parasympathetic, and even then it only appears to exert a significant effect under conditions requiring 'fight or flight'.

The limited importance of all these nervous systems is demonstrated by the success of transplanted lungs which are in fact denervated!

Gross structure of the respiratory system

As with other organs the general name for the functional tissue of the lungs is parenchyma. The vast majority of the volume of what we see as the lungs when the chest is opened is in fact alveolar tissue surrounding air spaces (see Table 2.1 ). These air spaces make the lungs so insubstantial and light that they are the only organ that floats when placed in water, hence the Middle English name for lungs: lights.

Each lung is anatomically divided into lobes, made up of segments which are subdivided into lobules ( Fig. 2.12 ).

The lungs lie on both sides of the mediastinum which contains the trachea, heart, major blood vessels, nerves and oesophagus. The trachea divides into the right and left main bronchi at the carina, which is close to the aortic arch and the division of the pulmonary artery into its left and right branches. The main bronchi, pulmonary arteries and veins penetrate each lung at the hila. The lobes of the lungs are covered, except at their 'roots' at the medial surface, by a thin layer of tissue called the visceral pleura. The mediastinum and chest wall are lined by the parietal pleura. It helps some students to visualize the arrangement of the pleurae by thinking of a plastic bag, full of lungs, inside a second plastic bag, the two bags being the visceral and parietal pleurae, respectively ( Fig. 2.13 ).

The pleurae secrete a few millilitres of viscous fluid which lubricates them as they rub against each other during breathing, this fluid constitutes a 'space' between the pleurae, but it is important to remember that this tiny space is fluid not air filled. Most animals have pleural space, although it is not essential for life. Elephants are said to lack one, and surgeons sometimes fix the lungs to the chest wall in patients with ruptured lungs, thereby obliterating the space.

Pleurisy

Inflammation of the pleura is called pleurisy and may be 'dry', where there is no appreciable effusion, or associated with an effusion, which may be of a variety of compositions. The pain of dry pleurisy is the result of the raw plurae moving over each other, and the patient complains of sharp localized pain associated with inspiration or coughing. Dry pleurisy occasionally accompanies pneumonia or carcinoma. Effusions of fluid into the pleural space result from a variety of conditions and can be of sufficient volume to collapse the lungs. If these effusions contain little protein they are known as transudates; if they contain much protein they are called exudates.

The diaphragm and chest wall

The walls of the thorax are made up of the ribcage ( Fig. 2.15 ), which consists of the sternum anteriorly, to which ribs 1-6 are joined at about 45° by the costal cartilages. At the spinal column the ribs articulate by costovertebral joints which may involve more than one vertebra. Ribs 7-10 are joined by costal cartilage to the ribs above, and ribs 11 and 12 are free-'floating' at their anterior end.

Case 2.1

Causes of OSA

In order for efficient gas flow to take place from the mouth to the alveoli, the airways that make up the respiratory system obviously need to be open and patent. The trachea and larger airways are held open by partial rings of cartilage within their walls. The smaller airways and the alveoli are held open by the tension in the lung tissue surrounding them. Above the larynx, the airway is held open by the actions of airway-dilating muscles, including genioglossus and palatopharyngeus. Were it not for the actions of these muscles, the upper airway would collapse, particularly in the supine position. During sleep, the tone in skeletal muscles throughout the body is reduced and this applies equally to the muscles which keep the upper airways patent. It is therefore normal for the upper airway to become narrowed during sleep.

In patients with OSA, the airway narrowing is more pronounced than normal and leads to periods of airway obstruction. There are a number of reasons why this happens, but obesity is the most important. It is thought that in obese patients, the pressure exerted by the fat in the neck tends to cause the airway to collapse. When the tone in the genioglossus and palatopharyngeus is reduced, as during sleep, airway obstruction may result.

The airway may remain obstructed for only a few seconds, or it may be well over a minute before the patient takes his next breath. During this time, the patient may become hypoxic and will begin to make vigorous efforts to try and breathe against the obstructed airway. Furthermore, he will become increasingly aroused from his sleep. Eventually, he regains the tone in his airway-dilating muscles and the airway obstruction is relieved. (Patients do not usually waken.) After the obstruction has been relieved, ventilation resumes and the patient's sleep deepens. This leads to a reduced tone in the airway-dilating muscles and the cycle starts to repeat itself.

Although obesity is probably the most important factor leading to OSA, there are other predisposing factors. These include anatomical variations predisposing to airway narrowing, such as enlarged tonsils, airway tumours and abnormalities of the mandible. Sedative drugs, including alcohol, may also predispose to sleep apnoea, probably by affecting sleep patterns and by reducing muscle tone. A small number of cases of OSA may be explained by abnormalities of neuromuscular function.

Between the ribs are the three layers of the intercostal muscles:

1.

External intercostals, running forward and downward

2.

Internal intercostals, at right-angles to the externals, therefore running downward and posteriorly

3.

Innermost intercostals, whose fibres run in the same direction as those of the internals.

These muscles are innervated by intercostal nerves from the anterior primary rami of spinal cord segments T1-T11.

Many muscles which do not have a primary role in respiration have their origins on the thorax. They move the head and neck and the upper limbs, for example. These muscles can be enlisted to aid breathing and are therefore called accessory muscles of respiration. The majority of these muscles aid inspiration, with only the flexors of the spine and the muscles of the anterior abdominal wall aiding expiration. Nevertheless, because of the mechanical advantage the accessory expiratory muscles have over the inspiratory muscles, we can blow out more powerfully than we can breathe in.

How breathing is brought about

Anyone who has sucked up fluid with a syringe has demonstrated how inspiration takes place. Before we go into the details of how the two processes are similar, we need to establish two very important facts:

1.

The lungs do not have muscles that contribute to breathing: the small amount of muscle they contain controls the diameter of the airways.

2.

Air will only flow from a region of high pressure to a region of low pressure. In inspiration the pressure in the elastic alveoli is made low by stretching them by reducing the pressure around them by expanding the chest. Air is thus sucked into the lungs. During expiration pressure in the lungs is increased by decreasing the size of the chest, thereby compressing the gas in the lungs.

The reduction in pressure around the lungs which brings about inspiration is mainly the result of activity in the phrenic nerves, causing the diaphragm to flatten and descend in the chest like a plunger in a syringe. This draws air into the chest. In quiet breathing inspiration is the only active part of breathing; expiration is largely passive and is the result of the elastic recoil of the lungs pulling them and the diaphragm back into their resting position - something like a balloon deflating when its neck is released.

The central tendon of the diaphragm moves 1-2 cm during breathing at rest, but can move up to about 10 cm during vigorous breathing. Movement of the diaphragm normally accounts for about 75% of the volume of breathing, but is not essential for life: if the diaphragm is paralysed, other respiratory muscles can take over to a large degree. In quiet breathing only some (and not always the same) diaphragmatic muscle fibres contract with each inspiration. This may explain why we rarely suffer from fatigue of the diaphragm.

If we liken the diaphragm to the plunger of a syringe, the ribs can be likened to its walls. The action of the intercostal muscles on the ribs (mainly the second to the tenth) can, however, alter the diameter of the chest and so actively draw air into and expel it from the lungs. This is largely because the ribs are set at an angle, sloping down from the horizontal, and are capable of being raised and lowered (see Fig. 2.14 ).

The external intercostal muscles cause two types of movement during inspiration:

1.

'Pump-handle' movements, in which the anterior end of each rib is elevated like the action of an old-fashioned water pump.

2.

'Bucket-handle' movements, in which the diameter of the chest increases, each rib on either side acting like the raising of the handle of a bucket from the horizontal position.

Both these types of action increase the diameter of the chest and thus draw air into the lungs by reducing the pressure in the chest. Not only do the external intercostal muscles help to bring about this reduction in pressure, but by stiffening the chest wall during inspiration they prevent a 'sucking-in' of the chest (just as you can suck in your cheeks) that would take place if they did not contract. The action of the intercostal muscles accounts for about 25% of maximum voluntary ventilation. The importance of the ribs and intercostal muscles to breathing is seen in patients whose ribs are broken and who exhibit what is known as 'flail chest' in which the chest wall moves in during inspiration and out during expiration.

Although expiration is largely passive during quiet breathing (resulting from the elastic recoil of the lungs-like a balloon collapsing) expiratory muscles can contract actively during high levels of breathing or if the airways are obstructed by disease. Under these conditions the abdominal muscles are the most important muscles of expiration. By squeezing the contents of the abdomen up against the diaphragm they force it up into the chest, thereby expelling air from the lungs. These abdominal muscles are especially active during a cough or a sneeze, as will be apparent if you press your fingers into your abdomen and cough. The internal and innermost intercostal muscles, like the external intercostals, occupy the spaces between the ribs and are innervated by segmental nerves. They pull the ribs down, reduce the diameter of the chest, and so contribute to expiration. Like the external intercostals, they reinforce the spaces between the ribs and prevent the chest from bulging out during expiration. The changes in size and shape of the chest brought about by the activity of the diaphragm, intercostals and accessory muscles are transmitted to the outer surface of the lungs. Because the lungs are so flexible, any change in pressure on their surface is rapidly transmitted to the air within the alveoli. This does not mean that the actual pressure in the fluid between the layers of pleura that form the covering of the lungs and the lining of the chest is the same as the pressure in the alveoli (see Chapter 5): in fact, it is important for the student to realize that they are very different.

Embryology

A knowledge of the embryological origins of anatomical structures is often of use in understanding their physiological function, and many clinical situations. For example, the phenomenon of referred pain can be explained on the basis of common embryological origins of structures. Development of the fetal and neonatal lung can explain many differences in the function of the immature and the adult lung.

Prematurity, particularly with birthweights less than 2500 g, can result in respiratory distress in the infant because of the immaturity of type II pneumocytes, which produce surfactant (pp. 18, 36). This respiratory distress syndrome, also called hyaline membrane disease, develops within minutes or hours of birth and is characterized by high breathing rates requiring great effort owing to the reduced compliance of the lungs. When premature delivery of an infant is threatened its ability to secrete surfactant is estimated by measuring the ratio of lecithin to sphingomyelin in its amniotic fluid. If necessary, the activity of the type II pneumocytes can be enhanced by the administration of corticosteroids, and after birth exogenous surfactant can be administered as an aerosol. Nevertheless, mortality can be as high as 40%, which demonstrates how, even in the full-term baby, the development of the respiratory system is only just sufficiently complete.

In the 4-week-old human embryo the beginnings of the respiratory system are first seen as an outpouching, the laryngotracheal bud, on the ventral surface of the endoderm of the digestive tract ( Fig. 2.16 ). As the bud elongates the proximal portion forms the trachea and the distal end bifurcates to form first the two main bronchi and then the more distal parts of the bronchial tree, eventually forming a limited number of alveoli. The whole of the epithelium lining the entire respiratory tract is therefore derived from endoderm. The cartilage, muscle and connective tissue which make up much of the structure of the lungs develop from embryonic mesoderm that becomes associated with the laryngotracheal bud.

The lung undergoes five overlapping phases of development:

microvascular maturation.

In the pseudoglandular phase, which lasts from the fifth to the 17th week, the lung resembles a primitive compound gland, with the airways down to terminal bronchioles becoming visible. From week 16 to week 26 is the canalicular stage, with the airway generations of the future respiratory regions being formed. At the same time the airways are pushing through the surrounding mesenchyme, picking up a sleeve of capillaries which forms a local network that grows with the airway. From week 25 to birth the future alveolar ducts and alveolar sacs are produced by growth and branching of the irregularly shaped saccules at the ends of the prospective respiratory bronchioles. Although alveolar formation has started as early as week 36 of gestation, at birth there are only 50 million alveoli present, compared with 300 million in the adult lung. Alveolization continues for about 2 years after birth. The maturation of the microvasculature of the lung parallels alveolization during the first 2 years of independent life. From then onwards, the lung compartments grow in proportion to each other and to body weight.

Air-conditioning

The characteristics of all respiratory surfaces do not lead to their physical robustness (thin walls, vascular, moist). Therefore, it is of evolutionary advantage to have the respiratory surface of the lungs protected from damage by the air, or anything in the air, that must be moved over them during respiration. Even under the most congenial conditions the air around us is cold and dry compared with the respiratory surface of the lungs.

Case 2.1

Signs and symptoms of OSA

Often, the first person to complain about a patient's OSA is his or her spouse! OSA is invariably associated with loud snoring as the airway becomes narrowed and this combined with the cycles of obstruction and arousal can lead to a very poor night's sleep for anyone in the same room as the patient. By the time a patient presents for treatment, their spouse has often resorted to sleeping alone.

The main symptom that the patient complains of is daytime drowsiness. Because their sleep patterns are so disrupted by cycles of apnoea and arousal, these patients are very tired and sleepy during the day. This somnolence may begin to impinge upon the patient's work and home life as their ability to concentrate for long periods of time begins to diminish. At worst, the patient may have a tendency to lose concentration or even fall asleep at the wheel of their car - motor accidents are more common in patients with OSA.

Other symptoms that the patient may complain of include morning headaches and night sweating and relatives may notice personality changes. For reasons that are not fully understood, patients often complain of having to get up to urinate during the night, sometimes on a few occasions.

Treatment is aimed at reducing the incidence of airway obstruction. The patient is advised to lose weight and to limit alcohol consumption, particularly before retiring to bed.

The most effective form of treatment, and the one tried by Mr Sinclair, is nasal continuous positive airway pressure (NCPAP). The patient wears the small mask strapped over his nose at night. The mask forms an airtight seal around the patient's nose. A continuous positive pressure, generated by a small pump, is applied to the mask. This pressure is transmitted to the upper airways and tends to prevent them from collapsing.

Other treatments are available - a surgical treatment of the condition that was at one time popular is the uvulopalatopharyngoplasty (UPPP). This operation involves removing the uvula and part of the soft palate. It has only a limited success rate and is associated with complications including fluid refluxing into the nose during drinking. It is therefore infrequently performed today.

Heat and water

Because temperature and water vapour gradients between mucosa and inspired air are greatest in the nose and upper airways, these regions carry a large portion of the air-conditioning burden. This burden is, however, shared with the lower airways. During nose breathing at rest air transit through the nose takes < 0.1 s. During that time temperature is raised (if in comfortable room air) from 20°C to 31°C by the time the air leaves the internal nares and to 35°C by the time it reaches the mid trachea. Humidification takes place equally rapidly, inspired air being close to saturation by the time it reaches the pharynx. Humidification of inspired air places a thermal demand on the body because of the high latent heat of vaporization of water. Five times as much heat is used to vaporize water to saturate inspired air than is used to warm that air. The air-conditioning process is a metabolic 'expense', and up to 40% of this cost is recovered from the expired air which warms and moistens the nasal mucosa as we breathe out. Desert animals such as camels and gerbils have highly developed turbinate systems in their noses which recover more heat and water than do ours.

This countercurrent exchange of heat and water in our nose is well demonstrated under cold conditions, when the mucosa of the nose is much colder than the exhaled air from deep in the lungs. Under these conditions sufficient water may condense to form a drop on the end of the nose. This is a purely natural physical phenomenon, not 'a cold' or other pathological condition.

At rest most people breathe through their nose, although 15% of the population are habitual mouth breathers. We all resort to mouth breathing during heavy exercise. The mouth is surprisingly good at air-conditioning, and by the time the air reaches the glottis conditions are very similar whether you are breathing through nose or mouth. The disadvantage of mouth breathing is in expiration, when much less heat and water is recovered. We have all experienced the discomfort of the dry mouth which often accompanies the nasal obstruction of a cold.

Particles and vapours

The respiratory system is threatened by many of the particles and chemical vapours in the air. The upper and conducting airways are much more robust than the respiratory surface, and they bear the brunt of protecting the respiratory surface by filtering these particles and vapours out of the inspired air.

Particles must be relatively small to penetrate the respiratory tract to any depth, and it is their size and shape that determine where they land. Where they land determines how they are dealt with.

An aerosol is a cloud of particles or droplets that remains stable and suspended in the air for some time. Because the volume (and hence the mass) of a drop is related to the cube of its diameter and its surface area is related to the square of its diameter, large drops fall faster than smaller ones. A shower of rain falls to the ground; a mist remains suspended for some time (Stoke's Law tells us that the terminal velocity of a falling sphere is proportional to the square of its radius). Scientists interested in the way aerosols behave in the lungs often convert the weight and shape of the particles into the size of the aerodynamically equivalent spheres. The mass median diameter of an aerosol is the diameter about which 50% of the total particle mass resides. The mass median aerodynamic diameter (MMAD) is the product of the mass median diameter and the square root of the particle density. Using this system we see 95% of particles > 5 mm MMAD impact on the walls of the nose and pharynx, where they are trapped by the sticky mucus. This impaction is the result of turbulence and the particles' momentum throwing them out of the airstream, when they rapidly change direction. In our noses the mucus that has trapped the dust is wafted to the pharynx by cilia. It is then swallowed. In dogs the cilia beat toward the outside and this contributes to the wet nose of a healthy dog. Slightly smaller particles (1-5 mm) survive the twists and turbulence of the upper airways and are removed by sedimentation in the small airways. Sedimentation is the settling of particles' under gravity, and this slow process is only effective in the small airways because their diameter is so small that the particles have only a little way to fall. Small though they are, these particles are too massive to be much affected by the buffeting of the gas molecules around them that constitutes the phenomenon of diffusion. Particles which reach the wall of the small airways are trapped in the mucus there and travel up the mucociliary escalator at a rate of about 2 mm s −1 to the pharynx in considerable amounts, to be swallowed. The mucus blanket which traps the particles is 5-10 mm thick and in two layers. The outer gel layer rests on a less viscous layer in which the cilia beat toward the mouth at a frequency of about 20 Hz.

The smallest particles of all (<0.1 mm) are deposited by diffusion of gas molecules producing Brownian motion. The particles are 'jostled' until they bump into the wall of a small airway or alveolus. In this region particles are stuck to the walls by surface tension because there is no secretion of mucus. They are also beyond the end of the ciliary escalator. In the alveolar region amoeboid macrophages ( Fig. 2.17 ) engulf particles and carry them to the escalator, or take them into the blood or lymph. When the dust load is large the macrophages dump their load around the respiratory, bronchioles, and any pathologist from a coal-mining area will have seen the black 'halos' so formed. Bacteria are particularly susceptible to the attentions of macrophages, which kill them with enzymes and oxygen-based free radicals (see Metabolic activity, p. 26) or transport them out of the lungs. The activities of these phagocytic cells ensure that the alveolar region of the lung is effectively sterile.

The free radicals and proteases produced by macrophages to deal with foreign material have the potential to damage the lung itself; how these dangerous substances are neutralized is described below (Metabolic activity, p. 36).

The influence of impaction, sedimentation and diffusion on particles of different aerodynamic diameters is illustrated in Figure 2.18 .

The majority of particles of 0.5 mm aerodynamic diameter are not deposited: they ride the airflow into the lungs and back out again with expiration. Figure 2.18 represents the case during quiet breathing. Treatment of disease with therapeutic aerosols requires slow deep breathing to ensure deep penetration and sufficient time for diffusion. The increased ventilation of exercise enhances impaction and the danger of heavy work in dusty environments.

Particles account for only a small fraction by weight of the pollutants we breathe ( Fig. 2.19 ).

Many gases and vapours also pose a serious threat, augmented by the self-abuse of tobacco smoking. Oxides of sulphur and nitrogen, hydrocarbons and chemicals produced by the action of sunlight on these substances inflame the respiratory tract. More than 1000 harmful constituents are inhaled in tobacco smoke. Smoking was identified by no less an authority than King James (VI of Scotland) I of England (1603-1625) as ' a custom loathsome to the eye, hateful to the nose, harmful to the brain and dangerous to the lungs '. Little wonder he was known as 'the wisest fool in Christendom'. Many harmful substances are produced by internal combustion engines, but the introduction of catalytic converters has significantly reduced production of carbon monoxide which has a particularly deleterious effect on the carriage of oxygen by the blood (see Chapter 8).

Metabolic activity

The metabolism of the tissues of the lung itself is unremarkable, with a metabolic rate only slightly higher than average for the whole body. Although it is the major extrahepatic site for mixed function oxidation by the cytochrome P450 systems, gram for gram it is much less active than the liver and much less tissue is involved. The major role of the P450 system in the lungs may therefore be in detoxification of inhaled foreign substances. Bloodborne toxic substances are extensively sequestered or detoxified in the lungs, with basic substances being particularly well processed. This protective activity on the part of the lung can be 'heroic' to a degree that causes fatal local damage: for example, the accumulation of oxygen-derived free radicals (useful in moderate concentrations to attack bacteria) is enhanced by the weedkiller paraquat (Weedol or Gramoxone), a dose of 1.5 g of which may be fatal because of its selective uptake by the lung. Although the initial clinical features of paraquat poisoning include dramatic ulceration of the mouth and oesophagus, diarrhoea and vomiting, it is usually the diffuse pulmonary fibrosis produced by the excess of free radicals that causes death. As well as free radicals the proteases, particularly elastase and trypsin, released by phagocytes in their normal defensive roles have to be neutralized or removed after they have carried out their function or they will attack the lung itself. Any of these substances caught up in the mucus of the mucociliary escalator will be carried out of the lung. In addition, their activity is terminated by conjugation with α₁-antitrypsin in the plasma. The importance of this mechanism is demonstrated by the high incidence and severity of pulmonary emphysema in people who lack antitrypsin because of a genetic deficiency.

Metabolism of circulating biologically active substances

As they are in series with the systemic circulation and receive the whole of cardiac output, the lungs are ideally situated to rapidly control levels of substances circulating in the blood. This they do by utilizing the enormous surface area of endothelium (100 m ²) to remove or degrade substances whose effects need to be rapidly terminated once they have carried out their function:

Noradrenaline (norepinephrine)

Substances which are more generally active and sustained in their actions pass through the pulmonary circulation unchanged, and include:

Of particular interest, as the only example of activation of a bloodborne substance by the lung is the transformation of angiotensin I in the plasma to the powerful vasoconstrictor substance angiotensin II by angiotensin-converting enzyme (ACE). Although this is not restricted to the lung, being found in plasma and endothelium, pulmonary vasculature does seem to be most plentifully supplied with this enzyme and 80% of plasma angiotensin I is converted in a single pass though the lungs. ACE is also responsible for the removal of bradykinin by the lung. The lung endothelium is also responsible for a tonic production of NO.

The vasoactive and bronchoactive leukotrienes and prostaglandins, which are released into the circulation under certain conditions, are metabolized from arachadonic acid (apparently so-called because its crystals look like hairy spiders) by the pulmonary capillary endothelium.

As well as modifying the blood the lung also produces mucopolysaccharides as part of the production of bronchial mucus and secretes immunoglobulins (Ig) into the airways to defend against infection.

The production of surfactant by type II pneumocytes is discussed on p. 36.

Non-respiratory functions

Filtration

The blood filtering function of the lungs, protecting the vulnerable cerebral and coronary circulations, is frequently and justifiably mentioned. However, the capillary diameter of the pulmonary circulation (about 7 mm) can not be regarded as the overall pore size of the filter. Many studies have shown that particles up to 400 mm diameter can pass through the pulmonary circulation. The effective filter size depends, in part, on the level of exercise the subject is undertaking, and may be affected by normally closed arteries opening to 'shunt' blood across the lungs. The particles filtered by the lungs include agglutinated white and red blood cells, fat droplets, and droplets of amniotic fluid during pregnancy. Tumour cells may lodge and grow in the lungs, but it is blood clots from the systemic circulation that form the major filtered load and interfere with the fluidity of the blood.

Blood fluidity

As well as trapping blood clots the lung contributes to blood fluidity by being the richest source of factors that promote (thromboplastin) or inhibit (heparin) clotting. The balance between their effects maintains the fluidity of the blood. Any blood clots already formed are broken down by the proteolytic enzyme plasmin, activated from its inactive precursor in the plasma by factors found in large quantities in pulmonary endothelium.

Blood capacity

Pulmonary blood volume is about 500 mL in a recumbent man. This volume can be halved by increases in pressure within the chest, such as forced expiration against a closed larynx. On the other hand, the volume of blood in the chest can be doubled by a forced inspiration. This phenomenon allows the pulmonary circulation to act as a reservoir, for example at the start of exercise, when the output of the left ventricle rapidly increases. Activity of the sympathetic nervous system may influence the capacity of the system by triggering contraction of smooth muscle in the blood vessel walls.

Cooling

The high latent heat of vaporization of water makes its evaporation from the respiratory surface a useful mechanism for cooling in small furry animals. This mechanism is less evident in humans, perhaps because we use evaporation from our particularly hairless skin. However, a residue of this mechanism can be seen if you stay too long in a very hot bath, or if you have a fever - you will notice you begin reflexly to breathe through your mouth.

Behaviour

Breathing is unique among the major functions of the body in that it is both voluntarily and involuntarily controlled. For example, our hearts and kidneys pump and filter our blood without our being aware of it. We cannot, however, consciously control the rate at which they work. Breathing goes on unconsciously for most of the time (except for those unfortunate individuals suffering from Ondin's Curse, see p. 135), but in an instant we can take control of our breathing, for example to allow us to speak.

Our respiratory muscles help other systems of the body in many non-respiratory ways. When lifting a heavy weight our breathing stops, the muscles of the chest contract and it forms a rigid cage against which the muscles of the arms can act.

The diaphragm and abdominal muscles contract simultaneously to raise intra-abdominal pressure during vomiting, defecation and childbirth. Conversely, inspiration is switched off while you swallow food or drinks, to prevent their inhalation (have you noticed that each swallow is followed by an expiration?).

Changes in patterns of breathing can signal emotion, amicable or otherwise, and above all we use our respiratory system to power speech and vocalization.

Relatively large particles are deposited in the nose by impaction.

Smaller particles are deposited in the airways by sedimentation.

Sedimented particles are removed to the mouth by the mucociliary escalator.

Macrophages deal with particles that reach the alveoli.

The pulmonary circulation forms an important filter of the blood, particularly of blood clots.

Further reading

Horsfield K. Morphometry of the lungs. In: Macklem P.T., Mead J., editors. Handbook of Physiology. Section 3, The Respiratory System. Vol III Mechanics of Breathing, Part I. American Physiological Society; Bethesda, MD: 1986. p. 75. [Google Scholar]

Murray J.F. second ed. WB Saunders; Philadelphia: 1986. The Normal Lung. [Google Scholar]

Silverman E.S., Gerritsen M.E., Collins T. Metabolic function of the pulmonary endothelium. In: Crystal R.G., West J.B., Barnes P.J., Weibel E.R., editors. The Lung: Scientific Foundations. second ed. Raven Press; New York: 1997. [Google Scholar]

Weibel E.R. Academic Press; New York: 1963. Morphometry of the Human Lung. [Google Scholar]

Weibel E.R. Design and morphometry of the pulmonary gas exchanger. In: Crystal R.G., West J.B., Barnes P.J., Weibel E.R., editors. The Lung: Scientific Foundations. second ed. Raven Press; New York: 1997. [Google Scholar]

Young B., Heath J.W. Churchill Livingstone; Edinburgh: 2000. Wheater's Functional Histology: A Text and Colour Atlas. [Google Scholar]

Articles from The Respiratory System are provided here courtesy of Elsevier

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STRUCTURE OF THE RESPIRATORY SYSTEM, RELATED TO FUNCTION

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The Respiratory System. 2010 : 11-28. Andrew Davies, MA PhD DSc Carl Moores, BA BSc MB ChB FRCA Just as each part of the respiratory system has its particular function, so each part has its particular pathologies.

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human respiratory system, the system in humans that takes up oxygen and expels carbon dioxide.

The design of the respiratory system

The human gas-exchanging organ, the lung, is located in the thorax, where its delicate tissues are protected by the bony and muscular thoracic cage. The lung provides the tissues of the human body with a continuous flow of oxygen and clears the blood of the gaseous waste product, carbon dioxide. Atmospheric air is pumped in and out regularly through a system of pipes, called conducting airways, which join the gas-exchange region with the outside of the body. The airways can be divided into upper and lower airway systems. The transition between the two systems is located where the pathways of the respiratory and digestive systems cross, just at the top of the larynx.

The upper airway system comprises the nose and the paranasal cavities (or sinuses), the pharynx (or throat), and partly also the oral cavity, since it may be used for breathing. The lower airway system consists of the larynx, the trachea, the stem bronchi, and all the airways ramifying intensively within the lungs, such as the intrapulmonary bronchi, the bronchioles, and the alveolar ducts. For respiration, the collaboration of other organ systems is clearly essential. The diaphragm, as the main respiratory muscle, and the intercostal muscles of the chest wall play an essential role by generating, under the control of the central nervous system, the pumping action on the lung. The muscles expand and contract the internal space of the thorax, the bony framework of which is formed by the ribs and the thoracic vertebrae. The contribution of the lung and chest wall (ribs and muscles) to respiration is described below in The mechanics of breathing. The blood, as a carrier for the gases, and the circulatory system (i.e., the heart and the blood vessels) are mandatory elements of a working respiratory system ( see blood; cardiovascular system).

Morphology of the upper airways

The nose is the external protuberance of an internal space, the nasal cavity. It is subdivided into a left and right canal by a thin medial cartilaginous and bony wall, the nasal septum. Each canal opens to the face by a nostril and into the pharynx by the choana. The floor of the nasal cavity is formed by the palate, which also forms the roof of the oral cavity. The complex shape of the nasal cavity is due to projections of bony ridges, the superior, middle, and inferior turbinate bones (or conchae), from the lateral wall. The passageways thus formed below each ridge are called the superior, middle, and inferior nasal meatuses.

Characteristics of the Human Body

On each side, the intranasal space communicates with a series of neighbouring air-filled cavities within the skull (the paranasal sinuses) and also, via the nasolacrimal duct, with the lacrimal apparatus in the corner of the eye. The duct drains the lacrimal fluid into the nasal cavity. This fact explains why nasal respiration can be rapidly impaired or even impeded during weeping: the lacrimal fluid is not only overflowing into tears, it is also flooding the nasal cavity.

The paranasal sinuses are sets of paired single or multiple cavities of variable size. Most of their development takes place after birth, and they reach their final size toward age 20. The sinuses are located in four different skull bones-the maxilla, the frontal, the ethmoid, and the sphenoid bones. Correspondingly, they are called the maxillary sinus, which is the largest cavity; the frontal sinus; the ethmoid sinuses; and the sphenoid sinus, which is located in the upper posterior wall of the nasal cavity. The sinuses have two principal functions: because they are filled with air, they help keep the weight of the skull within reasonable limits, and they serve as resonance chambers for the human voice.

The nasal cavity with its adjacent spaces is lined by a respiratory mucosa. Typically, the mucosa of the nose contains mucus-secreting glands and venous plexuses; its top cell layer, the epithelium, consists principally of two cell types, ciliated and secreting cells. This structural design reflects the particular ancillary functions of the nose and of the upper airways in general with respect to respiration. They clean, moisten, and warm the inspired air, preparing it for intimate contact with the delicate tissues of the gas-exchange area. During expiration through the nose, the air is dried and cooled, a process that saves water and energy.

Two regions of the nasal cavity have a different lining. The vestibule, at the entrance of the nose, is lined by skin that bears short thick hairs called vibrissae. In the roof of the nose, the olfactory bulb with its sensory epithelium checks the quality of the inspired air. About two dozen olfactory nerves convey the sensation of smell from the olfactory cells through the bony roof of the nasal cavity to the central nervous system.

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Human respiratory system | Description, Parts, Function, & Facts

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Human respiratory system, the system in humans that takes up oxygen and expels carbon dioxide. The major organs of the respiratory system include the nose, pharynx, larynx, trachea, bronchi, lungs, and diaphragm. Learn about the anatomy and function of the respiratory system in this article.

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Ants are common insects, but they have some unique capabilities-including their legendary communication skills that allow their colonies to function as superorganisms.

There are 20 quadrillion ants on Earth-that's 2.5 million ants for every human. Known ant species (members of the family Formicidae) number over 12,000, and some experts estimate upwards of 20,000 exist. They can be found almost anywhere in the world, with the exception of Antarctica, Iceland, Greenland, and some island nations.

Invasive ant species are becoming a problem, however, with research showing that over 500 species of ants were found in countries where they aren't native, having hopped a ride with

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Ants are common insects, but they have some unique capabilities-including their legendary communication skills that allow their colonies to function as superorganisms. There are 20 quadrillion ants on Earth-that's 2.5 million ants for every human. Known ant species (members of the family Formicidae) number over 12,000, and some experts estimate upwards of 20,000 exist.

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https://www.nwf.org/en/Educational-Resources/Wildlife-Guide/Invertebrates/Ants

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Family: Formicidae

Status: Not Listed

Description

Ants are most closely related to bees and wasps, which all have a narrow waist that segments their body. The body is separated into three parts-the head, thorax, and gaster (the part of the abdomen behind the waist). There are more than 12,000 species of ant, most of which are black, brown, or red in color.

Range

Ants are found almost everywhere on the planet. The only areas that don't boast populations of ants are Antarctica, Greenland, Iceland, and some island nations. Most species live in soil, leaf litter, or decaying plants.

Diet

The ant's diet varies among species, but most eat leaves, seeds, small insects, nectar, and honeydew. Ants carry food back to the nest and are capable of carrying more than 10 times their weight.

Behavior

Ants use their keen senses to communicate with colony members. They produce chemicals called pheromones, which are sensed by other ants using their antennae. They can also use their antennae or other body parts to send messages through touch. Touch messages are transmitted through stridulations, which are sounds and vibrations generated by one ant rubbing its body parts together. These forms of communication relay different messages, such as where food is located or what dangers are present.

Life History

Colonies of ants are separated into groups of individuals that have different jobs, such as workers, soldiers, and queens. The workers are all females that take care of the much larger queen and her young, or go out to find food. Winged males mate with queens and die soon after. Queens also have wings, but they break off after mating. Ants are an important prey species for many different reptiles, amphibians, arthropods, birds, and mammals. Longevity can't be generalized to all ants, but queens usually live for several years and workers for only a few weeks or months.

Conservation

Ant populations are stable. Ants often come into conflict with humans because they colonize homes and some-like fire ants-have stingers that can harm people. However, they are extremely important members of the ecosystems in which they're found, and they help to aerate soil just like earthworms.

Fun Fact

Ants usually form colonies with one nest and one queen-but some species have formed huge groups called supercolonies, which can have multiple nests and multiple queens. A supercolony may contain billions of ants that together span thousands of miles.

Sources

Arizona State University School of Life Sciences

Center for Insect Science Education Outreach, The University of Arizona STEM Learning Center

Evans, A. V. National Wildlife Federation Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc.: New York, NY 2007.

Ferreira R.S., Poteaux C., Delabie J.H.C., Fresneau D., Rybak F. 2010. Stridulations Reveal Cryptic Speciation in Neotropical Sympatric Ants. PLoS ONE 5(12): e15363.

National Geographic

New York University Langone Medical Center

Smithsonian's National Zoo & Conservation Biology Institute

University of Arkansas Division of Agriculture

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Learn facts about the ant's habitat, diet, life history, and more.

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Manny Mendoza- Muscular System of an Ant

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Manny Mendoza- Muscular System of an Ant

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Ants, those tiny creatures that scurry around tirelessly, are truly remarkable insects. With their intricate societies, complex communication systems, and unbelievable strength relative to their size, ants have captivated our curiosity for centuries. However, amidst all the marvels of these miniature organisms, a question arises: Do ants have hearts?

Brief Overview of Ants as Remarkable Insects

Ants belong to the order Hymenoptera and are closely related to bees and wasps. They have been wildly successful in adapting to various environments across the globe, colonizing almost every landmass except Antarctica. With over 12,000 known species of ants discovered so far, they display an incredible diversity in size, coloration, behavior, and habitat preferences.

Ants are social insects that live in colonies composed of individuals with different tasks or castes such as queens (reproductive females), males (drones), and workers (sterile females). These colonies of worker ants exhibit impressive coordination and division of labor, enabling them to build elaborate nests or anthills underground or within trees.

Do Ants Have Hearts?

The idea of ants having hearts may seem peculiar since we typically associate hearts with larger animals like mammals. However, when it comes to understanding an ant's circulatory system more comprehensively, this question becomes crucial.

In humans and many other animals like birds or reptiles, the heart embodies a vital organ responsible for pumping blood throughout the body via a network of blood vessels. But do ants possess a similar mechanism to pump blood around?

Could there be an equivalent structure serving as their "heart"? To unravel this mystery and explore the fascinating world hidden within an ant's body, let us delve into their anatomy and circulatory system.

Anatomy of an Ant

Ants are fascinating creatures that belong to the insect family, Formicidae. They are known for their highly organized societies and impressive teamwork. To understand whether ants have hearts, we first need to explore their anatomy.

Ants possess a segmented body structure, which consists of three main parts: the head, thorax, and abdomen. The head houses most ants' vital sensory and control organs that allow ants to interact with the environment.

They have compound eyes that help them collect visual information and detect light. Additionally, they possess antennae, which serve as highly sensitive appendages used for communication and detecting chemical signals in their surroundings.

Moving on to the thorax of queen ants, this region is responsible for supporting the six legs that enable ants to scurry swiftly across surfaces. Inside the thorax lies one chamber of the ant's circulatory system - an elongated tube known as the dorsal aorta.

We have the abdomen, which contains most of an ant's vital organs such as its digestive system and reproductive organs. It is also home to another segment of the circulatory system called "aortic arches," which act as pulsating organs responsible for propelling hemolymph through blood vessels present throughout their bodies.

The Ant Circulatory System

Unlike mammals with a closed circulatory system where blood is contained within vessels at all times, ants possess an open circulatory system. This means that instead of blood traveling exclusively within designated vessels like arteries and veins, they have a circulating fluid called hemolymph that bathes their internal tissues directly. The ant's heart beats in a rhythmic pattern but differs from what we typically envision as a human ant's heart rate.

In reality, they lack a centralized organ resembling our traditional understanding of hearts. Instead, they rely on specialized structures like the dorsal aorta and aortic arches distributed throughout their bodies.

The dorsal aorta, located in the thorax, acts as the primary vessel that helps transport oxygen and nutrients to various parts of the ant's body. From this main artery, a few organs and smaller vessels branch out and carry hemolymph to all the vital organs.

Functioning without a Centralized Heart

Ants have evolved to function efficiently without a centralized heart. While it may seem unconventional compared to our human circulatory system, this adaptation works well for these tiny creatures. The hemolymph plays a crucial role in transporting oxygen and nutrients throughout an ant's body and also aids in waste removal.

The absence of a centralized heart means that the circulation of hemolymph is not limited by set blood vessels. Instead, it flows more freely through interconnected spaces called sinuses or lacunae within their bodies.

This allows for efficient exchange of substances between the cells and interstitial fluid. Ants possess an intriguing anatomy that supports their unique circulatory system.

Although they lack a traditional centralized heart like mammals, they have adapted with specialized structures distributed throughout their bodies to ensure effective circulation of their vital circulatory fluid - hemolymph. Understanding how these systems work helps us appreciate the intricate biology present even within small creatures like ants.

The Ant Circulatory System

Insects, including ants, possess an open circulatory system. Unlike the closed circulatory system found in humans and other vertebrates, where blood is enclosed within vessels, ants rely on a different mechanism to transport vital fluids throughout their bodies.

Instead of blood vessels, they have a network of interconnected spaces called hemocoel that bathes their organs and tissues directly. This hemolymph is equivalent to the blood in our bodies and plays a crucial role in transporting nutrients, hormones, and immune cells.

Ants' Version of a "Heart"

While ants do not have a centralized heart like the human heart pumping blood through arteries and veins, they possess unique structures that aid in circulating hemolymph effectively. One key component is the dorsal aorta, which acts as the main channel carrying hemolymph along the ant's abdomen. It functions similarly to major arteries but without muscular contraction for propulsion.

The role of pulsating organs called "aortic arches" further contributes to circulation of ant organs. These arches are present throughout the ant's body and act as auxiliary pumps.

They rhythmically contract and relax to create pressure gradients that help propel hemolymph forward through the various interconnected spaces. This coordinated pulsation ensures proper distribution of essential fluids within an ant's segmented body.

The open circulatory system present in ants might seem quite different from our closed circulatory system with its intricate network of blood vessels, but it serves ants remarkably well. The absence of rigid tubes allows for flexibility in accommodating changes in body size during growth or accommodating environmental conditions such as squeezing through narrow passages within an ant colony or underground tunnels.

With this understanding of how the ant's circulatory system operates, let's explore some fascinating facts about these tiny creatures' hearts.

Functioning without a centralized heart

Comparison with human circulatory system

When it comes to the circulatory systems of ants and humans, there are some intriguing differences. While humans have a closed circulatory system with a centralized heart, ants possess an open circulatory system, lacking a central pump.

In our bodies, the heart propels blood through a network of vessels, ensuring that oxygen and nutrients reach all organs and tissues. However, ants have evolved a unique mechanism to achieve similar results without a traditional heart.

Hemolymph - the ant's blood equivalent

Instead of blood like fluid found in humans (containing red blood cells), ants have hemolymph flowing through their bodies. Hemolymph can be considered as an equivalent to our human blood, but with some differences. It is not contained within vessels like our circulatory system; instead, it flows freely within the ant's open body cavity called the hemocoel, bathing their organs directly.

This fluid serves multiple purposes beyond just transporting nutrients and oxygen. The composition of ant hemolymph consists of water along with various proteins, ions, hormones, and cells called hemocytes dispersed within it.

The primary function of an ant's hemolymph is to transport nutrients from the digestive system to different organs and tissues throughout the ant's body. Additionally, it plays essential roles in waste removal by carrying metabolic byproducts away for excretion.

Ants are fascinating creatures because their unique adaptations allow them to thrive despite not having a centralized heart or traditional circulatory system like ours. Their decentralized open circulatory system enables efficient distribution of resources without relying on high-pressure pumping mechanisms like human hearts do.

Overall, while ants may lack what we traditionally think of as a "heart," they have developed an equally effective way - through their open circulatory systems using hemolymph - to ensure the basic function of supplying nutrients and oxygen to their organs and tissues. It is yet another testament to the remarkable diversity and ingenuity found in the natural world.

Adaptations for Efficient Circulation in Ants

Ants are fascinating creatures that have evolved remarkable adaptations to facilitate their circulation despite their small size and decentralized nature. Unlike humans, ants do not have a closed circulatory system with a centralized heart pumping blood through intricate networks of blood vessels. However, they have developed alternative mechanisms to efficiently distribute vital nutrients and oxygen throughout their bodies.

One adaptation that aids circulation in ants is their small size. Due to their miniature stature, ants have a higher surface-to-volume ratio compared to larger organisms.

This means that they can exchange gases, such as oxygen and carbon dioxide, more effectively through their body's surface area. Additionally, the decentralized nature of an ant's circulatory system minimizes the distance between cells and vital organs, allowing for rapid nutrient delivery.

Antennae and Spiracles Aiding Oxygen Exchange

Ants utilize several unique features to facilitate oxygen exchange within their bodies. One such feature is the presence of antennae on their heads ant bodies. These sensory appendages not only help ants collect visual information about their surroundings but also play a crucial role in respiration.

The thin tube-like structures present in the antennae known as tracheae allow for the diffusion of gases, enabling ants body to efficient oxygen intake while expelling carbon dioxide. In addition to antennae, spiracles are another essential component involved in respiration for ants.

Spiracles are small openings located along the sides of an ant's body or abdomen through which oxygen enters and carbon dioxide exits the insect's respiratory system. By actively opening and closing these spiracles, ants can regulate gas exchange according to metabolic demands.

Limited Distance Between Cells for Effective Nutrient Delivery

Efficient nutrient delivery is crucial for any organism's survival, including ants. Despite not having a closed circulatory system, ants have evolved a decentralized network of interconnected tubes called the dorsal vessel or "heart." This thin tube runs along the ant's back, enabling the transport of hemolymph, the ant's equivalent of blood. The absence of blood vessels necessitates an alternative mechanism for nutrient delivery.

Ants use a system known as interstitial fluid circulation. The interstitial fluid bathes the cells directly, allowing for direct exchange of nutrients and waste products.

As a result, ants have limited distance between their cells and vital organs, ensuring efficient nutrient delivery and waste removal. Ants have developed an array of adaptations similar to blood to ensure efficient circulation despite not having a closed circulatory system like humans.

Their small size, decentralized nature, antennae for oxygen exchange, spiracles for respiration regulation, and interstitial fluid circulation mechanism all contribute to their impressive ability to distribute vital resources effectively throughout their bodies. These adaptations highlight the wonders of nature's diversity and emphasize that even creatures as small as ants have intricate physiological systems that enable their survival within an ant colony or in various environments.

Fascinating Facts About Ant Hearts

Ants, with their intricate social structures and diverse species, showcase an astonishing range of heart structures. Just as ants vary in size, behavior, and ecological role, their hearts exhibit adaptations tailored to their specific needs. Let's explore some remarkable examples.

Examples include Carpenter Ants, Leafcutter Ants, etc.

Carpenter ants (Camponotus spp.) are renowned for their ability to excavate wood and build elaborate nests. These industrious insects have relatively large hearts that enable efficient circulation throughout their robust bodies.

Their hearts exhibit complex branching patterns to deliver hemolymph-the ant's circulatory fluid-to all extremities efficiently. On the other hand, leafcutter ants (Atta spp.) are known for their proficiency in agricultural practices.

These tiny farmers cut leaves and use them as a substrate for cultivating fungi within their nests. The hearts of leafcutter ants differ from those of carpenter ants; they possess a more streamlined structure suitable for the smaller bodies of these diligent workers.

Variations in Heart Anatomy Based on Species' Needs

Interestingly, among different species of ants, variations in heart anatomy reflect specific physiological requirements dictated by varying lifestyles or ecological niches. While certain ant species have larger hearts with increased muscle mass to support demanding activities such as foraging or long-distance migrations, others may have more compact hearts optimized for energy conservation.

For instance, army ants (Eciton spp.), who embark on nomadic predatory raids in search of prey items like a terrifying army on the move, possess specialized heart adaptations. Their hearts tend to be elongated and segmented into multiple chambers to accommodate rapid changes in hemolymph distribution during dynamic hunting expeditions.

Intriguingly enough, some ant species have hearts that can adjust their pumping rate in response to external stimuli or internal conditions. This adaptability allows them to regulate circulation and respond swiftly to varying demands within the colony or even in different life stages.

The diversity in ant heart structures highlights the remarkable plasticity of these tiny organisms' circulatory systems, fine-tuned by evolutionary forces to suit their specific ecological niches. As we delve into the marvelous world of ants hearts, we uncover an astonishing array of heart adaptations that cater to their varied needs.

From carpenter ants with intricately branched hearts facilitating efficient hemolymph distribution throughout their bodies, to leafcutter ants with streamlined hearts optimized for their smaller frames, each species has its own unique cardiac architecture. These adaptations showcase nature's ingenious designs and remind us how diverse and fascinating life can be-even within the miniature universe of ants.

Evolutionary Significance

The intricate circulatory system found in ants is a testament to the wonders of evolution. Over millions of years, these fascinating creatures have adapted their circulatory system to suit their diverse lifestyles and environments.

The evolution of the ant's circulatory system has played a crucial role in their success as social insects, enabling them to thrive and survive in various conditions. One key aspect that shaped the ant's circulatory system is their transition from a closed circulatory system, like that of humans, to an open circulatory system.

This change occurred as ants evolved to become smaller in size and developed complex social structures. The adoption of an open circulatory system allowed for greater flexibility and efficiency in delivering nutrients and oxygen throughout their bodies.

Adaptation to Various Environments and Lifestyles: A Fluid Journey

The ant's adaptation to various environments is evident through its remarkable fluid transport system. Unlike humans whose red blood cells carry oxygen, ants rely on a fluid called hemolymph that serves multiple purposes within their bodies.

This hemolymph not only transports nutrients but also plays a vital role in waste removal and immune responses. In addition to adapting their circulatory systems for general survival, different ant species have further specialized based on their specific lifestyles.

For example, carpenter ants, which excavate wood galleries for nesting purposes, require greater circulation efficiency due to increased physical activity involved in nest building activities. Leafcutter ants, on the other hand, have developed an even more sophisticated circulation system as they carry heavy loads of leaf fragments back to the colony for fungal farming.

As we delve into understanding the evolutionary significance behind the ant's remarkable circulatory system, it becomes clear how nature has shaped these incredible creatures over eons. From transitioning to an open circulatory system to adapting to various environments and lifestyles, ants have developed a highly efficient means of transporting nutrients, oxygen, and waste throughout their bodies. Through evolution, the ant's circulatory system has become intricately intertwined with other vital systems such as their tracheal system for respiration and their sensory and control organs for navigation.

The decentralized nature of the ant's circulation allows for efficient nutrient delivery to cells while maintaining an impressive level of adaptability. The next time you observe a bustling column of ants or marvel at their ability to carry objects many times their body weight, take a moment to appreciate the evolutionary journey that has shaped not only their circulatory system but also the overall success of these incredible insects.

Conclusion

Recapitulation of key points on ant hearts

Throughout this exploration into the intricate world of how ants breathe, we have delved into the question of whether these fascinating creatures possess hearts. By examining their anatomy and circulatory system, it is clear that ants do not have a centralized heart like humans do.

Instead, they rely on a decentralized network of aortic arches and a dorsal aorta to pump their equivalent of blood - hemolymph - throughout their bodies. This hemolymph flows freely through their interstitial fluid and bathes all the vital organs, ensuring efficient nutrient delivery and waste removal.

Final thoughts on the marvels of nature's diversity

Studying the complex mechanisms that enable ants to survive and thrive in their environments gives us great insight into the marvels of nature's diversity. The fact that ants have evolved such an efficient circulatory system without a centralized heart is awe-inspiring. These tiny creatures have adapted to various habitats, from leafcutter ants bustling with activity in tropical rainforests to carpenter ants quietly constructing elaborate nests in our own backyards.

Their ability to communicate through chemical signals, navigate vast distances in search of resources, and work harmoniously within an ant colony showcases the remarkable intricacy and resilience found in even the smallest corners of our world. In closing, while it may be accurate to say that ants don't possess hearts as we traditionally understand them, this does not diminish their remarkable biology or importance within ecosystems worldwide.

Ants are truly captivating creatures with unique adaptations that allow them to thrive in diverse environments. As we continue unraveling nature's mysteries, let us find inspiration in these tiny wonders and appreciate how every organism plays its part in maintaining balance on our planet.

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Frequently Asked Questions:

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Decoding Ant Anatomy: Do Ants Have Hearts?

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Delve into the fascinating world of ants as we explore their intricate circulatory system and uncover the truth about ant 'hearts'.

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Grayson Tidwell- Skeletal System of an Ant

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Grayson Tidwell- Skeletal System of an Ant

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Everybody has seen ants in their surroundings. They are known for their hard work and unity. But have you ever noticed that when we accidentally crush an ant the blood coming out of it is not red? So, does this mean that there is no blood in an ant's body? Let's find out if ants have blood. There is no direct answer to the question but ants have something similar to blood, a fluid that is yellowish or greenish known as hemolymph. The main work of blood in vertebrates (animals with backbones) is to move important things like nutrients from food, wastes, and oxygen around the body.

In short, blood brings oxygen and nutrients to all the parts of the body to make it work properly. The reason behind blood being red is because it consists of lots of tiny red blood cells which carry oxygen around the body.

On the other hand, ants and other insects have haemolymph inside their body, which does some of the same jobs as blood like helping in moving nutrients around. The number of amino acids in them is very high.

The circulatory system of ants and other insects is similar to that of a human. The work of blood in insects is different from the human body. Like in humans, blood flows only in the veins and arteries, but in insects' bodies, the fluid is free to move in any direction. It does not move in any kind of artery but freely circulates throughout the body. Because of this, ants can live easily even in very difficult weather. Hemolymph also helps in healing their wounds. Hemocyanin is present inside the hemolymph just like red blood cells contain haemoglobin.

However, an important difference to note between hemolymph and blood is that hemolymph does not carry oxygen around the insects' body, they breathe through little holes on the side of their bodies known as spiracles, which brings oxygen directly to the insect's organs without red blood cells.

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Why is Ant's Blood Not Red Like We Humans Have? The Answer Lies in This - News18

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Ants and other insects have haemolymph inside their body, which does some of the same jobs as blood like helping in moving nutrients around. The number of amino acids in them is very high.

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Mike wrote to the “Consult-Ant” with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answe…

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first audio not video sorry :(