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The major components of the lymphatic system include lymph, lymphatic vessels, and lymphatic organs that contain lymphoid tissues.

Lymphatic Vessels
Lymphatic vessels are structures that absorb fluid that diffuses from blood vessel capillaries into surrounding tissues. This fluid is directed toward lymph nodes to be filtered and ultimately re-enters blood circulation through veins located near the heart. The smallest lymphatic vessels are called lymph capillaries. Lymphatic capillaries come together to form larger lymphatic vessels. Lymphatic vessels from various regions of the body merge to form larger vessels called lymphatic trunks. Lymphatic trunks merge to form two larger lymphatic ducts. Lymphatic ducts return lymph to blood circulation by draining lymph into the subclavian veins in the neck.

Lymph Nodes
Lymphatic vessels transport lymph to lymph nodes. These structures filter lymph of pathogens, such as bacteria and viruses . Lymph nodes also filter cellular waste, dead cells, and cancerous cells. Lymph nodes house immune cells called lymphocytes. These cells are necessary for the development of humoral immunity (defense prior to cell infection) and cell-mediated immunity (defense after cell infection). Lymph enters a node through afferent lymphatic vessels, filters as it passes through channels in the node called sinuses, and leaves the node through an efferent lymphatic vessel.

Thymus
The thymus gland is the main organ of the lymphatic system. Its primary function is to promote the development of specific cells of the immune system called T-lymphocytes. Once mature, these cells leave the thymus and are transported via blood vessels to the lymph nodes and spleen. T-lymphocytes are responsible for cell-mediated immunity, which is an immune response that involves the activation of certain immune cells to fight infection. In addition to immune function, the thymus also produces hormones that promote growth and maturation.

Spleen
The spleen is the largest organ of the lymphatic system. Its primary function is to filter blood of damaged cells, cellular debris, and pathogens. Like the thymus, the spleen houses and aids in the maturation of lymphocytes. Lymphocytes destroy pathogens and dead cells in the blood. The spleen is rich in blood supplied via the splenic artery. The spleen also contains efferent lymphatic vessels, which transport lymph away from the spleen and toward lymph nodes.

Tonsils
Tonsils are arrays of lymphatic tissue located in the upper throat region. Tonsils house lymphocytes and other white blood cells called macrophages. These immune cells protect the digestive tract and lungs from disease-causing agents that enter the mouth or nose.

Bone Marrow
Bone marrow is the soft, flexible tissue found inside bone. Bone marrow is responsible for the production of blood cells: red blood cells, white blood cells, and platelets. Bone marrow stem cells play an important role in immunity as they generate lymphocytes. While some white blood cells mature in bone marrow, certain types of lymphocytes migrate to lymphatic organs, such as the spleen and thymus, to mature into fully functioning lymphocytes.

Lymphatic tissue can also be found in other areas of the body, such as the skin, stomach, and small intestines. Lymphatic system structures extend throughout most regions of the body. One notable exception is the central nervous system.

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What Are the Components of the Lymphatic System?

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The major components of the lymphatic system include lymph, lymphatic vessels, and lymphatic organs that contain lymphoid tissues. Lymphatic Vessels Lymphatic vessels are structures that absorb fluid that diffuses from blood vessel capillaries into surrounding tissues. This fluid is directed toward lymph nodes to be filtered and ultimately re-enters blood circulation through veins located near the heart.

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The Formation of Lymph - A Level Biology

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For A Level Biology, Module 3 for OCR exam board.

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For A Level Biology, Module 3 for OCR exam board.

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Tissue fluid - The A Level Biologist - Your Hub

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This is your stop for learning resources, extra info and essential dates and documents. I've scoured the world just to bring you, the A Level biologists, all you need to succeed and enjoy your Biology A Level.

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Formation of Tissue Fluid | A-level Biology | OCR, AQA, Edexcel

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https://goo.gl/31T06Y to unlock the full series of AS, A2 & A-level Biology videos created by A* students for the new OCR, AQA and Edexcel specification. In this video we cover how tissue fluid is formed from the blood in capillary beds, and how it is returned to the blood through lymph.

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Blood

We all know that we have this warm fluid called blood flowing through our body. We even know that we need blood in order to stay alive. Things that you may not fully know or understand are exactly what blood is, what it is made up of, and how it is maintained. Blood is a type of tissue of our body that contains cells, chemicals, and other substances. Now on to the other two questions.

Formed Elements

About 45% of our blood is composed of what we refer to as formed elements. You likely call them blood cells. There are different types of blood cells found in our blood. Let's look at those now.

The first type of blood cells are the erythrocytes, or as they are commonly called, red blood cells or RBCs. These are the most numerous of the three types of blood cells. RBCs have the job of transporting oxygen and carbon dioxide. There are approximately 4.2 to 6.2 million RBCs per cubic mm of blood at any given point in time.

The next type of blood cell is the leukocyte, also known as white blood cells or WBCs. These are members of our body's defense team since they protect us from invading bacteria and other pathogens. There are anywhere from 5,000 to 9,000 per cubic mm of blood.

Not all leukocytes are the same. There are 5 different WBCs. The majority of our WBCs are neutrophils, making up around 65% of the WBCs. Lymphocytes make up 25% of the WBCs, and monocytes make up about 5%. Small amounts of eosinophils and basophils are also found in the blood, making up 4% and 1%, respectively.

The last of the 3 blood cell types are the thrombocytes, commonly referred to as platelets. These are also the tiniest of the blood cells. Platelets work in the body to help stop the bleeding whenever a blood vessel is damaged. We have 140,000 to 340,000 platelets per cubic mm of blood.

Plasma

The other 55% of our blood is composed of plasma. Plasma is the liquid portion of blood. Since this portion is liquid, you probably have figured out that the main component in plasma is water. Water makes up about 90% of the plasma. So, what is in the other 10% of the plasma?

Well, proteins make about 8% of plasma. There are 4 different types of proteins in the plasma. The most abundant of the plasma proteins at 57% are albumins. It is responsible for helping to maintain blood volume. Globulins are another plasma protein. They make up 38% of the proteins in the plasma, and they work with the WBCs. Fibrinogen at 4% and prothrombin at 1% are the final 2 plasma proteins, and they help in the clotting process.

The smallest portion of the blood plasma is made up of an assortment of different solids. These make up the remaining 3% of the plasma. Some solids you'll find in the plasma are ions, or electrolytes, such as potassium, sodium, and calcium. Various nutrients needed by the body - like glucose, amino acids, and lipids - and waste products from metabolism - like urea, uric acid, and creatinine - are also found in the plasma. Oxygen and carbon dioxide are the blood gases which are found in the plasma as well. The last of the solids are hormones. There are a wide assortment of hormones released by various glands in the body that are transported in the plasma of the blood.

Blood Regulation

The last thing we want to understand is how the blood is maintained. With all the work our blood cells have to do, they must get replenished at some point in time. And we certainly hope the old cells are removed from the blood at some point so we don't have those building up in our blood. That is exactly what happens.

New blood cells are created through a process called hematopoiesis. This process takes place in the red bone marrow, which is found in the long bone of our bodies, such as our thigh and arm bone. This process is not happening continuously in our bodies. Instead, there is a set control mechanism in place to ensure that the proper number of RBCs are in the blood at all times.

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what is the composition of blood? - video & lesson transcript | study.com

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What Is the Composition of Blood? - Video & Lesson Transcript | Study.com

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We all know that we have this warm fluid called blood flowing through our body. We even know that we need blood in order to stay alive. Things that you may not fully know or understand are exactly what blood is, what it is made up of, and how it is maintained.

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Just over half of the blood volume is made up of a pale yellow fluid called plasma. The rest of the blood is made up of cells (red blood cells and white blood cells) and platelets.
Blood has several vital functions:

Transport - oxygen in the red blood cells, absorbed, digested food by the plasma, excretory products by the plasma, hormones by the plasma etc.

- by the white blood cells (a.k.a. leucocytes).

Formation of lymph and tissue fluid.

Homeostasis.

Red blood cells

Also known as erythrocytes. These contain a pigment, haemoglobin, which gives them their colour.

Red blood cells are made in the bone marrow (the liver in a foetus) of many bones. They have a life span of about 120 days and are about 7µm in diameter (very small).

Being like a biconcave disc in shape, the surface area to volume ratio is very large. Oxygen can therefore diffuse very quickly into the cell and because the cell is so small, quickly bind to a haemoglobin molecule.

They lack organelles meaning that there is more room for haemoglobin. Their size and flexible membrane also means that they can squeeze through capillaries and transport oxygen extremely close to cells.

White blood cells

These cells all have a nucleus, most are much larger than red blood cells and are spherical or irregular in shape.

There are two basic types of white blood cells; the granulocytes (they have granular cytoplasm and lobed nuclei) and agranulocytes (the cytoplasm appears smooth and the nucleus is rounded or horseshoe in shape).

Agranulocytes:
Red bone marrow

Phagocytic against bacteria and antibody-coated viruses

Lymphocytes

Spleen, lymph nodes

Produces antibodies

Granulocytes:
Neutrophils

Red bone marrow

Phagocytic and contain lysosomes to break down ingested bacteria

Eosinophils

Red bone marrow

Phagocytic. Works against allergens by making antihistamines

Red bone marrow

Make antihistamines, make heparin (prevents unnecessary blood clotting) and make serotonin (makes the capillaries more leaky so that phagocytes can leave the blood and enter the site of infection

For more information, see the Learn It on Immunity.
Platelets

These are formed in the bone marrow and are fragments of larger cells. They have no nucleus but reactions do take place in the cytoplasm.

They have a variety of role such as blood clotting and the production of prostaglandins that regulate the degree of constriction or dilation in blood vessels.

Blood clotting: Platelets stick to damaged cells on the inner surface of blood vessels forming a plug. Unless the damage is small, platelets are involved in a chain of reactions by releasing particular chemicals. A soluble protein, fibrinogen (present in the plasma), becomes an insoluble protein, fibrin, and this forms layers of fibres across the wound. The mesh that this creates traps red blood cells and platelets and a scab is formed.
This has two useful effects:

1. Blood does not leak out of he vessel.

2. It is less likely that an infectious organism will enter from outside and cause harm.

Blood groups

The most commonly required blood-grouping system is the ABO system. It concerns two antigens that can occur on the surface of red blood cells. The antigens are called agglutinogens in this case and are: agglutinogen A and agglutinogen B.

Plasma also contains antigens, called agglutinins in this case, and they are agglutinin A and agglutinin B.

We shall call agglutinogens A or B and the agglutinins a or b. If A and a come into contact, the red cells will clump together. If B and b come into contact the red cells will clump together.

Therefore, in your blood you will not contain the agglutinogen and the agglutinin of the same type.

Blood transfusions

It is important to match blood correctly so that agglutinins in the recipient don't clump the red blood cells of the donor.

In transfusions it is important to remember that the volume of blood donated is relatively small compared to the volume of the recipients blood. The agglutinins in the plasma from the donor are so diluted that no harm is done. However the aggluinogens on the red blood cells are not so diluted so harm can be done. These are the possible transfusions (a is safe, a is not):

Recipient:

Donor:

A

B

AB

O

A

B

AB

O

Oxygen does dissolve in plasma but the solubility is low and decreases further if the temperature increases. The amount that could be carried by the plasma therefore would be completely insufficient to supply all cells.

There is a protein in the blood however that will carry 4 molecules of oxygen. The protein is called haemoglobin (Hb) and is made up of 4 polypeptide chains, each with a haem group. Each haem group can pick up 1 molecule of O ₂. The protein, being fairly small, could pass out of the blood during ultrafiltration in the kidneys so, to ensure that it is not lost, it is found within red blood cells.

Note: During this topic you will come across the term of partial pressure of oxygen. It does not mean the pressure of the blood itself. Essentially it is a measure of the concentration of oxygen. It is written in shorthand as and is measured in kilopascals (kPa).

Inhaled air in the alveoli has a pO ₂ = 14kPa. The pO ₂ of resting tissue = 5.3kPa (lower pO ₂ = lower O ₂concentration due to respiration) and the pO ₂ of active tissues = 2.7kPa. In either case, blood arriving at the lungs has a lower pO ₂ than that in the lungs.

There is therefore a diffusion gradient and oxygen will move from the alveoli into the blood. The O ₂ is then loaded onto the Hb until the blood is about 96% saturated with oxygen. The Hb is now called oxyhaemoglobin (HbO ₂).

Dissociation curves

The blood is then taken to tissues where the cells are respiring all the time, using oxygen. The pO ₂ will be low. As the red blood cell enters this region, the Hb will start to unload the O ₂, which will diffuse into the tissues and be used for further respiration. Since much of the Hb will have unloaded the O ₂, a much lower percentage of the blood will be saturated with O ₂.

A graph of the percentage saturation of blood with O ₂, i.e. the amount of HbO ₂ as opposed to Hb at different pO ₂ is shown below. It is called an oxygen dissociation curve:

It is S-shaped because of the behaviour of the Hb in different pO ₂.

The first molecule of O ₂ combines with an Hb and slightly distorts it. The joining of the first is quite slow (the flatter part of the graph at the beginning) but after the Hb has changed shape a little, it becomes easier and easier for the second and third O ₂ to join. This is shown by the curve becoming steeper. It flattens off at the top because joining the fourth O ₂ is more difficult.

Overall, it shows that at the higher and lower end of the partial pressures, there isn't a great deal of change in the saturation of the Hb, but in the middle range, a small change in the pO ₂ can result in a large change in the percentage saturation of the blood.

The effect of pH - The Bohr effect

The amount of O ₂ carried and released by Hb depends not only on the pO ₂ but also on pH.

An acidic environment causes HbO ₂ to dissociate (unload) to release the O ₂ to the tissues. Just a small decrease in the pH results in a large decrease in the percentage saturation of the blood with O ₂.

Acidity depends on the concentration of hydrogen ions.

H⁺ displaces O ₂ from the HbO ₂, thus increasing the O ₂ available to the respiring tissues.

HHb is called haemoglobinic acid.

This means that the Hb mops up free H⁺. That way the Hb helps to maintain the almost neutral pH of the blood. Hb acts as a buffer.

This release of O ₂ when the pH is low (even if the pO ₂ is relatively high) is called the Bohr effect.
When does the pH decrease because of free H⁺ in the blood?
During respiration, CO ₂ is produced. This diffuses into the blood plasma and into the red blood cells. Inside the red blood cells are many molecules of an enzyme called carbonic anhydrase. It catalyses the reaction between CO ₂ and H ₂O. The resulting carbonic acid then dissociates into HCO ₃− + H⁺. (Both reactions are reversible.)
Therefore, the more CO₂, the more the dissociation curve shifts to the right:
About 85% of the CO ₂ produced by respiration diffuses into the red blood cells and forms carbonic acid under the control of carbonic anhydrase.

The HCO ₃− diffuses out of the red blood cell into the plasma. This leaves a shortage of negatively charged ions inside the red blood cells. To compensate for this, chloride ions move from the plasma into the red blood cells. This restoration of the electrical charge inside the red blood cells is called the chloride shift.

About 5% of the CO ₂ produced simply dissolves in the blood plasma.

Some CO ₂ diffuses into the red blood cells but instead of forming carbonic acid, attaches directly onto the haemoglobin molecules to form carbaminohaemoglobin. Since the CO ₂ doesn't bind to the haem groups the Hb is still able to pick up O ₂ or H⁺.

Carbon monoxide

If carbon monoxide is breathed in (for example from car exhaust fumes), it binds irreversibly with haemoglobin to form carboxyhaemoglobin. This means that the Hb cannot load and carry O ₂.

To make matters worse, Hb combines with CO about 250 times more readily than it does with O ₂ so that, even if the CO concentration is fairly low, it can cause death due to lack of O ₂ to the tissues.

Cigarettes produce CO-containing smoke, which means that a small percentage of a smoker's blood is unable to transport O ₂.

Foetal haemoglobin

A foetus developing in the uterus must be able to load O ₂ from its mother's blood. Due to the respiration occurring in the foetus' cells, the pO ₂ is lower in the foetus blood than in the mother's blood. Some will unload from the mother's HbO ₂ and diffuse across to the foetus. However, because of the relatively small concentration difference, not much O ₂ is passed across.

To maximise the amount of O ₂ that the foetus receives, it has different haemoglobin - foetal haemoglobin. This has a higher affinity for O ₂ than adult Hb (it combines more readily with O ₂) so the foetus picks up enough O ₂. The dissociation curve shifts to the left.

Myoglobin

Skeletal muscle contains a pigment called myoglobin. It is very similar to Hb but has a higher affinity for O ₂.

It will load with O ₂ as Hb unloads and will store the O ₂ in the muscle until it is required. It only releases the O ₂ when the pO ₂ is very low - when the Hb cannot supply O ₂ fast enough and the demand is great. The dissociation curve shifts to the left.

Temperature

The higher the temperature, the less saturated the blood is with O ₂, i.e. the more the HbO ₂ unloads the O ₂.

This situation might arise during exercise - heat is produced during metabolic activity and during this time, the O ₂ supply will need to increase. The dissociation curve shifts to the right:

Environment

Animals living where there is a shortage of oxygen, animals living at high altitude need to be able to pick up O ₂ when it is at a very low pO ₂. Their dissociation curves will look like those of foetal haemoglobin and myoglobin - the curve shifts to the left.

If somebody were to climb quickly from sea level to high altitude, they are likely to suffer from altitude sickness, which can be fatal. However if the body is given time to adapt, most people can cope well with high altitudes. Instead of taking up the normal 45% of blood volume, the red blood cells can increase in numbers to take up 60%.

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Just over half of the blood volume is made up of a pale yellow fluid called plasma. The rest of the blood is made up of cells (red blood cells and white blood cells) and platelets.Blood has several vital functions:Transport - oxygen in the red blood cells, absorbed, digested food by the plasma, excretory products by the plasma, hormones by the plasma etc.Defence - by the white blood cells (a.k.a.

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Blood Vessels - Quick A Level Biology Revision

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Blood Vessels. AS Biology. OCR Exam Board - Module 3. The "You need to know..." section has come from the OCR specification.