# data[].attributes.body
I learned about the significant parts of the endocrine system such as how our hormones are controlled, the adrenal system, metabolism, blood pressure the organs in the endocrine system, and *sexual processes*.

This was the scariest one.

# data[].attributes.attachment_link.readable_text
What are the endocrine system organs?

Your endocrine system consists of three types of tissues:

Endocrine glands.

Organs.

Endocrine-related tissues.

Endocrine system glands

Glands are special tissues in your body that create and release substances. Endocrine glands make and release hormones directly into your bloodstream. The endocrine glands in your body from head to toe include:

Pineal gland: This is a tiny gland in your brain that's beneath the back part of your corpus callosum. It makes and releases the hormone melatonin.

Pituitary gland: This is a small, pea-sized gland at the base of your brain below your hypothalamus. It releases eight hormones, some of which trigger other endocrine glands to release hormones.

Thyroid gland: This is a small, butterfly-shaped gland at the front of your neck under your skin. It releases hormones that help control your metabolism.

Parathyroid glands: These are four pea-sized glands that are typically behind your thyroid. Sometimes they exist along your esophagus or in your chest (ectopic parathyroid glands). They release parathyroid hormone (PTH), which controls the level of calcium in your blood.

Adrenal glands: These are small, triangle-shaped glands on top of each of your two kidneys. They release several hormones that manage bodily processes, like metabolism, blood pressure and your stress response.

You have other glands in your body that aren't endocrine glands, such as sweat glands (a type of exocrine gland).

Endocrine system organs

Certain organs in your body also make and release hormones. An organ is a group of tissues that form a structure that performs specific important functions in your body. The organs that are part of your endocrine system include:

Hypothalamus: This is a structure deep within your brain (which is an organ). It's the main link between your endocrine system and your nervous system. It makes two hormones that your pituitary gland stores and releases (oxytocin and vasopressin) and makes and releases two hormones (dopamine and somatostatin).

Pancreas: This organ is in the back of your abdomen (belly). It's both an organ and a gland and is also part of your digestive system. It releases two hormones that are essential to maintaining healthy blood sugar levels: insulin and glucagon.

Adipose tissue (body fat): This is a connective tissue that extends throughout your body. It's found under your skin (subcutaneous fat), between your internal organs (visceral fat) and in the inner cavities of bones (bone marrow adipose tissue). Adipose tissue releases many different hormones, including leptin, angiotensin and adiponectin.

Ovaries: These are small, oval-shaped glands located on either side of your uterus. They produce and store your eggs (also called ova) and make sex hormones that control your menstrual cycle and pregnancy.

Testicles (testes): These are small, round organs underneath your penis in your scrotum. They make sperm and sex hormones, particularly testosterone.

Other tissues that release hormones

Other tissues in your body release hormones. But we don't typically think of them as endocrine system tissues because they have other, more significant functions or roles. They include:

Digestive tract (stomach and small intestine): Your digestive tract is the largest endocrine-related organ system. It makes and releases several hormones that play a role in your metabolism. Examples include gastrin and ghrelin.

Kidneys: Your kidneys are two bean-shaped organs that filter your blood. They're part of your urinary system, but they also produce hormones, like erythropoietin and renin.

Liver: Your liver is part of your digestive system, but it also produces hormones, including insulin-like growth factor 1 (IGF-1) and angiotensinogen.

Heart: When your blood pressure rises, your heart releases two hormones called A-type natriuretic peptide and B-type natriuretic peptide.

Placenta: The placenta is a temporary endocrine organ that forms during pregnancy. It produces hormones that are important for maintaining a healthy pregnancy and preparing your body for labor and breastfeeding (chestfeeding).

# data[].attributes.attachment_link.description
Your endocrine system consists of the tissues (mainly glands) that create and release hormones. Endocrine tissues include your pituitary gland, thyroid and others.

# data[].attributes.body
I learned about the different pathways stimulus reactions take in different senses. I learned about how senses are processed on a cellular level such as how color is seen and processed through rods and cones in the eyes and even flips like a mirror and the process of how taste buds absorb and process taste as well as smell, touch and hear, all on a cellular level.

# data[].attributes.attachment_link.provider_name
ExploreLearning : Get hands-on, minds-on in math and science

# data[].attributes.attachment_link.title
ExploreLearning Gizmos - Math & Science Simulations for Students

# data[].attributes.attachment_link.description
Hundreds of online simulations with lesson materials, supporting research-based strategies to build deep conceptual understanding in math and science.

# data[].attributes.body
I learned about neurotransmitters and the passing of information through neurons on a cellular level and the detailed process of synapses passing from neuron to neuron. I also learned about the different effects of drugs on the human brain and the bonus information that we know very little about a lot of things in our own brain including but not limited to the cannabinoid receptor in our brain.

# data[].attributes.attachment_link.readable_text
Bronze

This resource has undergone expert review.

Resource Overview

Year:

Year 9-10, Year 11-12

Time Allocated

1-6 lessons

Links to National Curriculum

Available

Developers

University of Utah, Genetic Science Learning Center, USA.

Summary

Players take a look inside the brains of mice that are under the influence of different drugs. The chemical interactions at the synaptic level are explored.

# data[].attributes.attachment_link.description
Bronze This resource has undergone expert review. Resource Overview Year: Year 9-10, Year 11-12 Time Allocated 1-6 lessons Links to National Curriculum Developers University of Utah, Genetic Science Learning Center, USA. Summary Players take a look inside the brains of mice that are under the influence of different drugs.

# data[].attributes.headline
Sympathetic vs Parasympathetic Nervous Systems

# data[].attributes.subject
Sympathetic vs Parasympathetic Nervous Systems

# data[].attributes.body
I learned about the sympathetic system that controls the fight or flight (or freeze) responses in the body based on external stimulation. I learned about how the sympathetic system is responsible for quick actions and responses like quick heartbeat and sweating in one of these responses. I learned about the Parasympathetic system and its role as the "rest and digest" system. I learned about the parasympathetic nervous system's function to shut up the sympathetic nervous system and calm ourselves down, using the same body functions.

# data[].attributes.attachment_link.readable_text
The central nervous system consists of the brain, spinal cord, and all of the nerves within our body. The autonomic nervous system is the part of the central nervous system that regulates involuntary body functions. Within the autonomic nervous system, we find the sympathetic and parasympathetic nervous systems, which both control the same parts of the body and same general functions of the body, but with opposing effects.

Understanding what sympathetic and parasympathetic responses

Understanding what sympathetic and parasympathetic responses are is not vital to them happening-they are involuntary responses to various stimuli. However, when we understand what each part of our autonomic nervous system does and what it needs to function properly, we become well-informed practice members at Experience Health & Wellness Center and can better explain why seeing a Cape Coral chiropractor is so beneficial.

The Sympathetic Nervous System: Fight or Flight Response

The fight or flight response is commonly known, but what may be lesser known is that this reaction to external stimuli is based completely on the sympathetic nervous system. When we are faced with a perceived threat of any kind, whether physical or emotional, our sympathetic nervous system kicks into gear and brings about automatic and involuntary responses, such as increased heart rate, elevated blood pressure, heightened awareness, elevated respiratory rate, and more sweating. The sympathetic nervous system also shuts down many parasympathetic responses in order to utilize more energy for the fight or flight response.

The Parasympathetic Nervous System: Rest and Digest

The parasympathetic nervous system affects the same body functions as the sympathetic nervous system, but in a completely different way. It works to slow down certain responses and bring about a state of calm to the body, allowing it to rest, relax, and repair itself. The primary function of the parasympathetic nervous system is to maintain long-term health and a healthy balance across all of the body's functions. Parasympathetic responses include an increase of digestive enzymes, decreased heart rate, constriction of bronchial tubes in lungs, and more relaxed muscles.

Why Does This Matter?

Both the sympathetic and parasympathetic nervous systems are vital to our health and survival. However, for our bodies to live with optimal health and proper function for as long as possible, there must be a balance between the two. If there is a miscommunication between your brain and the impulses that promote sympathetic responses, your body will be functioning in fight or flight mode far too often and for far too long, and this can have negative consequences on your overall health.

You want a healthy balance between the two parts of your autonomic nervous system, and that comes when your spinal cord and nerves are functioning properly. At Experience Health & Wellness Center, Dr. Clark's main focus is removing any nerve interference that could be getting in the way of proper sympathetic and parasympathetic responses through specific chiropractic care. This will allow your body to react appropriately and effectively to any stimuli and to ensure your body retains proper function and achieves optimal health, both short-term and long-term.

To learn more about your body's nervous system or to schedule a consultation with Dr. Omar Clark and his team, contact Experience Health & Wellness Center at 239-205-3700.
Sources
Gibbons, P.F., Gosling, C.M., Holmes, M. "Short-Term Effects of Cervical Manipulation on Edge Light Pupil Cycle Time: A Pilot Study." Journal of Manipulative and Physiological Therapeutics, 2000 Sep; 23(7): 465-469. https://www.jmptonline.org/article/S0161-4754%2800%2981597-3/abstract.

Welch, A., Boone, R. "Sympathetic and Parasympathetic Responses to Specific Diversified Adjustments to Chiropractic Vertebral Subluxations of the Cervical and Thoracic Spine." Journal of Chiropractic Medicine, 2008 Sep; 7(3): 86-93. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2686395/.

# data[].attributes.attachment_link.title
Sympathetic Vs. Parasympathetic and Why They Matter

# data[].attributes.attachment_link.description
The central nervous system consists of the brain, spinal cord, and all of the nerves within our body. The autonomic nervous system is the part of the central nervous system that regulates involuntary body functions.

# data[].attributes.body
I learned about the Peripheral nervous system and its entanglements with the somatic and autonomic systems. I learned about how fight or flight and reflexes are communicated throughout the brain and spinal cord and central and peripheral systems etc. i also learned the different nerves and structure of them.

# data[].attributes.attachment_link.readable_text
The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system consists of nerves that go to the skin and muscles and is involved in conscious activities. The autonomic nervous system consists of nerves that connect the CNS to the visceral organs such as the heart, stomach, and intestines. It mediates unconscious activities.

Structure of a Nerve
A nerve contains bundles of nerve fibers, either axons or dendrites, surrounded by connective tissue. Sensory nerves contain only afferent fibers, long dendrites of sensory neurons. Motor nerves have only efferent fibers, long axons of motor neurons. Mixed nerves contain both types of fibers.
A connective tissue sheath called the epineurium surrounds each nerve. Each bundle of nerve fibers is called a fasciculus and is surrounded by a layer of connective tissue called the perineurium. Within the fasciculus, each individual nerve fiber, with its myelin and neurilemma, is surrounded by connective tissue called the endoneurium. A nerve may also have blood vessels enclosed in its connective tissue wrappings.

Cranial Nerves

Twelve pairs of cranial nerves emerge from the inferior surface of the brain. All of these nerves, except the vagus nerve, pass through foramina of the skull to innervate structures in the head, neck, and facial region.

The cranial nerves are designated both by name and by Roman numerals, according to the order in which they appear on the inferior surface of the brain. Most of the nerves have both sensory and motor components. Three of the nerves are associated with the special senses of smell, vision, hearing, and equilibrium and have only sensory fibers. Five other nerves are primarily motor in function but do have some sensory fibers for proprioception. The remaining four nerves consist of significant amounts of both sensory and motor fibers.

Acoustic neuromas are benign fibrous growths that arise from the balance nerve, also called the eighth cranial nerve or vestibulocochlear nerve. These tumors are non- malignant, meaning that they do not spread or metastasize to other parts of the body. The location of these tumors is deep inside the skull, adjacent to vital brain centers in the brain stem. As the tumors enlarge, they involve surrounding structures which have to do with vital functions. In the majority of cases, these tumors grow slowly over a period of years. In other cases, the growth rate is more rapid and patients develop symptoms at a faster pace. Usually, the symptoms are mild and many patients are not diagnosed until some time after their tumor has developed. Many patients also exhibit no tumor growth over a number of years when followed by yearly MRI scans.

Spinal Nerves

Thirty-one pairs of spinal nerves emerge laterally from the spinal cord. Each pair of nerves corresponds to a segment of the cord and they are named accordingly. This means there are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve.

Each spinal nerve is connected to the spinal cord by a dorsal root and a ventral root. The cell bodies of the sensory neurons are in the dorsal root ganglion, but the motor neuron cell bodies are in the gray matter. The two roots join to form the spinal nerve just before the nerve leaves the vertebral column. Because all spinal nerves have both sensory and motor components, they are all mixed nerves.

Autonomic Nervous System

The autonomic nervous system is a visceral efferent system, which means it sends motor impulses to the visceral organs. It functions automatically and continuously, without conscious effort, to innervate smooth muscle, cardiac muscle, and glands. It is concerned with heart rate, breathing rate, blood pressure, body temperature, and other visceral activities that work together to maintain homeostasis.

The autonomic nervous system has two parts, the sympathetic division and the parasympathetic division. Many visceral organs are supplied with fibers from both divisions. In this case, one stimulates and the other inhibits. This antagonistic functional relationship serves as a balance to help maintain homeostasis.

# data[].attributes.attachment_link.description
The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system.

# data[].attributes.headline
Major Parts of the Brain and What They Do

# data[].attributes.subject
Major Parts of the Brain and What They Do

# data[].attributes.body
I learned about these five parts of the brain and their function individually. I learned about how we process information through our brains and how our senses work through different parts of our brains. I learned about what would happen if a stroke were to stop one-half of someone's brain in the detailed stages of that stroke. I learned that for some reason the occipital lobe is located on the opposite end of the eyes.

# data[].attributes.body
I learned about the central nervous system, which consists of the brain and spinal cord. I learned the pathways nerves take between the brain, spinal cord, and muscles through nerve endings. I learned the different necessities of the different pathways, and why some nerve impulses pass the brain entirely in form of relief or to get away from danger. I learned about the different parts of the brain and their functions.

# data[].attributes.attachment_link.title
Central Nervous System: The Brain and Spinal Cord (for Parents) - Nemours KidsHealth

# data[].attributes.attachment_link.description
The brain and spinal cord make up the central nervous system. Find out how they work together to control everything we do.

# data[].attributes.body
I learned how each muscle functions in relation to the others as well as the process of muscle contraction. I learned the details of muscle contraction and how the contraction is triggered by neurons and travels across the muscle. I learned the functions of the muscles and how it's controlled on a cellular level.

# data[].attributes.body
I learned the importance of every muscle and its place to go along with it as well as the different tissue cells that make up the muscles and connect both bone and muscle.

# data[].attributes.attachment_link.readable_text
human muscle system, the muscles of the human body that work the skeletal system, that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle-like the muscles of all vertebrates-is often divided into striated muscle (or skeletal muscle), smooth muscle, and cardiac muscle. Smooth muscle is under involuntary control and is found in the walls of blood vessels and of structures such as the urinary bladder, the intestines, and the stomach. Cardiac muscle makes up the mass of the heart and is responsible for the rhythmic contractions of that vital pumping organ; it too is under involuntary control. With very few exceptions, the arrangement of smooth muscle and cardiac muscle in humans is identical to the arrangement found in other vertebrate animals.

This article is concerned with the skeletal muscles of the human body, with emphasis on muscle movements and the changes that have occurred in human skeletal musculature as a result of the long evolutionary process that involved the assumption of upright posture. Smooth muscle and cardiac muscle and the physiology of muscle contraction are treated at great length in the article muscle. For descriptions of disorders that affect the human muscle system, see muscle disease.

The muscle groups and their actions

The following sections provide a basic framework for the understanding of gross human muscular anatomy, with descriptions of the large muscle groups and their actions. The various muscle groups work in a coordinated fashion to control the movements of the human body.

The neck

The motion of the neck is described in terms of rotation, flexion, extension, and side bending (i.e., the motion used to touch the ear to the shoulder). The direction of the action can be ipsilateral, which refers to movement in the direction of the contracting muscle, or contralateral, which refers to movement away from the side of the contracting muscle.

Rotation is one of the most-important actions of the cervical (neck) spine. Rotation is accomplished primarily by the sternocleidomastoid muscle, which bends the neck to the ipsilateral side and rotates the neck contralaterally. Together, the sternocleidomastoid muscles on both sides of the neck act to flex the neck and raise the sternum to assist in forced inhalation. The anterior and middle scalene muscles, which also are located at the sides of the neck, act ipsilaterally to rotate the neck, as well as to elevate the first rib. The splenius capitis and splenius cervicis, which are located in the back of the neck, work to rotate the head.

Side bending also is an important action of the cervical spine. The sternocleidomastoid muscles are involved in cervical side bending. The posterior scalene muscles, located on the lower sides of the neck, ipsilaterally bend the neck to the side and elevate the second rib. The splenius capitis and splenius cervicis also assist in neck side bending. The erector spinae muscles (iliocostalis, longissimus, and spinalis) are large, deep muscles that extend the length of the back. All three act to ipsilaterally side bend the neck.

Neck flexion refers to the motion used to touch the chin to the chest. It is accomplished primarily by the sternocleidomastoid muscles, with assistance from the longus colli and the longus capitis, which are found in the front of the neck. Neck extension is the opposite of flexion and is accomplished by many of the same muscles that are used for other neck movements, including the splenius cervicis, splenius capitis, iliocostalis, longissimus, and spinalis muscles.

The back

The back contains the origins of many of the muscles that are involved in the movement of the neck and shoulders. In addition, the axial skeleton that runs vertically through the back protects the spinal cord, which innervates almost all the muscles in the body.

Multiple muscles in the back function specifically in movements of the back. The erector spinae muscles, for example, extend the back (bend it backward) and side bend the back. The semispinalis dorsi and semispinalis capitis muscles also extend the back. The small muscles of the vertebrae (the multifidi and rotators) help rotate, extend, and side bend the back. The quadratus lumborum muscle in the lower back side bends the lumbar spine and aids in the inspiration of air through its stabilizing affects at its insertion at the 12th rib (the last of the floating ribs). The scapula (shoulder blade) is elevated by the trapezius muscle, which runs from the back of the neck to the middle of the back, by the rhomboid major and rhomboid minor muscles in the upper back, and by the levator scapulae muscle, which runs along the side and back of the neck.

# data[].attributes.attachment_link.title
Human muscle system | Functions, Diagram, & Facts

# data[].attributes.attachment_link.description
Human muscle system, the muscles of the human body that work the skeletal system, that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle-like the muscles of all vertebrates-is often divided into striated muscle, smooth muscle, and cardiac muscle.

# data[].attributes.body
I learned the placement of the muscles as well as the different roles of, support, attachment, or movement that axial and appendicular muscles play. I learned muscles how muscle placement and bone placement in the body effects each other and intertwine to form a strong working human body.

# data[].attributes.body
I learned the functions of the cells that make up the bone and how they work together to maintain the bone itself. I learned the complicated channels of cells in a bone and the job of blood cells in the bone, how they travel through the bone itself and the lifespan of a bone; how that bone develops through a person's life.

# data[].attributes.attachment_link.readable_text
Learning Objectives

By the end of this section, you will be able to:

Discuss the process of bone formation and development.

List the steps of intramembranous ossification

Explain the role of cartilage in bone formation

List the steps of endochondral ossification

Explain the growth activity at the epiphyseal plate

Explain how bones remodel overtime

Compare and contrast the processes of intramembranous and endochondral bone formation

Compare and contrast the interstitial and appositional growth

In the early stages of embryonic development, the embryo's skeleton consists of fibrous membranes and hyaline cartilage. By the sixth or seventh week of embryonic life, the actual process of bone development, ossification (osteogenesis), begins. There are two osteogenic pathways-intramembranous ossification and endochondral ossification-but in the end, mature bone is the same regardless of the pathway that produces it.

During intramembranous ossification, compact and spongy bone develops directly from sheets of mesenchymal (undifferentiated) connective tissue. The flat bones of the face, most of the cranial bones, and the clavicles (collarbones) are formed via intramembranous ossification.

The process begins when mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells ( Figure 6.4.1 a). Some of these cells will differentiate into capillaries, while others will become osteogenic cells and then osteoblasts. Although they will ultimately be spread out by the formation of bone tissue, early osteoblasts appear in a cluster called an ossification center.

The osteoblasts secrete osteoid, uncalcified matrix consisting of collagen precursors and other organic proteins, which calcifies (hardens) within a few days as mineral salts are deposited on it, thereby entrapping the osteoblasts within. Once entrapped, the osteoblasts become osteocytes ( Figure 6.4.1 b). As osteoblasts transform into osteocytes, osteogenic cells in the surrounding connective tissue differentiate into new osteoblasts at the edges of the growing bone.

Several clusters of osteoid unite around the capillaries to form a trabecular matrix, while osteoblasts on the surface of the newly formed spongy bone become the cellular layer of the periosteum ( Figure 6.4.1 c). The periosteum then secretes compact bone superficial to the spongy bone. The spongy bone crowds nearby blood vessels, which eventually condense into red bone marrow ( Figure 6.4.1 d). The new bone is constantly also remodeling under the action of osteoclasts (not shown).

Intramembranous ossification begins in utero during fetal development and continues on into adolescence. At birth, the skull and clavicles are not fully ossified nor are the junctions between the skull bone (sutures) closed. This allows the skull and shoulders to deform during passage through the birth canal. The last bones to ossify via intramembranous ossification are the flat bones of the face, which reach their adult size at the end of the adolescent growth spurt.

In endochondral ossification, bone develops by replacing hyaline cartilage. Cartilage does not become bone. Instead, cartilage serves as a template to be completely replaced by new bone. Endochondral ossification takes much longer than intramembranous ossification. Bones at the base of the skull and long bones form via endochondral ossification.

In a long bone, for example, at about 6 to 8 weeks after conception, some of the mesenchymal cells differentiate into chondroblasts (cartilage cells) that form the hyaline cartilaginous skeletal precursor of the bones ( Figure 6.4.2 a). This cartilage is a flexible, semi-solid matrix produced by chondroblasts and consists of hyaluronic acid, chondroitin sulfate, collagen fibers, and water. As the matrix surrounds and isolates chondroblasts, they are called chondrocytes. Unlike most connective tissues, cartilage is avascular, meaning that it has no blood vessels supplying nutrients and removing metabolic wastes. All of these functions are carried on by diffusion through the matrix from vessels in the surrounding perichondrium, a membrane that covers the cartilage, a).

As more and more matrix is produced, the cartilaginous model grow in size. Blood vessels in the perichondrium bring osteoblasts to the edges of the structure and these arriving osteoblasts deposit bone in a ring around the diaphysis - this is called a bone collar ( Figure 6.4.2b). The bony edges of the developing structure prevent nutrients from diffusing into the center of the hyaline cartilage. This results in chondrocyte death and disintegration in the center of the structure. Without cartilage inhibiting blood vessel invasion, blood vessels penetrate the resulting spaces, not only enlarging the cavities but also carrying osteogenic cells with them, many of which will become osteoblasts. These enlarging spaces eventually combine to become the medullary cavity. Bone is now deposited within the structure creating the primary ossification center (Figure 6.4.2 c).

While these deep changes are occurring, chondrocytes and cartilage continue to grow at the ends of the structure (the future epiphyses), which increases the structure's length at the same time bone is replacing cartilage in the diaphyses. This continued growth is accompanied by remodeling inside the medullary cavity (osteoclasts were also brought with invading blood vessels) and overall lengthening of the structure ( Figure 6.4.2 d). By the time the fetal skeleton is fully formed, cartilage remains at the epiphyses and at the joint surface as articular cartilage.

After birth, this same sequence of events (matrix mineralization, death of chondrocytes, invasion of blood vessels from the periosteum, and seeding with osteogenic cells that become osteoblasts) occurs in the epiphyseal regions, and each of these centers of activity is referred to as a secondary ossification center ( Figure 6.4.2 e). Throughout childhood and adolescence, there remains a thin plate of hyaline cartilage between the diaphysis and epiphysis known as the growth or epiphyseal plate ( Figure 6.4.2 f). Eventually, this hyaline cartilage will be removed and replaced by bone to become the epiphyseal line.

The epiphyseal plate is the area of elongation in a long bone. It includes a layer of hyaline cartilage where ossification can continue to occur in immature bones. We can divide the epiphyseal plate into a diaphyseal side (closer to the diaphysis) and an epiphyseal side (closer to the epiphysis). On the epiphyseal side of the epiphyseal plate, hyaline cartilage cells are active and are dividing and producing hyaline cartilage matrix. (figure 6.43, reserve and proliferative zones). On the diaphyseal side of the growth plate, cartilage calcifies and dies, then is replaced by bone (figure 6.43, zones of hypertrophy and maturation, calcification and ossification). As cartilage grows, the entire structure grows in length and then is turned into bone. Once cartilage cannot grow further, the structure cannot elongate more.

The epiphyseal plate is composed of five zones of cells and activity ( Figure 6.4.3). The reserve zone is the region closest to the epiphyseal end of the plate and contains small chondrocytes within the matrix. These chondrocytes do not participate in bone growth but secure the epiphyseal plate to the overlying osseous tissue of the epiphysis.

The proliferative zone is the next layer toward the diaphysis and contains stacks of slightly larger chondrocytes. It makes new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate. Chondrocytes in the next layer, the zone of maturation and hypertrophy, are older and larger than those in the proliferative zone. The more mature cells are situated closer to the diaphyseal end of the plate. The longitudinal growth of bone is a result of cellular division in the proliferative zone and the maturation of cells in the zone of maturation and hypertrophy. This growth within a tissue is called interstitial growth.

Most of the chondrocytes in the zone of calcified matrix, the zone closest to the diaphysis, are dead because the matrix around them has calcified, restricting nutrient diffusion. Capillaries and osteoblasts from the diaphysis penetrate this zone, and the osteoblasts secrete bone tissue on the remaining calcified cartilage. Thus, the zone of calcified matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis.

Bones continue to grow in length until early adulthood. The rate of growth is controlled by hormones, which will be discussed later. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces all the cartilage, longitudinal growth stops. All that remains of the epiphyseal plate is the ossified epiphyseal line ( Figure 6.4.4).

EDITOR'S NOTE: you should add an xray of a epiphyseal plate vs line
While bones are increasing in length, they are also increasing in diameter; growth in diameter can continue even after longitudinal growth ceases. This growth by adding to the free surface of bone is called appositional growth. Appositional growth can occur at the endosteum or peristeum where osteoclasts resorb old bone that lines the medullary cavity, while osteoblasts produce new bone tissue. The erosion of old bone along the medullary cavity and the deposition of new bone beneath the periosteum not only increase the diameter of the diaphysis but also increase the diameter of the medullary cavity. This remodeling of bone primarily takes place during a bone's growth. However, in adult life, bone undergoes constant remodeling, in which resorption of old or damaged bone takes place on the same surface where osteoblasts lay new bone to replace that which is resorbed. Injury, exercise, and other activities lead to remodeling. Those influences are discussed later in the chapter, but even without injury or exercise, about 5 to 10 percent of the skeleton is remodeled annually just by destroying old bone and renewing it with fresh bone.

Section Review

All bone formation is a replacement process. During development, tissues are replaced by bone during the ossification process. In intramembranous ossification, bone develops directly from sheets of mesenchymal connective tissue. In endochondral ossification, bone develops by replacing hyaline cartilage. Activity in the epiphyseal plate enables bones to grow in length (this is interstitial growth). Appositional growth allows bones to grow in diameter. Remodeling occurs as bone is resorbed and replaced by new bone.

Critical Thinking Questions

1. In what ways do intramembranous and endochondral ossification differ?

2. Considering how a long bone develops, what are the similarities and differences between a primary and a secondary ossification center?

3. Compare and contrast interstitial and appositional growth.

Glossary

appositional growth

growth by adding to the free surface of bone, can occur at endosteum or periosteum

endochondral ossification

process in which bone forms by replacing hyaline cartilage

epiphyseal line

completely ossified remnant of the epiphyseal plate

epiphyseal plate

junction between epiphysis and diaphysis of growing long bone, contains hyaline cartilage being replaced by bone, site of long bone elongation

interstitial growth

growth by adding within the interior of a structure, occurs by hyaline cartilage at epiphyseal plate

intramembranous ossification

process by which bone forms directly from mesenchymal tissue

ossification

(also, osteogenesis) bone formation

ossification center

cluster of osteoblasts found in the early stages of intramembranous ossification

osteoid

uncalcified bone matrix secreted by osteoblasts, contains collagen and collagen pre-cursors

perichondrium

membrane that covers cartilage

primary ossification center

region, deep in the diaphysis, where bone development starts during endochondral ossification

proliferative zone

region of the epiphyseal plate that makes new chondrocytes to replace those that die at the diaphyseal end of the plate and contributes to longitudinal growth of the epiphyseal plate

remodeling

process by which osteoclasts resorb old or damaged bone at the same time as and on the same surface where osteoblasts form new bone to replace that which is resorbed

reserve zone

region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis

secondary ossification center

region of endochondral bone development in the epiphyses

zone of calcified matrix

region of the epiphyseal plate closest to the diaphyseal end; functions to connect the epiphyseal plate to the diaphysis

zone of maturation and hypertrophy

region of the epiphyseal plate where chondrocytes from the proliferative zone grow and mature and contribute to the longitudinal growth of the epiphyseal plate

Solutions
Answers for Critical Thinking Questions

1. In intramembranous ossification, bone develops directly from sheets of mesenchymal connective tissue, but in endochondral ossification, bone develops by replacing hyaline cartilage. Intramembranous ossification is complete by the end of the adolescent growth spurt, while endochondral ossification lasts into young adulthood. The flat bones of the face, most of the cranial bones, and a good deal of the clavicles (collarbones) are formed via intramembranous ossification, while bones at the base of the skull and the long bones form via endochondral ossification.

2. A single primary ossification center is present, during endochondral ossification, deep in diaphysis. Like the primary ossification center, secondary ossification centers are present during endochondral ossification, but they form later, and there are at least two of them, one in each epiphysis.

3. Interstitial growth occurs in hyaline cartilage of epiphyseal plate, increases length of growing bone. Appositional growth occurs at endosteal and periosteal surfaces, increases width of growing bones. Interstitial growth only occurs as long as hyaline is present, cannot occur after epiphyseal plate closes. Appositional growth can continue throughout life.

# data[].attributes.attachment_link.description
By the end of this section, you will be able to: Discuss the process of bone formation and development.

# data[].attributes.body
I learned the placement of the different functions in bones including their cells and internal structures. I learned the necessities that make the cells that make up our bones bring. I also learned the difference between spongey and compact bone, bone marrows, different cells and even blood vessels and how muscles and bones connect.

# data[].attributes.attachment_link.title
6.3 Bone Structure – Anatomy & Physiology

# data[].attributes.attachment_link.description
By the end of this section, you will be able to:

# data[].attributes.body
I learned directional terms of the human body and how to locate areas correctly in my language. I learned the different planes of the body as well as their relevant bones in the area.

# data[].attributes.attachment_link.readable_text
Before we get into the following learning units, which will provide more detailed discussion of topics on different human body systems, it is necessary to learn some useful terms for describing body structure. Knowing these terms will make it much easier for us to understand the content of the following learning units. Three groups of terms are introduced here:

Directional Terms

Directional terms describe the positions of structures relative to other structures or locations in the body.

Superior or cranial - toward the head end of the body; upper (example, the hand is part of the superior extremity).

Inferior or caudal - away from the head; lower (example, the foot is part of the inferior extremity).

Anterior or ventral - front (example, the kneecap is located on the anterior side of the leg).

Posterior or dorsal - back (example, the shoulder blades are located on the posterior side of the body).

Medial - toward the midline of the body (example, the middle toe is located at the medial side of the foot).

Lateral - away from the midline of the body (example, the little toe is located at the lateral side of the foot).

Proximal - toward or nearest the trunk or the point of origin of a part (example, the proximal end of the femur joins with the pelvic bone).

Distal - away from or farthest from the trunk or the point or origin of a part (example, the hand is located at the distal end of the forearm).

Planes of the Body

Coronal Plane (Frontal Plane) - A vertical plane running from side to side; divides the body or any of its parts into anterior and posterior portions.

Sagittal Plane (Lateral Plane) - A vertical plane running from front to back; divides the body or any of its parts into right and left sides.

Axial Plane (Transverse Plane) - A horizontal plane; divides the body or any of its parts into upper and lower parts.

Median plane - Sagittal plane through the midline of the body; divides the body or any of its parts into right and left halves.

Body Cavities

The cavities, or spaces, of the body contain the internal organs, or viscera. The two main cavities are called the ventral and dorsal cavities. The ventral is the larger cavity and is subdivided into two parts (thoracic and abdominopelvic cavities) by the diaphragm, a dome-shaped respiratory muscle.

Thoracic cavity

The upper ventral, thoracic, or chest cavity contains the heart, lungs, trachea, esophagus, large blood vessels, and nerves. The thoracic cavity is bound laterally by the ribs (covered by costal pleura) and the diaphragm caudally (covered by diaphragmatic pleura).

Abdominal and pelvic cavity

The lower part of the ventral (abdominopelvic) cavity can be further divided into two portions: abdominal portion and pelvic portion. The abdominal cavity contains most of the gastrointestinal tract as well as the kidneys and adrenal glands. The abdominal cavity is bound cranially by the diaphragm, laterally by the body wall, and caudally by the pelvic cavity. The pelvic cavity contains most of the urogenital system as well as the rectum. The pelvic cavity is bounded cranially by the abdominal cavity, dorsally by the sacrum, and laterally by the pelvis.

Dorsal cavity

The smaller of the two main cavities is called the dorsal cavity. As its name implies, it contains organs lying more posterior in the body. The dorsal cavity, again, can be divided into two portions. The upper portion, or the cranial cavity, houses the brain, and the lower portion, or vertebral canal houses the spinal cord.

# data[].attributes.attachment_link.description
Before we get into the following learning units, which will provide more detailed discussion of topics on different human body systems, it is necessary to learn some useful terms for describing body structure. Knowing these terms will make it much easier for us to understand the content of the following learning units.