The gross structure of a long bone.

 A long bone, such as those of the limbs, shows both varieties of bone tissue. When sawn through longitudinally the distribution of compact and cancellous tissue can be seen. It is divided into a shaft, the central part, and two extremities or ends of the bone. If the shaft is cut across, dense bone tissue will be seen and a hollow center called the medullary cavity, containing yellow bone marrow. If the end of a long bone is cut, the space in the cancellous tissues will be seen containing red bone marrow. In the yellow marrow fat cells predominate; in the red marrow red blood cells are very numerous the red bone marrow is the birthplace of both red and white blood cells.

Cancellous bone tissue

Cancellous bone tissue is spongy in structure. It is found principally in the ends of the long bones, in the shorts bones, and as a layer in between two layers of compact tissue in the flat bones such as the scapula, cranium, sternum and ribs.

Compact bone tissue

Compact bone tissue is hard and dense; it is found in flat bones and in the shafts of the long bones, and as a thin covering over all bones.

Bone structure and growth.

 Bone is the hardest of the connective tissue of the body. It is composed of the nearly 50 per cent water; the remaining solid parts are divided into a composition of mineral matter, principally calcium salts 67 per cent, and cellular matter 33 per cent.

  The structure of bone may be examined by the naked eye when the gross structure is seen, and with the aid of a microscope, when the minute structure is examined. Bone consists of two kinds of tissue: compact tissue and cancellous tissue.

Elastic cartilage

Elastic cartilage is often called yellow elastic cartilage because it contains a great many elastic fibers which are yellow. It is found in the lining of the ear, the epiglottis and the Eustachian (pharyngotympanic) tubes; when compressed or bent it is very flexible and readily springs back into shape.

White fiber cartilage

White fiber cartilage which is composed of bundles of fibers having the cartilage cells arranged between the bundles of fibers is found where great strength is required. Fibro-cartilage deepens the cavities of bony sockets, as in the acetabulum of the innominate bone and the glenoid cavity of the scapula. It also form the inter-articular cartilages, as in semilunar cartilages of the knee and the connecting cartilages as in the intervertebral discs of the vertebral column and in the pad of the cartilage at the symphysis pubis.

Hyaline cartilage

Hyaline cartilage consists of collagen fibers embedded in a clear, glassy, tough ground substance or matrix. It is firm and elastic and is found covering the end of the long bones as articular cartilage, in the costal cartilages, in the nose, larynex, trachea and bronchial tubes where it keeps open the orifices. It is also the temporary cartilage from which bone is formed. In the developing embryo and fetus it acts as a temporary scaffolding supporting the other tissues until bone is lade down to replace it. The cells are hyaline cartilages are arranged principally in small groups. Set in though matrix.

Cartilage

Cartilage or gristle is a dense clear blue-white substance very firm but less firm than bone. It is found principally at joints and between bones. The bones of the embryo are first cartilage and when adult age is reached cartilage is found covering the bone ends. Cartilage does not contain blood vessels but it I covered by a membrane, the perichondrium, from which it derives its blood supply.

There are three main varieties of cartilage which demonstrate the characteristics of this substance firmness, flexibility and rigidity.

Fibrous tissue

Fibrous tissue is often spoken of as a white fibrous tissue because it is composed mainly of white collagen fiber arranged in definite lines. This arrangement gives great strength and fibrous tissue is found where resistance is required. Between the definite bundles of white fibers some areolar tissue lies, which contains the nerves, lymphatics, and blood vessels supplying the structure.

  Fibrous tissue is tough and strong. It forms ligaments except the elastic ones and tendons. The dura matter lining the skull and the natural canal, the periosteum covering bone the strongest layers of fascia separating muscular aheaths, the fibrous layer of the pericardium, and the sclerotic coat of the eye are example of the fibrous tissue.

Elastic tissue.

 This form of connective tissue contains a large proportion of elastic fibers. It is found in the walls of arteries and in the air tubes of the respiratory tract and assists in keeping these vessels and passages open. It is also present in certain ligaments, as in the ligamentum sub-flava of the vertebral column where because of its elastic and extensible qualities it materially assists in the performance of sustained muscular effort, as in maintaining the erect position of the spine.

Adipose tissue.

 Adipose or fatty tissue is deposited in most parts of the body. It is associated with areolar tissue by the deposition of fat cells specially adapted for storing droplets of fat, and is present in all subcutaneous tissue except that of the eyelids and the penis, and inside the cranial cavity.

 Function to help support and retain in position the organs of the body. The kidneys, for example, are deeply embedded in fat.

To from a protective covering for the body

To act as store of water and of fat which when required can be re absorbed and by combustion In the tissue during metabolism provided a source of heat and energy for the uses of the body.

Mucoid tissue

  Mucoid tissue is found in the umbilical cord at birth in the jelly of Wharton. It is also found in the adult in the vitreous humour of the eye.

Areolar tissue.

 This consists of loosely woven tissue which as distributed widely throughout the body. It is placed immediately beneath the skin amd mucous surface forming the subcutaneous and sub-mucous tissue and it also form the sheaths of fascia which support and bind and connect together muscles, nerves, blood vessels, and other organs.

  Areolar tissue consists of a matrix of intercellular substance in which lie connective tissue cells and into which are woven bundles of fine white fibers, composed of wavy strands, running through the matrix in every direction and so arranged that they form a network. These fibers consists of collagen, a gelatinous substance and they are held together by mucin.

 Elastic fibers which are yellow in appearance and composed of elastin also from part of the structures. These fibers are fine.

  The tissue spaces in which lymph collects are large and it is from the lymph contained in them that most of the nourishment of areolar tissue is derived. These lymph spaces communicate with each other and it is here, in these, that many of the immunizing substance which protects the body from disease are formed.

Retiform (reticular) lymphoid or adenoid tissue is similar to areolar but a particular kind of cell the lymphocyte is present in very large numbers and forms the bulk of the tissue. The lymphocytes are held together by fine connective tissue fibers called reticular fibers, called reticular fibers. These are like immature collagen fibers.

Connective tissue.

Connective tissue provides the framework of the body. There are several varieties of connective tissue.

Nervous tissue.

 The nervous tissue consists of three kinds of matter. (a) grey matter, forming the nervous cell, (b) white matter, the nerve fibers, and (c) neuroglia, a special kind of supporting cell, found only in the nervous system which holds together and supports nerve cell and fibers. Each nerve cell with it processes is called neurone.

   Nerves cell are composed of highly specialized granular protoplasm, with large nuclei and cell walls as other cells. Various processes arise from the nerve cells.

The energy of the muscular contraction

The energy of the muscular contraction is providing by the conversion of adenosine triphosphate (ATP) into adenosine diphosphate (ADP). ADP is then immediately turned back into ATP by energy provided by the breakdown of glycogen. In the presences of adequate supplies of oxygen, this breakdown is aerobic and produce carbon dioxide and water. If there is not enough oxygen the glycogen is only broken down to lactic acid (anaerobic glycogen) and the content of lactic acid in the blood increases. This is normal occurrence in vigorous athletes, but occurs to readily in patients whose heart or circulation does not supply the working muscles with enough blood.

Muscle tone.

Muscle is never completely at rest; it may appear to be, but it is always in a condition of muscle tone, which means ready to respond to stimuli. For instance, the knee-jerk obtained by sharply tapping the patellar tendon results in contraction of the quadriceps extensor of the thigh and slight extension of the knee joint. This is reflex produced by stimulation of the nerves. Posture is determined by the degree of muscle tone.

Muscular contraction.

 When a muscle is stimulated a short latent period follows, during which it is taking up the stimulus. It then contracts when it becomes short and thick and finally it relaxes and elongates.

  In the case of striped (voluntary) muscle fiber the contraction lasts only a fraction of a second and each contraction occurs in response to a single nerve impulse. Each single contraction is of the same force. The force with which a whole muscle contracts is adjusted by varying the number of the fibers contracting and the frequency with which each fiber contracts. When contracting vigorously the individual fibers may contract more than 50 times each second.

 Certain factors influence force with which a muscles fiber contracts. It contracts more forcibly when it is stretched and when it is warm. Fatigue and cold weaken the power to contract.

Unstriped muscles fibers contact much more slowly and are not dependent on nervous impulses, although these alter the force of contraction.

Cardiac muscle

Cardiac muscle is found only in the muscle of the heart. It is striated like voluntary muscle. But it differs in that its fibers branch and anastomose with each other; they are arranged longitudinally as in striated muscle, are characteristically red in colour and not controlled by the will.

    Cardiac muscles possesses the special property of automatic rhythmical contraction independent of its verves supply. This function is described as myogenic as distinct from neurogenic. Normally the action of the heart is controlled by its nerve supply.

sphincter muscle

A sphincter muscle is composed of a circular band of muscles fibers situated at the internal or external openings of a canal, or at the mouth of an orifice, tightly closing it when contracted. Examples include the cardiac and pyloric sphincters at the openings of the stomach, the ileo-colic sphincter or valve, the internal and external sphincters of the anus and urethra.

Unstriped (unstriated, smooth, or involuntary muscle).

 This type will contract without nervous stimulation although in most parts of the body its activity is under the control of the autonomic (involuntary) nervous system. This variety is composed of elongated spindle shaped muscle cells which retain the appearance of a cell. Involuntary muscle is found in the coats of blood and lymphatic vessels in the walls of digestive tract and the hollow viscera, trachea, and bronchi, in the iris and ciliary muscle of the eye, and in the involuntary muscles in the skin.

Striped

Striped (striated, skeletal or voluntary muscle). The individual muscle fibers are transversely striated by alternate light and dark markings. Each fiber is made up of a number of myofibrils and enclosed in a fine membrane the sarcolemma (meaning muscle sheath). A number of fibers are massed together to from bundles; many of these bundles are bound together by connective tissue to from large and small muscles. When a muscles contracts it shortens, and each individual fiber take part in the movement by contracting. This type only contracts when stimulated to do so by the nervous system.

Muscular Tissue.

 Muscle is a tissue which is specialized for contraction, and by means of this, movements are performed. It is composed of cylindrical fibers which correspond to the cells of other tissues. These are bound together into little boundles of fibers by a form of connective tissue which contains a highly specialized contractile element.

There are three types of muscle:

Serous membrane

Serous membrane are found in the chest and abdomen covering the organs contained therein and lining these cavities.

The pleura covers the lung and the lines the thorax.

The pericardium covers the heart as a double layer.

The peritoneum covers the abdominal organs and lines the abdomen. The characteristics which are common to all three serous membranes are, that each consists of a double layer of membrane having an intervening potential cavity which receives the fluid secreted by the membrane. This serous fluid is very similar to blood serum or lymph. It acts as a lubricant, and in addition it contains protective substances and removes harmful products passing these on the lymphatic system to be dealt with. 

Synovial membrane

Synovial membrane lines the cavities of joints. It consists of fine connective tissue, with a layer of squamous endothelialcell on the surface. The secretion of synovial membrane is thick and glairy in character.

Mucous membrane

Mucous membrane is found lining the elementary tract, the respiratory tract, and parts of the genitor-urinary tract. It varies in character in the different areas. In the digestive tract it consists of columnar epithelial cells closely packed together. Some of them become distended with mucous secretion and are then called goblet cells. The cell become more and more distended and finally ruptures and discharges its secretion on to the surface.

   Mucus is the secretion of the membrane and consists of water, salt and a protein, mucin, which give the sticky or viscid character to the secretion.

Membranes.

 Layer of specialized cells which line the cavities of the body are described as membrane. The three principle membrane are:

Mucous membrane.

Synovial membrane.

Serous membrane.

All these membrane secrete a fluid to lubricate or moisten the cavity the line.

Glands.

 A gland is a secretory organ which may exist as a separate organ such as the liver, pancreas, and spleen; or may be simple a layer of cells as the simple tubular glands of the alimentary canal, body cavities, etc. all glands have a reach blood supply. Their special function is to select from the blood stream certain substances which they then elaborate into their important juices or secretions.

  There is a tremendous variety of glands each with its different function making a collective description and classification difficult. A simple classification is as follow:

  Glands which pour their secretion directly on to the surface include the sweet glands, sebaceous glands, and the gastric and intestinal glands.

 Glands which pour their secretion indirectly by means of ducts on to the surface include the salivary glands, pancreas, and liver.

Ductless glands. These from the group described as endocrine organs. These are glands of internal secretion. A great deal of the well being of the body depends on these glands which through their secretions exert an important chemical control on the function of the body.

Function of epithelial tissue.

 The epithelial tissue which forms the covering of the body, the skin and the lining of the cavities which open on to the surface is mainly protective. It prevents injury to the underlying tissues, prevents the loss of fluid from these tissues and also prevents the passage of fluid into the structure which are covered by skin. Micro-organisms cannot pass through healthy skin but they can and do pass through abraded skin.

Secretory. Most of the secreting glands and their ducts are composed of columnar epithelium. Very often the epithelium lining the gland and its duct is continuous with that of the surface in which the glands lie. Simple tubular and simple saccular glands are just involutions from the surface such as the simple tubular glands of the intestine. When these involutions branch, the structure become more complicated, as in the formation of compound tubular glands such as those of the kidney, and compound racemose or saccular glands such as the salivary glands and the pancreas.

   The endocrine glands are also composed of epithelial cells which may be massed together or may line hollow vesicles as occurs in the thyroid gland where the vesicles are lined by columnar epithelial cells, cubical in shape. These cell produce their secretion colloid but there is no duct from these glands and therefore the secretion reach the blood stream either directly or through the lymphatics.

Transitional epithelium

Transitional epithelium is a compound stratified epithelium consisting of three layers of cells. It lines the urinary bladder, the pelvis of the kidney, the urethra. The deeper layers of cells in transitional epithelium are of the columnar type of cell with rounded ends which make them pyriform or pear shaped. As the cell in the deeper layers multiply by dividing, the superficial layers of cells are cast off. The superficial cell in transitional epithelium are less scale-like than those of stratified epithelium. Comparison of the illustrations will make this point clear.

Compound epithelium

Compound epithelium consists of more then one layer of cells. Stratified epithelium forms the epidermal layers of the skin.

  It also lines the mouth, pharynx, oesophagus, the lower part of the urethra, the anal canal and the vagina, and covers the surface of the cornea. In these areas it does not become cornified.

 The outer layers of cells near the urface comprise the horny layer of the skin; these cell are flattened and resemble scales. The deepest layer of cells are columnar in shape.these form the germinative layer and here the cell multiply by karyo-kinesis, pushing those above them nearer the surface until the superficial ones are cast of.

  The cells between the basal layer and the horny zone are called ‘prickle cells’ they are connected to each other by fine tendrils which give them a prickly appearance when examined under the microscope.

Goblet cells

Goblet cells are mucus-secreting cells which lie in the walls of glands and ducts lined by columnar cells, either plain or ciliated. Goblet cells secrete mucus or mucin and express it on to the surface; they act as mucus secreting glands and are most numerous where a considerable amount of mucus covers the surface as in the stomach, colon and trachea.

Ciliated epithelium

Ciliated epithelium is found lining the air passages and their ramifications such as the frontal and maxillary sinuses. It also lines the uterine tubes or oviducts and part of the uterus and the ventricles of the brain.

   Ciliated cells are like columnar cells in shape, but they have in addition fine hair-like processes attached to their free edge. These processes are called cilia. The ciliary processes keep up a continual movement directed towards the external opening. This movement has been likened to the movement seen in afield of corn, blown in one direction by the wind. In the respiratory passages the constant movement prevents dust, mucus, etc. entering the lungs, and in the uterine tubes the movement conveys the ovum into the uterus.

Columnar epithelium

Columnar epithelium  forms a single layer of cells which line the ducts of most glands, the gall-bladder, nearly the whole of the digestive tract, in which goblet cells are interspersed, and parts of the genitor-urinary tract.

   The columnar cells from the intestine; these have a slightly border. In some situations, as when lining the alveoli of secreting glands, the cell of columnar epithelium are short and have a cubical appearance.

Pavement or Squamous epithelium.

 Pavement epithelial cells are fine thin placed edge to edge like the particles in a mosaic pattern or the stone of pavement. These cells from the alveoli of the lungs. They are found whenever a very smooth surface is essential as in the lining of the heart (serous membrane), lining of blood vessels and lymphatic. When lining these structures the epithelial covering or lining is called endothelium.

Simple epithelium.

This class consists of a single layer of a cells, and is subdivided into three varieties.

Epithelial tissue .

 An epithelial tissue consists of cells which cover surface of the body, e.g. skin; or which line hollow organs, tubes or cavities, e.g. blood vessels, and the air cells. There are two main class of epithelial tissue, each containing several verities. All epithelial cells lie on and are held together by a homogeneous substance called a basement membrane.

The elementary tissues of the body.

 Four groups of tissues in the body are known as elementary tissues. These are epithelial tissue, muscular tissue, nervous tissue, and connective tissue.

Reproduction of cell.

 A cell does not go on growing indefinitely in size but at a certain optimum point divides into two daughter cells. Further certain cells will undergo division to replace worn-out cells or those destroyed by disease. This kind of cell division is called mitosis, or karyokinesis.

   Activity begins in the nucleus, the nuclear membrane disappear and the chromatin changes character and becomes long filaments called chromosomes. The centrosome divides and the two new centrosome moves away from each other to each end of the nucleus called the poles. The chromosome are then attract to the poles and lie near the new centrosomes. The chromatin of which the nucleus is formed now comes to rest and two new nuclei exist. Finally the protoplasm of the cell constricts and divides and the two new cells are complete.

   Each new daughter cell resulting from mitosis contains forty six chromosomes, so that during mitosis each chromosome must duplicate itself. The process of chromosomal duplication is one of the least understood of the cell’s activities.

  However, mitosis is not the only kind of cell division. In the sex organs, the ovary and testis, another kinds of cell division occurs called meiosis. During the formation of the sex cells, or gametes, the number of chromosomes is halved, so that spermatozoon contains only twenty three chromosomes and the egg cell, or ovum Twenty-three.

   When fertilization occurs, that is when spermatozoon and ovum fuse to form the cell (zygote) which develops into a new individual, the normal chromosomal complement of forty six is restores. By this means a mixing of the hereditary determinants, or genes, from male and female is achieved.

Nucleus.

 The nucleus consist of a more compact mass of protoplasm, separated from yhe cytoplasm by nuclear membrane which is also selectively porous, allowing substances to escape from the nucleus into the cytoplasm or substances to pass into it. The nucleus controls the cell and all its activities. Without a nucleus the cell would die.

The nucleus contains many protein-rich threads lying in a nuclear sap. In the ‘resting cell’ the threads are collectively spoken of as chromatin. These threads or chromosomes are vital to the everyday activities of the cell and are responsible for determining the hereditary characteristics of the human body. On the chromosomes in linear arrangement sit the genetic or hereditary determinants, the genes. The number of chromosome in a body cell is constant for a particular species of organism. In man there are twenty three pairs of forty six chromosomes.

Cytoplasm.

This contains the following essential requirements:

1.       Mitochondria, small rod-like structure which are closely connected with the catabolic, or respiratory, processes of the cell body.

2.       Golgi apparatus. A canal-like structure lying next to the nucleus and involved in the secretory activities of the cell.

3.       Ground cytoplasm. A highly complex colloidal material in which the other structures are embedded. It is largely concerned with the anabolic, or synthetic, activities of the cell.

4.       Centrosome. A minute dense part of cytoplasm, laying close to the nucleus. It plays an important part during cell division.

5.       Cell memberane. The cell boundary is no static envelope. Many important function are connected with it, but in particular its act as a selective sieve through which certain substances are allowed to pass into the cell, or which prevents other substances from gaining access to it. Thus it is most important in maintaining the correct chemical composition of protoplasm.

Cell Structure.

 In considering the structure of the cell it is essential to relate its parts to its function.

  The protoplasm of the cell is composed of a centrally placed body, the nucleus, and the cytoplasm or remainder of the protoplasm, which surrounds the nucleus.

Irritability and conductivity of a cell.

 Mention has been made of some of these cells’ characteristic functional properties, their metabolic activities and power of growth.

   By these two properties then cell is activity. When a cell is stimulated either by chemical, physical, mechanical, or nervous means, the cell responds; it may contract as does a muscle cell (fiber); it may produce a secretion, as do the cell of the stomach, pancreas, and other organs and glands; or it may conduct an impulse, as in the case of the nerve cell. This last is the best example of cell conductivities as a nerve impulse generated by the stimulation of a nerve cell may be conducted for a considerable distance, a yard or more, according to the length of the nerve fiber. But in all case a stimulus which excites a cell to action is conducted along the entire length, from end to end of the cell.

Excretion of a cell.

 The waste material resulting from the catabolic processes are eliminate from the cell into the interstitial fluid, and thence carried away by the blood. The blood transports the carbonic acid waste to the lungs where it is removed from the body as carbon dioxide. The other waste substances are eliminated via the kidneys, in the urine.

Respiration of cells.

 Oxygen brought from the lungs by the blood and the removal of the gaseous waste product, carbon dioxide, are essential for the function and survival of the cell.

Metabolism.

 On the other hand, the cell need a supply of energy for its activities and it will used some absorbed foodmaterials as a fuel. The food is broken down (catabolism) and the energy stored in its released and use by the cell to provide heat, glandular secretion, movement, and nervous activity. Anabolism and catabolism make up the total activities of the cell o metabolism.

Growth and repair of the cell.

 These material brought to the cell may be used by the cell to synthesize new protoplasm, in which case the cell increase in size, that is, it grows. They may also be used to replace worn out parts of the cell. These constructive activities growth and cell repair, are spoken as the anabolic function of the cell, or anabolism.

Ingestion and assimilation of cell.

 Cell selected from the intercellular or interstitial fluid which surrounds them chemical substances such as amino-acids, which the cell builds up into the very complicated substances, e.g., proteins, which make up protoplasm. Thus a cell is very active unit in which the nourishing food materials eaten by man are absorbed and assimilated.

The tissue cell

A cell is a minute (jelly-like) mass of protoplasm containing a nucleus held together by a cell membrane. In considering the structure of a cell its component parts may usefully be related to its function.

  Cells possess the qualities of all living matter, including those of self-preservation and reproduction.

Cardiac oedema

Cardiac oedema occurs in congestive heart failure. The venous pressure and consequently the capillaries pressure is raised. Oedema in the legs and feet occurs in those who habitually stand and walk. Over the sacrum in those who sit, and the lower part of the back and buttocks in those who lie. The kidneys are involved and the secretion of sodium is diminished. An important factor causing oedema is the inability of the kidney to excrete sodium.

  Oedema due to lymphatic obstruction is most characteristically, though not invariable, seen in the arm after radical mastectomy, as the surgeon has removed the lymph glands which drain the axillary area. This form of oedema also occurs in elephantiasis due to filariasis caused by a tropical parasite which blocks the lymphatics.

   Oedema is also seen in thrombosis of the deep veins of the leg which is a dangerous complication of prolonged confinement to be and which allows the blood flow to become too sluggish so that clots from. It may also be the result of infection.

Oedema

Oedema is waterlogging of the tissue due to a breakdown of the delicate balance described above. It can obviously arise from one of four reasons:

1.       Too high a mechanical hydrostatic pressure in the capillaries as happens, for example, if the venous drainage is blocked.

2.       Too low an osmotic pressure due to insufficient plasma proteins, particularly albumin.

3.       Blockage of the lymphatics.

4.       Damage to the capillary walls so that the plasma proteins leak out into the tissue and causes an osmotic pressure opposing the osmotic pressure of the protein in the blood stream.

Tissue fluid exchange.

The fluid of the plasma in under greater mechanical hydrostatic pressure than the interstitial pressure and therefore fluid tends to leave the capillaries. However, there are proteins in the plasma but not in the interstitial fluid; these plasma proteins exert an osmotic pressure which tends to suck fluid into the capillaries.

   At the arterial end of the capillaries the mechanical, hydrostatic pressure is greater than the osmotic pressure so the balance of the forces sends fluids out into the tissues. At the venous end the hydrostatics pressure is less; the osmotic pressure overcomes it and draws fluid back into the capillaries. Normally there is more fluid leaving the capillaries then there is fluid coming back into the them. This excess is removed by the lymphatics.

 Exchange between the extracellular and intracellular fluids is also depends on osmotic pressure, but the cell membrane too has a selective permeability, allowing some substances, such as oxygen, carbon dioxide and urea to cross freely, but pumping others either in or out to maintain different concentrations in the intra- and extracellular fluid, whilst sodium is pumped out.

The excretory system

The excretory system is the term sometimes employed to describe collectively the organs that deal with the excretion of waste products from the body. These organs include the urinary system, the lungs in their function of eliminating carbon dioxide, and the colon which excretes certain insoluble substances in the faeces.

The body fluids

Water with its solvents needed for the health of the cells is termed body fluid, and this fluid is partly inside and partly outside the cells.

Intracellular fluid from 50 percent of the body weight; it lies within the cells, and contains electrolytes including potassium and phosphates and food materials like glucose and amino-acids. Enzyme action is constant within the cells, breaking down and building up as in all metabolisms to maintain a balance.

  Extracellular or interstitial fluid represent 30 percent of the water in the body. It is the medium in which the cells live, obtaining from its salt, food, and oxygen and passing into it their waste products.

   Blood plasma from 5 percent of body weight and it is the transport system which serves the cells through the medium of the extracellular fluid.

The Special Sense Organs

The Special Sense Organs include taste, smell, sight and hearing, and also the tactile function of the skin. It is through these organs that the individual is kept aware of external forces and thus enable to protect himself. A chicken aware of the sound of traffic runs or files to safety.

The Nervous system

The Nervous system is composed of the central nervous system which includes the brain and spinal cord, the peripheral nervous systemconsisting of the nerves given off from brain and cord and the autonomic nervous system. The central and peripheral systems are often grouped together and described as the cerebrospinal nervous system. The autonomic nervous system includes the sympathetic and parasympathetic nerves. It is also described as the involuntary nervous system.

The Urogenital system

The Urogenital system includes the organs of the urinary system and the reproductive system. The waste product of the body, except carbon dioxide, are excreted by the kidneys.

The Ductless Glands

The Ductless Glands are grouped together because of the internal secretions they produce. The spleen is sometimes included in this grouped because it also has no duct, though as far as is known it does not produce an internal secretion; it is concerned with the formation of red blood cells.

The respiratory system

The respiratory system contains the passages and organs concerned with breathing. Oxygen from the air is taken into the blood and carried to the tissues the waste product, carbon dioxide, is carried by the blood from the body tissues to the lungs and breathed out in the expired air.

The digestive system

The digestive system consists of the alimentary canal and the glands and organs associated with it. Food is broken down by enzymes in the digestive tract and taken by the blood to the liver and finally to the tissue.

The blood-vascular system

The blood-vascular system includes the circulatory system and lymphatic system. Blood is the principle transport system: it is pumped round the body by the heart, oxygen is brought from the lungs and carbon dioxide collected from the tissues. Food passes to the liver and thence to the general circulation. Waste products are passed to the kidneys.

The locomotor system.

This includes the parts concerned in the movements of the body: the skeletal system which is composed of the bones, and certain cartilages and membranes, the articulatory system which deals with the joints or articulation and the muscular system which includes muscles, fascia and tendon sheaths.

The system of the body

Systematic anatomy or the division of the body into systems is arranged (a) according to the function they perform and (b) under the heading of the different terms employed to indicate the knowledge of certain parts.

  Osteology is knowledge of bones,

Arthrology is knowledge of joints,

Mycology is knowledge of muscles,

Splanchnology is knowledge of organs or viscera,

Neurology is knowledge of nerves and nerve structure.

When grouped according to function the general arrangement is as follows.

Terms used in anatomy

Many parts of the body are symmetrically arranged. For example the right and left limbs are similar; there are right and left eyes and ear, right and left lungs, and right and left kidneys. But there is also a good deal of asymmetry in the arrangement of the body. The spleen lies entirely on the left side; the larger part of the liver lies on the right side; the pancreas lies partly on each side.

    The human body is studied from the erect position with the arms by the sides and the palms of the hands facing forwards, the head erect the eyes looking straight in front. This is describes as the anatomical position.

    The various part of the body is then described in relation to certain imaginary lines or plane. The median plane runs through the center of the body. Any structure which lies nearer to the median plane of the body than another is said to be medial to that other. For example the hamstring muscles which lie on the inner side of the thigh are nearer the median plane than those which lie on the outer side and are therefore medial to the other group which as described as lateral. Similarly the inner side of the thigh is described as the medial aspect and the outer as the lateral aspect.

   The term internal and external are used to describe the relative distance of an organ or structure from the center of a cavity. The ribs for example have an internal surface which is near the chest cavity and an external surface which is on the outer side, farther away from the cavity. The internal carotid artery, is within the cranial cavity and the external is outside the cavity.

     The terms superficial and deep are used to denote relative distance from the surface of the body, and the term superior and inferior denote positions relatively high or low, particularly in relation to the trunk, such as the and inferior surfaces of the clavicle.

   The terms anterior and posterior are synonymous with ventral and dorsal. These terms are only applied to man in the erect attitude or ‘anatomical position’. For example the anterior and posterior tibial arteries lie in the front and behind in the leg.

    In describing the hand the terms palmar and dorsal are used instead of anterior and posterior, and in describing the foot the terms plantar and dorsal are similarly employed.

   The terms proximal or distal are employed to described nearness to, or distance from a given point, particularly in relation to the limbs. For example the proximal phalanges are nearer to the wrist and distal ones are the farthest away. When three structures in a line running from the median plane of the body outwards, they are described as being placed in medial, intermediate and lateral positions. An example of this is seen in the arrangement of three cuneiform bones of the foot. Similarly when three structure run from front to back (anterior to posterior) or from above downwards (superior to inferior), these are described as anterior, middle and posterior as happens in the arrangement of the three fossae of the skull and superior, middle and inferior, as occurs in the arrangement of the superior. Middle and inferior radio-ulnar joints.

Physiology of human body

Physiology is the study of the function of the normal human body. It is closely linked with the study of all living things in the subject of biology; as well as this there is the work of the cytologist, interested in details of the structure of the cells and that of biochemist, dealing with the chemical changes and activities of the cell and investigating the complex chemistry of life, and there is physics, the study of the physical relation and movements taking place in the body.

   The body is made up of many tissues and organs, each having its own particular function to perform. The cell is the unit or the smallest element of the body of which all parts are comprised. The cell are adapted to perform the special function of the organ or tissue they are in. some cells, such as those in the nervous system and muscle, are very specialized indeed: others, such as those in the connective tissues, are less highly developed. As a general rule the most highly specialized cells are the least able to withstand damage and also are the most difficult to repair or replace.

Anatomy

Anatomy is the study of the structure of the body and of the relationship of its constituent part to each other. In region, e.g. arm, leg, head, chest, etc., is found to consist of a number of structures common to all regions such as bones, muscles, nerves, blood vessels and so on. From this study it follows that a number of different systems exist. These have been grouped together and described under the heading systematic anatomy.

    A study of the position and relationship of one part of the body could not be separated from a consideration of the use of each structure system. This study led to the employment of the terms functional anatomy which is closely allied to the study of physiology. Then again it was found that certain structures could be examined by the naked eye and the term macroscopic anatomy was introduced to describe this study, in distinction to microscopic anatomy which necessitates the use of a microscope. Closely allied to the study of anatomy are histology, the study of the fine structures of the body and cytology, the study of the cells.

INTRODUCTION TO THE HUMAN BODY