SYSTEMS AND ORGANS OF THE BODY
How the Body is Built.—In a building such as the body it is well to begin with the unit—the building unit. In a house this is a brick or a stone; in all living structures, animal and vegetable, it is a cell.
All living structures, whether animal or vegetable, are built up of cells (which we shall consider in due course), and these cells are grouped together for different purposes to form different tissues. The tissues are the different materials of which the body is made. There are eight principal tissues in the body: bone, gristle, muscle, nerve, skin, fat, fiber, and connecting tissue.
ORGANS OF CHEST CAVITY IN RELATION TO STOMACH
THE BRONCHIAL TUBES
ORGANS INVOLVED IN FIRST STAGES OF DIGESTION
DIAGRAMS DISCLOSING HEART AND CONNECTIONS, RIBS AND LUNGS
(1) The Osseous, or bone tissue, is the framework of the body. This material is found, of course, in every part of the body and forms the skeleton.
(2) The Cartilaginous, or gristle, forms the joints of the body. This tissue covers the ends of the bones to form the joints; it unites the ribs with the breastbone; it forms the rings of the windpipe and the lid of the larynx at the back of the tongue; the lower part of the nose, the upper eyelid, and the ear.
(3) The Muscular, or muscle, forms the machinery of the body. This tissue covers all the bones with flesh, which is muscle, and is the chief part of a number of machines by which every movement is performed. It is also an important tissue in the wall of the abdomen and the floor of the chest.
(4) The Nervous, or nerve tissue, is the moving power of the body. It is the chief constituent of the brain and the spinal cord, inside the backbone or spine. It also forms the nerves, which run like white threads from the brain to all the muscles, and give them power to move.
(5) The Epithelial, or skin, forms the outer covering of the body. This tissue is the skin that covers the body outside, and lines it as mucous membrane inside, and also forms the teeth and nails.
(6) The Adipose, or fat, forms the under covering of the body. This tissue is the inner protective sheathing and padding of the body, beneath the skin, and round the internal organs. It consists of drops of oil, enclosed in separate cells.
(7) The Fibrous, or fiber or sinew, is the tissue that forms the cords and bands of the body. This tissue makes the strong tendons that fasten the muscles to the bones, and forms the covering or sheath of the bone itself, and the various organs.
(8) The Connective, or cementing tissue, joins all the parts and cells of the body together. This substance is found everywhere, all over the body, and is like the mortar in a house, fastening all the bricks together. It is a sort of network of cells and long fibers.
DIAGRAM ILLUSTRATING THE ALIMENTARY CANAL
[Large diagram] (345 kB)
![[Large diagram]](#535149607468238645_fig1533_lg.jpg.id-4895331980711076720.wrap-0.html.html){kind=link}
Special Systems.—These eight tissues are combined together into various groups of organs or systems for special purposes. These groups are six in number, and include: the circulatory, respiratory, digestive, excretory or secretory, locomotor, and nervous systems. There is also the reproductive system, which has to do with the propagation of the race, and involves many important and vital questions.
We may divide these six into three groups:
There are two in the chest:
(1) The Circulatory system is that by which the blood or liquid food is distributed throughout the body to all the tiny cells. This system includes the heart or force-pump, and the arteries, capillaries, and veins or the three kinds of pipes through which the blood travels.
(2) The Respiratory system is that by which we breathe, and by which the body is fed with oxygen, which gives the blood its bright red color. This system includes the nostrils and mouth, the windpipe and the lungs.
Then there are two in the abdomen, or stomach:
(3) The Digestive system, by which all the food is made into liquid and changed so as to nourish the body and pass into the blood. This system includes the mouth, gullet, stomach, liver, pancreas, intestines, and other organs.
(4) The Secretory, or excretory, system (for they are best grouped as one) manufactures the various fluids of the body, such as bile, urine, sweat, saliva, gastric juice, etc. It consists of various glands or secretory organs in different parts of the body, such as those in the skin, the kidneys, the lymphatic glands, the spleen, etc. It also gets rid of the refuse of the body.
Lastly, there are two in the head and limbs:
(5) The Locomotor system, by which all movement is effected. This includes the bones, joints, and muscles.
(6) The Nervous system, by which all the body is controlled, directed, and regulated. This system includes the brain, spinal cord, and the special senses, such as the ear, the eye, and all the nerves.
The Human Chest, or Thorax.—In it, the blood is purified and circulated. The thorax is closed above and below: above, by the neck, through which the windpipe enters it in front, conveying air to the lungs; and by the gullet behind, conveying food to the stomach. Below, the floor, dividing it from the abdomen beneath, is formed by a very large muscle stretching right across the body, called the Diaphragm, or partition wall; also called the Midriff. The thorax is walled in at the sides by the ribs, and behind by the backbone in which is the other tube that contains the spinal cord. The thorax contains the two organs of respiration and circulation.
The lungs are the organs of respiration. They are like two sponges filling the right and left halves of the chest. Wherever you can feel a rib there is part of the lung underneath. Each of these lungs is contained in a bag, like a skin, that separates it from the ribs, and is called the pleura (from pleuron = a rib), but the lung is not inside the bag.
The outer layer of the pleura is fixed to the side of the chest, the inner layer to the lung, and the two layers move on each other like a joint when we breathe.
The lungs are full of small air-cells with minute tubes leading from them. These gradually increase in size as they join together, till at last they unite in one large tube, or bronchus, for each lung. These two bronchi join together, and form the windpipe, or trachea, which conveys the air through the larynx into the mouth.
The windpipe is kept stretched widely open by a series of elastic rings of gristle. Behind the windpipe is the gullet, leading to the stomach.
PERICARDIUM OF THE HEART LEFT AURICLE AND LEFT VENTRICLE
The heart, the main pump of the circulatory system, rests on the diaphragm between the two lungs. The heart is enclosed in a smooth, moist membrane or sac, the pericardium, which allows it to dilate and contract without friction against the adjoining parts. There are four cavities in the heart, the right and left auricle, and the right and left ventricle. The auricles, which are thinner walled, collect blood from the veins, while the thicker and stronger walled ventricles force the blood into the arteries. The left auricle pumps the purified blood into the left ventricle, the valve between the auricle and ventricle opening to allow this passage. When the left ventricle is full the valve between its chamber and that of the auricle closes, the ventricle itself contracts down, and the blood is pumped out through the aorta to supply all the tissues of the body.
After leaving the left ventricle through the aorta the purified blood is carried to the head, arms, trunk, and lower limbs, etc. Finally, after being deprived of its oxygen as it passes through the tiny end-arteries, or capillaries, of the tissues it has to nourish, it is collected in the veins and is emptied into the right auricle. Passing from the right auricle to the right ventricle, this impure blood, which is of a dull purplish color, is pumped into the lungs, where it is deprived of its waste gases and once more takes up a fresh supply of oxygen. Bright scarlet in color again, it now is collected and carried to the left auricle by the pulmonary veins. From the auricle it passes through the mitral valve to the left ventricle, whence it is once more pumped out through the aorta to supply the tissues.
RESPIRATORY SYSTEM OR AIR PASSAGES OF THE BODY
Left: larynx from behind. Middle: cross-section of the pharynx. Right: section through larynx.
VIEWS OF THE LARYNX, SHOWING HOW THE AIR REACHES THE LUNGS
The organs of respiration are the nose, throat, larynx, windpipe or trachea, and the two lungs. On the outer walls of the nasal cavities are three shelves known as the turbinated bones, the surfaces of which contain blood-vessels to heat the air as it passes through the nose. The mucus which constantly forms on the lining membrane of the nose and the little hairs in the nostrils, act as screens, preventing dust being breathed into the lungs. The pharynx is the cavity behind the nose, mouth and larynx. The larynx forms a prominence in the throat known as the “Adam’s Apple.” It contains the vocal cords, the vibrations of which, as air from the lungs passes through them, give rise to voice sounds. The epiglottis is a cartilaginous curtain above the larynx which blocks up its entrance when food is being swallowed. The trachea or windpipe is a continuation of the larynx. Shortly after entering the chest it divides into two main branches, the right and left branches, which lead to all parts of the lungs. The lungs, two spongy, air-filled organs, take up most of the space in the chest-box or thorax. The smallest end-branches of the bronchial tubes open into numerous tiny sacs known as the air vesicles, in the walls of which the end-branches of the capillaries ramify. Here the impure gases in the blood escape through the vessel walls into the air vesicles, while the oxygen breathed into the lungs is taken up the same way by the blood in the vessels.
HOW THE HUMAN BODY IS CONTROLLED BY THE BRAIN
CORD WITH
DURA MATER
THE ARRANGEMENT OF
THE DURA MATER
[Large illustration] (375 kB)
![[Large illustration]](#535149607468238645_fig1536_lg.jpg.id-4690134781472648754.wrap-0.html.html){kind=link}
The nervous system consists of (1) the brain; (2) the spinal cord; (3) the nerves which run off from these structures; and (4) the sympathetic system. The chief mass of the brain is known as the cerebrum, or fore-brain, the small mass at the lower part being termed the cerebellum, or little brain. From the brain, which is contained within the bony skull, twelve pairs of cranial nerves proceed. The most important of these are the first or nerve of smell, the second (sight), eighth (hearing), and twelfth (taste). The fifth, one of the most important nerves of sensation, has three main branches running to the orbit and forehead, the jaws and teeth, and the skin of the face. Six of the twelve pairs of cranial nerves govern the movements of different parts (motor nerves), others have to do with the special sense organs, taste, smell, hearing, and sight (sensory nerves), and others are a combination of motor and sensory nerves. The spinal cord is a continuation of the brain, and is contained in the hollow canal running through the vertebræ of the spine. From it thirty-one pairs of nerves originate. The nerves which run to the arm are collected in a network called the brachial plexus. In the same way the great nerves to the leg come together in the lumbar plexus. The sympathetic nervous system consists of a main nerve trunk running downward along the spine from the skull to the coccyx. This sympathetic system communicates indirectly with the brain and spinal cord, and also with all the great arteries and other important structures in the abdomen.
The dura mater is the strong external cranial membrane which adheres to the skull and also penetrates into the cavities of the brain, dividing it into partially separate compartments. These dividing portions of the dura mater may be seen at A, A, in the diagram above. B marks the various venous blood sinuses of the brain, which receive blood from veins in the different parts of the brain, and, merging into one large sinus (seen at lower right of diagram), afterwards become the jugular vein. C is the great cerebral vein. The Roman numerals mark the great cranial nerves.
We take air into the lungs to pass thence into the blood, and thus be carried to all the cells of the body to enable them to live and breathe.
The Heart.—The heart is at the lower part of the chest, between the two lungs. It is a fleshy or muscular organ, about the size of the fist—flat above, and pointed below like a sugar-loaf. It lies in a slanting direction behind the breastbone—the broad part, or the base, of the heart being upwards and partly to the right of the breast-bone; the point, or apex of the heart, being downwards and to the left, where it can often be seen beating against the chestwall.
The heart is hollow, and acts like a pump, forcing the blood all over the body through the great vessel that leaves the heart at the upper part. The heart, like the lungs, is enclosed in a double layer of folded bag, called the pericardium, because it is round the heart.
The gullet runs right down the back of the thorax, and passes out through the diaphragm, which forms the floor, into the abdomen.
The abdomen forms the lower half of the trunk, and is often called the stomach. It is full of organs belonging to the digestive system and secretory system, by which the fuel or food is rendered fit for use in the blood and the body.
The walls of the abdomen are not protected by ribs like the thorax, but are all formed of flesh or muscle. The principal organs they contain are the stomach, the liver, the pancreas, or sweetbread, the spleen or milt, the kidneys, the intestines, and the bladder.
The Human Brain.—The head and spine contain the principal nervous systems of the body and four organs of special sense—sight, hearing, smelling, and tasting.
The brain, which fills the head, consists of two parts: the Cerebrum, or greater brain, and the Cerebellum, or lesser brain, placed behind and below the larger one. From this brain, nerves run to every muscle of the body, enabling them to move the limbs and body as the mind directs; and another set of nerves run from every part of the body and skin to the brain, enabling the mind to know and feel all that goes on.
The brain is connected with the spinal cord by a flat band of brain matter, that lies on the inside of the occipital bone, called the Medulla Oblongata, or the Oblong Marrow. The spinal cord runs through a large hole in the occipital bone and right down the open tube formed by the spinal vertebræ, to the bottom of the backbone, and, all along its course, nerves leave it and enter it, as in the brain.
The organ of sight consists of the two eyes, which receive every image that we see, and transmit it to the brain. The organ of hearing consists of the two ears, by which we receive all the waves of sound that we hear, and transmit them to the brain. The organ of smell is in the upper part of the nose; the organ of taste at the hinder part of the tongue.
The organ of the voice is contained in the larynx in the neck, which joins the head to the body. Just under the chin in front of the neck you can feel what is called the Adam’s Apple, which is the front of the larynx, or voice-box, by which the air coming out of the lungs is formed into sounds.
The sounds are formed into words by the mouth, tongue, and teeth.
PERMANENT TEETH AND THEIR NAMES
Upper Jaw: 1, 2, incisors; 3, canine; 4, 5, premolars; 6, 7, 8, molars.
Lower Jaw: 1, 2, incisors; 3, canine; 4, 5, premolars; 6, 7, 8, molars.