Saturday, March 22, 2008

The Big Chest Book - Chapter Seven

All photos - John Grimek

Anatomical Description of the Lungs

In the two lateral chambers of the thoracic cavity are the two cone-shaped organs we know as the lungs. They are separated from each other by the heart and other contents of the mediastinum. The outer surface of each lung is convex, a concave base to fit over the convex portion of the diaphragm, and extending about an inch and a half above the level of the sternal end of the first rib is an apex. The pulmonary artery connects each lung with the heart and trachea, the pulmonary vein, bronchial arteries and veins, and a number of other parts constitute the root of the lungs. The hilum or vertical notch is located on the inner surface. This provides a passage to the structures which form the root of the lung. Below and in front of the hilum there is a deep concavity, called the cardiac impression, which accommodates the heart. It is larger and deeper on the left than on the right lung, because the heart extends farther to the left side.

The right lung is the larger and heavier of the two. It has greater breadth than the left, owing to the inclination of the heart to the left side, and it is shorter by one inch, because the diaphragm rises higher on the right side to accommodate the liver. The right lung is divided by fissures into three lobes, which are titled superior, middle and inferior. The left lung is smaller, narrower and longer than the right and is divided into just two lobes, the inferior and the superior.

The material of which the lungs are formed is porous, soft and spongy. It floats in water owing to the presence of air which crepitates when handled. The lungs consist of bronchial tubes and their terminal dilations, numerous blood vessels, lymphatics, nerves and a great many fine, elastic, connective tissues which bind all parts together. Each lobe of the lung is composed of many lobules, and into each lobule a bronchiole enters and terminates in an atrium. Each atrium presents a series of air cells. In this way the amount of surface exposed to the air and covered by the capillaries is so immensely increased that it is estimated the entire surface of the lungs amounts to about ninety square meters, more than one hundred times the skin surface of the entire body.

There are two sets of blood vessels in the lungs. First the branches of the pulmonary artery, which transports the blood to the lungs to be aerated and the branches of the bronchial arteries which bring blood for nutritive purposes. Immediately beneath the layer of flat cells, and lodged in the elastic connective tissue, is a very close plexus of capillaries, and the air reaching the alveoli by the bronchial tubes is separated from the blood by the capillaries, which coalesce to form larger branches. These run through the substance of the lung, communicate with other branches, and form larger vessels, which accompany the arteries and bronchial tubes to the hilum. Finally the pulmonary veins open into the left auricle.

The branches of the bronchial arteries supply blood to the long substance – the bronchial tubes, coats of the blood vessels, the lymph nodes and the pleura. The bronchial veins formed at the root of each lung receive veins which correspond to the branches of the bronchial arteries.

Each lung is enclosed in a serous sac – the pleura, one layer of which is closely adherent to the walls of the chest and diaphragm; the other closely covers the lung. The two layers of the pleural sacs, moistened by serum, are normally in close contact, and the so-called pleural cavity is a potential rather than an actual cavity. They move easily upon one another and prevent the friction that would otherwise occur between the lungs and the walls of the chest with every respiration. If the surface of the pleura becomes roughened as occurs in inflammation (pleurisy) more of less friction results and the sound produced by this friction can be heard if the ear is applied to the breast. In health, only a small amount of fluid is secreted and its absorption by the lymphatics almost keeps pace with its secretion, so that normally the amount of serum is very small. In pleurisy the amount may be considerably increased, due to the extra activity of the irritated secretory cells and excessive transudation from the congested blood vessels. The amount may be sufficient to separate the two layers of the pleura, thus changing the potential pleural cavity into an actual one. This is known as pleurisy with effusion. The mediastinum, or interpleural space, lies between the right and left pleura in the median plane of the chest. It extends from the sternum to the spinal column and is entirely filled with thoracic viscera, namely the heart, aorta and its branches, pulmonary artery and veins, with other parts, various veins, lymph nodes and nerves.

The main purpose of respiration is to supply the cells of the body with oxygen and rid them of the excess carbon dioxide which results from the oxidation. It also helps to equalize the temperature of the body and get rid of excess water. To accomplish these purposes three processes are necessary:

1. Breathing. The process of breathing may be subdivided into inspiration or breathing in, and expiration or breathing out. 2. External respiration. This includes two processes – external oxygen supply or the passage of oxygen from the alveoli of the lungs to the blood and external carbon dioxide elimination or the passage of carbon dioxide from the blood into the alveoli of the lungs.

Internal respiration also includes two processes: internal oxygen supply or the passage of the oxygen from the blood to the cells of the tissues; internal carbon dioxide elimination of the passing of carbon dioxide from the cells of the tissues to the blood. It is evident that external respiration is a process which takes place in the cells that make up the tissues of the body. The thorax is a closed cavity which contains the lungs. The lungs may be thought of as membranous sacs, the interior of which communicates with the outside air by way of the bronchia, trachea, glottis, etc., while the outside is protected from atmospheric pressure by the walls of the chest.

During life the size of the thoracic cavity is constantly changing with the respiratory movements. When all the muscles of respiration are at rest, that is at the end of a normal respiration, the size and position of the chest may be regarded as normal. Starting with this normal position, any enlargement constitutes active inspiration, the result of which is to force the air into the lungs. Following this active inspiration, the thoracic cavity may return passively to its normal position, giving a passive expiration, that is, an expiration involving no muscular effort. Normal respiratory movements are of this type, an active inspiration followed by a passive inspiration.

Mechanism of inspiration is the result of the contraction of the muscles of inspiration; passive expiration is due to the elastic recoil of the parts previously stretched. The thoracic cavity is enlarged in all directions – vertical, dorso-ventral, and lateral. The increase in the vertical diameter is brought about by the contraction of the diaphragmatic muscle, which draws the central tendon downward. The dorso-ventral and lateral diameters are increased by the contraction of the intercostals and other muscles which cause the sternum and ribs to move upward and outward. The lungs are expanded exactly in proportion to the expansion of the thorax. As in the heart, the auricular systole, the ventricular systole, and then a pause follow in regular order, so in the lungs the inspiration, the expiration, and then a pause succeed one another.

There is considerable variation in the number of muscles employed in the inspiration, depending upon whether the breathing is quiet or labored. All the muscles which contract simultaneously, including the diaphragm, are classed as inspratory. Those classed as expiratory contract alternately. The external intercostals, levatores costarum, the scaleni, the sternocleidomastoid, the pectorals minor and the serratus posticus superior are the inspiratory muscles. The action of the muscles enumerated is supplemented by additional muscles of the trunk, larynx, pharynx, and face, in forced inspirations.

It is considered that gravity and the elastic recoil of the lungs cause normal expiration which is usually a passive act. Diminution of the thorax may be caused in two ways in forced expirations: Forcing the diaphragm farther up into the thoracic cavity, a result obtained not by direct action of the diaphragm but by contracting the muscular walls of the abdomen, the external and internal oblique, the rectus and the transveralis, and by depressing the ribs. The muscles which depress the ribs are the internal intercostals and the triangularis sterni.

It is noted that there are two distinct types of respiration. The sequence of movements is the distinguishing factor. In the costal type the upper ribs move first and the abdomen second. The elevation of the ribs is the more noticeable movement. In the abdominal type, the abdomen bulges outward first, and then is followed b a movement of the thorax.
Abdominal respirations are deeper; restriction of the action of the diaphragm by tight clothing is thought to be the cause of costal respiration.

The respiratory center which controls the inspiration and respiration has been described as an automatic center, but sensitive to reflex stimulation of any of the sensory nerves. This brings us to the question of the nature of the automatic stimulus. Experimentally it has been demonstrated that the condition of the gases in the blood has a marked effect upon the activities of the center. The activity is always increased in proportion to the venosity of the blood. On the other hand, the activity is decreased and may fail altogether, if the blood is more arterial than normal. In venous blood the carbon dioxide is increased and the oxygen is decreased. Which of these conditions, the increase in carbon dioxide or the decrease in oxygen, is the more effective stimulus has not been definitely determined. There is much evidence that either factor may act as the stimulus, but the accumulation of carbon dioxide is the more effective.

The average rate of respiration for an adult is about sixteen to eighteen per minute. This rate may be increased by muscular exercise or emotion, in the healthy body. Anything that affects the heartbeat will have a similar effect on the respiration. Age has a definite influence. The average rate during the first year of life is about forty-four to the minute, and at the age of five years about twenty-six per minute. It reduces during the age of fifteen to twenty-five and after that to the normal standard.

The term external respiration is applied to the interchange of gases that takes place in the lungs. Two or three times each minute all the blood of the body passes through the capillaries of the lungs. This means that the time during which any portion of the blood is in a position for respiratory exchange is only a second or two. Yet during this time the following important changes take place: It loses carbon dioxide and moisture, it gains oxygen which combines with the hemoglobin of the red cells and transforms it into oxyhemoglobin, and as a result of this the crimson color shifts to scarlet, and the temperature is slightly reduced.

It is helpful to compare the average amounts of oxygen and carbon dioxide found in the venous blood, and the amounts found in the arterial blood. Average figures for the dog are: Venous blood contains 12% oxygen, 45% carbon dioxide, 1.7 % nitrogen. In humans the actual amounts of oxygen and carbon dioxide in venous blood vary with the nutritive activity of the tissues, and differ therefore in the various organs according to the state of activity of each organ and the volume of the blood supply. There is always a considerable amount of oxygen in venous blood, also a considerable amount of carbon dioxide in arterial blood. Consequently the main result of the respiratory exchange is to keep the gas content of the arterial blood nearly constant at the figures given. Under normal circumstances it is not possible to increase appreciably the amount of oxygen absorbed by the blood flowing through the lungs. For the relief of pneumonia, a patient will often absorb unusual supplies of pure oxygen when administered to him which is the result of the oxygen content of the blood of the pneumonia patient being below normal.

The lungs when once they are filled are never completely emptied of air until death. No expiration ever completely empties the alveoli, neither are they ever completely filled. The quantity or air which a person can expel by a forcible expiration, after the deepest inspiration possible is called the vital capacity, and the average about 3500 to 4000 c.c. for an average adult man. Tidal air designates the amount of air that flows in and out of the lungs with each quiet respiratory movement. The average figure for the adult is 500 c.c. Complemental air designates the amount of air that can be breathed in over and above the tidal air by the deepest possible inspiration. It is estimated at about 1600 c.c.

Supplemental air is the amount of air that can be breathed out after expiration by the most forcible expiration. It is equal to about 1600 c.c. Residual air is the amount of air remaining in the lungs after the most powerful expiration. This has been estimated to be about 1000 c.c. Reserve air is the residual air plus the supplemental air in the lungs under conditions of normal breathing, that is about 2600 c.c.

There are other conditions that occur during breathing. However dry the external air may be the expired air is nearly or quite saturated with moisture. An average of about one pint of water is eliminated daily in the breath. On cool morning this vapor is easily visible. The expired air is nearly as warm as the blood regardless of the temperature of the outside air. A temperature of between 98 and 100 degrees F. is usual. Breathing is one of the subsidiary means by which the temperature and the water content of the body are regulated. The heat required to warm the expired air and vaporize the moisture is taken from the body and represents a daily loss of heat.

The exchange of gases in the tissues constitutes internal respiration and consists of the passage of oxygen from the blood into the lymph and from the lymph into the tissue cells, and the passage of the carbon dioxide from the tissue cells into the lymph and from the lymph into the blood. After the exchange of gases in the lungs, the aerated blood is returned to the heart and distributed to all parts of the body. In passing through the capillaries the blood is brought into exchange with the lymph, in which the oxygen pressure is low. The compound of oxygen and hemoglobin, oxyhemoglobin, is only stable in an environment where the oxygen pressure is relatively high. Consequently the blood in passing through the capillaries gives up much of its oxygen, which passes to the lymph and from there to the tissue cells. On the contrary, the pressure of carbon dioxide is higher in the cells than in the blood, and this facilitates the passing of carbon dioxide from the cells to the lymph, and from the latter to the blood.

It is important to remember that the blood does not give up all its oxygen in the tissues, nor all the carbon dioxide in the lungs. Excessive amounts of carbon dioxide will cause death by asphyxia, but in normal amounts it is as essential to life as oxygen.

As everyone knows the air we need to keep us alive should enter through the nose. Mouth breathing is not normally healthful, for the nose is so designed that it tests the air to see if it is hot or cold, too dry or it contains dust or other foreign particles. If it is cold it warms it; if too dry it moistens it; if dust-laden it filters it. Incidentally the nose is of paramount aid in making the sounds of talking and of singing. In mouth breathing there is no way to condition the air before it reaches the delicate linings of the lungs.

The function of filter the air will go on even for two or three days after death. Numerous glands keep the walls of the air passageway moist and thus the dust adheres to them. This lining is called epithelium, and the tiny outcroppings from it which stick out like hairs on a brush, and perform the function of filtering, are known as cilia. They sweep out the dust of the air we breathe and expel it through the nose openings or up into the pharynx.

Although we breathe normally seventeen times a minute, when we are quiet or sleeping, respiration will automatically speed up to seventy or eighty times a minute during severe muscular effort when the need for air is great. Breathing is done so automatically, so unconsciously, that few if any of us give the slightest thought to why we breathe or how we breathe. This important and amazingly complicated function is taken for granted. But it’s one of the most important phases of operation with this wonderfully made machine of ours, which is our body.

We need to form combustion which in turn produces motion, heat and chemical products. Every one of the millions of cells in the human body is a tiny engine designed to work somewhat similarly to man-made engines. The engines of our automobiles or factories utilize oxygen and throw off carbon dioxide to produce the motion, heat, electricity, etc., which cause the wheels to turn in factories or with transportation machines such as the truck, pleasure car, locomotive and tractor. Solid fuel formerly in the form of wood, now usually coal, or liquid fuel, oil or gasoline, provides the combustion which produces this power.

Each cell of the body obtains its energy from burning liquid fuel, similar to man-made machines. To do this they must burn oxygen and give off carbon dioxide. The operation of this tiny human engine is so much more complex than that of engines in a factory or in our transportation systems. In a factory and in the case of the locomotive the combustion chamber is separate from the part of the machine which produces the energy. The fire is under the boiler. In automobiles or tractors and in the body cells both combustion chamber and energy-producing parts are combined in one unit. Fire produces heat and light. The slow combustion in the cells of our bodies, while producing a fair amount of heat as in the cells of the muscles and liver, produces other forms of energy too – chemical as in the cells of the glands and electrical as in the cells of the nerves. Light is never produced in the human body, but it is produced in some other forms of life, such as the lightning bug, glow-worm, the little deep sea animal with the big name, Noctiluca miliaris.

Each tiny engine in the human body, each of the estimated twenty-five million millions, must be supplied with a regular supply of oxygen and must perform the function of throwing off the carbon dioxide. If the oxygen supply should fail for just one minute, some of the cells are injured and asphyxiated. To keep the body alive it’s evident that the supply of oxygen must be constant. In fact, in a reasonably active man, twenty square feet of oxygen is absorbed, transmitted by the blood and used for combustion in a single day. A similar amount in square feet of carbon dioxide is thrown out or excreted from the body. During intensive work a much greater supply of oxygen is required. Unlike some of the smaller animals it is not possible for a human being to absorb oxygen directly from the air through his skin. There is too little surface to supply the body requirements. This problem on which our existence depends has been solved by the action of the lungs. The lungs are an automatic, self-regulating bellows-like organ, which works and continues to perform the same function as long as there is life within us. Presently we well endeavor to explain and describe just how this huge and powerful bellows works. The lungs have mysterious power, in spite of the fact that they are made of soft, spongy, elastic tissue.

The lungs through the function they perform constantly supply the blood cells with oxygen and remove from the blood the waste in the form of carbon dioxide. They are so constructed that they include a surface fifty times as great as that of all the skin on the body. This surface brings in constantly fresh air on one side and with the constantly moving red cells and fluid blood on the other side it makes the exchange of molecules of oxygen for carbon dioxide on the other.

This exchange must take place about three times a minute, more frequently when training or in working intensively. The blood hurrying back and forth has much work to do as it must go through both sets of capillaries to the farthermost points of the body in this normal twenty seconds for a round trip. All of the blood of the body must pass through the lungs, just as it does through the heart and each capillary. The exchange, which takes place in the inner part of the lungs, finds as organ perfectly adapted for this exchange. It is a moist, spongy jelly-like substance designed to dissolve oxygen and carbon dioxide and pass them from one side of the lungs to the other. This vital function, the exchange it is commonly called, which is the essential part of respiration, takes place between the capillaries and the respiratory surface. The remainder of the breathing apparatus merely aids these functions by bringing the fresh air to the respiratory surface and forcing away the used air, rich in carbon dioxide and poor in oxygen. To us breathing is simple, and automatic. It takes place twenty-four hours a day as long as there is life within the body. As you must have gathered from this brief discussion, however, the apparently simple process is amazingly complicated when considered more carefully. We will describe the construction of the breathing system, so that you readers who are interested in “what makes us tick” will know more about what takes place within us to maintain or build our strength and our health.

The main part of the lungs is the bellows and it can be seen in the drawing which accompanies the article. It is connected to the outside by a stem, the end of which is the nose; farther along the stem we find the pharynx, the larynx, and the trachea. Man-made bellows have been in use for thousands of years. They have been used since the value of iron or other metals has been discovered. Ancient or modern, complex or simple, they work in a similar manner, with a valve to let the air in, near the handle, a nozzle to let it out where it can be applied to do the work for which the bellows is designed. This is not practical in the human body; the nozzle is the only opening and through it the air must pass in and out. To further complicate the process the passage of the air must cross the tunnel through the pharynx and the esophagus must pass.

The passage of both air and food is controlled by valves. It’s only occasionally that traffic becomes mixed up at these crossings and then you experience the condition of something going down the wrong way. The imaginary green light of the Go system is usually turned on for the air. At brief intervals when food is being consumed, the go sign is turned on for food and it rushes across as the air is held up momentarily.

The lungs are situated in the cavity of the thorax. You can visualize their position and their function if you imagine a rubber balloon inserted in a bottle. The normal air pressure at or near sea level is fifteen pounds per square inch. Therefore if the air surrounding the balloon is pumped out, air will be drawn in by atmospheric pressure until the sides of the balloon will be pressed out everywhere until they flatten against the sides of the bottle. The action of the lungs in the thorax is similar. A vacuum is created between the thoracic wall and the lungs, so that the outside air pressure is always distending or pressing the lungs against the wall and the lungs by their natural rubber-like elasticity are trying to contract. But the air pressure is always greater than the power of their elasticity, keeping the lungs always distended. It is not far from a balance and very little exertion is required to cause the lungs to function.

In a bellows there are two sides which move toward each other, to draw in and force out the air. In the thoracic cavity of man or all animals higher than the fish, which does not have lungs, an improvement has been made over the bellows because the four sides of the thoracic cavity move in and out. The walls of the cavity change their form with every breath, as they expand and contract. Both sides move in and out; the front wall moves in and out a great deal. There is little movement in the ceiling of the cavity or the back, but the floor moves up and down considerably. The expansion of this cavity sucks in the outside air; its contraction or expiration blows a current of air out.

The sides of the thorax of course are the ribs. Each of these is curved like a bow and to aid expansion they are made flexible through a cartilage which is inserted in the anterior part. The middle of each rib hangs down and when the muscles lift the ribs together, the chest gets wider from side to side. At the same time, the breastbone is then lifted up and shoved forward so that the chest becomes deeper from front to back. The outside air pressure forces the lungs to expand, and out against the rib box, so fresh air comes in. If the ribs were made entirely of bone they would break easily, but the cartilages, which have a capacity for twisting somewhat, permit the chest to expand; and yielding as they do to blows or unusual outside pressure in any form, usually prevent the bones from being broken.

It’s more difficult for the lungs of humans to work, for with the shoulders not fixed, their weight must be carried by the thorax, and lifted with each movement of breathing. You may have noticed that when a man is out of breath – as after a race or heavy, high-repetition deep knee bending – he will lie down of lean over a fence in the former condition, resting his elbows upon the fence. After the deep knee bend in the York courses, the breathing exercise is practiced in the supine position, lying upon a box or a bench, which serves the dual purpose of taking the load from the thorax, while enforced breathing is required, but makes possible greater temporary expansion which in time results in a permanent enlargement of the chest. In animals, the canines or quadrupeds who deep their four feet on the ground, the ribs are lifted from the shoulders which are fixed place. The animal’s breathing, you must have noticed, takes place almost entirely from side to side, while in the case of a human being, most of the movement is up and down, a movement of the chest floor which is created by the action and power of the diaphragm. That gives rise to the expression stomach breathing and chest breathing, most persons being comparatively shallow breathers and breathing principally through the diaphragm. Needless to say, any man who trains vigorously, especially with weights, will utilize all the space, all the expansion of his entire rib box or thoracic cavity.

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