XXVII. RESPIRATION AND EXCRETION

Problem LI. A study of the organs and process of respiration. (Laboratory Manual, Prob. LI.)

(a) Organs of respiration in frog.

(b) Mechanics of respiration.

(c) Process of respiration in the lungs.

Necessity for Respiration.

We have seen that plants and animals need oxygen in order that the life processes may go on. Food is oxidized to release energy, just as coal is burned to give heat to run an engine. As a draft of air is required to make fire under the boiler, so, in the human body, oxygen must be given so that foods or tissues may be oxidized to release energy used in growth. This oxidation takes place in the cells of the body, be they part of a muscle, a gland, or the brain. Blood, in its circulation to all parts

glottis, and into the windpipe. This cartilaginous tube, the top of which may easily be felt as the Adam's apple of the throat,

From

pulmonary
artery

Bronchial
Tybe

To pulmonary

vein

divides into two bronchi. The bronchi within the lungs break up into a great number of smaller tubes, the bronchial tubes, which divide somewhat like the small branches of a tree. This branching increases the surface of the air tubes within the lungs. The bronchial tubes, indeed all the air passages, are lined with ciliated cells. The cilia of these cells are constantly in motion, beating with a quick stroke toward the outer end of the tube, that is, toward the mouth. Hence, if any foreign material should get into the windpipe or bronchial tubes, it will be expelled by the action of the cilia. It is by means of cilia that phlegm is raised from the throat. Such action is of great importance, as it prevents the

Air

Oxygen

Carbon

dioxide

Water

Air

Heat

Other wastes

filling of the air passages with Diagram to show what the blood loses and foreign matter. The bronchi

gains in one of the air sacs of the lungs.

end in very minute air sacs called alveoli, little pouches having elastic walls, into which air is taken when we inspire or take a deep breath. In the walls of the alveoli are numerous capillaries, the ends of arteries which pass from the heart into the lung. It is through the very thin walls of the alveoli that an interchange of gases takes place which results in the blood giving up part of its load of carbon dioxide, and taking up oxygen in its place.

The Pleura. The lungs are covered with a thin elastic membrane, the pleura. This forms a bag in which the lungs are hung. Between the walls of the bag and the lungs is a space filled with lymph. By this means the lungs are prevented from rubbing against the walls of the chest. Breathing. In every full breath there are two distinct movements, inspiration (taking air in) and expiration (forcing air out). In man an inspiration is produced by the contraction of the muscles between the ribs together with the contraction of the diaphragm, the muscular wall just below the heart and lungs; this results in pulling down the diaphragm and pulling upward and outward of the ribs, thus making the space within

the chest cavity larger. The lungs, which lie within this cavity, are filled by the air rushing into the larger space thus made. An expiration is

simpler than an inspiration, for it requires no muscular effort; the muscles relax, the breastbone and ribs sink into place, while the diaphragm returns to its original position.

A piece of apparatus which illustrates to a degree the mechanics of breathing may be made as follows: Attach a string to the middle of a piece of sheet rubber. Tie the rubber over the large end of a bell jar. Pass a glass Y tube through a rubber stopFasten two small toy

per.

in (a) inspiration; (b) expiration. balloons to the branches of the tube. Close the small end of the jar with the stopper. Adjust the tube so that the balloons shall hang free in the jar. If now the rubber sheet is pulled down by means of the string, the air pressure in the jar is reduced and the toy balloons within expand, owing to the air pressure down the tube. When the rubber is allowed to go back to its former position, the balloons collapse.

Rate of Breathing and Amount of Air Breathed. - During quiet breathing, the rate of inspiration is from fifteen to eighteen times per minute; this rate largely depends on the amount of physical work performed. About 30 cubic inches of air are taken in and expelled during the ordinary quiet respiration. The air so breathed is called tidal air. In a "long breath," we take in about 100 cubic inches in addition to the tidal air. This is called complemental air. By means of a forced expiration, it is possible to expel from 75 to 100 cubic inches more than tidal air; this air is called reserve air. What remains in the lungs, amounting to about 100 cubic inches, is called the residual air. The value of deep breathing is seen by a glance at the diagram. It is only by this means that we clear the lungs of the reserve air with its accompanying load of carbon dioxide. Respiration under Nervous Control. The muscular movements which cause an inspiration are partly under the control of the will, but in

Apparatus

showing mechanics of breathing.

part the movement is beyond our control. The nerve centers which govern inspiration are part of the sympathetic nervous system. Anything of an irritating nature in the trachea or larynx will cause a sudden expiration or cough. When a boy runs, the quickened respiration is due to the fact that oxygen is used up rapidly and a larger quantity of carbon dioxide is formed. Thus the nervous center which has control of respiration is stimulated to greater activity, and quickened inspiration follows.

Problem LII. A study of the products of respiration. (Laboratory Manual, Prob. LII.)

Changes in Air in the Lungs. — Air is much warmer after leaving the lungs than before it enters them. Breathe on the bulb of a thermometer to prove this. Expired air contains a considerable amount of moisture, as may be proved by breathing on a cold polished surface. This it has taken up in the air sacs of the lungs. The presence of carbon dioxide in expired air may easily be detected by the limewater test. contains, by volume:

Nitrogen

Oxygen

Carbon dioxide

Air such as we breathe out of doors

Air expired from the lungs contains:

Nitrogen

Oxygen

Carbon dioxide

Water

79 20.96 .04

79

16.02

4.38

.60

In other words, there is a loss of between four and five per cent oxygen, and nearly a corresponding gain in carbon dioxide, in expired air. There are also some other organic substances present. HUNT. ES. BIO. 25

The volume of carbon dioxide given off is always a little less than the volume of oxygen taken in. This seems to show that some oxygen unites with some of the chemical elements in the body.

Changes in the Blood within the Lungs. Blood, after leaving the lungs, is much brighter red than just before entering them. The change in color is due to a taking up of oxygen by the homoglobin of the red corpuscle. Changes taking place in blood are obviously the reverse of those which take place in air in the lungs. Blood in the capillaries within the lungs gains from four to five per

a

b

cent of oxygen, which the air loses. At the same time blood loses the four per cent of carbon dioxide, which the air gains. The water, of which about half a pint is given off daily, is mostly lost from the blood.

Problem LIII. A study of ventilation.

Prob. LIII.)

(Laboratory Manual,

During

Need of Ventilation. the course of a day the lungs have lost to the surrounding air nearly two pounds of carbon dioxide. This means that about three fifths of a cubic foot is given off from each person during an hour. When we are confined for some time in a room, it becomes necessary to get rid of this carbon dioxide. This can be done only by means of proper ventilation. Other materials are passed off from the lungs with carbon dioxide. It is the presence of these wastes in combination with carbon dioxide that makes breathed air particularly unwholesome. The presence of impurities in the air of a room may easily be determined by its odor. The close smell of a poorly ventilated room is due to organic impurities given off with the carbon dioxide. This, fortunately, gives us an

Three ways of ventilating a room: i, inlet for air; o, outlet for air.

Which is the best method of ventilation? Explain.