PHYSIOLOGY OF THE RESPIRATORY ORGANS.
475. RESPIRATION, or breathing, is that process by which air is taken
into the lungs and expelled from them. The object of respiration is,
1st. To supply the system with oxygen, which is essential to the
generation of animal heat; 2d. To convert the chyle into blood. This
is done by the oxygen of the inspired air; 3d. To relieve the organs
of the body of the principal elements (carbon and hydrogen) that
compose the old and useless particles of matter. The organs of the
system, as already mentioned, are principally composed of carbon,
hydrogen, oxygen, and nitrogen.
476. By the action of the lymphatics and capillary veins, the old and
worn-out particles are conveyed into the veins of the systemic
circulation. The hydrogen, in form of watery vapor, is easily
discharged in the perspiration and other secretions. The nitrogen and
oxygen are, or may be, separated from the blood, through the agency of
several different organs; but carbon does not escape so readily. It is
probable that a part of the surplus carbon of the venous blood is
secreted by the liver; but a far greater amount passes to the lungs,
and these may be considered as special organs designed to separate
this element from the venous blood.
477. An ordinary inspiration may be accomplished by the action of the
diaphragm, and a slight elevation of the ribs. In full inspiration,
the diaphragm is not only more depressed but the ribs are evidently
elevated. To produce this effect on the ribs, two sets of muscles are
called into action. Those which are attached to the upper rib,
sternum, and clavicle, contract and elevate the lower and free
extremities of the ribs. This enlarges the cavity of the chest between
the spinal column and the sternum. But the lateral diameter, in
consequence, is only slightly increased, because the central portion
of the ribs sinks lower than their posterior extremities, or their
cartilaginous attachment to the sternum.
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475-494. _Give the physiology of the respiratory organs._ 475. What is
respiration? What is the principal object in breathing? 476. How are
the useless atoms of matter conveyed into the veins of the systemic
circulation? How may the principal elementary substances be separated
from the blood? 477. How may an ordinary inspiration be accomplished?
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[Illustration: Fig. 95. 6, Four of the vertebrae, to which are attached
three ribs, (7, 7, 7,) with their intercostal muscles, (8, 8.) These
ribs, in their natural position, have their anterior cartilaginous
extremity at 4, while the posterior extremity is attached to the
vertebrae, (6,) which are neither elevated nor depressed in respiration.
1, 1, and 2, 2, parallel lines, within which the ribs lie in their
natural position. If the anterior extremity of the ribs is elevated from
4 to 5, they will not lie within the line 2, 2, but will reach the line
3, 3. If two hands extend from 1, 1, to 2, 2, they will effectually
prevent the elevation of the ribs from 4 to 5, as the line 2, 2, cannot
be moved to 3, 3.]
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What effect has a full inspiration on the ribs and diaphragm? How is
the chest enlarged between the spinal column and sternum? What is said
of the lateral diameter of the chest? Explain fig. 95.
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478. The central portion of the ribs is raised by the action of
intercostal muscles. The first, or upper rib, has but little movement;
the second has more motion than the first, while the third has still
more than the second. The second rib is elevated by the contraction of
the muscles between it and the first. The third rib is raised by the
action of two sets of muscles; one lies between the first and second
ribs, the other between the second and third. The motion of each
succeeding rib is increased, because it is not only acted upon by the
muscles that move the ribs above, but by an additional intercostal; so
that the movement of the twelfth rib is very free, as it is elevated
by the contraction of eleven muscles.
479. The tenth rib is raised eight times as much as the second rib,
and the lateral diameter of the lower portion of the chest is
increased in a corresponding degree. At the same time, the muscular
margin of the diaphragm contracts, which depresses its central
portion; and in this way, the chest is enlarged forward, laterally,
and downward, simultaneously with the relaxation of the walls of the
abdomen.
480. The lungs follow the variations of capacity in the chest,
expanding their air-cells when the latter is enlarged, and contracting
when the chest is diminished. Thus, when the chest is expanded, the
lungs follow, and consequently a vacuum is produced in their
air-cells. The air then rushes through the mouth and nose into the
trachea and its branches, and fills the vacuum as fast as it is made.
This mechanical process constitutes _inspiration_.
481. After the expansion of the chest, the muscles that elevated the
ribs relax, together with the diaphragm. The elasticity of the
cartilages of the ribs depresses them, and the cavity of the chest is
diminished, attended by the expulsion of a portion of the air from the
lungs. At the same time, the muscles that form the front walls of the
abdominal cavity, contract, and press the alimentary canal, stomach,
and liver, upward against the diaphragm; this, being relaxed, yields
to the pressure, rises upward, and presses upon the lungs, which
retreat before it, and another portion of air is expelled from these
organs. This process is called _expiration_.
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478. Describe the action of the intercostal muscles upon the ribs.
479. How does the elevation of the tenth rib compare with the second?
What effect has this elevation upon the lateral diameter of the chest?
480. Describe the process of inspiration. 481. Describe the process by
which the air is forced out of the lungs.
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[Illustration: Fig. 96. A front view of the chest and abdomen in
respiration. 1, 1, The position of the walls of the chest in inspiration.
2, 2, 2, The position of the diaphragm in inspiration. 3, 3, The position
of the walls of the chest in expiration. 4, 4, 4, The position of the
diaphragm in expiration. 5, 5, The position of the walls of the abdomen
in inspiration. 6, 6, The position of the abdominal walls in expiration.]
482. Thus it is obvious that the enlargement of the chest, or
inspiration, is produced in two ways: 1st. By the depression of the
convex portion of the diaphragm; 2d. By the elevation of the ribs. On
the contrary, the contraction of the chest, or expiration, is
produced by the depression of the ribs, and elevation of the central
part of the diaphragm. These movements are successive during life, and
constitute _respiration_.
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Explain fig. 96. 482. In how many ways may the chest be enlarged, and
how is it accomplished? How is the contraction of the chest effected?
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[Illustration: Fig. 97. A side view of the chest and abdomen in
respiration. 1, The cavity of the chest. 2, The cavity of the abdomen. 3,
The line of direction for the diaphragm when relaxed in expiration. 4,
The line of direction for the diaphragm when contracted in inspiration.
5, 6, The position of the front walls of the chest and abdomen in
inspiration. 7, 8, The position of the front walls of the abdomen and
chest in expiration.]
_Experiment._ Place the ear upon the chest of a person, and a
murmuring sound will be heard, somewhat like the soft sighings of the
wind through forest trees. This sound is caused by the air rushing in
and out of the lungs, and is peculiarly distinct in the child.
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Explain fig. 97. How may the murmur of respiration be heard?
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483. It is not easy to decide how much air is taken into the lungs at
each inspiration. The quantity, however, must vary in different
individuals, from the difference in the condition and expansion of the
lungs, together with the size of the chest. From numerous experiments,
the quantity, at an ordinary inspiration, of a common-sized man, is
fixed at forty cubic inches. It has been estimated that one hundred
and seventy cubic inches can be thrown out of the lungs by a forcible
expiration, and that there remain in the lungs two hundred and twenty
cubic inches; so that these organs, in their quiescent state, may be
considered as containing about three hundred and ninety cubic inches
of air, or more than a gallon.
484. Respiration is more frequent in females and children than in
adult men. In diseases, particularly those of the lungs, it is more
increased in frequency than the action of the heart. In health, the
smallest number of inspirations in a minute by an adult, is not less
than fourteen, and they rarely exceed twenty-five. Eighteen may be
considered an average number. The quantity of oxygen taken into the
lungs at each inspiration is about eight cubic inches, one half of
which disappears in every act of respiration.
_Observation._ Under different circumstances, however, the consumption
of oxygen varies. It is greater when the temperature is low, than when
it is high; and during digestion the consumption has been found one
half greater than when the stomach was empty.
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483. Can it be ascertained with accuracy how much air is taken into
the lungs at each inspiration? Why not? What is the probable quantity
that an ordinary sized man inspires? How much can be thrown out of the
lungs at a forcible expiration, and how much remains in the lungs?
From these calculations, how much may they contain in their quiescent
state? 484. In whom is respiration most frequent? How in disease? How
in health? How many may be considered an average number? When is the
consumption of oxygen the greatest?
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485. Dr. Southwood Smith has lately performed a series of very
interesting experiments, from which he deduces the following general
results: "1st. The volume of air ordinarily present in the lungs is
about twelve pints. 2d. The volume of air received by the lungs at an
ordinary inspiration is one pint. 3d. The volume of air expelled from
the lungs at an ordinary expiration, is a little less than one pint.
4th. Of the volume of air received by the lungs at one inspiration,
only one fourth part is decomposed at one action of the heart. 5th.
The quantity of blood that flows to the lungs, to be acted upon by the
air at one action of the heart, is two ounces, and this is acted on in
less than one second of time. 6th. The quantity of blood in the whole
body of the human adult, is twenty-five pounds avoirdupois, or twenty
pints. 7th. In the mutual action that takes place between the air and
blood, every twenty-four hours, the air loses thirty-seven ounces of
oxygen, and the blood fourteen ounces of carbon."
486. Apparently, atmospheric air is a simple element. But chemical
analysis shows its composition to be oxygen and nitrogen, in the
proportion of twenty-one parts of the former, and about seventy-nine
of the latter. In addition, there is a small amount of vapor of water
and carbonic acid. The pressure of this invisible, elastic fluid upon
the body of an ordinary sized adult, is estimated to equal thirty-five
thousand pounds.
487. The principal substance of a vitiated character in the
dark-colored blood is carbonic acid. And since there is no chemical
affinity between the oxygen and nitrogen of the air, the former
readily unites with some of the elements of the blood. Hence, whenever
blood is presented to the air in the lungs, the oxygen leaves the
nitrogen, and becomes mixed with the circulating fluid. (Appendix J.)
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485. State the 1st, 2d, 3d, and 4th deductions from the experiments of
Dr. Southwood Smith. The 5th, 6th, and 7th. 486. Of what is
atmospheric air composed? What is the weight of air upon a common
sized man? 487. What is the principal substance of a vitiated
character in the dark-colored blood? What is said of the chemical
affinity between oxygen and nitrogen?
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488. Again, carbonic acid and water have a stronger affinity for
atmospheric air than for the other elements of the blood. Consequently,
when they are brought into contact with the air in the lungs, the
carbonic acid and water leave the other constituents of the blood, and
unite with the air. In this way the bluish, or impure blood is
relieved of its impurities, and becomes the red, or pure blood,
which contains the principles so essential to life. (Appendix K.)
489. The formation of carbonic acid and water, eliminated from the
system through the lungs and skin, is explained by the following
theory: In the lungs and upon the skin the oxygen separates from the
nitrogen and unites with the blood in the capillary vessels of these
organs. The oxygen is conveyed with the blood to the capillary
arteries and veins of the different tissues of the system. In these
membranes there is a chemical union of the oxygen with the carbon and
hydrogen contained in the blood and waste atoms of the system. This
combustion, or union of oxygen with carbon and hydrogen, is attended
with the disengagement of heat, and the formation of carbonic acid and
water. (Appendix L.)
490. The following experiment will illustrate the passage of fluids
through membranes, and the different affinity of gases for each other.
Put a mixture of water and alcohol into a phial and leave it uncorked.
Both the water and alcohol have a greater affinity for air than for
each other. Alcohol has a greater affinity for the air, and will be
diffused through it more readily than the water, when there is no
intervening obstacle. But tie a piece of bladder over the mouth of the
phial, and let it stand a few days,--the water will leave the
alcohol, and pass through the membrane. By the aid of this experiment,
we shall endeavor to explain the interchange of fluids in the lungs.
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488. What is formed when oxygen unites with carbon or hydrogen? 489.
Give the theory for the formation of carbonic acid and watery vapor
thrown out of the system. 490. Illustrate the passage of fluids
through membranes, and the different affinities of gases.
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491. The walls of the air-vesicles, and coats of the blood-vessels,
are similar, in their mechanical arrangement, to the membranous
bladder in the before described experiment. As the oxygen of the air
has greater affinity for blood than for nitrogen, so it permeates the
membranes that intervene between the air and blood more readily than
the nitrogen. As the carbonic acid and water have a greater affinity
for air than for the other elements of the blood, so they will also
pass through the walls of the blood-vessels and air-cells more readily
than the other elements of the dark-colored blood.
[Illustration: Fig. 98. 1, A bronchial tube divided into three branches.
2, 2, 2, Air-cells. 3, Branches of the pulmonary artery, that spread over
the air-cells. Through the pulmonary artery the dark, impure blood is
carried to the air-cells of the lungs. 4, Branches of the pulmonary vein,
that commence at the minute terminations of the pulmonary artery. Through
the pulmonary vein the red blood is returned to the heart.]
492. As the impure blood is passing in the minute vessels over the
air-cells, the oxygen passes through the thin coats of the air-cells
and blood-vessels, and unites with the blood. At the same time, the
carbonic acid and water leave the blood, and pass through the coats of
the blood-vessels and air-cells, and mix with the air in the cells.
These are thrown out of the system every time we breathe. This
interchange of products produces the change in the color of the
blood.
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Explain fig. 98. 492. How and where is the blood changed?
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_Experiment._ Fill a bladder with dark blood drawn from any animal.
Tie the bladder closely, and suspend it in the air. In a few hours,
the blood next to the membrane will have become of a bright red color.
This is owing to the oxygen from the air passing through the bladder,
and uniting with the blood, while the carbonic acid has escaped
through the membrane.
[Illustration: Fig. 99. An ideal view of the pulmonary circulation. 1, 1,
The right lung. 2, 2, The left lung. 3, The trachea. 4, The right
bronchial tube. 5, The left bronchial tube. 6, 6, 6, 6, Air-cells. 7, The
right auricle. 8, The right ventricle. 9, The tricuspid valves. 10, The
pulmonary artery. 11, The branch to the right lung. 12, The branch to the
left lung. 13, The right pulmonary vein. 14, The left pulmonary vein. 15,
The left auricle. 16, The left ventricle. 17, The mitral valves.]
493. The presence of carbonic acid and watery vapor in the expired
air, can be proved by the following experiments: 1st. Breathe into
lime-water, and in a few minutes it will become of a milk-white color.
This is owing to the carbonic acid of the breath uniting with the
lime, forming the _carbonate of lime_. 2d. Breathe upon a cold, dry
mirror for a few minutes, and it will be covered with moisture. This
is condensed vapor from the lungs. In warm weather, this watery vapor
is invisible in the expired air, but in a cold, dry morning in winter,
the successive jets of vapor issuing from the mouth and nose are
sufficiently obvious.
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Give the experiment showing that oxygen changes the dark-colored blood
to a bright red color. What is represented by fig. 99? 493. How can
the presence of carbonic acid in the lungs be proved?
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494. From the lungs are eliminated other impurities beside carbonic
acid, the perceptible quality of which is various in different
persons. The offensive breath of many persons may be caused by decayed
teeth, or the particles of food that may be retained between them, but
it often proceeds from the secretion, in the lungs, of certain
substances which previously existed in the system.
_Illustration._ When spirituous liquors are taken into the stomach,
they are absorbed by the veins and mixed with the dark-colored blood,
in which they are carried to the lungs to be expelled from the body.
This will explain the fact, which is familiar to most persons, that
the odor of different substances is perceptible in the breath, or
expired air, long after the mouth is free from these substances.
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How the watery vapor? 494. Are there other excretions from the lungs?
Give the illustration.
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_Note._ Let the anatomy and physiology of the respiratory organs be
reviewed from figs. 96, 97, and 99, or from anatomical outline plates
Nos. 5 and 7.