THE RESPIRATORY ORGANS.
463. The nutrient portion of the food is poured into the left
subclavian vein, (24, 27, fig. 88,) at the lower part of the neck, and
is carried to the right cavities of the heart. The fluid in these
cavities consists of the chyle incorporated with the impure blood.
Neither of these two elements is fitted to promote the growth or
repair the waste of the body. They must be subjected to a process, by
which the first can be converted into blood, and the second freed of
its carbonic acid gas and water. This is effected by the _Respiratory
Organs_.
ANATOMY OF THE RESPIRATORY ORGANS.
464. The RESPIRATORY ORGANS are the _Lungs_, (lights,) the _Tra'che-a_,
(windpipe,) the _Bronch'i-a_, (subdivisions of the trachea,) and the
_Air-Ves'i-cles_, (air-cells at the extremities of the bronchia.) The
_Di'a-phragm_, (midriff,) _Ribs_, and several _Muscles_, also aid in the
respiratory process.
465. The LUNGS are conical organs, one on each side of the chest,
embracing the heart, (fig. 88,) and separated from each other by a
membranous partition. The color of the lungs is a pinkish gray,
mottled, and variously marked with black. Each lung is divided into
lobes, by a long and deep fissure, which extends from the posterior
surface of the upper part of the organ, downward and forward, nearly
to the anterior angle of the base. In the right lung, the upper lobe
is subdivided by a second fissure. This lung is larger and shorter
than the left. It has three lobes, while the left has only two.
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463. What fluids are conveyed into the right cavities of the heart?
What is necessary before they can be adapted to the wants of the body?
By what organs are these changes effected? 464-474. _Give the anatomy
of the respiratory organs._ 464. Name the respiratory organs. What
organs also aid in the respiratory process? 465. Describe the lungs.
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[Illustration: Fig. 89. A back view of the heart and lungs. The posterior
walls of the chest are removed. 1, 2, 3, The upper, middle, and lower
lobes of the right lung. 8, 9, 10, The two lobes of the left lung. 6, 13,
The diaphragm. 7, 7, 14, 14, The pleura that lines the ribs. 4, 11, The
pleura that lines the mediastine. 5, 12, 12, The portion of the pleura
that covers the diaphragm. 15, The trachea, 16, The larynx. 19, 19, The
right and left bronchia. 20, The heart. 29, The lower part of the spinal
column.]
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Explain fig. 89.
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466. Each lung is enclosed, and its structure maintained by a serous
membrane, called the _pleu'ra_, which invests it as far as the root,
and is thence reflected upon the walls of the chest. The lungs,
however, are on the outside of the pleura, in the same way as the head
is on the outside of a cap doubled upon itself. The reflected pleurae
in the middle of the thorax form a partition, which divides the chest
into two cavities. This partition is called the _me-di-as-ti'num_.
[Illustration: Fig. 90. The heart and lungs removed from the chest, and
the lungs freed from all other attachments. 1, The right auricle of the
heart. 2, The superior vena cava. 3, The inferior vena cava. 4, The right
ventricle. 5, The pulmonary artery issuing from it. _a_, _a_, The
pulmonary artery, (right and left,) entering the lungs. _b_, _b_,
Bronchia, or air-tubes, entering the lungs. _v_, _v_, Pulmonary veins,
issuing from the lungs. 6, The left auricle. 7, The left ventricle. 8,
The aorta. 9, The upper lobe of the left lung. 10, Its lower lobe. 11,
The upper lobe of the right lung. 12, The middle lobe. 13, The lower
lobe.]
_Observation._ When this membrane that covers the lungs, and also
lines the chest, is inflamed, the disease is called "pleurisy."
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466. By what are the lungs enclosed? What is the relative position of
the lungs and pleura? What is said of the reflected pleurae? Explain
fig. 90. What part of the lungs is affected in pleurisy?
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467. The lungs are composed of the ramifications of the bronchial
tubes, which terminate in the bronchial cells, (_air-cells_,)
lymphatics, and the divisions of the pulmonary artery and veins. All
of these are connected by cellular tissue, which constitutes the
_pa-ren'chy-ma_. Each lung is retained in its place by its _root_,
which is formed by the pulmonary arteries, pulmonary veins, and
bronchial tubes, together with the bronchial vessels and pulmonary
nerves.
468. The TRACHEA extends from the larynx, of which it is a continuation,
to the third dorsal vertebra, where it divides into two parts, called
bronchia. It lies anterior to the spinal column, from which it is
separated by the oesophagus.
469. The BRONCHIA proceed from the bifurcation, or division of the
trachea, to their corresponding lungs. Upon entering the lungs, they
divide into two branches, and each branch divides and subdivides, and
ultimately terminates in small sacs, or cells, of various sizes, from
the twentieth to the hundredth of an inch in diameter. So numerous are
these bronchial or air-cells, that the aggregate extent of their
lining membrane in man has been computed to exceed a surface of 20,000
square inches, and Munro states that it is thirty times the surface of
the human body.
_Illustration._ The trachea may be compared to the trunk of a tree;
the bronchia, to two large branches; the subdivisions of the bronchia,
to the branchlets and twigs; the air-cells, to the buds seen on the
twigs in the spring.
470. The AIR-VESICLES and small bronchial tubes compose the largest
portions of the lungs. These, when once inflated, contain air, under
all circumstances, which renders their specific gravity much less than
water; hence the vulgar term, _lights_, for these organs. The trachea
and bronchial tubes are lined by mucous membrane. The structure of
this membrane is such, that it will bear the presence of pure air
without detriment, but not of other substances.
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467. Of what are the lungs composed? How retained in place? 468. Where
is the trachea situated? 469. Describe the bronchia. What is the
aggregate extent of the lining membrane of the air-cells? To what may
the trachea and its branches be compared? 470. What is said of the
air-cells and bronchial tubes?
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[Illustration: Fig. 91. A representation of the larynx, trachea,
bronchia, and air-cells. 1, 1, 1, An outline of the right lung. 2, 2, 2,
An outline of the left lung. 3, The larynx 4, The trachea. 5, The right
bronchial tube. 6, The left bronchial tube. 7, 7, 7, 8, 8, 8, The
subdivisions of the right and left bronchial tubes. 9, 9, 9, 9, 9, 9,
Air-cells.]
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What membrane lines the trachea and its branches? What is peculiar in
its structure? What does fig. 91 represent?
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_Observation._ The structure of the trachea and lungs may be
illustrated, by taking these parts of a calf or sheep and inflating
the air-vesicles by forcing air into the windpipe with a pipe or
quill. The internal structure may then be seen by opening the
different parts.
471. The lungs, like other portions of the system, are supplied
with nutrient arteries and nerves. The nervous filaments that
are distributed to these organs are in part from the tenth pair,
(par vagum,) that originates in the brain, and in part from the
sympathetic nerve. The muscles that elevate the ribs and the
diaphragm receive nervous fibres from a separate system, which is
called the respiratory.
[Illustration: Fig. 92. 1, A bronchial tube. 2, 2, 2, Air-vesicles. Both
the tube and vesicles are much magnified. 3, A bronchial tube and
vesicles laid open.]
_Observation._ When the mucous membrane of a few of the larger
branches of the windpipe is slightly inflamed, it is called a "cold;"
when the inflammation is greater, and extends to the lesser air-tubes,
it is called _bronch-i'tis_. When the air-cells and parenchyma become
inflamed, it is called inflammation of the lungs. Coughing is a
violent expulsory effort by which air is suddenly forced through the
bronchia and trachea to remove offending matter.
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How may the structure of the trachea and its branches be illustrated?
471. Are the lungs supplied with nutrient arteries? Where are the
respiratory nerves distributed? From what source do these organs
derive their nervous filaments?
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472. The RIBS are joined to the spinal column at their posterior
extremity; and in front, they terminate in cartilages, which unite
them to the sternum. They incline downward, from the spinal column to
the breast-bone, and form resisting walls that assist in producing the
partial vacuum necessary for inspiration.
[Illustration: Fig. 93. A section of the chest when the lungs are
inflated. 1, The diaphragm. 2, The muscular walls of the abdomen.]
[Illustration: Fig. 94. A section of the chest when the lungs are
contracted. 1, The diaphragm in common expiration. 2, 2, The muscular
walls of the abdomen. 3, The position of the diaphragm in forced
expiration.]
These engravings show the diaphragm to be more convex, and the walls
of the abdomen more flattened, when the lungs are collapsed, than when
they are inflated.
473. The DIAPHRAGM is a flexible circular partition, that separates
the respiratory from the digestive organs, and the chest from the
abdomen. Its margin is attached to the spinal column, the sternum, and
cartilages of the lower ribs. The lungs rest upon its upper surface,
while the liver and stomach are placed below it, (fig. 88.) In a
state of repose, its upper surface forms an arch, the convexity of
which is toward the chest. In forced expiration, its upper point
reaches as high as the fourth rib. In an ordinary inspiration, it is
depressed as low as the seventh rib, which increases the capacity of
the chest.
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472. Describe the ribs. Explain figs. 93 and 94. 473. Describe the
diaphragm.
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474. The RESPIRATORY muscles are, in general, attached at one
extremity to the parts about the shoulders, head, and upper portion
of the spinal column. From these, they run downward and forward, and
are attached, at the opposite extremity, to the sternum, clavicle,
and upper rib. Other muscles are attached at one extremity to a rib
above, and by the opposite extremity to a rib below. These fill the
spaces between the ribs, and, from their situation, are called
_in-ter-cost'al_ muscles.
_Observation._ 1st. There are several actions of common occurrence,
that are intimately connected with respiration; such as hiccough,
sneezing, &c. Hiccough is an involuntary contraction of the muscles of
respiration, particularly the diaphragm.
2d. Sneezing is a violent, involuntary contraction of the respiratory
muscles, as in hiccough. When an acrid stimulant, as snuff, is applied
to the mucous membrane of the nose, an irritation is produced which is
accompanied by a violent expulsion of air from the lungs. This is
owing to the connection between the nasal and respiratory nerves.
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What is its form when not in action? 474. Where do the respiratory
muscles make their attachment? What name is given to those muscles
that fill the places between the ribs? What is hiccough? What is
sneezing?
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