Some Physiology You Ought to Know
A close relation exists between the soil, plant, and the animal. One
really cannot exist without the other to fulfill its destiny. A soil
without plant or animal growth is barren, devoid of life. The soil comes
first; the elements contained in it and the air are the basis of plant
and animal life. The body of the animal is made up of the identical
elements found in the plant, yet the growth of the plant is necessary to
furnish food for animal life. The plant takes from the soil and from the
air the simple chemical elements, and with these builds up the plant
tissue which, in its turn, is the food of the animal.
The animal cannot feed directly from the soil and air; it requires the
plant first to take the elements and to build them into tissue. From
this tissue animals get their food for maintenance and growth. Then the
animal dies; with its decay and decomposition comes change of animal
tissue, back to soil and air again; back to single simple elements, that
new plants may be grown, that new plant tissue may be made for another
generation of animal life.
Thus the plant grows out of the soil and air, and the decay of the
animal plant life furnishes food for the plant that the plant may
furnish food for the animal. Thus we see the cycle of life; from the
soil and air come the soil constituents.
[Illustration: CIRCULATION AND DIGESTION
1 Mouth, 2 Pharynx, 3 Trachea, 4 Jugular Vein, 5 Carotid Artery,
6 Œsophagus, 7 Posterior Aorta, 8 Lungs, 9 External Thoracic Artery,
10 Left Auricle, 11 Right Auricle, 12 Diaphragm, 13 Spleen, 14 Stomach,
15 Duodenum, 16 Liver, upper extremity, 17 Large Colon, 18 Left Kidney
and its Ureter, 19 Floating Colon, 20 Rectum, 21 Anus, 22 Bladder,
23 Urethra, 24 Small Intestine, 25 Cæcum, 26 Venous Supply to the Foot,
27 Posterior Tibial Artery, 28 Internal Metatarsal Vein, 29 Internal
Metatcarpal Vein, 30 Posterior Radial Artery, 31 Metacarpal Artery,
32 Vertebral Artery, 33 Superior Cervical Artery, 34 Anterior Dorsal
Artery.]
=Meaning of Plant Building.=--Before the single simple elements were
taken into the plant, they were of little value. The animal could not
use them for food, they could not be burned to furnish heat, and they
stored up no energy to carry on any of the world’s work. What a change
the plant makes of them! So used, they become the source of the animal
food, and, as food, they contain five principal groups with which the
animal is nourished. These five groups are the air, water, the protein
compounds, the nitrogen free compounds, such as starch, crude fiber,
sugar and gums, and the fat or ether extract, as it is called.
DIGESTION OF THE FOOD
Before these different constituents of the plant can be used as food for
animals, they must be prepared for absorption into the system of the
animal. This preparation takes place in the mouth, œsophagus tube, the
stomach, and the intestines, aided by the various secretions incident to
digestion and absorption. Any withholding of any essential constituent
has its result in inefficiency or illness of the animal.
Withhold ash materials, for instance, from the food, or supply an
insufficient quantity, and the fact will be evidenced by poor teeth,
deficient bone construction and poor health in general. Let the feeding
ration be short in protein, and the result will be shown in the flesh
and blood. Let the carbohydrates and fat be withheld or supplied
insufficiently, and energy will be denied and a thrifty condition will
not be possible.
The supply of these different constituents in the proper proportion
gives rise to the balanced ration; and is concerned in a treatise of
this kind only in so far as it has to do with disease or health. For,
remember this fact: live stock are closely associated with right
feeding. If foods be improperly prepared, or improperly supplied, or the
rations poorly balanced, with too much of one constituent and too little
of another, the effect will be manifest in an impoverished condition of
the system. That means either disease, or disease invited.
Not only must these facts be considered, but other matters given
recognition also. The greater part of the trouble of the stockman in the
way of animal diseases is due to some disturbance of the digestive
system, or to the water supply, or to ventilation, or to the use to
which the animal is put from day to day. Attention to the details of
digestion has its reward in thrifty, healthy stock; a lack of this
attention brings trouble and either a temporary ailment or a permanent
disease.
=Process of Mastication.=--Food is taken in the mouth, where it is
masticated by means of the teeth, lips, cheeks, and the tongue. While
the process of mastication is taking place there is being poured into
the mouth large quantities of saliva, which softens the food and starts
the process of digestion. The active principle of saliva is a soluble
ferment, called ptyalin, that converts the starch of food into sugar.
The amount of saliva that is poured into the food is very great, being
often as much as one-tenth of the weight of the animal. This ferment is
active after the teeth have been formed, which explains why it is not
advisable to feed much starchy food to children before their teeth have
begun development.
The food, after being ground and mixed with the saliva fluid, goes to
the stomach. With the horse and hog the stomach is a single sac not
capable of holding very large quantities of food; with the cow and
sheep, on the other hand, we find a large storehouse for holding food--a
storehouse that is divided into four compartments, the rumen or paunch,
reticulum, omasum, and the abomasum. The first three communicate with
the gullet by a common opening. The cud is contained in the first and
second stomachs, and, after it has been masticated a second time, it
passes to the third and fourth, and to the bowels, where the process of
digestion is continued.
[Illustration: DISEASED KIDNEY
The kidney of the hog is pictured here. As a rule it is usually
impossible to diagnose kidney troubles in hogs and similar lower
animals.]
=Gastric Juice.=--From this it will be noticed that chewing the cud is
an act in the process of digestion; it refers only to rechewing the food
so as to get it finer and better ground for digestion. While in the
stomach the saliva continues the digestion of the starchy matter and is
assisted by the gastric fluid that pours in from the lining of the
stomach, which converts the protein or albuminoids into peptones. The
fatty matter is not acted upon at this point. There are three
constituents of gastric juice, which affect the changes in the food.
These are pepsin, rennet, and acid. With rennet you are acquainted. It
is used in the kitchen, in the making of cheese, and is obtained from
the stomach of calves or other young animals. Pepsin, also obtained
directly from the stomach, is now a conspicuous preparation in medicine.
The food, after leaving the stomach, goes into the bowels and is acted
upon by secretions of the liver and pancreas or sweetbreads. It should
be noted in passing that no secretion enters the first three divisions
of the ruminant’s stomach. It is only in the fourth or true stomach that
the gastric juice is found.
=The Stomach Churn.=--While food is in the stomach it is subjected to a
constant turning movement that causes it to travel from the entrance to
the exit or intestines. When it passes into the small intestines it is
subjected to the action of bile and pancreatic juices, which have
principally to do with the breaking up of the fat compounds. Both
resemble, to a certain extent, saliva in their ability to change starch
into sugar.
The secretion of the bile comes from the liver and the pancreatic juice
from the pancreas or sweetbreads, and both are poured into the
intestines near the same point, so that they act together. The ferments
they contain act in the following ways: They change starch into sugar,
fat into fatty compounds, they curdle milk, and convert protein
compounds into soluble peptones.
The process of digestion is finally ended in the intestines, where
absorption into the system takes place. There is no opening at all from
the bowels into the body, but the digestive nutriment is picked up by
the blood when handed into the body from the intestines by means of
countless little cells called villi, that line the walls of the
intestines. These villi cells have little hair-like projections
extending into the intestines, which constantly move; these protrusions,
as they move about, catch on to the digested nutriment, draw it into
the cells themselves, where it is handed on to the blood, when it is
later on distributed to all parts of the body. You can realize that an
immense number of these absorption cells are present when the length of
the intestine is considered. In the ox the intestine is nearly 200 feet
long. After the nutriment is drawn from the food the undigested portions
are voided periodically as feces or dung.
[Illustration: STOMACH OF RUMINANT
The four main divisions of the ruminant’s stomach are pictured here. The
first three divisions are the store-houses for food until it is fully
prepared for the fourth stomach or abomasum.]
=Absorption of the Nutriment.=--Digestion, therefore, is a dissolving
process; food is admitted to the system by means of cells. You remember
that all plant food first passes into a soluble state before it can
enter the roots and be conveyed to the parts of the plants that require
additional food for growth. In the case of plants the entrance is by
means of the root hairs. In the case of the animal, entrance in the body
is by means of the villi cells that line the intestines. From this we
see that digestion is both an intricate and delicate process. Any loss
of appetite, any disturbance of the digestion work, and any irregularity
of the bowels bear decided results, one way or the other, to the rest of
the system; and any disturbance of the body at other points, although
having no direct relation to the digestion system, sooner or later
affects the digestion and in so doing causes additional trouble.
Directly affecting digestion may be improper food, either liquid or
solid; and over-exercise or not enough of it may prove troublesome, for
exercise is clearly related to digestion. When the digestion process is
disturbed, air or gas may accumulate in the stomach or bowels and give
rise to colic or hoven. A watery action of the intestines, due to
inflammation or irritation, may lead to dysentery and enteritis; or some
obstruction like a hair-ball or a clover fuzzy ball, or the knotting of
the intestines, may occur, temporarily or permanently impairing
digestion so seriously often as to cause death itself.
CIRCULATION
As water in the plant is the carrier of plant food throughout the plant,
so is blood the carrier and distributor of food in the animal. When food
is absorbed, it either passes into the lymphatic system or into the
capillaries of the blood system. If in the former, it is carried to the
thoracic duct, which extends along the spinal column and enters one of
the main blood vessels. If collected by the capillary system, it is
carried to the portable vein, thence to the liver and finally to the
heart, where it meets with the blue blood collected from all parts of
the body.
At this point, the blood contains both the nutriment and the waste
matter of the body. Before it can be sent through the body again the
waste material must be thrown out of the system by means of the lungs.
This is accomplished by the heart forcing to the lungs the impure blood
with its impurities collected from all parts of the body and also the
nutriment collected from the digestive tract.
The chief organs, therefore, of the circulatory system are the blood and
lymphatic vessels containing respectively blood and lymph. The only
difference between these two materials is in the fact that lymph is
blood without the red-blood corpuscles. The body, after all, really
depends upon this lymph for nourishment, since it wanders to all parts
of the body, surrounds all the cells in all of the tissues and in this
way carries to the cells the very kinds of food that they need.
=Lymph Passes Through Cell Walls.=--The blood vessels have no openings
into the body at all. In this respect the blood system is like the
digestive system; it is separate and distinct in itself. The blood,
however, does creep through the walls of the blood vessels. In so doing
the blood corpuscles are left behind and lymph is the result.
[Illustration: HOW THE BLOOD CIRCULATES THROUGH THE BODY]
The center of the blood system is the heart. It is the engine of the
body. Going out from it is the great aorta, which subdivides into
arteries and farther away further subdivides until there is a great
network of little arteries; these in turn become very tiny and take the
name of capillaries. Thus the red blood, by means of arteries and
capillaries, is carried to all parts of the body. This plan of
distribution would not be complete unless some way were provided for the
return of the blood to the heart and lungs for purification. And just
such an arrangement has been provided. Another kind of network collects
this scattered blood at the extremities into separate vessels, which
gradually increase in size and finally empty their possessions into the
heart. These are the veins of the body, and have to do with the impure
blood of the body.
=How the Heart Does Its Work.=--The power back of blood distribution is
the heart. It is an automatic pump, as it were, that sends blood to the
lungs and through the arteries to all parts of the body. The heart is
divided into four divisions: the left and right ventricles and the right
and left auricles. The right auricle receives the blood from the upper
half of the body through a large vein and the lower half of the body
through another large vein, and the blood from both lungs empties into
the left auricle through two left and two right pulmonary veins. The
large arteries of the heart which carry the blood from the heart to the
different organs arise from the ventricle.
The blood always flows in the same direction. It goes into the auricle
from the veins, and from this into the ventricle. It then passes into
the arteries, then to the veins and then to the capillaries.
The action of the heart is very much like a force pump; the dark blood
flows into the right auricle, which contracts; when this is done, the
blood is forced into the right ventricle; this in turn contracts and
forces the blood into the lungs, where oxygen is taken on and carbonic
acid gas and other impurities are thrown off. From the lungs the blood,
now red and pure, passes into the left auricle and thence into the left
ventricle, from which it is forced into the aorta to be distributed to
all parts of the body.
We now see the close connection existing between the digestive system
and the circulatory system. The digested food in the intestines is
gathered in by villi cells. The question can now be asked, What do these
cells do with this nutriment or digested food? They pour it into the
absorbent vessels or lymphs, as they are called; these in turn empty the
assimilated stores of food into larger and still larger vessels, which
continues until the whole of the nutritive fluid is collected into one
great duct or tube, which pours its contents into the large veins at the
base of the neck, from whence it is carried into the circulatory system,
the very basis of which is the blood.
RESPIRATION
The dark and impure blood, after returning to the heart, is sent to the
lungs. It is, when collected from the body, just before being sent to
the lungs dark, dull and loaded with worn-out matter. It must now be
sent to the lungs, where it may be spread over the delicate thin walls
of millions of vesicles, to be exposed to the air, which is inhaled by
the acts of breathing. The blood gives off the broken-down material and
carbonic acid gas very readily. It is both unpleasant and disagreeable,
and the blood cells find it very unattractive.
The cells of the blood, however, have a great attraction for oxygen,
consequently the cells absorb oxygen with greediness, so that when the
blood returns to the heart it is fresh and bright and ready to take its
journey back over the body again. This is done just about every three
minutes. This endless round continues until stopped forever by death.
The relation existing between the animal and plant functions is brought
to light in another way. When the plant was building tissue it released
oxygen and exhaled it into the air. At the same time, by means of
leaves, it gathered in the carbonic acid to use in plant building. Of
course this was got from the air. The animal in performing its functions
and in building its tissue inhales oxygen from and exhales carbonic acid
gas into the air. Thus it is that animals take up what is unnecessary to
the plant and the plant uses what is waste and poison to the animal.