disturbance in the flow of this greenish-brown secretion being very
quickly shown both in stomach and intestinal digestion. It emulsonizes
and saponifies the fats, it aids in their absorption, and it lubricates
the intestinal mass, facilitating its passage through the entire length
of the intestines. Thus, it is a very potent agent in regulating the
bowel movements. A diminution in the flow of bile quickly expresses
itself in constipation.
Fats are almost entirely digested in the small intestine. The presence
of fat stimulates the flow of pancreatic juice, which, in turn,
stimulates the flow of bile from the liver. For this reason, if the
liver is sluggish, fatty foods are desirable. Olive oil is prescribed
for gall stones to stimulate the action of the bile ducts.
Before the fat molecules can be absorbed, they must first be broken up
into glycerin and fatty acids and further changed to a fine emulsion,
which gives the contents of the small intestine a milky appearance.
After they are broken up into these fatty acids and thus brought to
the finest state of emulsion, they are readily saponified, being
then soluble in water and in a state to be absorbed by the walls of
the intestines. The fats are absorbed almost entirely in the small
intestine,—mostly in the duodenum.
As a rule, the starches, or dextrin, will not be fully digested by the
saliva and those which have failed of salivary digestion are acted upon
by amylase (one of the solids of the intestinal juice) and changed
to maltose, while the trypsin from the pancreas, together with the
intestinal juice, acts upon any protein which has failed to be fully
digested in the stomach, changing it into peptone. In the form or
peptone it is absorbed through the “sucking” villi of the intestinal
walls.
The food is forced along the intestinal tract by peristaltic or
muscular relaxation and contraction waves, as in the stomach. As it is
so forced, the nutrient elements, after being put into condition for
absorption, are taken up through the villi of the intestinal walls by
the portal veins and the lacteals of the sub-mucous lining. (See page
78).
It is now believed that a larger proportion of food is digested and
absorbed than was heretofore realized, and that the excretions from the
intestines are, in many cases, made up almost entirely of refuse, and
of the catabolic waste of the system. In an ordinary, mixed diet, it is
stated that about ninety-two per cent of the proteins, ninety-five per
cent of the fats, and ninety-seven per cent of the carbohydrates are
retained by the body.
_In digestion, it is of the utmost importance that the muscular,
mucous, and the sub-mucous coats, and the secreting glands of the
stomach and intestines be kept thoroughly strong and active, that
the digestive juices may be freely poured out, the nutriment be
freely absorbed, and the food be moved along the digestive tract. The
strength of any organ is gained through the nutriment in the blood;
therefore, daily exercise, which calls the blood freely to these
organs, is imperative._
[Sidenote: Absorption of Food]
The greater part of the food is absorbed through the intestines, yet
some proteins, which have been fully digested by the gastric juice, and
certain fats, particularly the fats in milk, which are in a natural
state of emulsion, may be absorbed through the walls of the stomach.
However, the absorption through the stomach is small compared to that
through the intestines.
The small intestine is particularly fitted for absorption. Every inch
or so along its course the mucous lining is thrown up into folds, as
if to catch the food as it passes toward the large intestine, and
to hold it there until the villi have the opportunity to absorb it.
These transverse folds of the intestinal walls are called valvulæ
conniventes. The villi are fingerlike projections of the mucous lining
of the intestines, which stand out upon the lining somewhat as the nap
on plush. They have been called “sucking” villi, because during the
movements of the intestines they seem to suck in the liquid food. As
soon as the foodstuffs,—proteins, carbohydrates, and fats, are put in a
dissoluble state ready for absorption, they are very promptly absorbed
by the villi. If, for any reason, they remain unabsorbed, they are
liable to ferment by the action of the trypsin, or to be attacked by
the bacteria always present in the intestines.
The peptones, sugars, and saponified fats are rapidly absorbed, while
the undigested portion, together with the unabsorbed water, the bile,
mucus and bacterial products, are passed through the ileo-cecal valve
into the large intestine.
That the large intestine is also adapted to the absorption of fats is
shown by clinical experiments with patients who cannot retain food
in the stomach, the food in such cases being given through rectal
injections.
In the large intestine, the mass passes up the ascending colon, across
the transverse colon, and down the descending colon, losing, by
absorption, foodstuffs not absorbed in the stomach and small intestine.
While water and salt are absorbed both in the stomach and in the small
intestine, the evident purpose in leaving the larger part of the
water to be absorbed in the large intestine is that it may assist the
intestinal contents in passing along. The water also stimulates the
peristaltic movement.
As the food is absorbed through the walls of the alimentary canal, it
is picked up by the rootlets of the mesenteric veins[5] and by the
lymph channels,—the latter, through the abdominal cavity, are called
lacteals. Nearly all of the fats are absorbed through the lacteals. The
whitish color given to the contents of the lacteals, by the saponified
fats, gives rise to the term lacteal, meaning “whitish.”
Nearly all of the proteins and sugars pass through the mesenteric
veins and the portal veins into the liver. Here the sugars are at once
attacked by the liver cells and built up into glycogen as described on
page 81 and the proteins are passed through the liver into the arterial
blood stream. A small portion of the proteins, however, do not go to
the liver, but are passed directly into the lymphatics and thus into
the blood stream, where they are again carried to the liver.
To sum up,—the larger part of the absorption of sugars, starches,
proteins, and fats is through the small intestine, though some are
absorbed in the stomach and a very little through the large intestine;
while some water and salts are absorbed in the stomach and small
intestine, these are largely absorbed in the large intestine.
FOOTNOTES:
[3] A knowledge of the mucous lining of the stomach and intestines, and
of the tributary glands, such as the liver and pancreas, is important
to a thorough understanding of digestion, and the reader is referred to
“The Vital Organs: Their Use and Abuse” of this series. This takes up
the study of the secretion of digestive juices, the conditions favoring
normal secretions, etc.
[4] See “The Vital Organs; Their Use and Abuse” by Susanna Cocroft.
[5] For illustration see the frontispiece of “The Circulation, Lungs,
Heart,” of this series.
The Work of Various Organs Affecting Digestion
The purpose of this chapter is to show the work of other organs than
the digestive organs in converting the digested food to use in the
body, in tearing down waste, and in eliminating waste and an excess of
material above the body needs.
* * * * *
[Sidenote: Work of the Liver]
The liver is commonly called the chemical work-shop of the body. The
proteins and sugars are carried through the blood (portal veins) to
the liver directly they are absorbed from the alimentary canal. As the
food materials filter through the blood capillaries, between the liver
cells, several substances are absorbed, particularly sugar, which is
here changed into animal starch called _glycogen_. It is held in the
liver for a few hours in the form of glycogen and then redigested by
the action of an amylolitic ferment and again gradually given out
into the blood in the form of sugar; hence sugar is subject first to
the anabolic change of being built up into glycogen, and then to the
catabolic change of oxidation and breaking down.
While the conversion of the sugar is one chief office of the liver,
it also acts upon the proteins,—not as they are first passed through
the liver in the blood, but as they are returned to the liver from the
muscle tissue, partly oxidized and broken up into simpler products.
The liver cells absorb and further oxidize and combine them into
nitrogenous waste, which the kidneys throw off in urea.
The liver and the spleen also break up the pigment or coloring matter
of the red blood corpuscles. As they become worn out, they are retired
in the liver and the spleen from the circulation. The iron is retained
by the liver cells and the remainder is thrown off from the liver, in
the bile.
The liver is often called the watch dog of the body, because it
is on guard for all poisons which pass through it in the blood.
The large part of these toxic substances are absorbed through the
alimentary canal with other foodstuffs. Many of them are the result
of the fermentation of foods which are not digested as promptly as
they should be, on account of an insufficient secretion of digestive
juices, or a failure to secrete them in normal proportions, or due to
inactivity of the stomach and intestines.
It surely is a wise provision of nature to supply a guard to oxidize,
or break down these poisons and make them harmless, so that they do not
pass to all parts of the body as poisons, thus affecting the nerves and
the blood stream, and, through these, the entire system.
The necessity of correct habits of deep breathing will be readily seen,
because oxygen is required to break down the poisons as well as to
oxidize the waste of the system.
One example of the action of the liver in rendering substances
harmless, is its oxidation of alcohol. From one to three ounces of
alcohol a day are oxidized and made harmless in the liver, varying
according to the individual and to the condition, at different times,
in the same person. If the limit of one to three ounces is exceeded,
the excess is not oxidized and intoxication results. These evidences of
intoxication are in the nature of narcosis; _alcohol is now regarded as
a narcotic along with ether and chloroform_.
It was formerly held by physiologists that alcohol was a food, because
its oxidation liberates body heat and it was assumed that this
liberation of heat, was the same as that freed by the combustion of
fats, starches, and sugar uniting with oxygen. More recent knowledge,
however, has unquestionably determined that heat, resulting from
oxidation of alcohol, does not keep up body temperature; the pores of
the skin are opened and there is a greater loss of heat through the
skin. This really makes the system less able to resist cold. Large
doses of alcohol actually cause a fall in body temperature and every
force of the body is decreased in efficiency, while if alcohol were
an actual food the efficiency would be increased. We are forced to
the conclusion, therefore, that alcohol is a _pseudo-food_ as it is a
_pseudo-stimulant_.
* * * * *
[Sidenote: Work of the Muscles]
The muscles play an important part in the use of foods. Most of the
heat is generated in them, by the sugar and fats coming in contact
with the oxygen in the blood. This heat is liberated during every
moment of the twenty-four hours, asleep or awake. Of course, more is
liberated during exercise, since the movement of the muscles sets
all tissues into activity and the blood circulates more strongly,
bringing a greater supply of oxygen to them. It is always well during
active exercise to stop frequently and fully inflate the lungs. The
effort should always be made to breathe fully and deeply—otherwise
the pressure of the liberated carbon dioxid will cause a pressure
throughout the blood stream, particularly about the heart and in the
head. This pressure is relieved when the excess of carbonic acid gas
liberated has been thrown off by the lungs. Nature makes the effort to
throw off the excess of carbonic acid gas by forcing one to breathe
more rapidly while running or taking unusual exercise.
The oxidation changes are simply a combustion of sugars and fats,
liberating latent heat as they are brought into contact with the
oxygen. Exercise and a regulation of the amount of carbohydrates and
fats consumed in the foods is the natural, scientific method for the
reduction of an excess of fat.
A certain amount of protein is constantly oxidized in the muscles,
also, being broken down into carbon dioxid, water and a number of
nitrogenous mid-products. The carbonic acid gas and water are thrown
off by the lungs and the partially oxidized, nitrogenous waste is
carried to the liver, where it is further oxidized and prepared for
excretion, through the kidneys, lungs, skin and intestines.
When sugar is carried to the muscles in larger quantities than can be
utilized by them, it is often built up into animal starch and stored in
the form of glycogen, similar to its chemical change and storage in the
liver.
This storage of glycogen in the muscles and in the liver is a wise
provision of Nature. It is a reserve to be called upon whenever the
expenditure of heat and energy exceeds the amount supplied in any day’s
rations.
* * * * *
[Sidenote: Work of the Nerves]
The nerves oxidize food materials, but not to any great extent,
excepting during nervous activity. During periods of rest, food
materials are stored in the nerve cells in grandular form. They
represent concentrated nerve foods and are the result of anabolic
processes. During nervous activity they are oxidized and carried away
through the blood and the lymph. This oxidation of the food, stored in
the nerves, creates nervous energy and heat.
The energy liberated by the nerves resembles electrical energy.
Where one subjects himself continuously to an excess of nervous
activity, all reserve food material, stored in the nerve cells, is used
and the result is a trying nerve tension. Such individuals need plenty
of easily digested food.
* * * * *
[Sidenote: Work of the Lungs]
The lungs absorb oxygen and eliminate carbon dioxid. They occasionally
throw off a very little organic material.
The carbon dioxid is carried to the lungs from the tissues through the
venous stream and diffused through the capillary walls of the lungs.
The oxygen is absorbed into the capillaries through the thin air sacs
in the walls of the lungs.
* * * * *
[Sidenote: Work of the Kidneys]
The kidneys do not absorb as do the lungs, neither do they perform any
anabolic work as does the liver, nor catabolic work as the muscles,
nerves and the liver. They simply throw off waste matter.
The blood passes through them in a transverse branch from the
abdominal aorta. In its circuit urea, uric acid, urates, sulphuric
acid, sulphates and sodium phosphates pass from the blood with the
water and are thrown from the system; hence the kidneys are purifying
organs, as are the lungs. The blood returning from the kidneys through
the veins is pure, just as the blood in the pulmonary vein is pure,
while that in the arteries to the kidneys and the lungs is impure.
The above substances cannot be thrown off from the lungs. They are the
products of oxidation of proteins, partly of the living tissues and
partly those broken down direct as they are supplied in the foods, in
excess of the needs of the system.
Interference in the action of the kidneys results in a hoarding of
these substances in the blood, and may produce an intoxicated condition
known as uremic poisoning.
Water in abundance and diuretic fruits and vegetables, which increase
the activity of the kidneys, should be taken where uremia is indicated.
(Foods which cause a free flow of urine are called diuretic foods.)
[Sidenote: Work of the Skin]
The sweat glands also throw off an excess of water and salts. The
kidneys and the skin are interdependent; if the kidneys are inactive
the skin throws off a larger quantity and if the skin is inactive, or
if for any reason the pores of the skin are closed, the kidneys are
more active. This is evidenced by the sudden immersion of the body in
cold water; the pores of the skin being closed the kidneys immediately
act.
During the summer, or at any time when the skin throws off more water
than usual, the kidneys are less active and the urine, being more
concentrated, is darker.
The skin also throws off carbon dioxid and, to a slight extent, it
absorbs oxygen.
* * * * *
[Sidenote: Work of the Intestines]
The intestines, in their work of elimination, pass off all undigested
matter. They also carry off bile pigment, bile salts, mucus, amino
acids, and other decomposition of proteins,—also a little unabsorbed
fats and bacterial decomposition taking place in the intestines. Coarse
articles of food containing fibres which do not digest, such as the
bran of grains and the coarser fruits and vegetables (though much of
their substances are not food in the strictest sense) are valuable to
increase the peristaltic movements of the intestines and to act as a
carrying body to move the waste excretions along their course.
The combustion, or burning of fuel in any form, (oxidation for the
release of latent heat and energy) always leaves some parts which
are not used as heat or energy, and it is the work of the intestines
to eliminate much of this refuse. When coal is burned, gas, smoke
and cinders or clinkers, constitute the waste and if these were not
allowed to escape from a stove the fire would soon go out—the smoke and
gas would smother it and the clinkers would prevent the circulation
of oxygen and soon clog and fill the stove. The same is true in the
body—the carbonic acid gas not being allowed to pass off would soon put
out the fires of life; it would poison the body and stunt the action of
the nerves. If the nitrogenous waste (like ashes and cinders) is not
eliminated by the kidneys, one will die in convulsions in one or two
days.
The absolute necessity of a free elimination of waste will be readily
seen.—If the engine is to do its best work, the engineer sees that it
is kept perfectly clean—otherwise it becomes clogged, does inefficient
work and the clogging soon wears out some parts. The same is true in
the body,—clogging in any part overworks and wears out other parts
dependent upon the work of the one.
Summary
Let us sum up the processes which the food undergoes in its conversion
into condition to be absorbed by the body; in its absorption through
the walls of the intestines and stomach; and the metabolic processes
which it undergoes in being converted into heat and energy and again
broken down and eliminated as waste.
_The Saliva_ begins the digestion of starches and sugars in the mouth.
This digestion is continued by the saliva in the stomach.
_The Stomach_, when in normal condition, thoroughly digests the
proteins. If any proteins fail of digestion in the stomach the process
is completed in the intestines.
The _Intestines_, aside from their work of digestion and absorption,
excrete bile pigment, bile salts, animal acids, mucus and other
decomposition of proteins, with bacterial fermentation and
putrefactions; also such food materials as are not digested.
The small intestine digests and absorbs the fats and continues the
digestion of starches, sugars and fats when this digestion is not
completed in the stomach.
The large part of the food is absorbed through the small intestine,
though a small part is absorbed through the walls of the stomach and
through the large intestine.
Fats are almost entirely absorbed in the small intestine. They are
absorbed through the lacteals and are carried into the blood stream.
_The Liver._ The proteins and the starches (converted into maltose)
and sugars pass into the liver. The sugar (including the sugar in
vegetables, milk, fruits and that used for sweetening, as well as the
carbohydrates which have been changed into maltose), is converted into
glycogen in the liver, stored here for a time and again broken down
into sugar that it may be in condition to be absorbed into the blood.
The proteins pass through the liver but are not acted upon by this
organ until they again return to the liver through the blood stream,
after they have been partly oxidized in the tissues. The liver further
oxidizes them putting them into condition to be excreted by the kidneys
and intestines.
The liver also breaks up the worn out red corpuscles, putting them into
condition to be eliminated in the bile.
It oxidizes and renders harmless poisonous substances absorbed in the
food, such as fermented food products and alcohol.
The _Muscles_ oxidize the fats and sugars liberating the latent heat
and energy.
They partly oxidize proteins which are further broken up in the liver.
The _Nerves_ oxidize food materials stored in the nerve cells,
providing nervous energy.
The _Lungs_ absorb oxygen and throw off carbon dioxid, watery vapor and
some organic substances.
The _Kidneys_ and The _Skin_ purify the blood by excreting water,
carbon dioxid and nitrogenous waste.
FACTORS INFLUENCING DIGESTION
As before stated, it is not the food eaten, but that which the body
digests and assimilates, or appropriates to its needs, which counts;
many factors influence such nourishment. The principal ones are the
forceful circulation, the breathing of plenty of oxygen, and the
resultant free elimination of waste.
* * * * *
[Sidenote: The Appetite]
If one has no appetite, by far the safest method is to abstain from
food until the system calls for it, or to eat but a very little of the
lightest food at regular meal times; be careful not to mince between
meals nor to eat candy nor pickles. Be sure that the lack of appetite
is not due to mental preoccupation which does not let the brain relax
long enough for the physical needs to assert themselves. One should
relax the brain in pleasant thoughts during a meal.
If the appetite is lacking, because of physical exhaustion, it is
unwise to eat, because the digestive organs are tired, and to load
a tired stomach with food, still further weakens it and results in
indigestion. The better plan is to drink two glasses of cold water
and lie down for an hour; if there is still no desire for food, drink
freely of water, but abstain from food until hungry.
This should not lead one into forming the habit of irregular eating,
however. The stomach forms habits and the supply of food must be
regular, just as the nursing child must be fed regularly, or digestive
disturbance is sure to result.
A wise provision of Nature makes the system, in a normal condition, its
own regulator, protesting against food when it has not assimilated or
eliminated that consumed. One should learn to obey such protests and
cut down the quantity when Nature calls “enough.”
There are exceptions, however. Some phases of indigestion result in a
gnawing sensation in the stomach, which is often mistaken for a desire
for food. This is not a normal appetite. Water will usually relieve it.
Often loss of appetite is the result of a clogging of intestines
or liver, or to an excess of bile, which, not having been properly
discharged into the intestines, has entered the blood stream. An excess
of bile and poisons, indicating a torpid liver, often expresses itself
in a dull mental force, the toxins deadening the nerve cells. Nature
does not call for more food until she has eliminated the excess of
waste.
It is commonly stated that the body will call for what the system
requires. This may have been true of the aborigines, who ate their food
in its natural state, and, to a certain extent, it is true to-day, but
condiments and stimulants, to make the food “appetizing,” have unduly
stimulated the nerves and perverted the natural taste; foods containing
their natural amount of spices or extractives no longer tempt one.
Those whose nerves are highly keyed, form the habit of seasoning the
food too strongly, making it too stimulating. This undue stimulant
calls for more food at the time of eating than a normal appetite would
demand. The taste being cultivated for the stimulant, the habit of
eating too much food is formed.