THE ABDOMEN AND THE ORGANS OF DIGESTION AND EXCRETION.
=The Abdominal Cavity.=--Below the diaphragm and separated from the
lowest cavity of the trunk, the pelvis, only by an invisible plane
drawn through the brim of the true pelvis, is the abdominal cavity,
which may be said in a general way to contain the organs of digestion
and the kidneys. It is protected behind by the vertebræ and anteriorly
by the lower ribs above and below by muscular walls, which make
possible the complete bending of the body. These muscles are for the
most part large and very strong and the greater number are inserted,
in part at least, into a median tendinous line, the _linea alba_,
which passes from the ensiform cartilage of the sternum above to the
symphysis pubis below.
=Muscles.=--The _external oblique muscles_ form the outermost layer of
the abdominal wall. They rise from the external surface of the eight
lower ribs on either side and are inserted in the anterior half of the
iliac crest as well as by aponeurosis in the linea alba, where each
joins its fellow from the opposite side, the fibers running downward
and inward like the fingers in the trouser’s pocket. Along the lower
border of the aponeurosis is a broad fold, _Poupart’s ligament_.
The _internal oblique_ rises on either side from the outer half of
Poupart’s ligament and the anterior part of the crest of the ilium
and is inserted into the crest of the os pubis, the cartilages of the
lower ribs, and the linea alba. Its fibers run at right angles to those
of the external oblique. These oblique muscles serve to compress the
viscera, to flex the body, and also assist in expiration.
The deepest of the abdominal muscles is the _transversalis_, which
rises from the outer third of Poupart’s ligament and the adjoining part
of the crest of the ilium, from the six lower costal cartilages, and
by a broad aponeurosis, the _lumbar fascia_, from the lumbar vertebræ.
It is inserted into the pubic crest and by aponeurosis into the linea
alba. There is one of these muscles on either side.
[Illustration: FIG. 51.--Muscles of the trunk from before (left side,
superficial; and right side, deep): 1, Pectoralis major; 2, deltoid;
3, portion of latissimus dorsi; 4, serratus magnus; 5, subclavius; 6,
the pectoralis, sternocostal portion; 7, serratus magnus; 12, rectus
abdominis; 13, internal oblique; 14, external oblique; 15, abdominal
aponeurosis and tendinous intersections of rectus abdominis; 16, over
symphysis pubis; 17, linea semilunaris; 18, gluteus medius; 19, tensor
vaginæ femoris; 20, rectus femoris; 21, sartorius; 22, femoral part of
iliopsoas; 23, pectineus; 24, adductor longus; 25, gracilis. (Dorland’s
Dictionary.)]
The _rectus abdominis_ is also really two muscles and extends from the
symphysis pubis to the cartilages of the fifth, sixth, and seventh
ribs. At first it passes back of the oblique and transversalis
muscles, but about a fourth of the way up it passes in front of the
transversalis and between two layers of the internal oblique, which
thereafter forms its sheath. Its chief duty is to flex the chest on the
pelvis, though it also compresses the abdominal viscera.
One other muscle, a small one, is found in front, the _pyramidalis_,
which rises from the pubic crest and is inserted into the linea alba
midway to the umbilicus.
At the back the open space over the kidneys, between the lower ribs
and the os innominatum, is closed in on either side by the _quadratus
lumborum_, which extends from the three or four lower lumbar vertebræ
and the adjacent iliac crest to the last rib and the upper four
lumbar vertebræ. It flexes the trunk laterally or forward according
as one muscle or both are used, and may aid in either expiration or
inspiration.
The _nerves_ of the abdominal muscles are chiefly the internal
intercostals.
=The Peritoneum.=--Lining the abdominal cavity is a serous membrane,
the peritoneum, which is reflected back over the viscera within in such
a way as to cover each one wholly or in part. Folds of peritoneum,
the _omenta_, connect the stomach with the other viscera, the most
important being the _great omentum_, which has one layer descending
from the anterior and another from the posterior wall of the stomach.
The _mesenteries_ are double layers of peritoneum which hold the
intestines to the vertebræ and posterior wall. Between their folds run
the blood-vessels.
[Illustration: FIG. 52.--Diagram showing the nine regions of the
abdominal cavity: 1, Right hypochondriac; 2, epigastric; 3, left
hypochondriac; 4, right lumbar; 5, umbilical; 6, left lumbar; 7, right
iliac; 8, hypogastric; 9, left iliac. (Ashton.)]
=Abdominal Regions.=--For convenience of description the abdominal
cavity has been divided into nine regions by means of two transverse
parallel lines, the one through the ninth costal cartilages and the
other just over the iliac crests, and two perpendicular parallel
lines through the cartilage of the eighth rib and the middle of
Poupart’s ligament on either side. These nine regions have been named
as follows: The right and left hypochondriac regions up under the ribs
with the epigastrium between, the right and left lumbar regions next
below with the umbilical between, and the right and left inguinal with
the hypogastric between. Others divide it into quadrants by one line
drawn across and another down through the umbilicus. The contents of
the abdomen in full are the stomach, intestines, liver, gall-bladder,
spleen, pancreas, kidneys, suprarenal capsules, and the great vessels,
that is, the organs of digestion and excretion. When distended the
bladder extends up into the abdominal cavity, as does the uterus also
when enlarged.
=Salivary Digestion.=--Although most of the digestive organs are
situated in the abdomen, the food enters the body through the mouth,
where its prehension is a voluntary act. Here digestion also begins and
from the first the process is a double one, mechanical and chemical,
mechanical digestion consisting largely of muscular movements by which
the food is ground up and carried through the digestive tract. Thorough
mastication or grinding of the food by the teeth is necessary, while
the tongue assists by moving the food about and by mixing it thoroughly
with the _saliva_, a viscid fluid composed of water and salts and
having a slightly alkaline reaction. The saliva is secreted by the
parotid, sublingual, and submaxillary glands, and serves to soften and
dissolve the food and by virtue of its unorganized ferment, _ptyalin_,
to convert starch into sugar. Upon proteins and fats it has practically
no digestive action. Moderate warmth and an alkaline medium favor its
action, while extremes of heat or cold or an acid medium hinder it.
There is little absorption in the mouth, though starch, nicotine, and
alcohol may be absorbed in small quantities.
=The Pharynx.=--When the food is ready for deglutition or
swallowing, it is thrust back into the pharynx, a somewhat conical,
musculo-membranous sac, situated, base upward, behind the nose and
mouth and behind, but somewhat above, the larynx. The pharynx is about
four and a half inches long and ends on a level with the cricoid
cartilage in the esophagus or gullet. It is attached to the vertebræ
at the back and opens in front into the mouth. The posterior nares,
the Eustachian tubes, and the larynx also open into it, the last being
protected by the _epiglottis_, which closes during deglutition to
prevent food from entering the air passages, just as the soft palate
is drawn back to prevent regurgitation of food into the nose. There
are three coats to the pharynx: 1. a mucous coat continuous with that
of the mouth and ciliated down to the floor of the nares; 2. a fibrous
coat, and 3. a muscular coat containing among others the constrictor
muscles which serve to carry the food down to the esophagus. Its
arteries are branches of the external carotid and its nerves come from
the spinal accessory and the sympathetic. Occasionally a _foreign
body_ gets lodged in the pharynx just out of reach of the finger and
threatens strangulation. _Retropharyngeal abscess_ on the posterior
wall occurs rarely.
[Illustration: FIG. 53.--Position of the thoracic and abdominal
organs, front view. (Morrow.)]
=The Esophagus.=--From the pharynx the food passes to the cardiac
orifice of the stomach, opposite the tenth dorsal vertebra, through
the esophagus, a muscular tube about nine inches long, which collapses
when empty, its lumen then appearing as a transverse slit. It, too,
has three coats: 1. an inner mucous coat; 2. an areolar coat, and 3.
a muscular coat, the muscles being arranged in two sets, an outer
longitudinal layer and an inner circular layer. By a series of rhythmic
contractions, especially of the circular fibers, the food is pushed
along, though sometimes with liquid food there is no peristaltic action
of the esophagus, the pharyngeal muscles alone sending it to the
stomach. At the lower end of the esophagus an especially strong band
of circular muscle fibers form a sort of sphincter, which prevents the
regurgitation of food. The whole act of swallowing is a reflex, not a
voluntary act and is due to irritation set up by the stimulus of the
foreign body, the food. _Stricture of the esophagus_ is common and
may be of three kinds: 1. spasmodic, occurring in nervous women; 2.
fibrous, due to scar tissue, or 3. malignant, due to cancer.
=The Stomach.=--The stomach is a pear-shaped dilatation of the
alimentary canal, lying under the liver and diaphragm in the epigastrium
and left hypochondrium and connecting the esophagus with the small
intestine. It lies largely behind the ribs, but the greater curvature
is only two fingers’ breadth above the umbilicus and can be manipulated
through the skin. The _cardiac end_, into which the esophagus enters,
is the larger and points upward to the left. The lesser and lower end,
known as the _pylorus_, is at the right and its opening into the small
intestine is guarded by the _pyloric sphincter_. The lesser curvature
is concave and on the upper surface; the greater, convex and on the
under surface. The great omentum is attached to the latter.
In _size_ the stomach varies more or less, that of a man generally
being larger than that of a woman, but it is usually about ten inches
long and four or five inches across. It has a capacity of about five
pints and serves as a storehouse for food.
The stomach has four _coats_: 1. a serous coat derived from the
peritoneum; 2. a muscular coat of three layers with longitudinal fibers
continuous with those of the esophagus, circular fibers, and oblique
fibers; 3. an areolar coat, and 4. a mucous coat, which, when the
stomach is empty, is thrown into longitudinal folds or _rugæ_, and
whose surface is covered with glands, the _gastric glands_, for the
secretion of the digestive fluids.
The _arteries_ come from the celiac axis and the _nerves_ from the
pneumogastric and the solar plexus.
_Ulcer_ and _cancer_ of the stomach are both rather common. In
the former there is apt to be _hyper_-acidity and in the latter
_hypo_-acidity, but the rule does not always hold. In cases of ulcer
there may be hemorrhage and even perforation. Such hemorrhage can be
distinguished from hemorrhage from the lungs by its slightly acid odor
and by the frothy character of hemorrhage from the lungs. There is much
irritation at the pylorus and where there is irritation there is liable
to be cancer.
=Gastric Digestion.=--In the stomach the food is churned and thoroughly
mixed with the gastric juices, and it is also subjected to a propulsive
movement that drives it on to the intestine. When it comes to the
stomach it is semi-solid and when it has become fluid or semi-fluid, in
which state it is known as _chyme_, it is ready to pass on. Before it
can do so, however, it must overcome the strong pyloric sphincter, and
this it does by the muscles about the sphincter pushing it constantly
on until the sphincter gives way. Probably most of the propulsive
movements take place within a few inches of the pylorus.
The _gastric juice_ is secreted by glands in the wall of the stomach
and poured out through little tubules which project from the surface.
It is a thin, almost colorless fluid with a sour taste and odor due
to the presence of free _hydrochloric acid_, an important element in
digestion. Probably when the stomach is empty and for some twenty
minutes after the appearance of food there is no hydrochloric acid
present and, the food being alkaline, salivary digestion continues.
Then, called forth by the presence of the food, the hydrochloric acid
appears and salivary digestion ceases in the acid medium. Little
digestion of starches or fats takes place, the chief action being
on proteins, which are converted into soluble peptones. For besides
hydrochloric acid the gastric juice contains two ferments: 1. _pepsin_,
which is particularly active in aiding the digestion of proteins, and
2. _rennin_, which especially affects milk. Neither hydrochloric acid
nor pepsin seems capable of digesting food alone, but each is essential
to the other. They are secreted by different types of cells, secretion
depending upon the nerve supply and upon the presence of food. Gastric
digestion is favored by minute subdivision of the food and by the
right proportion of hydrochloric acid, which should be 0.2 per cent.
Body temperature is also advantageous. Except that proteins are put in
solution and partly digested, little digestion goes on in the stomach,
and though the rugæ afford a large absorbing surface, little absorption
takes place, although more takes place than in the mouth and in time
most foods, except fats, can be absorbed. The time of digestion varies
with different foods and in different people, but probably three to
five hours are necessary. The food leaves the stomach as _chyme_, a
fluid of about the consistency of pea soup.
_Vomiting_ is more or less the reverse of swallowing and is generally
preceded by a feeling of _nausea_, which starts up _retching_, a more
or less involuntary effort of the stomach to throw off its contents.
To relieve the retching a long breath is taken, followed by a deep
expiration that opens the cardiac end of the stomach and allows the
abdominal muscles to force the food out. After much vomiting and
prolonged retching the pyloric end of the stomach may be affected and
bile will then appear in the vomitus. _Artificial vomiting_ may be
produced by irritation of the gastric nerve center in the brain or by
irritation of the stomach itself.
[Illustration: FIG. 54.--The intestinal canal: 1, Stomach; 2, duodenum;
3, jejunum; 4, ileum; 5, cecum; 6, vermiform appendix; 7, ascending
colon; 8, transverse colon; 9, descending colon; 10, sigmoid flexure;
11, rectum. (Leidy.)]
=Intestinal Canal.=--From the stomach the food passes into the
intestinal canal, a convoluted tube which extends from the stomach to
the anus and in which, more particularly in the upper portion, the
greater part of the digestion and absorption of food takes place. This
tube, which is about six times the height of its possessor, consists of
two parts, the small and the large intestines, the first four-fifths,
or about 25 feet, being small intestine. It occupies the central and
lower parts of the abdominal cavity and a small portion of the pelvic
cavity, and is attached to the spine by the mesentery, which, however,
allows great freedom of motion, so that there is little fixation to the
loops of the small intestines.
=The Small Intestine.=--The small intestine opens out of the stomach
and has three divisions: 1. the _duodenum_, which is only about ten to
twelve inches long; 2. the _jejunum_, so called because it is generally
empty after death, which is about two-fifths of the remainder and lies
chiefly in the umbilical region and the left iliac fossa, and 3. the
_ileum_ or _curved intestine_, the remaining three-fifths, which gets
its name from its numerous coils and which lies in the middle and the
right side of the abdomen. There is no direct division between the
jejunum and the ileum, but the first part of the former and the last
part of the latter are quite different in character. At its entrance
into the large intestine the ileum is guarded by the _ileo-cecal valve_.
[Illustration: FIG. 55.--1, Central lacteal; 2, capillary network; 3,
columnar cells.]
The same _coats_ continue in the small intestine as were found in the
stomach, but they are here much thinner and the inner coat is shaggy,
like velvet, with innumerable minute processes called _villi_, which
greatly increase the absorbing surface. In fact, the great length of
the intestine as well as the presence of the villi is aimed to provide
a large surface to absorb the food as it passes, an even greater
increase of surface being provided by the fact that the intestinal wall
is thrown into folds, the _valvulæ conniventes_. Each villus is covered
with a layer of columnar epithelial cells and has within connective
tissue, in which are found a fine capillary network and open lymph
spaces from which leads a single lacteal vessel.
Closely connected with the lymphatic vessels are the _solitary glands_,
small round bodies the size of a small pin’s head. _Peyer’s glands_
or _patches_ are patches of solitary glands opposite the mesenteric
attachment and are largest and most numerous in the ileum. In typhoid
fever they are involved and may become the seat of ulcers. There are
also the _glands of Lieberkühn_ which secrete the succus entericus.
The _arteries_ of the small intestine, which include the superior
mesenteric, are from the celiac axis and the _nerves_ are from the
superior mesenteric plexus of the sympathetic. The _veins_ empty
chiefly into the portal system.
The _movements_ of the intestine, like those of the esophagus, are
peristaltic, but the action is complicated by the fact that the tube is
not straight but in coils.
=Intestinal Digestion.=--The food, which enters the duodenum as chyme,
there comes in contact with the bile and the pancreatic juice, which
together but unmixed enter the duodenum from their respective ducts
by a common orifice. As in the stomach, the digestive juices are
called forth by the presence of food. The _bile_ is secreted in the
liver, from which it flows away through the hepatic duct, which joins
the cystic duct from the gall-bladder to form the common bile duct.
Through this it flows into the intestine during digestion, but between
whiles it passes up into the gall-bladder, where it is stored for
future use and whence it is expelled when needed. When pure it is a
thick, viscid liquid, varying from a bright red to a greenish-yellow in
color according to the pigments present, and of an alkaline reaction.
It consists chiefly of the bile pigments, _biliverdin_, which gives
the green color, and _bilirubin_, which gives the red color, and of
bile salts in solution, _cholesterin_, which probably forms the basis
of many gall stones, is also present. Bile is a disinfectant to the
bowel and a lubricant for the feces. How much digestive action it has
is a question, but it affords the necessary alkaline medium for the
pancreatic juice to act in.
The _pancreatic juice_ is secreted by the pancreas, from which it
enters the intestine through the pancreatic duct, and is probably the
most important fluid in the digestive process. It is clear, practically
colorless, slightly viscid or gelatinous, and quite strongly alkaline
in reaction, owing to the presence of sodium carbonate. It contains
three ferments, _amylopsin_ for the digestion of starch, _trypsin_ for
the digestion of proteins, and _steapsin_ for the digestion of fats.
By it, as by the saliva, starch is turned into sugar or maltose, in
which form it is absorbed, while proteins are converted into peptones,
as they are in the stomach. Since, however, fats are acted on nowhere
else, the chief function of the pancreatic juice may be considered
to be the digestion of fats. Having broken through their albuminous
envelope, it divides them into glycerine and fatty acids and then
emulsifies them with the assistance of the bile.
The food also comes in contact with the _succus entericus_, a juice
secreted by the glands of Lieberkühn in the small intestine, whose
chief action is the conversion of sugar into glucose.
=Absorption.=--As the food is absorbed from the intestine it is
liquid and entirely digested and is known as _chyle_. Practically all
absorption takes place from the small intestine, though there is a
little in the large intestine. It takes place in two ways: 1. through
the portal vessels and 2. through the _lacteals_, which are the
lymphatic vessels of the small intestine. Fats are absorbed practically
entirely by the lacteals. They enter the cells covering the villi,
travel thence to the lymph spaces, and so into the lacteal or main
lymph channel, whence they are carried to the thoracic duct and the
general circulation. From the blood they are absorbed as fat and stored
up as adipose or fatty tissue, which is found throughout the body in
connective tissue about the organs. Organic salts and water are for
the most part absorbed by the portal system, which they reach through
the capillaries of the villi and through which they go to the liver.
Starches, in the form of sugar, pass between the cells of the villi
into the lymph spaces, from which they are taken up by the capillaries.
On the way to the liver maltose becomes dextrose. Proteins, in the form
of peptones, pass through the layer of epithelial cells to the lymph
spaces and then to the capillaries, an active part being taken by the
cells. By the time they reach the liver the peptones have been changed
back into proteins. In fact, peptones seem to have some poisonous
effect upon the blood if they get into it as such.
=The Large Intestine.=--The large intestine differs from the small
in size and in fixity of position, lying curved in horseshoe shape
above and around the small intestine. It is five or six feet long,
large in caliber, and is thrown into crosswise folds. It has the same
four _coats_ as the small intestine, but the mucous coat is pale and
smooth, without villi. Its _glands_ are the crypts of Lieberkühn and
the solitary glands. The _arteries_ are branches of the superior and
inferior mesenteric and the _nerves_ come from sympathetic plexuses.
The blind sac lying in the right iliac fossa, with which the large
intestine begins, is called the _cecum_, and into this the ileum
opens, the ileo-cecal valve preventing regurgitation. Just below the
ileo-cecal opening is the _vermiform appendix_, a narrow, worm-like
tube with a blind end, varying in length from one to nine inches, but
generally about four and one-half inches long, which, so far as is
known, is functionless as well as dangerous. People have been born
without an appendix and it has in rare instances grown again after
operation. Its base is located in the living by _McBurney’s point_, a
point two inches from the anterior superior spine of the ilium on a
line drawn from the spine to the umbilicus.
From the cecum the intestine ascends in what is known as the _ascending
colon_ along the abdominal wall at the right to the under surface of
the liver, where it turns in the _hepatic flexure_ abruptly across
the body to the left, passing below the liver, stomach, and spleen
in the _transverse colon_. In the _splenic flexure_ it turns down
the left abdominal wall, the _descending colon_ passing to the crest
of the ilium, where there is another curve, the _sigmoid flexure_,
leading to the _rectum_, which passes for six or eight inches down
along the vertebræ, a little to the left, to the _anus_, the external
opening. This opening is guarded by two _sphincter muscles_, about an
inch apart, the internal and external sphincters. The coils of the
small intestine lie below the transverse colon, covered mostly by the
omentum. The splenic flexure is behind the stomach and below the spleen
and is slightly higher than the hepatic flexure. The sigmoid flexure
can be felt in the left inguinal region in thin people.
The fact that the _rectum_ is somewhat to the left is of importance in
childbirth because if the rectum is packed, it may turn the child’s
head in the wrong direction.
No digestion goes on in the large intestine, the function being to
dry by absorbing water. The _movements_ are practically the same
as those of the small intestine except that they are much less
active. Fermentation makes the contents acid. By the time food
reaches the rectum it has been thoroughly digested and has given up
its nourishment. It is then expelled as waste matter or _feces_.
_Defecation_ combines the involuntary movements of peristalsis and
relaxation of the sphincters with the voluntary aid of the abdominal
muscles. The _ano-spinal reflex_, by which movements of the bowel are
regulated, is in the lumbar enlargement of the cord.
The _hemorrhoidal veins_ in the lower rectum are connected with both
the systemic and the portal veins and have no valves so that, as they
are subjected to much strain, they often become varicose and dilated.
This condition is called _hemorrhoids_ or _piles_. _Obstruction_ of
the intestine may be caused by the growth of a constricting band, by
_intussusception_ or telescoping of the intestine on itself, especially
at the ileo-cecal valve, or by _volvulus_ or twisting. _Foreign bodies_
are sometimes found in the appendix but they are not usually the cause
of appendicitis. _Cancer of the intestine_ is common and its mass
is apt to cause obstruction with all its attendant symptoms. It may
necessitate an artificial anus. _Hernia_ or _rupture_ may also occur
and the hernia may become strangulated.
=Food and Metabolism.=--Anything serves as food that replaces or
hinders the loss to which the component parts of the body are liable.
Proteins, carbohydrates, fats, some mineral matters, as salt and
perhaps iron, and water are needed. The energy once expended by plants
or animals in the formation of the materials which serve as food is set
free in the body by the breaking up of these complex substances into
their original elements, which are then recombined into the complex
materials needed for the body’s life and growth. This process of
building up complex materials from simple ones is known as _anabolism_
and that of breaking them down as _katabolism_, while the two combined
form the complete cycle of _metabolism_. Those foods have the best
value that give up their energy most readily. For their combustion,
heat, oxygen, and water are needed. Hunger indicates that the supply of
material for katabolism has been used up and that more is needed, just
as thirst indicates the need of the system for more fluids.
The proteins or nitrogenous foods include all animal foods except fats,
fish, crustaceans, eggs, milk and its products, certain vegetables,
especially the lentils, that is, peas and beans, and gelatine. The fats
include various fats and oils commonly eaten. The carbohydrates are
the starchy foods, as cereals, sugars, fruits, and most vegetables,
in fact, practically all except the lentils. Various beverages and
condiments have no great nutritive value but serve to stimulate the
appetite and to excite the secretion of the digestive juices. Coffee,
tea, and alcohol are stimulants.
The different classes of foods have different functions in the
nourishment of the body. The proteins are primarily tissue-builders
and also help somewhat in force production. The fats are essentially
heat-producers, though they too help in force production. The
carbohydrates are chiefly important as force-producers, though they
also produce heat and to a certain extent save protein oxidation. Fat
is formed by all three but only in small amount by proteins. So no one
food can form the whole diet but there must be variety. Carbohydrates
and fats are not sufficient for life, some protein is necessary.
Carbohydrates are more digestible than fats but have less potential
energy. Gelatine saves waste of nitrogen, though it does not increase
the supply. Water and salts are not nutritive but they aid the body
processes, the water helping to dilute and dissolve substances for
digestion.
The end-product of the consumption of protein is _urea_, which is
eliminated by the kidneys. Just where it is formed is unknown, but many
think in the liver. A trifling amount of urea is also eliminated in
the sweat and in the breath as well as in the feces. Proteins increase
nitrogenous metabolism and also the metabolism of other foods, but the
amount of nitrogen eliminated is just equal to that taken in. Probably
some comes from the tissues themselves and not from the food. The
oxidation of carbohydrates and fats is measured by the amount of carbon
excreted. At first as much is given off as is taken in, but after a
while the carbohydrate is stored up as glycogen in the liver and the
fats are stored as fat.
The amount of food needed varies with the person’s size and occupation,
less being needed for a child than for an adult and more for a
hard-working man than for one who is doing less work. In general, 100
to 130 grams of protein, 40 to 80 grams of fat, 450 to 550 grams of
carbohydrates, 30 grams of salts, and 28,000 grams of water is a fair
amount.
Foods are cooked to make them more digestible and to develop their
flavor, so that they will taste better. Cooking also kills germs and
parasites that might be harmful. Meats should be cooked rapidly on
the outside to coagulate the surface albumen and keep in the juices.
The heat, besides coagulating the albumen, turns the tough parts to
gelatine. In cereals the tough envelope of cellulose is broken up
and in vegetables the tough fibrous parts are softened and made more
digestible.
=The Liver.=--Below the diaphragm on the right and extending across
above the stomach, resting in a way upon the transverse colon and the
small intestine, is the liver, the largest gland in the body. It is
dark reddish-brown in color and is larger in proportion in the child
than in the adult. The upper surface is convex and lies in contact
with the diaphragm, while the lower surface is concave to fit over the
organs beneath. With a full breath it comes downward and forward, with
the edge against the abdominal wall, and can be easily felt. Numerous
strong ligaments, including the suspensory ligament from the diaphragm,
hold it in place, and it is more firmly fixed than any other of the
abdominal organs, probably on account of its large size. It is divided
by fissures into five _lobes_, of which the most important are the
right and left, the right one being the largest and containing the
gall-bladder in one of its fissures.
[Illustration: FIG. 56.--The liver, seen from below. 1, Inferior vena
cava; 2, gall-bladder. (Morrow.)]
The liver tissue contains a large number of _cells_ collected into
_lobules_, in the center of each of which is a blood-vessel, the
_intralobular vein_, from which a network of capillaries extends to
the edge of the lobule, there being a capillary on either side of each
row of cells. Between the cells also are the _intercellular biliary
passages_, roots of the bile ducts which exist in the connective tissue
between the lobules and which join to form two main ducts, one from
the right and the other from the left lobe. By the union of these two
ducts the _hepatic duct_ is formed, which, after a course of one or two
inches, joins the cystic duct from the gall-bladder to form the _ductus
communis_ or _common bile duct_.
The liver has a double _blood supply_, the _hepatic artery_ from the
celiac axis bringing nourishment to the connective tissue and the walls
of the blood-vessels, while the capillaries between the cells come from
the _portal vein_, which, being formed by the junction of the superior
and inferior mesenteric, the splenic and the gastric veins, contains
the proteins and carbohydrates absorbed during digestion. After its
passage through the liver this blood from the portal vein is collected
once more into the hepatic veins, which convey it to the inferior vena
cava. During its passage, however, various changes take place, for the
liver plays an important part in the metabolic processes of the body.
The liver has two principal _functions_, the secreting of bile and
the storing up of glycogen. The secretion of _bile_, which is a very
important aid to digestion, is probably a reflex act, the presence of
peptones in the portal blood after meals acting as a stimulant to the
liver cells. For food at once increases the secretion of bile, which
is poured from the cells into the small bile ducts and finally passes
into the hepatic duct and so to the gall-bladder, where it is stored
until needed. Although the flow from the liver is constant, the amount
secreted reaches its maximum when the food gets down into the small
intestine, that is, four or five hours after eating, there being a
lull before that. Apart from the process of secretion, the manufacture
of the bile pigments, _bilirubin_ and _biliverdin_, which are made from
the hemoglobin of the blood, seems to require some special action on
the part of the liver cells.
The _glycogen_, which is manufactured and stored in the liver cells,
is a clear hyaline substance, akin to starch and capable of being
converted into sugar by the starch ferment. Probably there is some
such ferment in the blood which converts the glycogen into sugar as
soon as it passes from the liver into the blood, though what it is,
is not known. Neither is it known just how glycogen is formed, but
it is manufactured chiefly after a mixed meal in which carbohydrates
predominate, proteins having little and fats no effect upon its
formation. It is undoubtedly formed from the sugar in the portal blood
and the process requires some work on the part of the liver cell
itself. Probably there is always some sugar in the circulating blood
which, as it is used up, must be made good. If there it not enough in
the diet, the liver supplies the deficiency from its store of glycogen.
Glycogen is found also in the muscles, in the placenta as food for the
fetus, in leucocytes, and to a slight extent in cartilage. In fact, it
is the form in which carbohydrate material is supplied to the tissues
as needed. Normally, much of the sugar is used up by the blood and
its cells in metabolism, giving rise to heat and energy. In muscles
glycogen is probably digested as lactic acid, as before action muscle
is neutral or slightly alkaline and after action acid.
When the liver is deranged and allows the glycogen to pass out into the
blood too freely, or when the glycogen is not held as such but turned
to sugar and passed out in large quantities, _sugar in the urine_ or
_diabetes mellitus_ results.
Besides its secreting function the liver has an _eliminative function_
and plays an important part in purifying the blood, removing from
it many poisonous and narcotic substances. It is thought by some,
though it has not been proved, that _urea_, the end-product of protein
metabolism, which is brought by the blood to the kidneys and there
excreted, is formed in the liver. At any rate, urea is formed not only
from the nitrogenous food eaten but from the metabolism of protein
substances in the tissues, being purely a waste product, from which
the nutritious substances have been absorbed. The amount thrown off is
an accurate gauge of the amount of protein metabolism going on. The
process of its manufacture is doubtless very complex.
_Ptosis_ or _dropping_ of the liver sometimes occurs and is due to the
stretching of the ligaments. _Rupture_ is common, generally as the
result of a fall from a height, on account of its size and friability.
The liver is also subject to many diseases. _Cirrhosis_ occurs in
people who drink a good deal and in its later stages is accompanied by
_ascites_, an accumulation of fluid in the abdominal cavity. When there
is a general accumulation of fluid throughout the body it is known as
_anasarca_. _Syphilis_ causes enlargement of the liver. _Abscesses_
occur, perhaps oftener in the tropics than farther north, and may break
into the lungs, stomach, or intestine.
=The Gall-bladder.=--The gall-bladder, which is simply a reservoir
for the bile, is a pear-shaped organ three inches long and one inch
broad. It lies in a fossa on the under side of the liver, with the
large end or fundus touching the abdominal wall just below the ninth
costal cartilage. Here it can be felt as a small mass in empyema of
the gall-bladder. Normally it holds a little over one ounce, but with
occlusion it may become stretched. Its duct is the _cystic duct_, which
joins the hepatic duct in the common bile duct, but bile only passes
up into the gall-bladder when the opening into the duodenum is closed,
that is, between meals.
If one of the bile ducts is stopped up by a stone or cancer or for
any other cause, the bile backs up in the liver, the pigments are
absorbed into the circulation, and _jaundice_ results. In this
condition operation is dangerous, as the time of coagulation of the
blood, normally five minutes or less, is much delayed. _Gall stones_,
formed largely of bile pigments and cholesterin, sometimes collect in
the gall-bladder, where they cause irritation and may give rise to
_empyema_ of the gall-bladder. The stones vary in size from a pea to a
hen’s egg and when small may be very numerous.
[Illustration: FIG. 57.--The pancreas, spleen, gall-bladder, etc.,
showing their relations. (After Sobotta.)]
=The Pancreas.=--Another accessory organ of digestion is the pancreas,
the _abdominal salivary gland_, as it is sometimes called on account
of its close resemblance to the parotid gland. This is a grayish-white
racemose gland, six and a half inches long by one and a half inches
wide and one inch thick, lying behind the stomach on a level with the
first and second lumbar vertebræ and shaped like a pistol with its
handle toward the right. In an emaciated person it can be felt. The
_pancreatic duct_ runs the whole length of the gland from left to right
and conveys the _pancreatic juice_ from various little glands in the
substance of the organ to the duodenum, into which it empties along
with the common bile duct by a common orifice. The _arteries_ are from
the celiac axis and superior mesenteric, the _veins_ belong to the
portal system, and the _nerves_ come from the solar plexus.
Surgically the pancreas is of no special importance, though _acute
pancreatitis_ does occasionally occur and is a very serious condition
and one hard to diagnose.
=The Spleen.=--The largest and most important of the ductless glands
is the spleen, an oblong, flattened organ lying deep in the left
hypochondriac region between the stomach and diaphragm above the
descending colon, and corresponding to the ninth, tenth, and eleventh
ribs. It is soft, brittle, and very vascular. Its _artery_ is a branch
of the celiac axis and the _vein_ belongs to the portal system. Its
_nerves_ are the pneumogastric and branches from the solar plexus. The
_function_ is not well understood but probably it is connected with or
related to the vascular system in some way. Perhaps it manufactures
blood corpuscles.
The spleen varies more in size than any other organ. Normally it cannot
be felt, but in typhoid it usually can. It is generally atrophied in
old age and hypertrophied in almost all acute infectious diseases,
especially in typhoid fever and malaria. In leukemia it is often
greatly enlarged. Sometimes in violent falls it is _ruptured_ and there
is considerable hemorrhage.
=The Suprarenal Capsules.=--The other ductless glands, the suprarenal
capsules, yellowish triangular bodies, are situated just above and
in front of the kidneys. Their function is important but not well
understood. Death, accompanied by great muscular weakness, follows
the removal of both, and when they are diseased, similar weakness is
observed and the skin becomes bronzed. Injection of the extract of
the suprarenals stimulates the muscular system. So probably they
secrete into the blood minute quantities of a substance or substances
beneficial to the body, especially to the muscular system.
[Illustration: FIG. 58.--Diagram of the relation of kidney to viscera,
spine, and surface points. (American Text-Book of Surgery.)]
=The Kidneys.=--The two kidneys lie on either side of the vertebræ at
the back of the abdominal cavity and behind the peritoneum, between the
last dorsal and the third lumbar vertebræ, their inner edge being about
one inch from the spinous processes. They are bean-shaped, four inches
long, two inches wide, and one inch thick, and are embedded in a mass
of fat and loose areolar tissue. They can be felt only when misplaced
or when enlarged, as by tuberculosis or malignant disease.
The whole kidney is enveloped in a fibrous _capsule_ which normally
may be peeled off but which in some diseases becomes adherent. On the
internal border is a _fissure_ or _hilum_, through which pass the
blood-vessels and the ureter. Upon entering, the ureter dilates into
a sac, the _pelvis of the kidney_, into which project the _Malpighian
pyramids_ of the _medullary substance_, a substance made up of the
straight uriniferous tubules and blood-vessels. Outside the medullary
substance and just under the capsule is the _cortex_, containing the
_Malpighian bodies_, blood-vessels, and the _convoluted tubules_ or
_loops of Henle_. Each Malpighian body contains within a capsule a
plexus of capillaries, the _glomerulus_, with an afferent arteriole and
an efferent vein. The _renal artery_ is a branch of the aorta and the
_nerves_ are from the solar plexus.
[Illustration: FIG. 59.--A longitudinal section of the kidney. (Leroy.)
_a_, Renal artery; _c_, cortex; _m_, medulla; _u_, ureter.]
[Illustration: FIG. 60.--A Malpighian body or corpuscle. (Leidy.)
_a_, Afferent artery; _e_, efferent vessel; _c_, capillaries; _k_,
commencement of uriniferous tubule; _h_, uriniferous tubule.]
_The Urine._--As the blood passes through the glomeruli, the urine is
filtered off as it were, probably by a process of transudation rather
than simple filtration. The cells lining the tubules also play an
important part in its formation, not by secreting new substances but
by taking up those brought by the blood and discharging them into the
convoluted tubules, from which the urine passes through the straight
tubules of the medulla to the pelvis, to be carried thence by the
ureter. The process of the formation of the urine, therefore, is not
purely a process of secretion but requires some action on the part of
the kidney, though no new substances are secreted in the kidney.
The passage of the urine down through the ureters is assisted by a kind
of peristaltic action in the walls of the ureters and it is expelled
from the body by the act of _micturition_, which is mostly voluntary,
though a certain amount of nervous mechanism controls it. The seat of
this nervous mechanism is in the lumbar enlargement of the spinal cord.
In some nervous conditions, especially where there is injury to the
spinal cord, there is _involuntary micturition_.
The urine is a watery solution containing many waste products,
especially urea. It is generally amber in color, varying in shade with
circumstances, with an aromatic, characteristic odor when fresh. It
is acid in reaction and has a specific gravity of about 1020, though
this too varies with circumstances. Besides water, which is its chief
constituent, it contains urea, uric acid, organic acids, urates,
inorganic salts, including sodium chloride and phosphates of calcium
and magnesium, a certain amount of ammonia, and certain pigments. Its
acidity is due to acid sodium phosphate in solution but varies with the
food, and in disease the urine may become alkaline when passed. After
standing a few hours in a warm place it decomposes and becomes alkaline.
The quantity, which is normally three pints or fifteen hundred cubic
centimeters in twenty-four hours, varies with the amount of fluid
drunk, the amount of perspiration, etc. The amount secreted depends
chiefly, however, upon the flow of the blood through the kidneys; the
greater the flow of blood, the larger the amount of urine formed; and
the blood flow is determined by blood pressure and by vasomotor action.
Secretion also seems to be increased by the presence of urea, which
apparently serves as a stimulant to the kidney cells.
The excretion of waste materials takes place by three main channels,
the lungs, skin, and kidneys, and the materials are of four kinds,
_urea_, _carbon dioxide_, _salts_, and _water_. The lungs carry off
carbon dioxide and water chiefly, the skin these and inorganic salts,
while the kidneys eliminate practically all the urea as well as
inorganic salts and water. When the kidneys are not working the skin
carries off much urea. In fact, a close relationship exists between the
kidneys and the skin in the matter of excretion. Thus, with increased
perspiration in warm weather comes decreased urine, while in cold
weather the blood is sent in and the urine increased in amount.
To incite action of the kidneys drugs known as _diuretics_ may be used.
These act in two ways, by stimulating the kidney cells directly and by
acting on the general circulation or nervous system. Any emotional or
nervous excitement increases the flow of urine.
There are certain abnormal constituents of urine, of which the two most
important are _albumen_ and _sugar_. The former is found only when
there is some disturbance of the kidneys, ureters, or bladder, and its
presence usually denotes some change in the cells lining the urinary
tract. It may occur in congestion of the kidney as well as in disease.
Sugar is found only in _diabetes_, the amount varying with the severity
of the disease. In _jaundice_ certain bile pigments are present in the
urine, giving it a dark brown color and to the foam a greenish-yellow
color. Even normal urine has some sediment upon standing, consisting
of cells from the urinary tract and mucus. In very acid urine after
standing a heavy sediment, whitish or pinkish, _i.e._, brick dust, in
color, is thrown down. It does not necessarily denote disease, but
shows the urine is acid and concentrated. In _alkaline urine_ there is
a sediment due to phosphates.
_Rupture_ of the kidney occurs but is not so serious as rupture of
the liver or spleen because the kidney is situated outside of the
peritoneum. It necessitates the removal of the kidney, however, and
when for any reason one kidney is removed the other increases in size
and does double work to compensate for the loss. Removal of both
kidneys means death. Sometimes the kidney becomes loose and moves
about, a condition known as _floating kidney_. _Perinephritic abscess_
is abscess in the loose fatty tissue about the kidney.
[Illustration: FIG. 61.--The urinary organs viewed from behind.]
=The Ureters=, one for each kidney, are tubes the size of a goose
quill and about fourteen inches long, extending from the hilum of the
kidney to the base of the bladder. They have three _coats_, an internal
mucous, a muscular, and an external fibrous coat, this last being
continuous with the cortex of the kidney and the fibrous tissue of the
bladder. In the female the ureters may be felt through the wall of the
vagina as they come into the bladder. In tubercular disease of one
kidney the ureter becomes inflamed and enlarged and through the vagina
feels almost like a lead pencil, a sure diagnostic sign.
=The Bladder and Urethra.=--In their course to the bladder the ureters
pass from the abdominal into the pelvic cavity, but before describing
the pelvis itself it will be well to complete the account of the
urinary organs by considering the bladder and urethra. The _bladder_ is
the reservoir for the urine and has muscular walls lined with mucous
membrane. A peritoneal coat covers the upper surface and is reflected
to the walls of the abdomen and pelvis. It is situated back of the os
pubis, the front bone of the pelvis, with its base or fundus directed
downward and backward. Normally it is in the pelvis, but when much
distended it mounds up into the abdominal cavity, where it can be
felt in front as a tumor. It rests on the rectum in the male and on
the cervix in the female and is held in place by numerous ligaments.
When empty it may be Y-shaped, but it becomes oval when distended. Its
capacity is about one pint.
The lower abdominal wall and the anterior wall of the bladder may be
wanting congenitally. In paralysis of the sphincter at the neck of the
bladder distention results. _Stones_ may be found in the bladder.
From the neck of the bladder the urine passes out of the body through
the _urethra_. This in the male passes down through the penis and is
about ten inches long. Except when urine is passing it is a transverse
slit with the upper and under surfaces in contact, while at the end of
the penis the slit of the meatus urinarius is vertical. When the penis
is flaccid, the urethra describes a sharp curve before its entrance
into the bladder, but it becomes approximately straight when the penis
is raised at right angles to the body--an important point to remember
in catheterization.
In the female the urethra is straight and much shorter, being only
about one and a half inches long. The _meatus urinarius_ is in the
anterior vaginal wall about one inch behind the clitoris.
Sometimes the urethra is _ruptured_ in a fall. _Stricture_ of the
urethra occurs sometimes after gonorrhoea, owing to the formation of
scar tissue following ulcer.