digestion - DOC by mrsurgeon

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      The sensation of hunger and the associated increase in appetite are
determined by periodic contractions of empty stomach and the transmission of the
excitation caused by these contractions along afferent nerve fibres to the brain. The
sensation of hunger arises as a result of a change in the functions of the
diencephalon. Stimulation of its corresponding part may be produced not only by
afferent impulses originating on the periphery, but also by the effect of the altered
composition of the blood.
      Certain diseases are atended with insatiable hunger-bulimia-which is
accompanied by headache and general debility. The result of the insatiable hunger
is a sharp increase in food conSumption-polyphagia. It is observed in
neuroses,certain lesions in the subcortical region, as a result of increased or
perverted metabolism (exophthalmic goitre, diabetes mellitus) and in cases of
accelerated evacuation of the stomach contents.
      A lack of appetite-anorexia-is in infectious diseases, gastroenteritides,
emaciating diseases and avitaminoses. In anorexia the secretion of digestive juices
is perceptibly diminished.
      Perverted appetite-parorexia-is characterised by the patient"s tendency to
consume nonalimentary substances, for example, vinegar, chalk.
      Thirst is a sensation associated with the need of the body for water or with
its excessive excretion. It is particulary pronounced in cases of excessive
consumption of sodium chloride or considerable dehydration of the organism by
profuse sweating, vomiting, diarrhea, excessive urination or bleeding. Excessive
thirst as a pathologic phenomenon-polydipsia-is observed in diabetes insipidus and
diabetus mellitus and is accompanied by polyuria (excessive passage of urine)
which is characteristic of these diseases. The sensation of thirst is explained in two
ways. Some hold the main factor to be ageneral dehydration of the organism with a
resultant stimulation of sensory nerve endings reflexly projected to the region of
the pharynx. From this point of view the sensation of dryness in the mouth and
pharynx in thirst is a secondary phenomenon. According to others,the sensation of
thirst arises only in connection with the primary appearence of dryness in the oral
and pharyngeal mucosa. Thirst therefore arises from the action of such factors as
produce dryness in the mouth, for example, inhalation of warm air. prolonged
speaking, depression of the salivary secretion by strong emotins (fear).The origin
of thirst is apparently based on both factors-the reflex from the oral and pharyngeal
mucosa, and diminished water in the tissues, while the sensation of thirst is always
formed in the central nervous system.
      Disturbances in digestion may begin in the oral cavity with disorders of
mastication. Normally mastication of food reflexly causes secretion of gastric and
pancreatic juices, for which reason disturbances in mastication and in the
processing of food in the oral cavity affect the function of the lower parts of the
digestive tract.
      Disturbances in mastication arise as a result of affections of the teeth. The
absence of a large number of teeth or inflammation of the dental pulp hinders
thegrinding of food. Gaining entrance into ythe stomash poorly ground food causes
disorders of gastric digestion, which not infrequently give rise to inflammination of
the gast*~'c mucosa (gastritis). Disorders of mastication may be the result of
central paralyses and inflammatory processes in the mucosa of the mouth
(stomatitides) and the gums (gingivitides). Stomatitides and gingivitides are most
commonly the result of the action of infections and traumatic factors
      or of the secretion by the oral mucosa of mercury and lead salts which have
gained entrance into the organism. Lastly, mastication is impaired by inflammatory
processes in the muscles participating in mastication.
                         DISTURBANCES IN DEFECATION
      Defecation is essentially a reflex act. The following defecation centres are
known: the higer centre - diencephalon arid ascending frontal gyrus, and subsidary
spinal centre - lumbar segments of the spinal cord (relaxion of sphincters) and
sacral segments of the" spinal cord (contraction of sphincters).
      Disorders of defecation arise as a result of affection of the centres which
control this reflex. Defecation may be hindered as a result of contraction of the
sphincters, levator ani muscles and a number of voluntary muscles of the perineum
due to excitation of corresponding centres. Rectal incontinence is observed in
paralysis of the sphincters resulting from dysfunction of he centres, for example, in
advanced age, tumours, epilepsy, fear.
      • The mechanism of defecation disorders sometimes consist in a weakening
of the sensory nerves in the rectum, the nerves perceiving the stimulation by fecal
mater, with the result that he defecation reflex is inhibited. In other causes the
sensitivity of the mucosa, on he contrary, increases, increasing the urge to defecate,
as in inflammation of he mucosa in the region of the sphincters.
      Lastly, defecation may be hindered as a result of diminished intestinal
peristalsis or flabbiness of he abdominal muscles, as in women after childbirth or
in old people.
                     FUNCTIONS OF THE INTESTINES.
      Disturbances in absorption are an important form of hastrointestinal
dysfunction. They are observed in connection with disorders of the secretory and
motor functions of the gastrointestinal tract, especially resulting from deficiency in
bile secretion and in the secretory function of the pancreas. Absorption is
diminished in diarrheas when the intestinal contents are quickly expelled to the
      Absorption is also disturbed as a result of changes in intestinal blood
circulation. Diminished blood circulation due to general circulatory disorders,
congestion in the portal vein or massive loss of blood decreases the processes of
absorption. Disorders of the lymph circulation in the intestines (for example, in
inflammation of lymph nodes) are responsible for diminished fat absorption.
Lastly, inflammatory changes in the intestinal mucosa also cause disorders of
absorption. Absorption takes place mainly in the small intestine. If the absorptive
capacity of the small intestine is greatly decreased, the absorption in the lower
parts of the intestines increases.
      The absorptive capacity of the intestines may be disturbed experimentally by
injury to the intestinal mucosa with sodium fluoride. The animal dies soon after
administration of sodium fluoride.
      In certain acute inflammations pf the intestinal mucosa fats and coarser
complexes of proteic substances begin to be absorbed and on gaining entrance into
the organism play the role of antigens, sensitising the organism. In chronic atrophic
inflammation absorption is diminished.
      Disorders of gastrointestinal digestion cause disturbances not only in the
absorptive capacity. They also affect the excretory function of the intestinal wall.
In some measure the secretory and excretory' functions are independent of each
other. This is evident from the fact that an increase in one may be accompanied by
a depression or lac1' of change in the other.
      The main causes of the excretory dysfunction of the small intestine are
organic and functional changes in the intestinal wall.
      Abnormal excretion of water through the intestinal wall causes dilution of
the intestinal contents and hastens development of diarrhea. It is difficult to
distinguish this phenomenon from the increased excretion of digestive juices into
the intestinal lumen, which is observed in certain secretory dysfunction of the
digestive glands.
      Diminished peristalsis is not a rare phenomenon in disorders of the intestinal
function. It is due to the absence or inadequate action of the mechanical and
chemical factors which maintain normal peristalsis. Peristalsis diminishes in
connection with neurogenic disorders, for example, decreased excitability of the
receptor apparatus of the intestines, and inflammatory processes (especially of a
chronic character) which, depending on their course, may give rise to either
diarrhea or constipation. In inflammatory processes the diminution in peristalsis
may also be due to dysfunction of the nervous system.
      Diminshed intestinal peristalsis, of whatever character, causes constipation.
      The small and large intestines participate in the origin of constipation to
various extents. An important part in the pathogenesis of constipation is played by
the large intestine where the fecal masses are consolidated and formed.
      ' Constipation may be atonic and spastic, depending on the mechanism of its
      Atonic constipation isdue to relaxation of the muscular layer of the intestinal
wall and diminution in peristalsis in the upper parts of the large intestine.
      Spastic constipation is the result of prolonged spasm of the circular muscles
of the intestinal wall, which obstructs the movement of the intestinal contents. At
the same time the density of the feces is increased and the feces are sometimes
eliminated in lumps.
      Constipation arises as a result of general dysfunction of he nervous system,
the vegetative innervation of the intestines in particular. A cerain part in also
played by decreased stimulation of the receptors of the mucosa, especially when
there is no cellulose in the intestinal contents or there is too much fat or too little
organic acids and monosaccharides which stimulate peristalsis. As a result of
constipation the intestine absorbs more water, the fecal masses become
consolidated, the appetite diminishes, general weakness develops and meteo-rism
      Meteorism is the result of diminished intestinal peristalsis, increased
processes of fermentation and putrefaction, and accumulation of gases (methane,
hydrogen sulfide, carbon dioxide, ammonia, etc) in the intestines. In severe
meteorism the venous pressure rises, the arterial pressure at first rises and then
drops, respiration is disturbed, the pulse grows weak, the secretory function of the
digestive glands diminishes, and painfull sensations in the region of the intestines
appear. All these phenomena are due to mechanical compression of the vessels, the
high position of the diaphragma and stimulation of the mechano- and chemorecep-
tors in the intestinal wall.
      The foregoing disturbances in intestinal function are particulary marked in
ileus (intestinal obstruction). Two main forms of ileus are distinguished:
mechanical ileus caused by mechanical closure of the intestinal lumen (obstruction
by externic pressure, volvulus, intussusception) and dynamic ileus caused by
paralysis or, less frequently, spasm of the intestinal muscles. The part of the
intestine   situated   above   the   obstruction   becomes    considerably    dilated.
Antiperistaltic movement appear and lead to vomiting, sometimes stercoaraceous.
      Volvulus, strangulation or intussusception are characterised, in addition to
the aforementioned phenomena, by circulatory disturbances as a result of
compression of the mesen-teric vessels with subsequent mortification of the
corresponding portion of the intestine.
      Intestinal obstruction leads to development of deep general changes in the
organism particulary manifested in general circulatory disturbances and
characteristic alteration of the blood composition. The organism becomes
dehydrated, and hemoconcentration, hypochloremia, azotemia and alkalosis
develop. These changes are in large measure due to increased secretion of digestive
juices and their discontinued reabsorbtion, intractable vomiting and corresponding
disturbances in renal function.
      In the pathogenesis of the disorders observed in ileus an important part is
played by intoxication due to absorption of the poisons formed and retained in the
intestines; of some importance also are the reflex influences produced by the
affected intestine on the blood circulation and other vitally important functions.
      The small intestine contains few microbes, whereas the number of microbes
in the large intestine is very great. Bacteria participating in processes of
fermentation predominate in the upper part of the large intestine. Lactic and acetic
acids, carbon dioxide and methane are formed in the process of fermentation. The
intestinal flora helps to split cellulose which makes its assimilation possible.
Microorganisms also synthesise certain vitamins, for example, vitamin K, eneurin,
biotin, folic acid. The lower part of the large intestine contains. Es-cherichia coli,
Aerobacter aerogenes and some other bacteria. The large intestine contains
anaerobes and 6which participate in the processes of putrefaction of proteic
      The contents of the different parts of the intestines possess poisonous
properties variously manifested in accordance with the character of the processes
of fermentation and putrefaction operating in them. The most poisonous, for
example, are the contents of the large intestine. Intravenous administration of
extracts from the contents of the large intestine poisons the animal 2-3 times as fast
as does that of extracts from the contents of the lower part of the small intestine.
Poisoning with products of putrefaction is accompanied by a drop in blood
pressure. No poisoning takes plase in the organism because of the barrier
properties of the intestinal wall and the liver.
      Changes in the processes of fermentation and putrefaction are observed in
cases of disturbed digestion. These processes operate more intensely and do so in
such parts of the intestines where they are not normally observed, for example, the
jejunum and even the duodenum.
      Absorbed and gaining entrance into the liver the products of putrefaction are
usually rendered harmless because of the formation of paired compounds. But in
pathology they may accumulate to such an extent as to make it impossible for the
liver to detoxicate them. Of these substances special mention must be made of
certain aromatic compounds formed from amino acids by a splitting off of
ammonia and further transformations (phenol, cresol, skatole and indole).
      Decarboxylation of amino acids leads to formation of a number of amines -
putrescine, cadaverine, histamine, tyramine, etc.
      On being absorbed the foregoing substances may produce phenomena of
intestinal autointoxication. Intestinal autointoxication manifests itself with greater
intensity not only in cases where more products of putrefaction are fnnned and
absorbed (as in inflammation of the mucosa), but also where intestinal peristalsis is
weakened, the barrier role of the liver is decreased and the excretory capacity of
the kidneys is diminished.
      Phenomena of intoxication may arise in inflammatory processes in the
intestines, especially in intestinal obstruction. In such cases intoxication leads to
impaired metabolism and not infrequently to dysfunction of the nervous system.
      The patients general condition changes for the worse, headaches and
increased irritability appear, lack of appetite and insomnia are observed.
      The phenomena ascribed to autointoxication are today believed to arise as a
result of reflexes originating in the intestines abnormally distended by gases.

                          Motor Dysfunction of the Inestines.
      The disorders of the motor function of the intestines vary in origin and are
discovered in different parts of the intestines. They consist in excessive or
diminished peristalsis.
      Excessive peristalsis arises as a result of various inflammatory processes in
he intestinal mucosa, as well as of mehanical or chemical irritation produced by
coarse and barely digestible parts of food, accumulated decompositon products,
acids and toxic substances. Not infrequently motor disorders may also be the result
of dysfunction of the nervous system. For example, increased peristalsis is
observed in connection with strong emotions (fear) which cause stimulation of the
vegetative nervous system (Fig. 124) and in cases of hypersensitivity of the
receptor apparatus ,as in association with inflammatory of the mucosa. The waves
of contraction very easily arise in the most excitable and mobile parts of the
intestines and spread in the direction of the moe sluggish parts, for example, from
the pylorus and duodenum in the direction of the large intestine.
      Excessive intestinal peristalsis results in diarrhea-increased frequency of the
stool. In diarrhea caused by changes in the motor properties of the small inestine
the feces contain barely digested particles of food. In addition to excressive
peristalsis inceased secretion of the mucosa an diminished absorption of water also
play some part in the increased frequency of the stool.
      Diarrhea is usually caused by excessive peristalsis of the lare intesine,
especially when associated with similar phenomena in the small intestine. The
reason for excessive peristalsis of the large intestine, in addition to neurogenic
factors, is poorly digested contents o f the small intestine, which iritate the large
      Products of fermentation and putrefaction (indole, scatole, phenol, ammonia,
methane, hydrogen sulfide), when abundantly formed, infectious agents and toxins,
as well as adrenal insufficiency and the resultant diminished tone of the
sympathetic nervous system, may be causes of diarrhea. Diarrhea is often
accompanied by decreased absorption and considerable discharge of water into the
lumen of the intestine (espeially in certain inflammatory processes), as a result of
which the intestinal contents become still more diluee. Increased se cre-tion of
mucus may simultaneously occur in the intestine; sometimes the secretion comes
out to the exterior in layers whose shape is determined by the intestinal lumen, as
in cases of membranous colitis ( colitis membranacea). Frequen diarrheas lead not
only to digestive disorders, but also to general nutriional disturbances.

      kaline reaction and cantains enterokinase, the enzime that activaters
trypsinogen. Processes of digestion opewrate all along the small intestine. In the
upper parts of the duodenum and of the remainder of the small intestine digestion
is the most intensive, and all the main nutritive substances-proems, fats and
carbogydrates-udergo digestion there. Absorption takes plase mainly in the small
inestine. The absorbed sugar and amino acids pass into the lymphatic vessels.
                        Secretory Dysfunction of the Intestines.
      Secretory disorders are caused by disturbances in the activity of the central
nervous system and resultant dysfunction of the innervation apparatus of the
intestines. Stimulation of the vagus nerve evokes an increase in the amount and
enzymatic activity of the inesinal juice.
      The secretory disorders of reflex origin include those which arise as a result
of disorders of gastric secretion. The composition of the gastric juice, as well as the
extent to which the food has been digested in the stomach as prepared for intestinal
digestion affect the secretory function of the intestine. For example, digestive
disorders in the duodenum are associaed with hyperacidity of gastric juice and
retarded evacuation of the food from the stomach. Accelerated passage of the
chyme into the duodenum in achylia causes overloading and increased peristalsis
of the small intestine.
      The secretory function of the intestines is altered also during inflammatory
processes for example, duodenitis, enteritis, colitis and duodenal pepic ulcer.
      Inflammatory processes are also characterised by secretion of mucus all
along the inestine. The inflamatory phenomena in the intestinal mucosa ust not be
considered apart from inestinal dysfunction caused by disorders of the nervous
system, since they are closely interrelated. Disorders of the secretory and motor
functions of the intes
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