Absorption in gastrointestinal tract and motility of gastrointestinal tract

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Absorption in gastrointestinal tract and motility
of gastrointestinal tract
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Determine of notion absorption

• Absorption is a complex of processes, which are
  provide transport of substances from digestive
  tract into internal surroundings of organism
  (blood, lymph, intercellular substances)

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Main types of transport of nutritive substances
in internal surroundings of organism

• 1. Passive diffusion and osmosis. This transport
  do not need presents of energy. In this case
  substances transport through the mucus shell by
  help of concentrative gradient. This way of
  transport have water, water dissolved vitamins
  (C, B6, B2).
• 2. Active pinocytosis and active transport by
  help of protein and energy. Active transport need
  energy of ATP. This way characteristic of amino
  acids, monosaccharide, vitamin B12, ions of
  calcium, enzymes. Pinocytosis by help of
  pinocytic bulb, where secreted enzymes for
  proteins hydrolysis. Products of hydrolysis
  adsorbed by cell.

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• The total quantity of fluid that must be absorbed
  each day is equal to the ingested fluid (about
  1,5 liters) plus that secreted in the various
  gastrointestinal secretions (about seven liters).
  This comes to a total of approximately 8 to 9
  liters. All but 1,5 liters of this is absorbed in
  the small intestine, leaving only 1,5 liters to
  pass through the ileocecal valve into the colon
  each day.

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Absorption in the mouth cavity and stomach

• In the mouth cavity absorbed water, water soluble
  medicines (validol, nitroglycerin). In our oral
  cavity, under the tongue present a big quantity
  of vessels. That is why all water soluble
  substances absorbed. They go to the bloodstream,
  and have immediately action on our receptors.
  They do not go through the liver, and do not
  desintoxicated, that is why may be toxic effect
  of some substances. In stomach absorbed alcohol
  and small quantity of other substances.

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stomach

• The stomach is a poor absorptive area of the
  gastrointestinal tract because it lacks the
  typical villi type of absorptive membrane and
  also because the junctions between the epithelial
  cells are tight junctions. Only a few highly
  lipid-soluble substances, such as alcohol and
  some drugs like aspirin, can be absorbed in small
  quantities.

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Absorption in intestines

• Small intestines has a big length 3-8 meters
  large quantity of substances absorbed in a middle
  part of small intestines common surface of
  intestines 200 m2. The structure bases of
  absorption in small intestines are villi. In
  large intestines absorbed water and completed
  absorption of a small quantity of hydrolytic
  substances of carbohydrates, proteins and lipids.
  By help of this way may absorbed components of
  nutritive elements (glucose, vitamins, water etc).

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• The Absorptive Surface of the Intestinal Mucosa
  The Villi. The absorptive surface of the
  intestinal mucosa, showing many folds called
  valvulae connivances (or folds of Kerckring),
  which increase the surface area of the absorptive
  mucosa about threefold. These folds extend
  circularly most of the way around the intestine
  and are especially well developed in the duodenum
  and jejunum, where they often protrude as much as
  8 mm into the lumen.

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• The intestinal epithelial cells are characterized
  by a brush border, consisting of about 600
  microvilli 1 µm in length and 0,1 µm in diameter
  protruding from each cell. This increases the
  surface area exposed to the intestinal materials
  another 20-fold. Thus, the combination of the
  folds of Kerckring, the villi, and the micro
  villi increases the absorptive area of the mucosa
  about 600-fold, making a tremendous total area of
  about 250 square meters for the entire small
  intestine about the surface area of a tennis
  court.

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ABSORPTION IN ORAL CAVITY, ESOPHAGUS AND STOMACH

• In the mouth cavity absorbed water, water soluble
  medicines (for example, validol, nitroglycerin,
  adelphan, furosemid, corinfar and others). In our
  oral cavity, under the tongue present a big
  quantity of vessels. That is why all water
  soluble substances absorbed in this place. They
  go to the bloodstream, and have immediately
  action on our receptors. They do not go through
  the liver, and do not desintoxicated, that is why
  may be toxic effect of some substances, for
  example products of food, drugs.
• In esophagus do not absorbed nutritive substances
  as a rule.
• In stomach absorbed alcohol, water and small
  quantity of other substances.

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ABSORPTION IN THE SMALL INTESTINE

• Normally, absorption from the small intestine
  each day consists of several hundred grams of
  carbohydrates, 100 or more grams of fat, 50 to
  100 grams of amino acids, 50 to 100 grams of
  ions, and 7 to 8 liters of water. However, the
  absorptive capacity of the small intestine is far
  greater than this as much as several kilograms of
  carbohydrates per day, 500 to 1000 grams of fat
  per day, 500 to 700 grams of amino acids per day,
  and 20 or more liters of water per day. In
  addition, the large intestine can absorb still
  more water and ions, though almost no nutrients.

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ABSORPTION IN THE LARGE INTESTINE

• Approximately 1500 ml of chyme pass through the
  ileocecal valve into the large intestine each
  day. Most of the water and electrolytes in this
  are absorbed in the colon, usually leaving less
  than 100 ml of fluid to be excreted in the feces.
  Also, essentially all the ions are also absorbed,
  leaving only about 1 mEq each of sodium and
  chloride ions to be lost in the feces.
• Most of the absorption in the large intestine
  occurs in the proximal half of the colon, giving
  this portion the name absorbing colon, whereas
  the distal colon functions principally for
  storage and is therefore called the storage colon.

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Methods of absorptions investigation

• 1. Angiostoma.
• 2. X-ray investigation.
• 3. Biochemical method of investigation.

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Regulation of absorption

• Absorption regulated by nervous system, for
  example by cortex by vegetative nervous system
  endocrine glands, for example adrenocorticotropin,
  aldosteron, glucocorticoids, insulin, thyroxin,
  local factors of food, for example pepper,
  mustard.

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Peculiarities of absorption of organic and
inorganic substances

• Water and mineral salts
• Products of proteins hydrolysis
• Products of carbohydrates hydrolysis
• Products of fats hydrolysis

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Water

• Main quantity of water absorbed in small
  intestines, small quantity in stomach and large
  intestines. Water absorbed by help of osmotic
  gradient. Water absorbed together with amino
  acids, carbohydrates, salts vitamins absorbed
  with water. Main role of water transport through
  the membrane have sodium and chloride.

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Mineral salts

• Sodium transport in two stages passive (sodium
  go through the apical part of enterocytes
  membrane from chyme) and active (sodium go by
  help of Na,K-ATPase on base-lateral part of
  enterocytes membrane in blood). Chloride and
  HCO3- go together with sodium. Ca2, Mg2
  absorbed actively.

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Products of proteins hydrolysis

• Proteins absorbed in free amino acids,
  dipeptides, three peptides appearance. Their
  absorption into cell through the apical part of
  membrane connects with secondary active sodium
  transport. Most actively absorbed arginine,
  methionine, leucine L-form of amino acids. Then
  they transport through the base lateral part of
  membrane in blood by help of concentrative
  gradient.

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Products of carbohydrates hydrolysis

• Carbohydrates absorbed in monosaccharide
  appearance. Most actively absorbed glucose and
  galactose. Their absorption into cell through the
  apical part of membrane connects with secondary
  active sodium transport. Then glucose transport
  through the base-lateral part of membrane in
  blood by help of concentrative gradient. Mannose
  and fructose transport by help of diffusion.

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That the transport of most monosaccharide through
the intestinal membrane is an active process is
demonstrated by several important experimental
observations

• 1. Transport of most of them, especially glucose
  and galactose, can be blocked by metabolic
  inhibitors, such as iodoacetic acid, cyanides,
  and phlorhizin.
• 2. The transport is selective, specifically
  transporting certain monosaccharide without
  transporting others. The order of preference for
  transporting different monosaccharide and their
  relative rates of transport in comparison with
  glucose are

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• 3. There is a maximum rate of transport for each
  type of monosaccharide. The most rapidly
  transported monosaccharide is galactose, with
  glucose running a close second. Fructose, which
  is also one of the three important
  monosaccharide's for nutrition, is absorbed less
  than half as rapidly as either galactose or
  glucose also, its mechanism of absorption is
  different, as will be explained below.
• 4. There is competition between certain sugars
  for the respective carrier system. For instance,
  if large amounts of galactose are being
  transported, the amount of glucose that can be
  transported simultaneously is considerably
  reduced.

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Products of fats hydrolysis

• In small intestines developed micelles
  connection of fat acids, cholesterol,
  monoglycerides, phospholipids with bile acids
  salts. Bile salts acids act transport role of
  micelles to apical part of membrane. Then by help
  of diffusion fat acids, cholesterol,
  monoglycerides, phospholipids penetrate into
  enterocyte, where synthesis new triglycerides.
  Inside enterocyte develop chilomicrones. It
  consists from triglycerides, phospholipids,
  cholesterol and other lipids. They penetrate in
  lymph vessels by help of pinocytosis.

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