Water absorption.minerals,vitamines

1. Absorption of
water,vitamins,minerals and
electrolytes.
Movement of GI Tract.
Rahana Moideen Koya.V.K
Asst.Professor of Zoology,Farook College.

2. Absorption of Vitamins-
Vitamins are organic molecules necessary for normal metabolism
in animals, but either are not synthesized in the body or are
synthesized in inadequate quantities and must be obtained from
the diet.
Essentially all vitamin absorption occurs in the small intestine.
Absorption of vitamins in the intestine is critical in avoiding
deficiency states, and impairment of intestinal vitamin absorption
can results from a number of factors, including intestinal disease,
genetic disorders in transport molecules, excessive alcohol
consumption and interactions with drugs.

3. Absorption of Water-soluble Vitamins
Most water soluble vitamins are available for intestinal absorption from
two sources: 1) the diet, and 2) synthesis by microbes in the large
intestine or, in the case of ruminants, the rumen.
These dual-origin vitamins include biotin, folic acid, pantothenic acid,
riboflavin and thiamin.
Ascorbic acid can be synthesized by many animals, but not by primates or
guinea pigs, in which it is a true vitamin and must be obtained from
dietary sources.
Niacin is also a bit different - it can be synthesized within the body from
tryptophan but is also absorbed in the intestine from dietary sources.

4. Water soluble vitamins of dietary origin are absorbed predominantly
in the small intestine, whereas those synthesized by microbes in the
large intestine are absorbed there.
For most of these vitamins, specific carrier-mediated transport
systems have been identified that allow uptake from the intestinal
lumen into the enterocyte and for export from the basolateral
surface of the enterocyte. Some of these transporters are sodium-
dependent, while others are not.
Most of the vit are absorbed in upper part of small intestine and vit
B12 cobalamin(prod of RBC and DNA,NS functioning) absorbed in
ileum.Absorption of water soluble vit. Is faster.

5. Absorption of Fat-soluble Vitamins
The fat soluble vitamins A, D, E and K are absorbed from
the intestinal lumen using the same mechanisms used
for absorption of other lipids.
In short, they are incorporated into mixed micelles with
other lipids and bile acids in the lumen of the small
intestine and enter the enterocyte largely by diffusion.
Within the enterocyte, they are incorporated into
chylomicrons and exported via exocytosis into lymph.

6. Overview
GI Water and Electrolyte Absorption
The GI system secretes nearly 8L of fluid into the GI tract which is
combined with the nearly 2L of ingested fluid;
however, only a 0.1-0.2L of fluid is excreted in the feces.
Therefore, the GI system must absorb nearly 9L of fluid,
composed of water and electrolytes, each day.
Water and electrolyte absorption primarily occurs in the small and
large intestines.
Dysregulation of this absorption can either lead to diarrhea or
constipation.

7. Large intestine—Water, Electrolytes, Organic substances like glucose ,
alcohol, Drugs like anesthetic agents, sedatives and steroids.
Bacterial flora of large intestine synthesizes Folic acid , Vit B12,Vit.K.
By this function large intestine contributes in erythropoietic activity and
blood clotting mechanism.
Vitamin B12 occurs in foods that come from animals.
Normally, vitamin B12 is readily absorbed in the last part of the small
intestine (ileum), which leads to the large intestine.
.

8. However, to be absorbed, the vitamin must combine with intrinsic
factor, a protein produced in the stomach. Two steps are required for
the body to absorb vitamin B12 from food.
First, hydrochloric acid in the stomach separates vitamin B12 from
the protein to which vitamin B12 is attached in food. After
this, vitamin B12 combines with a protein made by the stomach
called intrinsic factor and is absorbed by the body.
Once bound with IF, vitamin B-12 is resistant to further digestion.
A carrier glycoprotein (Castle's gastric intrinsic factor) binds
to vitamin B12 and delivers it to receptor sites on the brush border of
the ileal mucosal cell, to which it attaches in the presence of calcium
and alkaline pH, thence to be absorbed.

9. In small intestine Na absorbed actively
. It is responsible for absorption of glucose ,a acids and other
substances by means of sodium co-transport.
Water moves in and out of the intestinal lumen until the osmotic
pressure of intestinal contents becomes equal to that of plasma.
In ileum ,Chloride ion is actively absorbed in exchange for
bicarbonate
Ca is is actively absorbed mostly in upper part of small intestine.

10. Luminal membrane Na+ resorption occurs via a number of
symporters and antiporters throughout the small and large
intestines.
In all cases, the luminal membrane resorption is powered
by a NaK ATPase on the basolateral enterocyte membrane.
This NaK ATPase actively transports Na+ past the
basolateral membrane, thus reducing intracellular
Na+ concentration, which subsequently creates an
electrochemical gradient for inward Na+ transport on the
luminal membrane.

11. Duodenum and Jejunum:
Luminal resorption occurs on a variety of Na-Nutrient
symporters, which include monosaccharides, as well as
amino acids, dipeptides, and tripeptides.
These mechanisms of sodium resorption are constitutively
active and are not physiologically regulated.

12. Large Intestine
Na+ absorption in the large intestine is very similar to that occurring
in the Principal Cells during late distal tubule and collecting duct
transport.
diffusion of Na+ through luminal membrane ion channels is
powered by a basolateral NaK ATPase.
As in the late distal tubule and collecting duct aldosterone
significantly enhances sodium resorption in the large intestine by
increasing expression of the basolateral NaK ATPase and luminal
Na+ ion channels.

13. Water absorption---Water is always absorbed in the alimentary
tract through passive osmosis via a mostly paracellular route
between enterocyte tight junctions.
Consequently, water absorption is primarily actuated (motivated)
by active absorption of osmotic electrolytes, especially sodium.
In cases where a high concentration of unabsorbable solutes
remain in the GI lumen, water cannot be resorbed and thus
causes an osmotic diarrhea.

14. Chloride resorption---
Absorption of Cl- largely occurs through passive
diffusion via a paracellualr route.
Substantial resorption of Na+ may create a lumen
negative charge, thus creating a strong
electrochemical gradient for passive resorption of Cl-.
The majority of chloride is resorbed in the small
intestine, especially the duodenum and jejunum.

15. a

16. Bicarbonate resorption-
A large amount of bicarbonate is secreted during pancreatic secretion and
maintenance of proper acid-base balance requires that some must be
resorbed.
A CO2 molecule is converted to H+ and HCO3
- by carbonic anhydrase in
the enterocytes. The HCO3
- is transported past the basolateral membrane
while the H+ is transported into the intestinal lumen on an Na+-
H+ Antiporter.
The H+ probably then combines with luminal bicarbonate, and is then
converted to CO2 which then diffuses into the blood and is breathed off
by the respiratory system. The net effect is resorption of a bicarbonate
ion.

17. a

27. Mouth—tongue
Nasopharynx—Elevation of soft palate along with extension called uvula
Larynx--Epiglottis

29. Esophagial stage-peristaltic waves.-Peristalsis—a wave of contraction
followed by wave of relaxation of muscle fibers of GI tract which travel
aboral direction-away from mouth.
When bolus reaches the esophagus .the peristaltic waves are initiated
,which propel the bolus into the stomach .Two types of peristaltic
contractions produced by esophagus.
1– primary-when bolus reaches the upper part of esophagus ,the
peristalsis starts. perstatalic contractions pass down through the rest of
the esophagus propelling bolus towards stomach.. The pressure developed
during this contraction propel the bolus.

31. Secondary peristaltic contractions—if primary contraction
unable to propel bolus this occur ,this contractions arise in
esophagus locally due to distention of upper esophagus by the
bolus .
Role of lower esophageal sphincter—The distal 2 to 5 cm of
esophagus acts like a sphincter-lower esophagial sph.When
bolus enter this part of esophagus ,this sphincter relaxes and
contents enter stomach.

32. Deglutition Reflex-Swallowing at the Beginning it voluntary act ,later involuntary and is
carried out by a reflex action called deglutition reflex,.It occurs during the pharyngeal and
esophageal stages.
Stimulus—When the bolus enters oropharyngeal region ,the receptors present in this
region stimulated,
Afferent fibers—afferent impulses from oropharyngeal receptors pass via the
glossopharyngeal nerve fibers to the deglutition centre.
Centre—Deglutition centre is at the floor of vthe fourth ventricle in medulla oblongata
.
Efferent fibres—The impulses from centre travel through glossopharyngeal(Pharyngeal
stage) and vagus neves(esophagial stage) to soft palate,pharynx,and esophagus.
Response—The reflex causesupward movt. Of soft palate,to close nasopharynxand
upward movt.of larynx to close respiratory passage so that bolus enters the esophagus
.Now peristalsis occurs in esophagus pushing bolus into stomach.

33. Movements of stomach-
Hunger contractions—the activities of smooth muscles of stomach
stomach increased during gastric digestion –stomach filled with food and
when stomach empty.
The movts of empty stomach are related to the sensation of hunger.so
this movts-hunger contractions.hunger contractions are peristaltic waves
superimposed over the contractions of gastric muscle as a whole.the
digestive peristaltic contraction occur in body and pyloric part of
stomach.persaltic contractions of empty stomach involve the entire
stomach.
contractions disappear when food consumed

34. Type1-when the tone of the stomach is low it appears lasts for 20
sec..interval bet con is 3-4 sec.
Type11 hunger contraction—appear when the tonus of stomach is
stronger,the tonus increases in stomach if food intake is postponed,even
after the appearance of type1 con it lasts for 20 sec.
Type111—or incomplete tetanus appear when the hunger becomes severe
and tonus increases to a great extent. these contractions are rare we take
food before this. Lasts for 1-5 minutes
Normal type 1 followed by type 11 –soon after food is consumed hunger
contractions disappear.

35. Receptive relaxation—Relaxation of upper portion of stomach when bolus
enters stomach from esophagus
It involves the fundus and upper part of the body of stomach.
Peristalsis of stomach---When food enters the stomach ,the peristaltic
contraction appears with a frequency of 3/minute .it strats from the lower
part of stomach passes through the pylorus till the pyloric sphinctor.

40. Initially contractions appear as a slight indentatation on the greater and
lesser curvatures and travel towards pylorus..finally it ends with constriction
of pyloric sphincter.this type of peristaltic contraction is called digestive
peristalsis.because it is responsible for grinding mixing.
Filling and emptying of stomach-
Filling—the first eaten food is placed againt the greater curvature in the
fundus.and body of the stomach.
the successive layers of food particles lie nearer the lesser curvature until
the last portion of food eaten lies near the upper end of lesser curvature
adjecent to cardiac sphincter.
the liquid remains near lesser curvature and flows towards the pyloric end
of stomach along a V shaped groove formed of smooth muscles it is called
magenstrasse

41. Emptying of stomach---Food remains in stomach for 3 hrs..chyme
emptied into intestine slowly by peristaltic contraction.
the peristaltic waves in the body and pyloric part of of the stomach
and simultaneous relaxation of pyloric sphincter necessary for
gastric emptying.
Regulation of gastric emptying---emptying of stomach stops due to
the inhibition of gastric motility. the inhibition of motility by nervous
and hormonal factor.

42. Nervous factor is enterogastric reflex—when chyme enters intestine ,the
gastric muscle is inhibited and motility stops and arrest of gastric emptying..
this is called enterogastric reflex, this reflex involves vagus nerves.
Hormonal factors-when chyme enters duodenum ,duodenal mucosa releases
hormones which enter stomach thrugh blood and inhibit gastric motility.
Hormones inhibit motility and emptying of stomach
VIP,GIP,Secretin,Cholecystokinin,somatostatin PeptideYY