Medical

1. The small intestine –Digestion
& absorption

2. Small Intestine – Anatomy
Longest portion of the alimentary canal
Site of most enzymatic digestion and
absorption.
Main site of absorbtion of nutrient
It extends from the pylorus to the caecum.
The small intestine is formed of three
segments:
Duodenum, jejunum, and ileum

3. con

4. Mucosa
 Contain villi (finger like projection) .Composed of
enterocyte & microvilli.
 Intestinal glands between the bases of the villi secrete
intestinal juice.

5. Intestinal secretion
 Crypts of lieberkhun at the base of villi secrete
intestinal secretion (succus intericus).
 paneth cells secrete defensin (protective )
 Goblet cells secrete mucus (lubrication)
 Number of enterocytes secrete water ,electrolytes (
slightly alkaline) , rapidly absorbed by villi .

6.  Brunner's glands in the duodenum secrete mucus
and large amount of alkaline (rich in Hco3) In
response to:
1 -tactile or irritating stimuli of the mucosa
2-Vagal stimulation
3- secretin

7. con

8. Small intestine receive about 9 liter of
fluid per day as follows:
 1.5 L from saliva
 2.5 L from stomach
 1.5 L from pancreas
 .5 L from bile
 1.0 L from intestine
 2.0 L from drinking

9. 99% of this fluids is reabsorbed, with a
daily fluid loss of only 200 mL in the
stool.

10. Con
Secondary active transport of Na+ is
important in bringing about
absorption of glucose, some amino
acids, and other substances such as
bile acids.

11. Digestion &Absorption

12. Con
Digestion is breaking down of proteins,
fats, and complex carbohydrates into
absorbable units .
Absorption is t he process by which
products of digestion ,vitamins, minerals,
and water cross the mucosa and enter the
lymph or the blood.

13. Carbohydrates digestion
 Types of CHO in diet :-
1. Monosaccharides : glucose , fructose
2. Disaccharides : sucrose ,maltose,
lactose , trehalose
3. Polysaccharides : starch , glycogen

14.  Sucrase hydrolysis sucrose into: glucose &
fructose.
 Lactase hydrolysis lactose into: glucose &
glactose.
 Deficiency of one of the oligosachridases
may cause diarrhea, bloating, flatulence
after the ingestion of sugqr.
??lactose intolerance

15. CHO digestion
 Digestive enzymes :
1. salivary Alpha amylase : act on starch .
2. Pancreatic alpha amylase : act on starch.
The end products are oligosacharides (di, trisacharides
and (α-limit dextrins)
3. Oligosacharidases responsible for further digestion of
the starch derivatives(in the brush border membrane)

16. o α dextrinase: Acts on alpha dextrins, maltose &
maltotriose
o Maltase: Acts on maltose to give glucose + glucose
o Sucrase: Acts on sucrose to give glucose + fructose
o Lactase: Acts on lactose to give glucose + galactose
o Trehalase: Acts on trehalose to give glucose + glucose

19. CHO absorption
 Only occur for the monosaccharides .
 Absorption is almost 100% befor reaching the
terminal part of the ileum.
 The transport of glucose and glactose is Na
dependent, sodium-glucose transporter (SGLT-1)
secondary active transport, at the lumenal
membrane.
 Glucose is transported to the interstitial by , GLUT-2
then to the capillaries.

20.  Fructose absorption is independent to the sodium:
By facilitated diffusion in the intestinal lumen (GLUT5)
and to the interstitium by GLUT2
Galactose absorption: Similar to glucose (i.e. co
transported with sodium“secondary active transport”)

21. Protein digestion
 No enzymes in the mouth.
 Digestion Starts in the stomach by pepsins
 In the intestine by pancreatic endopeptidases
(trypsin,chemotrypsin & elastase) and pancreatic
exopeptidases (carboxypeptidase A, B ) hydrolyze the
amino acids.

22. Protein digestion:
 Products of protein digestion in the
intestinal lumen :
1. Free amino acids
2. Dipeptides
3. Tripeptides
 These are further digested by peptidases in
the brush border and cytoplasm of
intestinal cell.
 About 95- 98 % of proteins are digested

23. Protein absorption
 Seven different transport system for amino acids in
the enterocytes:
Five require sodium(cotransporter with Na)
 Di-tripeptides transported by peptide transporter
1(Pep T1) that require H+ instead of Na.
 Approximately 50% of the ingested protien is from
digestive juice and cellular debris
(desquamated epithelial cells)

24.  Even whole protein and polypeptide can be absorbed
(immunoglobulin from athe maternal colustrum)by
pincytosis to the enterocytes and exocytosis to the
blood.

27. Digestion of lipids
 Starts in the mouth by lingual lipase
 Stomach also secretes gastric lipase, of little
importance except in pancreatic insufficiency
 In the intestine pancreatic lipase will continue.
 Fat digestion and absorption require bile

28. Micelles
release their
lipids, which
diffuse freely
across the
plasma
membrane.

30. The role of bile in the digestion and
absorption of lipids
1/ Emulsification of fat:
This is the breaking down of fats into
small particles by the action of bile. This
facilitates digestion of lipids by lipase
enzyme.
The lipids are digested to produce fatty
acids, monoglycerides and cholesterol.

31. Absorption of lipids
 -Fats pass freely by passive diffusion into mucosal cells.
 The mono acyleglycerides, long chain fatty acids, and
cholesterol after entering the enterocytes reestertified
to triglyceride and cholesterol ester and then
surrounded by layer of lipoprotein , cholesterol,
phospholipids to form chylomicrons enter the
lacteals and enter the thoracic ducts
 Most of absorption in the upper intestine.
 Stool contain 5g of fat per day.

33. Motility of small intestine
The function of movements of the small
intestine are the mixing and propulsion
of chyme to aid digestion and absorption.
There are four types of movements:
1. Migrating motor complex MMC.
2. Segmentation contraction- mixing
movement .
3. Peristalsis propulsion movement.
4. Movements of villi

34. Segmentation contraction
 Ring like contractions of the circular
muscle layer .
Appearing at regular intervals along
the small intestine , they disappear and
replace by another set of ring
contractions .
Primarily they are mixing movement
.but they have a propulsive effect on
contents .

36. Peristalsis
Travelling wave of contraction above
the bolus preceded by relaxation at the
bolus side and bellow it .
Usually travels in an oral- caudal
direction .
At rates 2 - 25 cm/s .

38. Go and Read about the electrolyte absorption
please