1. SMALL INTESTINE-I Motility ,Secretion and Digestion
بسم الله الرحمن الرحيم
SMALL INTESTINE-I Motility ,Secretion and Digestion
Dr.Mohammed Sharique Ahmed Quadri
Dr. Abdelrahman Mustafa
Department of Basic Medical Sciences
Division of Physiology
Faculty of Medicine
Almaarefa Colleges

2. SMALL INTESTINE
In small intestine MOST digestion and absorption takes place.
Small intestine is divided into
duodenum
jejunum
ileum.

3. SMALL INTESTINE ‘MOTILITY’
Motility in small intestine includes:
1. Segmentation
2. Migrating Motility Complex [MMC]

4. SMALL INTESTINE ‘MOTILITY’
Segmentation
Definition
oscillating, ring like contractions of smooth muscle.
Description
Contractile ring occur every few centimeter, dividing the small intestine into segments.
Between the contracted segments are relaxed area containing small amount of Chyme.
Segmentation occur about 12/min in duodenum and 9/min in terminal ileum.
Contents take 3 to 5 hours to move through small intestine.

5. ‘MOTILITY’ Initiation
Interstitial cells of Cajal which produce Basic Electrical Rhythm [BER] or slow wave
When BER reaches the threshold level in the circular smooth muscle segmentation are induced.
Control
Increased segmentation is caused by
--local distension
-gastrin secreted in stomach [gastro ileal reflex],
- parasympathetic stimulation.
Sympathetic stimulation decreases segmental activity.
Functions –
Mixing of food with digestive juices.
Exposing all Chyme to small intestine mucosa for absorption.
move(propelling) the food.

6. 2. Migrating Motility Complex [MMC]
INTESTINAL HOUSEKEEPER
Defintion
weak, repetitive peristaltic wave that move a short distance in the small intestine before dying out
Description
When most of the meals are absorbed, segmentation contraction stop and they are replaced by MMC in between the meals.
MMC starts at the stomach and migrate down the intestine.
MMC sweeps the intestine between meals.

7. Migrating Motility Complex [MMC]
Function
to move [sweep] the remaining contents of previous meal to the colon
Initiation
Interstitial cells of Cajal
Control
hormone motilin.
Motilin hormone is secreted by endocrine cells of small intestinal mucosa.

8. Ileocecal Sphincter Ileum opens into the cecum.
Ileocecal Sphincter prevents contamination of small intestine from chronic bacteria.
Two factors contribute to this
ileocecal valve: valve like folds of tissue protrude from ileum into the lumen of caecum
Ileocecal sphincter smooth muscle in the wall of last several centimeter of ileum is thickened to form sphincter

9. Ileocecal Sphincter
Pushing of Ileal contents forward in cecum causes Ileocecal valve to open .
Ileocecal Sphincter [smooth muscle] is under neural [local myentric] and hormonal control.
Distension on ileal side causes the sphincter to open ---reaction mediated by intrinsic plexus
Gastrin release at onset of meal causes relaxation.

10. SMALL INTESTINE ‘SECRETION’ –
Small intestinal secretion divided into TWO types
1)Succus entricus.
2) intestinal Enzymes

11. SMALL INTESTINE SECRETION
Succus Entricus is secreted into the lumen by exocrine glands present in small intestine mucosa. It consist of:
- Water
- Mucus
- Mineral Salts
- pH 7.8
Secreted 1.5 liters per day.
Secretion increases after meal due to local stimulation of small intestine mucosa by presence of Chyme.

12. SMALL INTESTINE SECRETION
In the lumen surface of small intestine on the epithelial cells there are MicroVilli – hair like projection forming the brush border.
What is brush border?
It is plasma membrane and contains three types of enzyme:
1. Enterokinase – which activates pancreatic Proteolytic enzyme Trypsinogen.

13. SMALL INTESTINE SECRETION
2. Diasaccharidases – maltase, sucrase and lactase, which complete digestion of maltose, sucrose, and lactose into manosaccharides. 3. Amino pepti dases – which hydrolyze small peptides into amino acids, thereby completing protein digestion. Therefore, carbohydrate and protein digestion are completed in brush border.

14. SMALL INTESTINE ‘DIGESTION’
In small intestine, enzyme present in the brush border membrane complete the digestion.
FAT: In the lumen of small intestine, pancreatic enzyme are acting for fat digestion, being held by bile, therefore, fats are completely reduced to absorble units of manocylecrides and free fatty acids.

15. SMALL INTESTINE ‘DIGESTION’
Protein: are broken down into peptide fragments and amino acids by trypsin and chymotrypsin.
Carbohydrate: are reduced to diasaccharides and monosaccharides.

17. Applied Lactose Intolerance
Occurs due to deficiency of lactase enzyme, therefore, digestion of lactose [milk and milk products] are not digested properly and lead to action of bacteria in the large intestine producing large quantity of CO2 and methane gas, distension of intestine, cramps and diarrhea.

18. References Human physiology by Lauralee Sherwood, seventh edition
Text book physiology by Guyton &Hall,11th edition
Text book of physiology by Linda .s contanzo,third edition