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1. LARGE INTESTINE 2. GIT HORMONES

LECTURE - 9Dr. Zahoor Ali Shaikh

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LARGE INTESTINE Large Intestine consist of cecum,

appendix, colon [ascending colon, transverse colon and descending colon, end part of descending colon forms sigmoid colon] and rectum.

Large Intestine does the function of water and electrolyte absorption and works as storage organ [primary function of large intestine is to store feces].

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LARGE INTESTINE The colon normally receives 500ml of

Chyme from the Small Intestine each day.

The contents coming to the colon consist of

- Indigestible food residues e.g. cellulose, Unabsorbed Biliary components ,Fluid.

Colon absorbs water and salt, what remains behind is to be eliminated is know as feces.

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LARGE INTESTINE We will discuss 1. Motility 2. Secretion 3. Digestion 4. Absorption

MOTILITY IN LARGE INTESTINE Haustral Contraction or Segmentation Peristaltic wave Mass movement [strong peristaltic waves]

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MOTILITY IN LARGE INTESTINE Haustral Contraction [Segmentation

Contraction]

They help to mix the contents of colon and expose contents to mucosa to facilitate absorption.

They occur less frequently may be after every 30mins [they are like segmentation contraction in small intestine but in small intestine they occur 10-12/min].

Haustral contraction are largely controlled by locally mediated reflexes involving the intrinsic plexus.

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MOTILITY IN LARGE INTESTINE Peristaltic wave They propel the contents towards the rectum.

Mass movement [strong peristaltic waves] They move the material from one portion of intestine

to another. They occur 3-4 times per day, generally after meals

and increase in motility moves the feces forward in few seconds.

When material reaches the rectum, rectal distention initiates the defecation reflex.

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MOTILITY IN LARGE INTESTINE Mass movement [strong peristaltic

waves] Gastro-colic Reflex – when food enters

the stomach, mass movements are triggered in the colon by gastro-colic reflex also.

It is mediated from stomach to the colon by gastrin and extrinsic autonomic nerves.

It pushes the colonic contents into rectum triggering the defecation reflex.

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LARGE INTESTINE SECRETION Large intestine secretes alkaline

NaHCO3, mucus solution. Its function is to protect large intestine

from mechanical and chemical injury. Mucus provides lubrication to facilitate

the passage of feces.

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LARGE INTESTINE DIGESTION There are no digestive enzymes

secreted, therefore, no digestion takes place in large intestine.

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LARGE INTESTINE ABSORPTION Na+ is actively transported and water

follows along the osmotic gradient. Secretion of K+ and HCO3. Due to absorptive capacity, some drugs

are given per rectum especially in children e.g. anesthetics, steroids.

There are no villi in Large Intestine.

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FECES About 500ml of material entering the

colon per day from the small intestine, colon absorbs about 350ml, leaving 150g of feces to be eliminated per day.

Feces contains 100g of water and 50g of solid [undigested cellulose, bilirubin [stercobilinogen], bacteria, unabsorbed food residue.

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LARGE INTESTINE BACTERIA They are commensals, which have no

effect on host [they are not pathogen which cause disease].

Bacteria present are E.coli, bacteroides – fragilis.

Some bacteria synthesize vitamin K, vitamin B-complex, folic acid.

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DEFECATION REFLEX Feces are eliminated by defecation reflex. How this reflex works? When mass movements of colon move the

feces into the rectum. Distention of rectum initiates the reflex.

Stretch receptors in the wall of rectum send impulses to the spinal cord ( S2,S3,S4), parasympathetic nerves causes contraction of smooth muscle of rectum and sigmoid colon and relaxation of internal sphincter.

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DEFECATION REFLEX If external anal sphincter [which is

skeletal muscle is also relaxed defecation occurs].

External anal sphincter is under voluntary control, therefore, can prevent defecation despite defecation reflex.

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DEFECATION REFLEX When defecation occurs, it is assisted

by voluntary straining movements that involve contraction of abdominal muscles and forceful expiration against closed glottis which increases intra-abdominal pressure.

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CONSTIPATION When more water is absorbed from the feces,

they become hard and dry. Normally frequency of passing stool vary. It

maybe once a day, or after every meal or once every 2 or 3 days.

CAUSES OF CONSTIPATION Decreased colonic motility due to low bulk diet,

aging, emotion, anxiety. Colonic spasm, tumor in colon. Injury to nerve pathway.

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INTESTINAL GAS OR FLATUS It is derived from two sources 1. Swallowed air [up to 500ml of air may be

swallowed during a meal]. 2. Gas produced by bacterial fermentation in

the colon. Most gas in the colon is due to result of bacterial activity, but the quantity and the nature of gas produced depend on the type of food eaten and colonic bacteria.

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INTESTINAL GAS OR FLATUS Food such as beans, contain

carbohydrate that human can not digest but can be attacked by gas producing bacteria.

Gases produced are Hydrogen, Hydrogen Sulphide, Nitrogen, Carbon dioxide and Methane.

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INTESTINAL GAS OR FLATUS Amount of gas per day passed is about

200ml. The smell is largely due to sulphides. Gas passing through the luminal

contents give rise to gurgling sounds known as BORBORGYMI.

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2. OVERVIEW OF GASTRO-INTESTINAL HORMONES

We will discuss the following hormones: Gastrin Secretin CCK Motilin Somatostatin GIP VIP

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GASTRIN Produced by G-cells in the stomach. Stimulates the release of HCL and

Pepsinogen in the stomach. Increases gastric motility. Increases ileal motility . Relaxes Ileocecal Sphincter. Induces mass movements in colon [because

to help the contents moving through GIT on arrival of new meal in the stomach].

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SECRETIN Secretin is released from small intestine when

stomach acid contents come to duodenum. Functions It inhibits gastric emptying to delay the acid

contents of stomach to enter in the duodenum. It inhibits gastric secretion. It acts on pancreatic duct to produce large

volume of watery, NaHCO3 secretion. It stimulates the secretion of NaHCO3 rich bile in

the liver by acting on the bile ducts.

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CCK [CHOLECYSTOKININ] CCK is released from the duodenum in

response mainly to fat, to a lesser extent to protein products.

CCK causes (i). Inhibition of Gastric motility and secretion(ii). Stimulates pancreatic Acinar cells to secrete

pancreatic enzymes [amylase, lipase, Trypsinogen, Chymotrypsinogen].

(iii). It causes contraction of gall-bladder and relaxation of sphincter of Oddi.

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MOTILIN It is polypeptide and secreted by

entrochromaffin cells and Mo cells in the stomach, small intestine and colon.

It causes contraction of smooth muscles in the stomach and intestine.

Its level increases during inter-digestive state and controls GIT motility, Migrating motility complex (MMC) between the meals.

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SOMATOSTATIN It is secreted by D-Cells in pancreatic

islets and by similar D-cells in GIT mucosa.

Somatostatin inhibits secretion of Gastrin, VIP, GIP, Secretin and Motilin.

Somatostatin secretion is stimulated by acid in the lumen of intestine.

It acts probably in a paracrine fashion.

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GIP [GLUCOSE DEPENDENT INSULINOTORPHIC PEPTIDE]

GIP is released from the duodenum. GIP causes release of insulin. Insulin causes uptake and storage of

glucose. GIP – before it was called Gastric

Inhibitory Peptide [this role is minimum].

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VIP [VASOACTIVE INTESTINAL PEPTIDE]

VIP is found in nerves in the GIT. It stimulates intestinal secretion of electrolytes

and water. Other action – relaxation of intestinal smooth

muscle including sphincters. Inhibition of gastric acid secretion. It potentiates the action of acetylcholine in

salivary glands. VIP is also found in brain, blood, autonomic

nerves.

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REMINDER REGARDING GIT ENZYMES

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REMINDER REGARDING GIT ENZYMES

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REMINDER REGARDING ABSORPTION IN INTESTINE

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WHAT YOU SHOULD KNOW FROM THIS LECTURE

Large Intestine Motility, Secretion, Digestion, Absorption Feces Intestinal Bacteria Defecation Reflex Flatus Constipation GIT Hormones

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THANK YOU