Gastrointestinal hormones

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GASTROINTESTINAL HORMONES •OVERVIEW •GENERAL FEATURES •CHOLECYSTOKININ •FEATURES AND FUNCTIONS •MECHANISM OF ACTION •REGULATION

Transcript of Gastrointestinal hormones

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GASTROINTESTINAL HORMONES

•OVERVIEW•GENERAL FEATURES•CHOLECYSTOKININ•FEATURES AND FUNCTIONS•MECHANISM OF ACTION•REGULATION

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WHAT IS THEIR IMPORTANCE?

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Robust control systems are required to coordinate

digestive processes in man and animals, and are provided

by both the nervous and endocrine systems. Endocrine

control over digestive functions is provided by

the so-called enteric endocrine system.

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FEATURES OF GI Modulate activity of digestive system They are peptides Not released by endocrine glands but

secreted throughout large areas of the GI Mucosa.

These cells called enteroendocrine cells.

They enter the circulatory system and not the lumen of the GI tract

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LOCATION OF ENTEROENDROCRINE CELLS

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CHOLECYSTOKININ (CCK)

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ABOUT CHOLECYSTOKININ It is a linear peptide synthesized by I

cells ( a type of entero-entocrine cell) of duodenum and Jejunum

Made up of 8 to 59 amino acids Also synthesized in small amounts by

the Brain Have two receptors, CCK A(present

mainly in the pancreatic acinar cells) and CCK B

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Diagram showing location of I cells and secretion of CCK into the bloodstream

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FUNCTIONSRelease of digestive enzymes from the pancreas into the duodenum. Older literature refers to cholecystokinin as pancreozymin, a term coined to describe this effect.

Contraction of the gallbladder to deliver bile into the duodenum. The name cholecystokinin (to "move the gallbladder") was given to describe this effect.

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Inhibits gastric emptyingIncreases the action of EnterokinaseMy increases motility of intestines and colonTogether with Gastrin enhance glucagon secretionAugments contraction of pyloric sphincterPlays an important role in satiety by suppressing hunger

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WHAT CAUSES CCK TO ACT?

The most potent stimuli for secretion of cholecystokinin are the presence of partially-digested fats and proteins in the lumen of the duodenum

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HOW?LET’S TAKE A LOOK

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MECHANISM OF ACTION

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REGULATIONPOSITIVE FEEDBACK MECHANISM:CCK increases bile and pancreatic juice secretion causing more digestion of protein and fat and which further increases CCK secretion

This positive feedback mechanism stops when absorption is completed or when the products of food moves on to the lower portion of the GI tract.

Increased blood levels of cholecystokinin can be found 15 minutes after a meal has begun and levels remain raised for three hours afterwards.

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What happens if I have too much cholecystokinin?

There are no known cases of too much cholecystokinin. However, weight loss drugs are currently under development that copy the appetite-reducing actions of cholecystokinin.

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What happens if I have too little cholecystokinin?

There appears to be evidence of less than average cholecystokinin in very obese people, unlike the levels in obese and slim people. This low level of cholecystokinin may contribute to reduced feelings of fullness and difficulty in losing weight in very obese people. However, more research is needed to confirm this finding.

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