GI Hormones

8/10/2019 GI Hormones

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Seminar

On


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Introduction

Gastrointestinal hormones arebiologically active polypeptides

Hormones fall into one of the twofamilies

1. Gastrin familyPrimary members aregastrin and cholecystokinin

2. Secretin family members are secretinglucogon, VIP, GIP and Glicentin


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Enteroendocrine Cells

Hormones secretingcells of GIT.

Identified in mucosa of

stomach, small intestineand colon.

Cells that manufactureamines in addition topolypeptides are AMINE

PRECURSOR UPTAKEDECARBOXYLASECELLS.


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Mechanism of GI hormonesAnimation
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GASTRIN

Major physiological regulator ofgastric acid secretion

Site of production G cells in thelateral wall of the glands in the

antral portion of gastric mucosa Gastrin is a linear polypeptide with

macroheterogeneity andmicroheterogeneity

Predominant circulating form is

gastrin-34 Full biological activity in gastrin-14

or mini gastrin

Gastrin-17 is the principle form withrespect to gastric acid secretion.


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Control and physiological

effects of gastrin

Stimulates gastric acid secretion and

pepsin secretion

Promotes growth of gastric mucosa andstimulation of gastric motility

Stimulates insulin secretion after

proteinaceous meal


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Pathology of Gastrin

ZollingerEllisonsyndrome ischaracterized by

multiple pepticulcerations instomach,duodenumand Jejunum owing

to excess gastrinsecretion by tumor(Gastrinomas)


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Cholecystokinin Pancreozymin

Site of secretionCells inthe mucosa in the firstsegment of small intestine

Control and physiological

effects

1. Causes contraction ofgallbladder

2. Responsible for secretionof pancreatic juice rich inenzymes

3. In brain, regulates foodintake

4. Inhibits gastric emptying

5. Enhances the secretion ofenterokinase


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Secretin

Site of production- Scells that are located inglands of mucosa ofthe upper portion ofsmall intestine

Physiological effects-1. Increases secretion of

bicarbonate ions bythe ducts cells of thepancreas and biliary

tract2. Augments the action ofCCK

3. Decreases gastric acidsecretion and

contraction of pyloricsphinctor


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Gastric inhibitory polypeptide

Site of production- K cells in the mucosa

of Duodenum an Jejunum

Inhibits gastric secretion and motility GIP also known as GLUCOSE

DEPENDENT INSULINOTROPIC

POLYPEPTIDE


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Vasoactive intestinal polypeptide

Site of production- found in nerve of

gastrointestinal tract

Physiological effects1. Stimulates intestinal secretion of electrolytes

but inhibits gastric acid secretion

2. Causes relaxation of intestinal smooth

muscles

3. Causes dilatation of peripheral blood vessels


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Pathology of VIP

VIP secreting tumors

are VIPomas have

been observed in

patients with severe

diarrhea


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Peptide YY

Site of production-

Released from small

intestine and colon

Physiological effects

1. Reduces appetite in

normal and obese

subjects

2. Inhibits gastric acidsecretion and motility


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Ghrelin

Site of production synthesis occurs inepithelial cells lining the fundus of

stomach Physiological effects

1. Stimulation of growth hormonesecretion

2. Central as well as peripheraladministration increases food intake


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Disease states

PRADER-WILLI Syndrome

is a disorder in which

patients develop extreme

obesity withuncomfortable appetite. It

is a complex disease with

several defects

One of its causes isexcessive secretion of

ghrelin


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Somatostatin

Site of production secreted by D cells in

the pancreatic islets and

gastrointestinal mucosa Exist in tissue in two forms

1. Somatostatin14

2. Somatostatin28


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Pharmacologic Uses

Somatostatin and its synthetics

analogues are used to beat a variety of

neoplasms Also used to treat Gigantism and

Acromegaly


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Motilin

Site of production

Secreted by

ENTEROCHROMAFFIN

cells and MO-cells in the

stomach, small intestine

and colon


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Physiological effects

Major regulator of migrating motor

complexes

Increases the duration MMCs andregulates intestinal motility during

interdigestive phases


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Other GIT hormones

Other hormones

Neurotensin

Substance P

Gastrin releasing peptide

Glucagon

Guanylin

Glicentin

Cells secreting GITpolypeptide can form tumors.50% are gastrinomas,25%are Glucagonomas. Othersare VIPomas andNeurotensinomas


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Documents

GI Hormones