Sindirim Sistemi

1
General Intestinal Histology
2
Activities of the Gastrointestinal Tract

• Motility
• Secretion
• Digestion
• Absorption

3
Intestinal Autonomic Nervous System
4
Parasympathetic Nervous System
5
Vagovagal or Long reflex
6
The Enteric Nervous System
7
Peptide Secretion
8
Criteria for GI Hormones

• a physiologic stimulus in one part of the GI
  tract produces a response in another part
• the response must be independent of the nervous
  system
• the physiologic response can be duplicated with
  an extract from the stimulus site
• the substance must be isolated, purified,
  identified chemically, and synthesized

9
Gastrin

• Stimulates gastric acid secretion and growth of
  gastric oxyntic gland mucosa.
• Released from the gastric antrum and perhaps the
  duodenum.
• Release is stimulated by peptides, amino acids,
  gastric distention and stimulation of the vagus.

10
Structure of Human little Gastrin
11
Cholecystokinin (CCK)

• Stimulates gallbladder contraction, pancreatic
  enzyme and bicarbonate secretion, and growth of
  the exocrine pancreas
• Inhibits gastric emptying
• Released from the duodenum and jejunum
• Release is stimulated by peptides, amino acids
  and gt8C fatty acids, and to a lesser extent by
  acid

12
Structure of porcine Cholecystokinin
13
Secretin

• Stimulates pancreatic bicarbonate secretion,
  biliary bicarbonate secretion, growth of the
  exocrine pancreas, and pepsin secretion
• Inhibits gastric acid secretion and the trophic
  effect of gastrin
• Secreted by the duodenum
• Secretion is stimulated by acid and to a lesser
  extent fat

14
Secretin Family of Peptides
15
Gastric Inhibitory Peptide (GIP)

• Stimulates insulin release
• Inhibits gastric acid secretion
• Secreted by the duodenum and jejunum
• Secretion is induced by glucose, amino acids and
  fatty acids

16
Motilin

• Stimulates gastric and intestinal motility
• Released by the duodenum and jejunum
• Release is stimulated by nerves, fat and acid

17
Candidate Hormones

• Pancreatic polypeptide-a 36 amino acid peptide
  released from the pancreas in response to all
  three food stuffs
• Peptide YY-a 36 amino acid peptide released from
  the ileum and colon in response to meals,
  especially fat
• Enteroglucagon-is present in the distal small
  intestine and released into the bloodstream

18
Paracrines

• Act on cells in the immediate vicinity, not
  through the blood stream.
• Somatostatin
• Histamine

19
Somatostain

• Inhibits gastrin release, release of other
  peptide hormones and gastric acid secretion.
• Released from the GI mucosa and the pancreatic
  islets.
• Release is induced by acid.
• Release is inhibited by vagal stimulation.

20
Histamine

• Stimulates gastric acid secretion.
• Released from oxyntic gland mucosa and
  enterochromaffin-like (ECL) cells.
• Released in response to gastrin.

21
Neurocrines

• Released from neurons by an action potential,
  then diffuse across the synaptic cleft to the
  target tissue
• Vasoactive intestinal peptide (VIP)
• Bombesin or gastrin-releasing peptide (GRP)
• Enkephalins

22
Vasoactive Intestinal Peptide

• Stimulates intestinal and pancreatic secretion.
• Relaxes sphincters and gut circular smooth muscle
  in general.
• Released by cells in the mucosa and smooth muscle
  of the GI tract.

23
Bombesin or Gastrin-releasing peptide

• Stimulates gastrin release.
• Released by cells in the gastric mucosa.

24
Enkephalins

• Stimulates smooth muscle contraction.
• Inhibits intestinal secretion.
• Released from cells in the GI mucosa and smooth
  muscle.

25
Smooth Muscle Cells

• They are smaller than skeletal muscle cells and
  long, narrow and spindle-shaped.
• Cells that belong to a bundle are functionally
  coupled by gap junctions.
• There are no sacromeres, therefore no striations.
• The ratio of thin to thick filaments is 151.

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• Robert D. Specian, Ph.D.
• rspeci_at_lsuhsc.edu