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General Intestinal Histology. Activities of the Gastrointestinal Tract. Motility Secretion Digestion Absorption. Intestinal Autonomic Nervous System. Parasympathetic Nervous System. Vagovagal or Long reflex. The Enteric Nervous System. Peptide Secretion. Criteria for GI Hormones.

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Presentation Transcript
activities of the gastrointestinal tract
Activities of the Gastrointestinal Tract
  • Motility
  • Secretion
  • Digestion
  • Absorption
criteria for gi hormones
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
gastrin
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.
cholecystokinin cck
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 >8C fatty acids, and to a lesser extent by acid
secretin
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
gastric inhibitory peptide gip
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
motilin
Motilin
  • Stimulates gastric and intestinal motility
  • Released by the duodenum and jejunum
  • Release is stimulated by nerves, fat and acid
candidate hormones
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
paracrines
Paracrines
  • Act on cells in the immediate vicinity, not through the blood stream.
    • Somatostatin
    • Histamine
somatostain
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.
histamine
Histamine
  • Stimulates gastric acid secretion.
  • Released from oxyntic gland mucosa and enterochromaffin-like (ECL) cells.
  • Released in response to gastrin.
neurocrines
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
vasoactive intestinal peptide
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.
bombesin or gastrin releasing peptide
Bombesin or Gastrin-releasing peptide
  • Stimulates gastrin release.
  • Released by cells in the gastric mucosa.
enkephalins
Enkephalins
  • Stimulates smooth muscle contraction.
  • Inhibits intestinal secretion.
  • Released from cells in the GI mucosa and smooth muscle.
smooth muscle cells
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 15:1.
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Robert D. Specian, Ph.D.
  • rspeci@lsuhsc.edu