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Gastric Motility & Secretion
Dr. Mohammed Alzoghaibi
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Stomach
Main Functions Storage Preparing the chyme for digestion in the
small intestine Absorption of water and lipid-soluble
substances (alcohol and drugs)
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Stomach
Types of Gland (located in gastric mucosa):
Cardiac Glands Pyloric glands (many G cells) Oxyntic glands (most abundant, found in
fundus and corpus)
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Types of Cell
Parietal cellsmost distinctive cells in stomach (HCl &
intrinsic factor) Chief cells pepsinogenMucus neck cells:
- HCO3-
- Mucus
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Types of Cells
G Cells: Gastrin (hormone) ---> HCl secretion
D Cells: Somatostatin (antrum)
Enterochromaffin-like cell: Histamine
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Gastric juice
HCL Pepsinogen Electrolytes Intrinsic factor Mucus (mucus gel layer)
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Gastric motility
Functions
1. allows the stomach to serve as reservoir
2. breaks food to small particles and mix it with gastric juice
3. empties gastric contents at a controlled rate
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Gastric motility
Reservoir part
fundus + 1/3 corpus
(tonic contraction) Antral pump
2/3 corpus + antrum & pylorus
(phasic contraction)
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Mixing & emptying of gastric contents
Gastric contents may remain unmixed (1h) Fat takes longer time for empty than other Liquids are emptied easier and first Major mixing activities in the antrum Retropulsion
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Constriction of pyloric sphincter
Hormones promote constriction
1. CCK
2. Secretin
3. Gastrin
4. GIP Sympathetic innervation
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Regulation of gastric emptying
Acidity (stomach) Secretin antral contraction
Fat (monoglycerides) CCK, GIP gastric emptying
Hyperosmotic solutions gastric emptying
Amino acids G cells Gastrin contraction of sphincter
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Gastric reservoir
Functions: To maintain a continuous compression To accommodate the received food with
out significant gastric wall distention or pressure
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Relaxation in gastric reservoir
Receptive relaxation
- triggered by swallowing reflex Adaptive relaxation
- triggered by stretch receptors (vago-vagal reflex)
- lost in vagotomy
threshold of fullness and pain Feedback relaxation
- triggered by chyme in small intestine
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Gastric juice
HCL Secretion Secreted by parietal cells
Fundus Body
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HCL Secretion (cont)
Mechanism of HCl production: H/K ATPase Inhibited by: omeprazole H/K pump depends on [K]out
[HCl] drives water into gastric content to maintain iso-osmolality
During gastric acid secretion:amount of HCO3
- in blood = amount of HCl being secreted
Alkaline tide
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Neural & Hormonal Control of Gastric Secretion
Vagus nerve (neural effector)Gastrin (hormonal effector)Enterochromaffin-like cellsHistamine ---
H2 receptor (parietal cells) acid secretion
Cimetidine (H2 receptor blocker) peptic ulcer and gastroesophageal reflux
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Phases of Acid Secretion
Cephalic phase(30%): Smelling, Chewing and swallowing Stimulates parietal G-Cells GRP
Gastric phase (60%): gastric distention proteins
Intestinal phase (10%): digested proteins
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Inhibition of Acid Secretion
Inhibitory hormones (Enterogastrones): Somatostatin (D-cells) in antrum Secretin (S-cells) in duodenum Glucose-dependent insulinotropic peptide
(GIP) in duodenum