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Digestive PhysiologyDigestive Physiology
Physiological functions of the stomach
By: M.H.Dashti
Lecture 4
Anatomy of StomachAnatomy of Stomach
Size when empty?– large sausage– stretches due to rugae
Parts of stomach
– cardia
– fundus---air in x-ray
– body
– pylorus---starts to narrow as approaches pyloric sphincter
Physiological functions of the Stomach - secretions
Physiological functions of the Stomach - secretions By Oxyntic and Pyloric
glandular cells exocrine
Gastric juice-2-3 L/day– Water & electrolytes – enzymes
Mucus Endocrine: Gastrin Paracrine
– Histamine– Somatostatin
Gastric glandular cells & their secretionsGastric glandular cells & their secretions
surface mucous cells & mucous neck cells Alkaline Mucin
Parietal cell– Hydrochloric acid and
Intrinsic factor Chief ,peptic or
zymogene cell– Gastric lipase,
pepsinogen and rennin G cell
– Gastrin hormone
,rennin
Entrochromafin cells produce paracrine secretions of Histamine & D cells
Somatostatin
Mechanisms of acid secretion Mechanisms of acid secretion
ATPNa+
K+
control of acid secretioncontrol of acid secretion
M3
CckB
Histamine
Ach
Gastrin
Somatostatin
Prostaglandins
EGF
PGE2
cAMP-
IP3IP3
Ionic concentrations of gastric juice as a function of secretion rate
Ionic concentrations of gastric juice as a function of secretion rate .At low flow rates the
juice is hypotonic At high flow rates it
approaches isotonicity and contains predominantly H+ and Cl-
Gastric alkaline mucosal barrierGastric alkaline mucosal barrier
Factors affecting Gastric alkaline mucosal barrierFactors affecting Gastric alkaline mucosal barrier
stimulation– Prostaglandins– parasympathetic
inhibition– Sympathetic– Bile salts– Alcohol– Citric acid
pH~7 at Cell surface
Helicobacter pylori & GastritisHelicobacter pylori & Gastritis
cytokines
Control of the chief cellsControl of the chief cells Secretin , VIP &
β-adrenergic agonists act via CAMP
Ach Gastrin & cck act via IP3 & Ca2+
Mechanism for Potentiation effect of H+ is not known
Pepsinogen &Gastric
lipase
Gastric motility : Gastric motility :
Gentle mixing waves (type I)– every 20 seconds
(BER)– mixes bolus with
2 .5 L/day of gastric juice to turn it into chyme
More vigorous waves (type II) – travel from body of
stomach to pyloric region
Intense waves Intense waves (type III )(type III )
open theopen the pylorus and pylorus and squirt out 3ml of chyme squirt out 3ml of chyme
with each wavewith each wave type II & III are stimulated by Ach & type II & III are stimulated by Ach &
Gastrin and inhibited by NEGastrin and inhibited by NE
type Itype I
type IItype II typeIIItypeIII
Gastric motility: Mechanical DigestionGastric motility: Mechanical Digestion
Pyloric sphincter & Pyloric pump Pyloric sphincter & Pyloric pump
antrumduodenum
Myenteric plex
Sub mucosal plexus
Circular muscle layer Longitudinal muscle
layerPyloric sphincter
Control of Gastric functions Three PhasesControl of Gastric functions Three Phases
Cephalic Phase = “Stomach Getting Ready”
Cephalic Phase = “Stomach Getting Ready”
Sight, smell, taste & thought – stimulate
parasympathetic nervous system
– Vagus nerve– increases
stomach muscle and glandular activity
Receptive relaxation
Gastric Phase = “Stomach Working”
Gastric Phase = “Stomach Working” Nervous control via
stretch receptors & chemoreceptor keeps stomach active– vigorous peristalsis
and glandular secretions continue
– chyme is released into the duodenum
Endocrine gastrinEndocrine gastrin hormone increases hormone increases stomach churning and pyloric sphincter stomach churning and pyloric sphincter relaxationrelaxation
Intestinal Phase = “Stomach Emptying”
Intestinal Phase = “Stomach Emptying” Stretch receptors in
duodenum slow stomach activity & increase intestinal activity
Distension, fatty acids or sugar signals medulla – sympathetic nerves slow
stomach activity Hormonal influences (from
SI) – secretin hormone
decreases stomach secretions
– cholecystokinin(CCK) decreases stomach emptying
Takes 2-4 hrs to completely empty the stomach
Hormones ,short&
Inhibit gastric
function
Regulation of Gastric Emptying
Chemical Digestion in the StomachChemical Digestion in the Stomach
Protein digestion begins– HCl denatures (unfolds) protein molecules– HCl transforms pepsinogen into pepsin that
breaks peptides bonds between certain amino acids (aromatics)
– Rennin in infants Fat digestion continues
– gastric lipase splits the triglycerides in milk fat most effective at pH 5 to 6 (infant stomach)
Absorption of Nutrients by the StomachAbsorption of Nutrients by the Stomach
Water especially if it is cold Electrolytes Some drugs (especially aspirin) & alcohol
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