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Anatomically , the stomach is usually divided into two major parts : (1) the body

Anatomically , the stomach is usually divided into two major parts : (1) the body (2 ) the antrum . Physiologically, it is more appropriately divided into the “ orad ” portion, comprising about the first two thirds of the body

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Anatomically , the stomach is usually divided into two major parts : (1) the body

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  1. Anatomically, the stomach is usually divided into two major parts: (1) the body (2) the antrum. Physiologically, it is more appropriately divided into • the “orad” portion, comprising about the first two thirds of the body • the “caudad” portion, comprising the remainder of the body plus the antrum

  2. Basic electrical rhythm • They are the slow,undulating changes in the RMP of smooth muscle of GIT. Intensity-5 to 15 mv Frequency-3 to 12/min 3/min-In body of stomach 12/min-In duodenum 8 to 9/min-In terminal ileum

  3. Causes of slow waves- • Complex interactions among smooth muscle cells and interstitial cells of Cajal. • Interstitial cells undergo cyclic changes in membrane potential due to unique ion channels that periodically open and produce inward current which generate slow wave activity.

  4. Peristaltic wave • It is the basic propulsive movement of GIT and is an inherent property of syncytial smooth muscles. • Stimulation at any point causes a contractile ring to appear which moves forward and food in front of ring also moves in forward direction • Stimulus is distention of gut-stretching stimulates enteric nervous system to cause contraction 2 to 3 cm behind this point

  5. Receptive relaxation of stomach • When peristalsis appears, the gut relaxes several centimeters in analward direction which facilitates the propulsion of food in forward direction. Mechanism:-stretching – Vagovagal reflex – impulses go to brain stem and back to stomach - inhibitory neurons of the myenteric plexus mediate this receptive relaxation

  6. Motor Functions of theStomach • Storage of large quantities of food • Secretions of gastric glands • Mixing of this food with gastric secretions until it form Chyme • Digestion • Absorption • Slow emptying of the chyme from the stomach into the small intestine

  7. Storage Formation of concentric circles Stretch Vagovagal reflex Decreased tone in the muscular wall of stomach-Bulging of wall-Accomodates 0.8 to 1.5 litre of food in relaxed stomach

  8. Secretion • Lined by simple columnar epithelium • Mucus glands • Gastric (oxyntic) glands • Pyloric glands

  9. Four different types of cells make up the gastric glands: • Mucous cells • Parietal cells • Chief cells • Endocrine cells

  10. Mixing and Propulsion of Food

  11. Peristaltic Wave

  12. Chyme • It is the murky semifluid or paste that results from thorough mixing of food with gastric secretions Fluidity depends on:- • Relative amount of food • Water • Stomach secretion • Degree of digestion

  13. Hunger Contractions • Rhythmical peristaltic contractions in the bodyof the stomach • Strong tetanic- lasts for 2 to 3 minutes • Intensity is increased • young healthy individuals • Low BSR • Hunger pangs

  14. Digestion • Digestion of carbohydrates- starts in mouth by enzyme ptyalin – only 5% of starch will be hydrolyzed in mouth • Digestion continues in fundus and body of stomach for almost 1 hour • Then activity of salivary amylase is blocked by acid • 30 to 40% of starch is hydrolyzed to form maltose

  15. Digestion of proteins- Pepsin is most active at pH 2 to 3 and inactive at pH 5.HCl is secreted at pH of 0.8 • It digests protein collagen- the major constituent of intercellular connective tissue of meats

  16. Absorption • Stomach is the poor absorptive area of GIT b/c it lacks typical villus type of absorptive membrane and presence of tight junctions b/w epithelial cells • Highly lipid soluble substances like alcohol and aspirin are absorbed in small quantity

  17. Intrinsic factor • Secreted by the parietal cells • Necessary for absorption of vitamin B12 in ileum

  18. Stomach Emptying • Promoted by intense peristaltic contractions in the stomach antrum. • Emptying is opposed by varying degrees of resistance to passage of chyme at the pylorus.

  19. Pyloric Pump • Peristaltic waves, in addition to causing mixing in the stomach, also provide a pumping action called the “pyloric pump” and it forces several milliliters of chyme into the duodenum

  20. Mostly weak contractions- cause mixing. • (20% of the time the food stays in the stomach) strong intense contractions very tight ring like constrictions which squeeze the contents of stomach- cause stomach emptying

  21. Role of the Pylorus in Controlling Stomach Emptying • Distal opening- pylorus • Increased thickness of circular muscles • Tonically contracted • Pyloric sphincter • The degree of constriction  nervous-humoral reflex signals from stomach & duodenum • Allow passage of water and other fluids

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