4. 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

5. 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

6. 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.

8. 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

9. 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

10. Motor Functions of the Stomach
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

11. 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

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

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

15. Mixing and Propulsion of Food
Presence of food in stomach causes weak peristaltic constrictor wave called slow wave to begin
Begin in mid to upper portions of stomach wall and moves towards antrum
Appears once every 15 to 20 seconds

16. Initiated by gut basic electrical rhythm
When constrictor wave progresses from body towards antrum, becomes more intense, some are so intense that they provide peristaltic action potential
It pushes the antral contents under high pressure towards pylorus

17. It digs deeply into the food contents in the antrum
Opening of pylorus is small and allows only few ml or less of antral contents to empty into duodenum
Also when peristaltic wave approaches pylorus, pyloric muscle contracts which narrows the pyloric opening

18. Retropulsion results in mixing of food
Resulting in antral contents to squeeze upstream towards body of stomach
Retropulsion results in mixing of food

19. Peristaltic
Wave

20. 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

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

22. 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

23. 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

25. 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

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

27. 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.

28. 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

29. 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

30. 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