Stomach ANATOMY, FUNCTIONS AND SECRETIONS (the guyton and hall physiology)

ANATOMY, FUNCTIONS AND SECRETIONS
Anatomically, the stomach is usually divided in to two major parts:
1. Body 2. Antrum


Physiologically, the stomach is divided in to
1. the “ ORAD” portion, comprises of about first two thirds of the body.
2. the “CAUDAD” portion, comprises the remainder of the body plus the antrum.
The esophagus empties into the orad stomach.
primary function is to store food.
800 -1500 mL of food. Or 0.8 – 1.5 L
Little mixing occurs in the orad stomach because the contractions are weak and infrequent, so the ingested food remains in unmixed.

vagovagal reflex :
“initiated by swallowing or distention  is define as,” A reflex that occurs from the stomach to the brain stem and then back to the stomach reduces the tone in the muscular wall of the body of the stomach so that the wall bulges progressively outward, accommodating greater and greater quantities of food up to a limit in the completely relaxed stomach”.
mixing
The digestive juices of the stomach are secreted by Gastric glands
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Gastric glands are present in body of stomach except along a narrow strip on the lesser curvature of the stomach
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As long as food is in the stomach. WEAK PERISTALIC CONSTRICTOR WAVES called Mixing waves begins in the mid portion of stomach and move towards antrum about once every 15 to 20 seconds.
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These waves are initiated by the “BASIC ELECTRICAL RHYTHM”
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Consisting of SLOW WAVES. That occurs from the body and providing powerful PERISTALIC ACTION POTENTIAL
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Driven constrictor rings that force the antral contents towards pylorus.
Strong peristalsis in the body of stomach
after 12-24 hour of last meal sometimes last for 2-3 min
Reach its max. 3-4 days
Due to hypoglycemia

1. STOMACH ANATOMY, FUNCTIONS AND SECRETIONS source: The Guyton and Hall Physiology Maryam Fida (o-1827)

2. STOMACH Anatomically , the stomach is usually divided in to two major parts: 1. Body 2. Antrum Physiologically , the stomach is divided in to 1. the “ ORAD” portion , comprises of about first two thirds of the body. 2. the “ CAUDAD” portion , comprises the remainder of the body plus the antrum. [email protected]

3. Storage motor functions of stomach Mixing Emptying

4. 1. Storage : The esophagus empties into the orad stomach. primary function is to store food. 800 -1500 mL of food. Or 0.8 – 1.5 L Little mixing occurs in the orad stomach because the contractions are weak and infrequent, so the ingested food remains in unmixed. vagovagal reflex : “initiated by swallowing or distention  is define as,” A reflex that occurs from the stomach to the brain stem and then back to the stomach reduces the tone in the muscular wall of the body of the stomach so that the wall bulges progressively outward, accommodating greater and greater quantities of food up to a limit in the completely relaxed stomach”.

5. Mixing & propulsion The digestive juices of the stomach are secreted by Gastric glands | Gastric glands are present in body of stomach except along a narrow strip on the lesser curvature of the stomach | As long as food is in the stomach. WEAK PERISTALIC CONSTRICTOR WAVES called Mixing waves begins in the mid portion of stomach and move towards antrum about once every 15 to 20 seconds. | These waves are initiated by the “BASIC ELECTRICAL RHYTHM” | Consisting of SLOW WAVES. That occurs from the body and providing powerful PERISTALIC ACTION POTENTIAL | Driven constrictor rings that force the antral contents towards pylorus.

6. Retropulsion : moving peristalsis+ upstream squeezing in pylorus Chyme Food mixed with stomach contents in murky semifluid form or paste is called chyme . Tanveer Raza MD MS MBBS [email protected]

7. Hunger contraction In empty stomach Strong peristalsis in the body of stomach after 12-24 hour of last meal sometimes last for 2-3 min Reach its max. 3-4 days Due to hypoglycemia If very strong  fuse  tetanic contraction Hunger pain

8. STOMACH EMPTYING Stomach emptying is promoted by intense peristaltic contractions in the STOMACH ANTRUM. PYLORIC PUMP: Most of the time stomach contractions are weak and function mainly to cause mixing of food and gastric secretion. However, for about 20 percent of time while food is in the stomach; the contractions become intense, beginning in the midstomach and spreads towards caudal region. These strong peristalic contractions causes Stomach Emptying. They are often create 50 to 70 centimeters of water pressure, which is about six times as powerful as the mixing type of peristalic waves. Tight ,ring like powerful constricting wave in addition to mixing causing pumping action is called Pyloric Pump. Role of PYLORUS IN CONTROLLINGSTOMACH EMPTYING: The distal opening of the stomach is called PYLORUS. Here the thickness of the circular wall muscle becomes 50 to 100% greater and remains slightly tonically contracted almost all the times. These pyloric circular muscle is called the PYLORIC SPHINCTER. Pylorus is usaually open enough for water and other fluids to empty from stomatch in to the duodenum. Function of this is, it prevent passage of food particles until they have become mixed in the chyme to almost fluid consistency. [email protected]

9. Emptying of the stomach (pyloric pump) Peristalsis + relaxation of pyloric sphincter

10. REGULATION OF STOMACH EMPTYING [email protected] This is regulated by: 1. Gastric factors that promote emptying 2. Duodenal factors that inhibit stomach emptying.

11. Stomach emptying Gastric factors Duedenal factors Others + + + + + _ _ _ _ _ 1- volume of gastric contents by stretching the wall ENSinc pyloric pump act 2- gastrin hormone Stimulus is fat in duodenum Nervous factor called “ Enterogastric reflex” 2- Hormonal factor Secretin , CCK from jejunum GIP, somatostatin 1- chemical composition. CHO-PROTEIN-FAT 2-emotions 3-consistency &type of food

12. Stomach emptying Gastric factors + + + + + 2. PH of gastric content is directly proprotional to gastric emptying

13. ENTEROGASTRIC REFLEX [email protected] “ The reflex that inhibits gastric emptying is called Enterogastric reflex” FACTORS WHICH INITIATE REFLEX. Duodenal distention Irritation of the duodenal mucosa Acidity of the chyme Breakdown products of protein and fats. Sympathetic stimulation.

14. SECRETION OF STOMACH

15. TYPES OF TUBULAR GLAND Stomach mucosa has two types of tubular glands 1. OXYNTIC GLAND (Gastric gland) 2. PYLORIC GLAND [email protected]

16. OXYNTIC GLAND ( ( GASTRIC GLAND) (Acid Forming Gland) Location: Inside surfaces of the body and fundus of the stomach. Constituting the proximal 80 percent of the stomach. Types of cell Oxyntic gland has three types of cells. Mucous neck cells secrete mainly mucous Peptic or chief cells secrete mainly pepsinogen Parietal or oxyntic cells secrete Hydrochloric acid ( HCl ) and intrinsic factor PYLORIC GLAND Location: Antral portion of the stomach, constituting the distal 20 % of the stomach. Secretion: mainly secrete mucous for protection of the pyloric mucosa from the stomach acid . They also secrete the hormone “Gastrin”.

17. Pepsinogen production: Secreted by peptic( chief ) cells of gastric(oxyntic) glands Packaged in zymogen granules released by exocytosis. Pepsin catalyzes breaking of covalent bonds in proteins. Pepsinogen( inactive )  pepsin Proteolytic enzyme in a highly acidic medium at a PH (1.8-3.5) Intrinsic factor secretion: Secreted by parietal (oxyntic) cells alongwith HCL Essential for absorption of vit B12  maturation of RBC Destruction of parietal cells as in gastritis  Achlorhydria & Pernicious Anemia

18. Location of Hydrochloric Acid Secretion Parietal cell have large branching intracellular canaliculi | HCL is formed at the villus – like projections inside these canaliculi and then conducted through the canaliculi to the secretory end of the cell | About 160 mmol /L of HCL is formed The main driving force for HCL secretion is a Hydrogen- Potassium Pump ( H –K ATPase)

19. Location of gastric acid secretion

20. Mechanism of HCL secretion Water inside the parietal cell becomes dissociated in to H and OH in the cell cytoplasm. | Hydrogen is then actively secreted in to the canaliculus in exchange for Potassium and is catalyzed by H-K ATPase. | Potassium ions transported in to the cell by the Na – K ATPase pump on the basolateral side of the membrane tend to leak in to the lumen but are recycled back in to the cell by the H-K ATPase

21. The basolateral Na-K ATPase creates low intracellular Na, which contributes to Na reabsorption from the lumen of the canaliculis | Most of the K and Na in the canaliculis is reabsorbed in to the cell cytoplasm, and hydrogen ions take their place in the canaliculis | The pumping of H out of the cell by the H-K ATPase permits OH to accumulate and form HCO from co2. | This reaction is catalyzed by Carbonic anhydrase

22. The HCO3 is then transported across the basolateral membrane in to the extracellular fluid in exchange for chloride ions,Which enter the cell and are secreted through chloride channels in to the canaliculis giving a strong solution of HCL in the canaliculis | The HCL is then secreted outward through the open end of the canaliculus in to the lumen of the gland. Water passes in to the canaliculus by osmosis. The final secretion from the canaliculus contain Water, HCL at a concentration of 150 to 160 m Eq/L, KCL aat a concentration of 15 m Eq/ L and a small amount of NaCl.

23. Mechanism of secretion of HCL

24. Function of HCL Kills bacteria Stops carbohydrate digestion by inactivating salivary amylase Denatures proteins Helps convert pepsinogen to pepsin Tanveer Raza MD MS MBBS [email protected]

25. Factors Stimulating the secretion of HCL. Acetylcholine Gastrin Histamine Vagal stimulation Factors inhibit the secretion of HCL. Secretin Gastric inhibitory polypeptide Tanveer Raza MD MS MBBS [email protected]

26. Phases of Acid Secretion Cephalic Phase= 30% Start before the food enters in stomach. Results from sight, smell, thought or taste of food. Neurogenic signals originate in the cerebral cortex, amygdala and hypothalamus. Stimulates parietal G-Cells Nerve : Vagus nerve. Blocked by : vagotomy . 2. Gastric phase = 60% Start once food enters in stomach. gastric distention Activation of stretch receptors (neural activation) Activation of chemoreceptors by peptides, caffeine, and rising pH Release of gastrin to the blood proteins 3. Intestinal Phase = 10% digested proteins HORMONES INHIBIT GASTRIC SECRETIONS: Secretin Gastic Inhibitory peptide Vasoactive intestinal polypeptide Somatostatin