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Digestion in the stomach Gastric secretion and regulation Movement of stomach 1 Stomach: a reservoir, mixing, ingestion and empting • gastric juice(acid) • proteins (pepsins ) small peptides • absorption of little water and alcohol 2 Secretion of gastric fluid Composition and functions of gastric juice endocrine: G cell — gastrin D cell-SS (somatostatin) enterochromaffin-like cell (ECL)-- histamine cardiac mucous cell:mucus HCO3 gland Exocrine pyloric mucous cell: Acidsecrete gland colorless、insipidity 、acidity(pH 0.9- 1.5)1.5-2.5L/day G cell-gastrin mucus HCO3 Neck mucous cell:mucus parietal cell:HCI、intrinsic factor chief cell:pepsinogen 4 Composition and functions of gastric juice 1、gastric acid(HCl) 1)volume ejection of gastric acid acid secretion(mmol/H) basic acid output :on empty stomach (after fasting overnight)(0-5) maximal acid output:after food or chemicals stimulation (20-25) man> woman young >old 5 Secretion of HCL primary active transporter parietal cell antiport carrier Function of HCL 1. activates pepsinogen, convert it into pepsin. providing a medium of low pH favoring pepsin action. 2. kills bacteria 3. promotes pancreatic secretion and biliation, intestinal secretion. 4. promotes Fe++ and Ca++ absorption in initial part of small intestine. 5. Degeneration of protein and facilitates digestion. 7 proton pump H+/K+ - ATPase inactivator—omeprazole Gastric ulcer duodenal ulcer 8 2、Pepsinogen ----- precursor of pepsin HCl and self activation pepsinogen pepsin protein proteose, peptone Ph2 — Ph 5 9 3. Mucous-HCO3- barrier Mucus is secreted by the stomach surface cells,mucous neck cells,cardiac gland and pyloric gland. It is strong viscous. The surface mucous cells also secrete HCO3- , It can neutralise with H+ from the lumen of the stomach. this structure and its function are called Mucous-HCO3- barrier Mucous protect mucosa against mechanical injury by acid-pepsin and other agent. 10 Mucus bicarbonate barrier Mucosal barrier: Alcohol,Aspirin, Epinephrin, Helicobacter pylori. 11 Helicobacter pylori • For their discovery(1983) of bacterium Helicobacter pylori and its role in gastritis and peptic ulcer disease, •In 2005, they won the Nobel Prize for physiology. Helicobacter pylori • So, • Awards word said, they are put a chronic recurrent disease into a short term and controllable disease in 2005 Nobel Prize in physiology awards ceremony. • Great! 4、Intrinsic factor: forming complex with B12, allowing it to be absorbed in the terminal ileum. the deficiency of it can cause the disease macrocytic anemia 15 Composition of gastric juice HCL pepsinogen Mucous bicarbonate barrier Intrinsic factor 16 Regulation of gastric juice secretion Endogenous substance acting directly on parietal cells that stimulate gastric secretion: 1. Acetylcholine (Ach): release from nerve termination, M3-receptor Blocking agent --- atropine 17 Regulation of gastric juice secretion 2. G cell gastrin Parietal cell H2-receptor 3. ECL cell histamine (Enterochromaffin-like cell) Blocking agent of H2- R:Cimetidine 18 Inhibition of gastric secretion G cell Parietal cell SS (somatostatin) ECL cell 19 Regulation of gastric secretion in different phase The major physiological stimulant to acid secretion is the ingestion of meal. Gastric secretion after a meal can be divided into three phases according to stimulus location. cephalic phase gastric phase intestinal phase 20 Sham feeding gastric fistula esophageal fistula 21 cephalic phase • Sham feeding • Conducted by Pavlov and his students in 1898 1) unconditional reflex and conditional reflex 2) relationship between the time of sham feeding and the volume of gastric secretion in cephalic phase 3) appetite related to cephalic phase of gastric secretion 4) abolished by bilateral vagotomy Abolished by bilateral vagotomy Gastrin HCL pepsin sectioning of the vagi abolishes nervous reflex mechanism∶ ⅠⅡⅧ Vision smell hearing receptor G cell encephalic nerves Conditional reflex Sham feeding oral pharynx receptor Ⅴ Ⅶ Ⅸ Ⅹ nonconditional reflex 24 Ⅹ Acidsecre ting gland 胃 gastric 液 juice 24 Characteristics juice in cephalic phase • Occupy 30% of total quantity of digestive phase. • Acidity and pepsin content are very high. 25 Characteristics juice in gastric phase • Occupy 60% of total quantity of digestive phase. • But pepsin content lower than the content of cephalic phase. 26 regulatory mechanism of gastric phase distension chemical stimulus food long vagovagal reflexes local enteric reflexes G cell Acidsecret ing gland gastrin gastric juice 27 27 Characteristics juice in intestinal phase • Occupy 10% of total quantity of digestive phase. Gastrin、entero-oxyntin • Small intestine juice gastric 28 • The acid secretion begins immediately following a meal and reaches to peak in one or two hours. The three phases of secretion start almost simultaneously and overlap each other. 29 Inhibitory regulation of gastric secretion (1) acid inhibition duodenum pH<2.5 secretin and bulbogastrone Gastric antrum pH<1.2-1.5 G cell Gastric acid inhibition D cell This is a negative feedback mechanism preventing overloading of the small intestine with acid content. 30 Inhibitory regulation of gastric secretion (2) Fat inhibition The inhibitory action of fat on gastric secretion only be achieved when fat entered into duodenum. May be related to some humoral factors such as enterogastrone. 31 Inhibitory regulation of gastric secretion (3) Hypertonic inhibition Hypertonic solution Osmoreceptor In intestine Gastric acid Inhibitory hormones 32 Gastric Movement Forms of movement 1.Receptive relaxation 1)concept:With each swallow of food, the bolus stimulating the stretch receptors in the pharynx and esophagus, the smooth muscle relaxation of the fundus and body in stomach by a reflex mediated by the vagus nerves. 2)Significance:With the intaking of food, intragastric pressure retains invariable. 33 2.Peristalsis: Each wave begins in the body (middle part) of the stomach and produces only a ripple as it spread down the antrum at a rate of 3 per minute. At the beginning, the wave is too weak, but it gets more and more powerful when it reaches antrum. The pyloric sphincter muscles contract upon arrival of the wave. Only a small amount of chyme is expelled into the duodenum with each wave . 34 Function of gastric peristalsis: ① mix the chyme with digestive juice ② grind food ③ push chyme gastric emptying 35 (3)Migrating motor complex (MMC) There is a very strong contraction migrating from the upper to lower stomach on an empty stomach, 1/90mins. Significance: sweep the remainder of the stomach. Gastric emptying and it’s regulation 1. Concept : A process of gastric contents moving from stomach into duodenum. 2. Motivity Food enter stomach gastric motility pyloric sphincter muscle relax intragastric pressure > pressure in duodenum Gastric emptying 37 Effective factor of gastric emptying The rate at which gastric contents pass into the duodenum depends on their chemical and physical characteristics. 1)Characteristics of food Carbohydrate > protein > fat finely ground > Coarse food liquid > solid isotonic solutions > greater or reduced osmolality 38 2)The promoting factors in stomach The gastric factors that promote emptying. chemical stimulus emptying mechanical Vago-vagal reflex stimulation of food gastric motility G cell-gastrin 39 3)the inhibitory factors in duodenum secretory cell in the mucosa secretin CCK(cholecystokinin ) emptying Food entero-gastric reflexes gastric motility receptor in the wall 40 • When food enters the duodenum, multiple nervous reflexes are initiated from the duodenal wall and pass back to the stomach to slow or even stop stomach empting as the volume of chyme in the duodenum becomes too much. 41 (the inhibitory) emptying Entero-gastric Reflex KEY POINTS 1. Receptive relaxation 2. Gastric emptying 3. Peristalsis 4. Composition and functions of gastric juice 5. The function of HCL. 43