3 The Pyloric SphincterA ring of smooth muscle and connective tissue between the gastric antrum and the duodenum.Has 2 Functions:Allows the regulated emptying of gastric contents at a rate consistent with the ability of the duodenum to process chyme.Prevents the regurgitation of duodenal contents back into the stomach
4 Gastric JuiceHow many litres of gastric juice are produced by the stomach each day?300ml500ml1L3L5L
5 Gastric Juice What are the main components of gastric juice? (4) Hydrochloric acid (HCl)2. Mucus3. Enzymes: pepsinogens, gastric lipase4. Intrinsic Factor
6 What are the major types of secretory epithelial cells in the stomach? Surface mucous cellMucous neck cellParietal cellChief cellG cellEnterochromaffin-like (ECL) cellDelta (D) cellMucusHCl and IFPepsinogenGastrinHistamineSomatostatin
7 Mucus What is it? What is the Gastric Mucosal Barrier? A mixture of glycoproteins and glycopolysaccharides.What is the Gastric Mucosal Barrier?Mucus and the alkaline secretions entrapped within it.It protects the stomach against acid, proteolytic enzymes and mechanical damage.
8 Hydrochloric Acid Produces a gastric luminal pH of 1-2 Stimuli of acid secretion also promotes increased mucus and HCO3- secretion.Stimulated by:gastrinacetylcholinehistamineInhibited by:somatostatinprostaglandins E2 and I2enteric hormones
10 Inhibition of Gastric Acid Secretion ECLcellSomatostatin-SSRCholinergicnerveBlood vesselMuscarinic-RGastrin-R++HistamineAChGastrin+-Somatostatin++Muscarinic-RH2-RGastrin-R+PGE2-R-SSRPGE2-Parietal cellK+H+Cl-PCAAH+Cl-K+
11 The Parietal Cell1. Truncated pyramidal shape, with apex oriented towards gastric lumen.2. Canaliculi (envaginations of luminal membrane) lined with ion pumps: increased surface area3. Many mitochondria: provides energy for H+ pump
12 The Parietal Cell4CO2 and H2O are converted into H+ and HCO3- by carbonic anhydraseH+ is pumped into the lumen by a H+/K+-ATPase transporterHCO3- leaves the cell and enters the bloodstream via antiport with Cl-.Cl- diffuses passively into the lumen via a Cl- channel.213
13 Intrinsic Factor Glycoprotein secreted by parietal cells Intrinsic factor production is the only indispensable function of the stomach.Is essential for the absorption of vitamin B12 in the intestines.
14 Pepsinogen Pepsin secretion parallels acid secretion. Parietal CellHClChief CellPepsinogenPepsinProteinPeptidePepsin secretion parallels acid secretion.Pepsin is active only at low pH.
15 Gastric Hormones Hormone Production Site Gastric Functions Gastrin G cells in antrum of stomachStimulates Acid SecretionStimulates Gastric MotilityInhibits Gastric EmptyingStimulates Intestinal MotilityHistamineECL cells in gastric mucosaIncreases Local Blood FlowSomatostatinD cells in antrum and body of stomachInhibits GastrinInhibits Acid Secretion
16 What is the one indispensable function of the stomach? SECRETION OF INTRINSIC FACTOR