Stomach Anatomy and Activity Cells of the Mucosa Chemical Digestion Control of Digestion Be able to discuss the function of the major cell types found in the stomach. Be able to discuss how pepsins and acid interact to promote protein digestion. Be able to discuss how the three stages of controlling the stomach including excitatory and inhibitory effects. Handout: Reflexes in the Stomach (in class) Marieb: 23 1

Layers of the Stomach: Mucosa Gastric Pits 2

Gastric Pits Produce Stomach Acid Depths are lined with specialized cells 3

Parietal (Oxyntic) Cells HCl Intrinsic Factor (needed for B12 absorption) Decrease pH

Acids Denature Proteins

Gastric Juice Production 3L/Day G Cells Gastrin Gastrin Inhibitors 6

Mucus Protects the Mucosa Superficial Epithelial Cells Bicarbonate (HCO3-) Absorbs protons (H2CO3) 7

Protein Digestion in the Stomach Denaturation Pepsin Rennin

Aka Zymogenic Cells Produces Pepsinogen Chief Cells

Pepsinogen  Pepsin Requires H+ Pepsin can activate Pepsinogen Pepsin most efficient pH 1.5-2.5 10

Precursor Cells Replenish the Epithelium Stem Cells Stomach surface replaced every 3-6 days 11

Controlling Gastric Juice Levels 1. Cephalic 2. Gastric 3. Intestinal 12

Phase 1: Cephalic or Reflex Phase 1”-5” before food enters stomach Small gastric acid release + Taste, thought of food - Low appetite, depression, Ghrelin

Phase 2: Gastric ENS, G Cells 3-4’, 2/3 of Gastric acid + Proteins Increase pH Distension - Too low pH

Proteins Change pH 15

Phase 3: Intestinal Phase (Mostly Inhibitory) Too much acid, protein, fats Gastrin Inhibitors CCK Secretin 16

Phase 3: Intestinal Phase (Mostly Inhibitory) Distention of SI Pyloric sphincter closes 17

Mechanical Digestion and Distension Cyclic Slow Waves: 3/minute Stronger with distension Stronger as you move distally through stomach

Pyloric Region: The Stomach’s Blender Pyloric antrum Stomach 30ml  SI SI 27ml Stomach Net 3ml/contraction 19