Anatomy and Physiology Part 3: Stomach and Stomach Control Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 23 Digestive System Lectures 9 & 10 Part 3: Stomach and Stomach Control Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1] Slides 16 – 38; 50 min [Lecture 2] 118 min (38 slides plus review of course Web sites and syllabus)

Esophagus Veins drain into hepatic portal vein (via gastric veins) Esophagus is about 25 cm long. Straight course through the mediastinum. Solid foods pass from the oropharynx to the stomach in about 8 sec.; fluids in about 1-2 sec. Innvervated by CN X (via connection with myenteric plexus). Lower esophageal (cardiac) sphincter prevents reflux (backup) of stomach acid into the esophagus. Esophagus conveys food from pharynx to stomach by peristalsis

Stomach Rugae flatten as stomach fills Stomach can hold about 1-1.5 liters of material Gastric glands M G cells D cells Greater curvature Stomach Functions: - Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B12 - Secretion of gastrin, somatostatin Range of stomach volume is about 50 ml (empty) to about 4L, or 1 gallon (very distended). Rugae flatten as stomach fills

Blood Supply and Drainage of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Lining and Gastric Glands of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Gastric Secretions mucus (cardia) from goblet cells and mucous glands protective to stomach wall hydrochloric acid from parietal cells needed to convert pepsinogen to pepsin ‘p’ in parietal and ‘p’ in pH pepsinogen from chief cells inactive form of pepsin intrinsic factor from parietal cells required for vitamin B12 absorption pepsin from pepsinogen in presence of HCl protein splitting enzyme mucus, gastrin, somatostatin from pyloric glands protective to stomach wall gastrin and somatostatin are hormones H.Pylori is difficult to eradicate, so three medications are used simultaneously. This is called "Triple Therapy". The best treatment at present is called OAC, taken for 7 days: O = Omeprazole (which decreases the acid level in the stomach) A = Amoxicillin (a penicillin antibiotic). C = Clarithromycin (an antibiotic related to erythromycin) OMC is used in those who are penicillin allergic, where M = Metranidazole. INFANTS ONLY rennin (chymosin) gastric lipase

Secretion of H+ by Parietal Cells Important functions of the stomach pH (1.5 – 2.0) - kills microorganisms - denatures proteins - breaks down plant material and CT in meats - activates pepsin Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Three Phases of Stomach Control Cephalic phase triggered by smell, taste, sight, or thought of food begin secretion and digestion Gastric phase triggered by distension, presence of food, and rise in pH in stomach enhances secretion and digestion Intestinal phase triggered by distension of small intestine and pH change controls rate of gastric emptying; may slow emptying NOTE that all these phases control activity in the STOMACH Know what each phase does (shown in red)

Cephalic Phase of Gastric Secretion Emotional states can exaggerate or inhibit this phase Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Gastric Phase of Gastric Secretion Secretion stimulated by: 1) ACh 2) histamine 3) gastrin. Small peptides and amino acids cause secretion of gastrin. Below pH 2, gastrin secretion is inhibited. Proteins, alcohol, and caffeine can markedly increase secretions by stimulating gastric chemoreceptors Histamine stimulates acid secretion by parietal cells Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Intestinal Phase of Gastric Secretion Enterogastric reflex (inhibits gastric activity) –reduces gastric motility, stimulates contraction of pyloric sphincter (pylorus) Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Overview of Gastric Control/Secretion Key + Stimulation - Mucous Cells Inhibition Emptying of Stomach ( [H+ ]) Stomach Molility (Segmentation/Peristalsis) ECL Cells Histamine Endocrine Factor + + + Exocrine Factor + (cephalic/gastric phases) Parasympathetic NS G cells Gastrin + Both + D cells Somatostatin Intrinsic Factor + B12 Parietal Cells pH < 3.0 - + H+ + Cl- HCO3- (alkaline tide) + + + + + (intestinal phase) Stretch of stomach Fats in Small Intestine pH > 3.0 (dilution of H+) Peptides Chief Cells Pepsinogen Pepsin Protein Breakdown Food in Stomach Fat Breakdown Lipases

Mixing and Emptying Actions

Gastric Absorption Gastric absorption is very limited due to: - blanket of mucus covering cells - tight junctions between adjacent epithelial cells - epithelial cells lack specialized transport mechanisms - gastric lining is relatively impermeable to water - chyme usually contains only partially digested material Some substances can be absorbed by the stomach: some water certain salts certain lipid-soluble drugs, e.g., aspirin alcohol (slowed by presence of fats)