1. 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)

2. 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

3. Stomach Rugae flatten as stomach fills
Stomach can hold about 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 B 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

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

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

6. 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

7. 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

8. 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)

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

10. 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

11. 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

12. 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

13. Mixing and Emptying Actions

14. 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)