Overview
This lecture covers the anatomy and functions of the stomach, small intestine, and large intestine, emphasizing digestive processes, histological structures, and nutrient absorption.
Stomach Anatomy & Function
- The stomach is a muscular sac in the left upper abdominal quadrant, divided into cardia, fundus, body, and pylorus.
- Main functions: storage of food, mechanical breakdown, and chemical digestion, producing chyme.
- The stomach wall has three muscle layers: longitudinal, circular, and oblique, allowing effective mixing.
- Rugae are folds in the stomach lining enabling expansion and aiding in mixing food.
- The lower esophageal sphincter (weak) and pyloric sphincter (strong) control one-way food movement; weak LES can cause acid reflux.
- Gastric glands have three main cell types: parietal (secretes HCl), chief (secretes pepsinogen), and G cells (secretes gastrin).
- Gastrin stimulates acid/enzyme secretion and stomach contractions; its release is regulated by stomach pH.
- Little nutrient absorption occurs in the stomach due to a thick mucus barrier, but some drugs like aspirin can be absorbed.
Small Intestine Structure & Function
- The small intestine is about 20 feet long, divided into duodenum, jejunum, and ileum (DJ ileum).
- Majority of digestion and 90% of nutrient absorption occur here.
- Surface area is greatly increased by circular folds (plicae circulares), villi, and microvilli (brush border).
- Blood capillaries absorb most nutrients; lacteals (lymphatic vessels) absorb lipids and fat-soluble vitamins.
- Duodenum contains Brunner's glands secreting mucus to neutralize gastric acid.
- Jejunum has prominent folds and villi for maximal absorption.
- Ileum has fewer folds and contains Peyer's patches (immune tissue) to protect from large intestine bacteria.
Large Intestine Structure & Function
- Composed of cecum (with appendix), colon (ascending, transverse, descending, sigmoid), rectum, and anus.
- Functions: absorbs water/electrolytes, produces/absorbs vitamins, compacts and stores feces.
- Intestinal flora (e.g., E. coli) help break down residues and produce vitamins (especially K).
- Lacks villi; lined with simple columnar epithelium and goblet cells for mucus secretion.
- Longitudinal muscle reduced to teniae coli; haustra are pouches holding feces.
- Internal anal sphincter (smooth muscle) is involuntary; external anal sphincter (skeletal muscle) is under voluntary control.
Key Terms & Definitions
- Chyme — partially digested, acidic food mixture in the stomach.
- Rugae — folds in the stomach lining aiding mixing and expansion.
- Plicae circulares — circular folds in the small intestine increasing surface area.
- Villi — finger-like projections on intestinal mucosa for absorption.
- Microvilli — tiny projections on villi cells forming the brush border.
- Lacteal — lymphatic vessel in villus absorbing fats.
- Peyer's patches — lymphoid tissue in ileum preventing bacterial invasion.
- Teniae coli — longitudinal muscle strip on large intestine.
- Haustra — pouches of the large intestine.
Action Items / Next Steps
- Watch the next video covering the liver, gallbladder, and pancreas.
- Review lab materials on identifying the left gastric artery.
- Prepare questions for clarification if needed.