Digestive System Lecture Notes

Overview

• Discussion on various peptide hormones affecting the intestinal tract.
• Hormones target different parts of the digestive system including accessory glands like the pancreas, liver, and gallbladder.

Key Hormones

Secretin

• Released from the duodenum when food arrives.
• Stimulates secretion of bile and buffers from the liver and pancreas.

Cholecystokinin (CCK)

• Secreted in the duodenum in response to chyme with lipids and proteins.
• Increases bile and protease enzyme production.
• Targets the hepatopancreatic sphincter.
• Stimulates gallbladder contraction.

Gastric Inhibitory Peptide (GIP)

• Inhibits stomach activity when fats and carbohydrates enter the small intestine.

Vasoactive Intestinal Peptide (VIP)

• Dilates intestinal capillaries to increase nutrient absorption.
• Inhibits stomach acid production.

Gastrin

• Released in response to incompletely digested proteins in the duodenum.
• Increases stomach motility and enzyme production.

Intestinal Movement and Absorption

Small Intestine

• Food takes approximately 5 hours to travel from the duodenum to the ileum.
• Peristalsis and weak peristaltic action help in mixing and absorption.

Large Intestine

• Horseshoe-shaped, extends from ileum to anus,
• Major functions include reabsorption of water and absorption of vitamins.
• Stores fecal material before defecation.
• Contains normal flora.

Anatomy of the Large Intestine

Ileocecal Valve and Cecum

• Ileocecal valve controls food entry from ileum to large intestine.
• Cecum is a pouch that begins moisture removal and compaction.

Colon

• Ascending, transverse, descending, and sigmoid colons.
• Flexures: Hepatic, splenic, and sigmoid flexures.

Rectum and Anus

• Rectum stores fecal matter temporarily.
• Anal canal ends with anal orifice.
• Internal and external anal sphincters control defecation.

Absorption and Enzymatic Activity

• Reabsorption of water, bile salts, and vitamins.
• Vitamins absorbed include Vitamin K, Biotin, and Pantothenic Acid.
• Organic waste processing by intestinal bacteria.

Nutrient Processing

• Carbohydrates, lipids, and proteins are broken down enzymatically.
• Absorbed nutrients can be used for ATP production, cellular building, and secretion.

Protective Mechanisms

• High presence of goblet cells for mucus production.
• Immune cells present to prevent pathogen entry.

Structural Support

• Mesenteries such as lesser omentum, greater omentum, and mesentery proper hold organs in place.

Digestive Regulation

• Nervous system and hormonal control.
• Local mechanisms within organs regulate digestion.
• Example: coffee can stimulate digestive system awakening.