Human Digestive System Overview

Introduction

• Focus on the gastrointestinal system.
• Essential GI functions: ingestion, digestion, absorption, elimination.

Functions of the Digestive System

Ingestion

• Intake of food.
• Initiated in the mouth.

Digestion

• Breakdown of biomolecules into building blocks.
• Chemical digestion: Enzymatic breakdown.
  • Saliva contains enzymes like salivary amylase for carbohydrates.
• Mechanical digestion: Physical breakdown of food by teeth.

Absorption

• Nutrients absorbed by the body.
• Deliver nutrients to cells through cooperation with bodily systems.

Elimination

• Expulsion of indigestible substances.

Digestive Process Details

Mouth

• Food intake and initial digestion.
• Saliva roles: digestion, lubrication, protection against acidity.
• Formation of boli for swallowing.

Esophagus

• Peristalsis: Wave-like muscle contractions moving bolus to stomach.
• Epiglottis: Prevents food from entering the trachea.

Stomach

• Capacity: ~2 liters of food and liquid.
• Highly acidic environment for chemical digestion (HCL, pepsin).
• Mechanical digestion through muscle churning.
• Formation of semi-liquid mixture, chyme.
• Sphincters:
  • Lower esophageal sphincter: Prevents reflux into esophagus.
  • Pyloric sphincter: Controls passage to small intestine.

Small Intestine

• Site of digestion completion and nutrient absorption.
• Sections: duodenum, jejunum, ileum.

Duodenum

• First, shortest segment following stomach.
• Chemical digestion aided by pancreatic enzymes and bile.
• Absorbs iron and minerals.

Jejunum

• Middle section; primary absorption site.
• Villi increase surface area for nutrient absorption.

Ileum

• Final section; absorbs vitamin B12, bile salts, fat-soluble vitamins (A, D, E, K).

Large Intestine

• Segments: ascending colon, transverse colon, descending colon.

Ascending Colon

• Absorbs water and salts.

Transverse Colon

• Storage site; continues absorption of water and salts.

Descending Colon

• Carries solid waste towards rectum.

Elimination

• Rectum: Final segment where feces are stored.
• Expulsion through anus.

Accessory Organs

• Liver: Produces bile for lipid breakdown.
• Gallbladder: Stores bile.
• Pancreas: Produces digestive enzymes and bicarbonate.

Key Hormones and Enzymes

Gastrin

• Stimulates gastric glands to secrete digestive juices.

Cholecystokinin (CCK)

• Stimulates gallbladder contraction and pancreatic enzyme secretion.

Secretin

• Regulates pH by stimulating bicarbonate production.

Insulin

• Facilitates glucose uptake; lowers blood sugar.

Glucagon

• Raises blood glucose by converting glycogen to glucose.

Bile

• Emulsifies fats for enzyme access.

Conclusion

• Focus on understanding the GI system functions and anatomy for exams.
• Additional resources available for study support.