Human Digestive System Overview

Essential Functions

• Ingestion: Intake of food.
• Digestion: Breakdown of large biomolecules into building blocks.
• Absorption: Nutrient uptake by the body, delivering nutrients to cells.
• Elimination: Expulsion of undigested substances, clearing waste.

Ingestion

• Begins when food enters the mouth.
• Saliva release can be triggered by thought of food.

Digestion

Chemical and Mechanical Digestion

• Chemical Digestion: Enzymes in saliva (e.g., salivary amylase) start breaking down carbohydrates.
• Mechanical Digestion: Physical breakdown of food by teeth.
• Saliva Functions: Contains enzymes, neutralizes acidity, lubricates food, forms bolus.

Protection Mechanisms

• Epiglottis: Prevents food from entering the windpipe, avoiding choking.
• Peristalsis: Wave-like muscle contractions moving bolus down the esophagus.

Stomach

• Holds ~2 liters of food/liquid.
• Chemical Digestion: Acidic gastric juices (HCl, pepsin) break down proteins.
• Mechanical Digestion: Stomach muscles churn contents into chyme.
• Sphincters:
  • Lower Esophageal Sphincter: Prevents backflow into esophagus.
  • Pyloric Sphincter: Controls passage to small intestine.

Small Intestine

Sections

• Duodenum: Chemical digestion with pancreatic enzymes and bile.
• Jejunum: Absorption of nutrients via villi.
• Ileum: Absorption of vitamin B12, bile salts, fat-soluble vitamins (A, D, E, K).
• Mnemonic: Digestive Juices Intake (Duodenum, Jejunum, Ileum).

Large Intestine

Segments

• Ascending Colon: Absorbs water/salt.
• Transverse Colon: Stores digested food, further absorption.
• Descending Colon: Moves solid waste towards rectum.
• Mnemonic: Ascending Absorbs, Transverse Transports, Descending Drives Down.

Elimination

• Rectum: Stores feces until expulsion.

Accessory Organs

• Liver: Produces bile for lipid breakdown.
• Gallbladder: Stores bile.
• Pancreas: Produces digestive enzymes and neutralizes acidic chyme.

Hormones and Enzymes

• Gastrin: Stimulates gastric glands for protein digestion.
• Cholecystokinin (CCK): Stimulates gallbladder and pancreas for digestion.
• Secretin: Regulates pH by controlling gastric acid and bicarbonate.
• Insulin: Facilitates glucose uptake, lowers blood sugar.
• Glucagon: Raises blood glucose by breaking down glycogen.
• Bile: Emulsifies fats for easier digestion.

Additional Resources

• For further study and exam preparation, resources are available at NurseChunStore.com.