Human Digestive System Overview

Oral Cavity

• Food is ingested
• Teeth mechanically break down food, increasing surface area for enzyme action.

Carbohydrate Digestion

• Carbohydrate digestion begins in the oral cavity by enzymes secreted from the salivary glands.
• Amylase is used in this process.

Oral Cavity to Esophagus

• The oral cavity connects to the esophagus

Esophagus

• Connects the mouth to the stomach
• Peristaltic action moves digested food (bolus) to the stomach
• No digestion occurs here

Stomach

• Mechanical digestion (churning) increases the surface area of food.
• Gastric glands secrete gastric juice containing enzymes and hydrochloric acid (HCl).
• Mucus lining protects the stomach from HCl.
• Protein digestion begins here.

Small Intestine

• Carbohydrate, protein, and lipid digestion are completed.
• Accessory organs (liver, gallbladder, pancreas) secrete enzymes into the small intestine for chemical digestion.

Liver

• Produces bile to aid in the emulsification of fat in the small intestine.
• Emulsification breaks down large fats into smaller fats.

Gall Bladder

• Stores bile and secretes it into the small intestine.

Pancreas

• Located near the stomach
• An exocrine gland that secretes proteases to break down proteins into amino acids and lipases to break down lipids into fatty acids and glycerol.

Nutrient Absorption

• End products of digestion are absorbed in the small intestine by villi.
• Villi are finger-like projections that increase surface area for absorption.

Absorption in the Villi

• Lacteal absorbs fatty acids and glycerol into the lymphatic system.
• Capillary network absorbs glucose and amino acids into the circulatory system.

Large Intestine

• Water absorption only (no digestion)
• Habitat for helpful bacteria that digest and produce vitamins.
• Passes feces to the rectum for storage before egestion through the anus.

Anus

• Opening through which feces leave the body (egestion).