The Human Digestive System and Its Functions

Digestive System

The human digestive system (also called the alimentary canal) is a long muscular tube where food is broken down mechanically and chemically, absorbed into the bloodstream, and waste is expelled.

Mouth

Where digestion begins.

Teeth

Break food down mechanically (chewing).

Salivary glands

Release amylase, which begins the chemical digestion of starch into maltose.

Tongue

Rolls food into a bolus for swallowing.

Oesophagus

Muscular tube connecting the mouth to the stomach.

Peristalsis

The process by which food is moved through the digestive system using waves of muscular contraction.

Stomach

Muscular sac that churns food mechanically and secretes protease enzymes (e.g. pepsin) to digest proteins into smaller peptides.

Hydrochloric acid

Produced in the stomach to kill bacteria and provide the correct pH (around 2) for enzymes.

Pancreas

Produces a range of digestive enzymes including amylase, protease, and lipase.

Small Intestine

Made up of two sections: duodenum (where enzymes complete digestion) and ileum (where absorption of digested food occurs).

Duodenum

First part of the small intestine; where enzymes complete digestion.

Ileum

Second part of the small intestine; where absorption of digested food occurs.

Villi

Finger-like projections that line the walls of the ileum, adapted for absorption.

Large Intestine

Includes the colon and rectum; absorbs water and forms solid faeces.

Colon

Absorbs water and forms solid faeces.

Rectum

Stores faeces until egestion through the anus.

Amylase

Enzyme that breaks down starch into maltose.

Maltase

Enzyme that breaks down maltose into glucose.

Proteases

Enzymes that break down proteins into amino acids.

Lipases

Enzymes that break down lipids into fatty acids and glycerol.

Bile

Produced by the liver and stored in the gall bladder; neutralises stomach acid and emulsifies lipids.

Lacteal

A lymph vessel in the villi that absorbs lipids.