The Digestive System

Vocabulary flashcards detailing key anatomical structures, enzymes, chemical reactions, and mechanical processes of the human digestive system.

Digestion

The breakdown of food—converting carbohydrates to sugars, fats to fatty acids and glycerol, and proteins to amino acids—into forms that can be absorbed by cells in the body.

Six basic activities of digestion

1. Ingestion of food and water; 2. Mechanical digestion of food; 3. Chemical digestion of food; 4. Movement of food along the alimentary canal; 5. Absorption of digested food and water into blood and lymph; 6. Elimination of unabsorbed material.

Mechanical digestion (oral cavity)

The physical breakdown of food into smaller pieces by the teeth, increasing its surface area to volume ratio ($\text{SA:VOL}$).

Teeth

incisors, canines, molars and premolars responsible for biting, cutting, and slicing food in the oral cavity, Pointed teeth specialized for tearing food during mechanical digestion, Broad, flat teeth designed for crushing and grinding food.

Salivary amylase

An enzyme contained in saliva(squirted whilst chewing) that chemically converts starch (a polysaccharide) into maltose (a disaccharide).

Bolus

A rounded lump of food formed by the tongue after chewing, prepared to be swallowed down the pharynx and oesophagus.

Epiglottis

A flap of skin that lowers to cover the entrance to the trachea and block the larynx when food is being swallowed.

Swallowing reflex

An involuntary reflex response initiated as soon as food touches the back of the pharynx (back of the throat).

Muscle layers of the oesophagus

Two muscular coats: circular muscle (with fibres arranged around the oesophagus) and longitudinal muscle (with fibres arranged along its length).

Peristalsis

Waves of circular muscle contraction along the oesophagus that push food down toward the stomach.

Cardiac sphincter

A one-way muscular valve at the junction between the oesophagus and stomach that closes once food enters the stomach.

Stomach retention time

Food stays in the stomach between $2$ to $6\text{ hours}$; meals high in carbohydrate exit sooner, while meals high in fat stay longer.

Mucosa (stomach)

The stomach wall membrane containing gastric pits and gastric glands that secrete gastric juices.

Chyme

The semi-fluid acidic mixture of gastric juices, food, and saliva formed in the stomach.

Pepsin

A gastric digestive enzyme, activated from pepsinogen in acidic conditions, that breaks down proteins into peptides.

Hydrochloric acid ($HCl$)

A component of gastric juice that creates acidic stomach conditions to activate pepsinogen and breaks food into smaller particles.

Gastric lipase

A stomach enzyme that breaks down fats into fatty acids and glycerol.

Gastric mucus lining

A thick protective layer that shields the stomach wall from digestive juices; it prevents absorption of most nutrients while allowing absorption of alcohol and aspirin.

Muscle layers of the stomach

Three specialized muscular layers—circular muscle, longitudinal muscle, and oblique muscle—that produce churning waves to mechanically digest food and mix it with gastric juices. (churning is mechanical)