Human Digestion Process

Study Notes

Digestion begins in the alimentary canal where food needs to be broken down into smaller molecules for absorption.
Enzymes, biological catalysts, play a crucial role in this process; for example, salivary amylase in saliva breaks down starch into simple sugars.
Food is mixed with saliva and mechanically processed in the mouth, facilitated by the muscular tongue.
The alimentary canal's lining contains muscles that contract rhythmically, aiding in the movement of food through peristaltic movements.
Food travels from the mouth to the stomach via the oesophagus.

The stomach, a large organ, expands upon food entry and mixes it thoroughly with digestive juices.
Gastric glands in the stomach walls release hydrochloric acid, pepsin (a protein-digesting enzyme), and mucus.
Hydrochloric acid creates an acidic environment that enhances pepsin's activity, while mucus protects the stomach lining from acid damage.
The sphincter muscle at the stomach's exit regulates the release of food into the small intestine.

The small intestine, the longest part of the alimentary canal, varies in length among animals, adapted to their diets.
Herbivores have longer small intestines to digest cellulose, while carnivores have shorter intestines for digesting meat.
Complete digestion of carbohydrates, proteins, and fats occurs in the small intestine with assistance from liver and pancreatic secretions.
Bile juice from the liver neutralizes stomach acidity and emulsifies fats into smaller globules, facilitating enzyme action.
Pancreatic juice contains enzymes like trypsin (for proteins) and lipase (for fats) that further aid digestion.
Intestinal glands secrete intestinal juice, which converts proteins into amino acids, carbohydrates into glucose, and fats into fatty acids and glycerol.

In organisms like Paramecium, food intake occurs at specific spots, aided by cilia movement across the cell's surface.

The alimentary canal functions as a continuous tube from mouth to anus, with specialized regions for different digestive processes.
Physical food processing involves crushing and wetting to generate uniform particle sizes, enhancing ease of movement through the digestive tract.
Saliva, which contains enzymes and fluids, plays a role in preparing food for digestion, triggered by the sight or thought of appetizing food.