Nutrition and Digestion in Humans

Nutrients are substances in food that provide energy, promote growth and repair, and regulate body processes. There are six main classes of nutrients.

These are the body's primary source of energy. They are found in foods like bread, pasta, rice, potatoes, fruits, and sweets. Carbohydrates can be simple (sugars) or complex (starch, fibre). Fibre is important for healthy digestion.

Proteins are essential for growth, repair of body tissues, and the production of enzymes and hormones. They are made up of smaller units called amino acids. Good sources include meat, fish, eggs, dairy, and beans.

Fats provide a concentrated source of energy, insulate the body, protect organs, and help absorb fat-soluble vitamins. They are found in oils, butter, nuts, and fatty meats.

Vitamins are organic compounds needed in small amounts to regulate various body processes and maintain health. They are categorised as fat-soluble (A, D, E, K) or water-soluble (B vitamins, C).

Minerals are inorganic elements required for various body functions, such as bone formation (calcium), oxygen transport (iron), and nerve function. They are found in a variety of foods.

Water is vital for life. It acts as a solvent, transports nutrients and waste, regulates body temperature, and is involved in many chemical reactions.

Digestion is the process of breaking down large, complex food molecules into smaller, simpler molecules that can be absorbed into the bloodstream and used by the body's cells.

This is the physical breakdown of food into smaller pieces, increasing its surface area for chemical digestion. Examples include chewing in the mouth and churning in the stomach.

This is the chemical breakdown of large food molecules into smaller, absorbable molecules using digestive enzymes. For example, starch is broken down into glucose, and proteins into amino acids.

The digestive system is a long tube, called the alimentary canal, with associated accessory organs. Food passes through the alimentary canal, while accessory organs produce substances that aid digestion.

Ingestion of food. Mechanical digestion (chewing by teeth) and chemical digestion (saliva containing amylase enzyme begins starch breakdown).

A muscular tube that transports food from the mouth to the stomach through wave-like muscle contractions called peristalsis.

Muscular sac where food is churned (mechanical digestion) and mixed with gastric juice. Gastric juice contains hydrochloric acid (kills bacteria, provides optimum pH for enzymes) and pepsin enzyme (begins protein digestion).

The primary site for chemical digestion and absorption of nutrients. It is very long and coiled, with an inner surface covered in tiny finger-like projections called villi, which increase the surface area for absorption. It has three parts: duodenum, jejunum, and ileum.

Absorbs water from the remaining indigestible food matter and compacts it into faeces. It includes the colon and rectum.

The opening through which faeces are expelled from the body (egestion).

Produces bile, which emulsifies fats (breaks large fat globules into smaller ones) in the small intestine, aiding fat digestion.

Stores and concentrates bile produced by the liver.

Produces digestive enzymes (e.g., amylase for carbohydrates, lipase for fats, protease for proteins) that are released into the small intestine. It also produces hormones like insulin.