Digestive system

Oesophagus-

Carries food from the mouth to the stomach. It is therefore adapted to transport rather than for digestion or absorbtion. It is made uo from a thick muscular wall. 

Stomach-

A small muscular sac with an inner layer that produces enzymes. It has lots of folds, allowing the stomach to expand.

The entrance and exit of the stomach are controlled by sphincter muscles.

The stomach walls produce gastric juice, which helps break down food. Gastric juice consists of hydrochloric acid (HCl), pepsin (enzyme) and mucus. Pepsin hydrolyses proteins into smaller peptide chains. It only works in acidic conditions (provided by the HCl).

Peristalsis of the stomach turns food into an acidic fluid called chyme.

Small intestine-

It is a long muscular tube.

Food is further digested in the small intestine by enzymes that are produced by its walls and by glands that pour their secretions into it

The inner walls of the small intestine are folded into villi which gives them a large surface area. The surface area of the villi is further increased by millions of tiny projections, called microvilli, on the epithelial cells of each villus. This adapts the small intestine for its purpose of adsorbing the products of digestion into the bloodstream.

Large intestines-

The large intestines absorbs the most water. Most of the water that is reabsorbed comes from the secretions of the many digestive glands.

The food within the large intestines therefore becomes drier and thicker inconsistency and forms faeces.

Rectum-

The rectum is the final section of the intestines. The faeces are stored here before periodically being removed via the anus in a proce** called egestion.

Physical breakdown- If the food is large, it is broken down into smaller pieces by the teeth. Providing a large surface area for chemical digestion. Food is churned by the muscles in the stomach wall.

Chemical breakdown- Chemical digestion breaks down large, insoluble molecules into smaller soluble ones. It is carried out by enzymes. All digestive enzymes function by hydrolysis.

Hydrolysis- The splitting up of molecules by adding water to the chemical bonds that hold them together.

The different types of digestive enzymes:

• Carbohydrases- break down carbohydrates to monosaccharides.
• Lipases- break down lipids into glycerol and fatty acids
• Proteases- break down proteins into amino acids.

Assimilation- The smaller soluble molecules being absorbed into the small intestines into the blood. They are carried to the different parts of the body and built up again into large molecules and incorporated into body tissue and used in processes in the body.