Salivary glands, Oesophagus, Stomach, Pancrease
Salivary Glands: Situated near the mouth. They pass their secretions via a duct into the mouth.These secretions contain the enzyme amylase,which breaks down starch to maltose.
Oesophagus: This carries food from the mouth to the stomach. It is adapted for transport, it has a very thich muscular wall.The food moves down by peristalsis.
Stomach: This is a muscular sax with an inner layer that produces enzymes.Its role is to store and digest food,especially proteins.Glands in the stomach wall produce mucus, this mucus prevents the stomach being digested by its own enzymes.
Pancreas: Large gland positioned below the stomach.It produces pancreatic juice.This juice contains proteases to digest proteins, amylase to digest starch and lipase to digest lipids.
Small intestine, Large intestine, Rectum
Small Intestine: Long musuclar 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 are folded into villi, which increases the surface area.
Large Intestine: This part absorbs the water,meaning that any food in the large intestine becomes drier and thicker.This forms faeces.
Rectum: This is the final section of the intestines. The faeces are stored here before being periodically removed via the anus.
If the food is too large, it is broken down into smaller pieces by means of structures such as the teeth. This not only makes it possible to ingest the food, but also provides a large surface area for chemical digestion.
Chemical: Chemical digestion breaks down large, insoluble molecules into smaller, soluble ones. This is carried out by enzymes.All digestive enzymes function by hydrolysis. This is when molecules are split up by adding water to the chemical bonds that hold them together.There are different enzymes that break down different things. These are:
Carbohydrases break down carbohydrates to monosaccharides.
Lipases break down lipids into glycerol and fatty acids.
Proteases break down proteins to amino acids.
The molecules that are absorbed( the ones listed above) are carried to different parts of the body and are often built up into large molecules again. However,these are not necessarily of the same type as the molecules from which they were derived, These molecules are incorporated into body tissues and/or used in processes within the body.This is called assimilation.