Digestive system

The digestive system
Mouth
1. Mastication (chewing of food) occurs where food is broken up into pieces that are more easily digestible.
2. Salivary glands secrete saliva into the mouth which provides lubrication and acts as a buffer.
Oesophagus
1. Receives food from the mouth and passes it into the stomach by a series of contractions called peristalsis.
Stomach
1. The stomach has many functions:
a. It is used a storage tank due to the folds in the stomach, it can expand and store up to 2-4 litres of food. This is important as we eat food faster then we can digest it into nutrients.
b. The stomach can churn and mix water and the gastric juice within it to produce a think mixture called chime.
c. The stomach can break food down food physically and chemically. The hydrochloric acid which is secreted by the parietal cells unfolds proteins that are present in the stomach and also kill any bacteria that we may have digested along with our food. Chief cells secrete pepsin in an inactive form called pepsinogen. HCl converts pepsinogen into pepsin and protein digestion in the stomach begins.
Small intestine
1. Mechanical digestion occurs by segmentation which mixes the enzymes (from the pancreas and small intestine) and chyme together.
2. Chemical digestion occurs by enzymes which are present and theybreak down all four food groups (polysaccharides, fats, proteins and nucleic acids) into their component molecules. The bile from the liver emulsifies any fats present into smaller fat globules
3. The small intestine is the primary location for absorption
4. Peristalsis moves the chyme along the small intestine.
Pancreas
1. Secretes pancreatic juices which contains enzymes which are secreted into the duodenum and break down all four food groups.As the fluid secreted is alkaline, it neutralizes any acidity that may be present in the chyme so that the enzymes can function.
Liver and Gall bladder
1. Bile is produced in the liver which consists of bile salt, bile pigments (mostly bilirubin), cholesterol, phospholipids and electrolytes. The excess bile is stored in the gall bladder is released in response to chyme being present.
Large intestine
1. Contractions of the muscle walls form segmentations which mix and move the contents further along.
2. Absorption of water happens
3. Mucus is produced by goblet cells for lubrication.
4. Bacteria present digest the remiaing nutrients and produce vitamin K and B which are then absorbed.
5. The remaining undigestible materials are removed from the body as feces.