Digestion

A few brief notes on the digestive system

Sources;

The Usbourne Illustrated Dictionary of Science,

Edexcel IGCSE Biology

My own notes from lessons

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Digestive System

Food is ingested through the mouth. Digestion breaks down the food and the substances are absorbed into the blood vessels around the system and transported to the body's cells.

Pharynx: A cavity at the back of the mouth where the mouth cavity and the nasal cavities meet. When food is swallowed the soft palate closes thes the nasal cavities and the epiglotiss closes the trachea. 

Oesophagus: A tube which the swallowed food travels down to the stomach. Diagram on p294 of The illustrated dictionary. 

The Cardiac Spincter: A ring of muscle between the oesophagus and the stomach which relaxes and opens to let the food through.

The Stomach: PH1 or 2 (HCl) kills the bacteria which travelled in the bolus from the mouth. Pepsin begins the digestion of protein into Polypeptides. 

Liver: The largest organ. It regulates the amount of glucose in the blood. Destroys worn-out red blood cells, stores vitamins and iron and makes important blood proteins.

Pancreas: A large gland which produces pancreatic juices and enzymes. The enzymes are released into the small intestine:

Amylase- Starch -> Maltose, protease - protein, amino acids lipase - fats -> fatty acids + glycerol (p338) 

Phloric Sphyincter: Muscular ring between the stomach and the small intestine which relaxes to let the bolus through only if it has undergone certain digestive changes.

Small intestine: Made up of three parts; The Duodenum, Jejunum and the Ileum.  Contains Villi meaning there is a larger surface area to absorb the food. A LACTEAL (lymph vessel) absorbs fat particles. The remaining semi-liquid waste is passed onto the large intestine.

The Large Intestine: absorbs remaining water and leaves a semi-solid mass called FAECES which is pushed out of the body through the rectum, **** canal and ****. This is called Egestion.

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