Biology - Digestion

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  • Created by: tolulah
  • Created on: 29-11-15 16:22


Digestion is the breakdown of large, insoluble food molecules into small, water-soluble molecules using mechanical and chemical processes. Starch, proteins and fats are insoluble - they are broken down into soluble substances so they can be absorbed into the bloodstream through the wall of the small intestine.

In the large intestine, much of the water mixed with food is absorbed into the bloodstream. The indigestible food which remains makes up the bulk of the faeces. (Faeces leaves the body via the anus)


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Functions of digestive organs

Mouth - Where foods enters digestive system (ingestion). Once in the mouth, the food is chewed to form a bolus. This passes down the oesophagus and into the stomach.

Salivary glands - Amylase is produced here to catalyse breakdown of starch to sugar (maltose) in mouth.

Oesophagus - Food is transported through the oesophagus to the stomach by a process called peristalstis, where muscles produce wave-like contractions to push food through gut

Liver - Produces bile, which is stored in the gall bladder before being released into the small intestine. Bile neutralises acid that was added to food in stomach, and provides alkaline conditions for the small intestine's enzymes. It also emulsifies fats to increase surface area over which lipase enzymes can work. Also detoxifies chemicals and metabolises drugs.

Gall bladder - This is where bile made in the liver is stored until it is released into the small intestine

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Functions of digestive organs

Stomach - Where food is broken down and digested to extract nutrients.  Stomach produces hydrochloric acid which kills bacteria and provides right pH for protease (pepsin).

Pancreas - Produces digestive enzymes: amylase, protease and lipase which are used in small intestine. Also monitors and controls glucose concentration in blood and produces insulin.

Small intestine - Where digested food undergoes absorption. Most absorption happens in the ileum (longest part of small intestine). The small intestine has a large surface area for fast and efficient absorption. It has many villi (small, finger-like structures) which increase surface area. They have many important features, as they are one cell thick (allows for shorter diffusion/active transport time), have a blood capillary network (to transport sugars and amino acids) and a lacteal (to transport glycerol and fatty acids).

Large intestine - Where water from undigested food molecules is absorbed, leaving semi-solid waste called faeces.

Rectum - Where faeces is stored until it is egested

Anus - Where egestion occurs and faeces are allowed to pass out of sphincter

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Digestive enzymes

Enzymes can break down nutrients into small, soluble molecules that can be absorbed.

  • Amylase (starch to sugar)

Produced in: salivary glands, pancreas, small intestine

Used in: mouth, small intestine

  • Protease (proteins to amino acids)

Produced in: stomach, pancreas, small intestine

Used insmall intestine

  • Lipase (lipids to fatty acids and glycerol)

Produced in: pancreas, small intestine

Used in:small intestine

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