Digestion

These cards cover digestion and the digestive tract.

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Stages in Digestion

Ingestion - taking large pieces of food into the body

Digestion - breaking down the food by mechanicall or chemical means i.e. chewing, enzymes (mouth, stomach)

Absorbtion - taking up the soluble products of digestion (small intestine)

Assimilation - using the absorbed materials (glucose in respiration)

Egestion - eliminating the undigested materials

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The ailimentary Canal

Mucosa - sectretes digestive juices, folded into villi to increase S.A.

Submucosa - contains blood vessels and lymph vessels. Also secretes digestive enzymes.

Muscle layer - made up of circular and longitudinal smooth muscle. Moves muscle through the ailimentary canal via peristalsis.

Serosa - tough connective tissue which holds the gut together and attatches it to the abdomen.

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Mouth

Teeth and tounge physically break food into small pieces, to increase S.A and form a ball of food which can easily be swallowed.

The salivary glands secrete saliva, which contains - water, mucus, lysosomes and amylase

Water dissolves soluble substances.

Mucus for lubrication

Lysosomes to kill bacteria

Amylase partially digests starch

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Oesophogus

Connects the mouth to the rest of the gut.

Glands secrete mucus to lubricate the foods passage down.

Food is moved down by peristalsis (an involuntary muscle contraction)

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Stomach

This is an expandable bag where food is churned up into a liquid called chyme.

Gastric pits in the stomach release gastric juice, ehich contains - HCl, mucus and pepsin.

HCl kills bacteria.

Mucus lines the epithelium to protect it from the acid.

Pepsin digests proteins.

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Small intestine - Duodenum

Pancreatic juice secreated from the pancrease contains enzymes ( carbohydrase, protease, and lipase)

Bile, secreated by the liver stored in the gall bladder, contains bile salts to help with lipid digestion, and sodium hydrogen caronate to neutralise the HCl.

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Small intestine - illeum

Mucosa and sub mucosa secrete more enzymes, mucus and sodium hydrogen carbonate.

The S.A i increased by folds called villi and also cells with microvilli. These increase the rate of absorbtion.

The illeum is extremely long, which increases S.A. for the absorbtion of food.

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Large Intestine - Colon

Water is absorbed from the undigested materials to form semi-solid faeces. This is then pushed towards the anus via peristalsis, where it is released by the anul sphincter in excretion.

Mucus is secreted in the colon to lubricate the foods movement along the colon.

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