Digestion #1 Topic 6.1

The Stomach Hydrochloric acid lowers the pH to around two killing and denaturing proteins. Pepsin begins protein digestion. Muscular actions aid mechanical digestion. Stretch receptors in the muscular wall triggers release of enzymes.

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Muscular wall contract for mechanicaldigestion and mixing enzymes withfood.

Gastric pits release gastric acid, protective mucus and enzymes.Muscular sphincters control entry of Food exit of chyme.

Lumen: space in which food is storedWhile in the stomach

The Small Intestine The small intestine completes digestion of food molecules. Chyme enters the duodenum (1st section). Bile from the gall bladder and liver is emptied into the duodenum, neutralizing the acid and emulsifying fats. Pancreatic enzymes are released (amalayse and trypsin) . Enzymes are further released into the jejunum.

The ileum is the last section of the smallintestine. Here, absorption of digested foodmolecules takes place. Villi (finger-like projections) increase the surface area for absorption and have a rich blood supply.

A wave of muscular contractions (peristalsis)keeps the mixture of digested and undigestedfood moving through the intestine.

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The Large Intestine Once absorption takes place in the ileum, undigested food is pushed into the large intestine. The job the of large intestine is to reclaim as much water as possible to the blood, before allowing egestion of solid faeces.

The large intestine (colon) maximizes surfaceArea for absorption of water by being longAnd folded. Mucus is secreted to lubricateThe passage of fecaes and muscle contractionsKeep the fecaes moving.

A diet rich in fibre helps clear out waste productsAnd dead cells, reducing the risk of colon cancer.

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Absorption and AssimilationDigestion breaks down large food molecules into smaller molecule. Absorption is the uptake of these molecules into the bloodOnce in the blood, they carried to the tissues where they are assimilated—taken and to be used.

Absorption into the blood (or lacteals)

Transport

Assimilation

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