Digestive system notes

6.1.4 draw and label a diagram of the digestive system

6.1.5  outline the functions of the stomach, small intestine and large intestine

stomach

• the wall of the stomach is grandular, secreting mucus, hydrochloric acid and protease
• hydrochloric acid creates very acid conditions that kill bacteria in food that has been swallowed. To avoid food poisoning.
• Acid conditions denature proteins and suit protein digestion by hydrolysis protease secreted in the stomach ( pepsin) begins the process by breaking up polypeptides into shorter chains of amino acids
• The wall of the stomach is elastic ( large meals can be swallowed quickly, stored and then gradually released in the small intestine)
• The wall of the stomach is muscular and contracts rthymically to squeeze the food, mixing it and breaking it into smaller lumps

Small intestine

• pancreatic juice is secreted into the small intestine containing protease, amlyse and lipase so the three main groups of macromolecules
• the wall of the small intestine secretes variety of other enzymes which digest other substances. Nucleases; secreted to digest DNA and RNA in foods. Because of the great length of small intestine, food spends hours passing through
• digested foods are absorbed by the small intestine
• areas in the wall of the small intestine ( peyers patches) contain lymphocytes that detect pathogenic organsims in the food in small intestine and help on production of antibodies against them
• contains villi used for food absorption

large intestine

• moves material not digested from small intestine and absorbs water; produces feces and egests them through the anus

6.1.6  distinguish between absorption and assimilation

- absorption occurs when food enters the body as food molecules pass through a layer of cells into body tissues; in the small intestine which has many villi suitable for absorption

• assimilation: food molecules become part of the bodies tissues; after they have been resembled in a form suitable to body tissues.

6.1.7 explain how the structure of villus is related to its role in absorption and transport of the products of digestion

villi are ( 0.5 – 1.0 mm long – as many as 50 of them per square)

• villi increase surface area of absorption
• their outermost tissue is a single layer of epithelium cells, which are permeable to digested foods
• they have a dense network of blood capillaries; close to epithelium so that the distance substances have to travel to reach the blood system after absorption is very small. Capillary walls consist of a single layer of thin cells; with pores between adjacent cells these have larger pores; allowing more rapid entry of foods
• branch of lympathetic system in the centre ( lacteal) absorbs lipoprotein droplets; which aren’t absorbed into blood capillaries; formed from absorbed fatty acids and glycerol carries fats away after absorption
• protusions of the exposed part of the plasma membranes of epithelium cells increase surface area for absorption; these projections are called microvilli
• protein channels in microvilli membranes allow rapid absorption of foods by facilitated diffusion and pumps allow rapid absorption by active transport
• mictochondria in epithelium cells provide ATP needed for active transport