BIOLOGY-the digestive system

one long tube called thegut

if unravelled-about 9 metres long!

begins with teeth, ends with anus

normally takes food 24-48 hours to pass through digestive system

mouth-contains teeth that begin digestion by breaking up food

salivary glands-secrete amylase which is a carbohydrate enzyme-mucus lubricates the food as it passes down the oesophagus

stomach-has muscular walls which churn up the food and mix it with the gastric juices that the stomach produces

gastric juices-contain protease enzymes and hydrochloric acid

hydrochloric acid-provides tha acidic conditions for a protease enzyme called pepsin to work

rectum-where the faeces are stored before they leave the body via the anus

samall intestine-also produces all three types of enzymes-where digestion is completed and dissolved food is absorbed into the bloodstream-the inner surface is covered in tiny finger-like projections called villi

large intestine-recieves any food that has not been absorbed into the blood.excess water and salts are removed from the food. the remaining solid food turns into faeces.

pancreas-produces carbohydrase, protease and lipase enzymes

gall bladder-is where the bile is stored until it is released into the small intestine via the bile duct.

liver-produces bile, which neuralises stomach acid and helps break down fat.

oesophagus- sometimes called the gullet

the small intestine is where the digested food is absorbed into the blood

the small intestine is well designed for absorption

it has a thin lining, a good blood supply and a very large surface area

the large surface area is provided by the villi (single-villus) that extend from the inside of the small intestine wall

the wall of a villus is only one cell thick

it contains a network of cappillaries

blood arriving at the villus to pick up food molecules

the products of protein digestion(amino acids) and carbohydrate digestion (glucose) are absorbed into the capillaries

the products of fat digestion (fatty acids and glycerol) are absorbed into the lacteal

blood leaving the villus, taking the food molecules to the rest of the body

digestion is the breaking down of large, insoluble molecules into small soluble molecules so that they can be absorbed into the bloodstream through the small intestine wall

the large, insoluble molecules are starch(carbohydrates), protein and fat

this action is speeded up (catalysed) by enzymes

enzymes in the small intestine are also found throughout the digestive system

food is moved through the digestive system by the action of muscles in the gut wall. this is called peristalsis.