the tube via which food passes through the body - from mouth to anus, its lining is the surface in which nutrients are absorbed
order : mouth cavity, pharynx, oesophagus, liver, stomach, smallintestine, largeintestine
Ingestion occurs at mouth
food is chewed in a process called mastication
Chemical and mechanical digestion commence before food is swallowed
Pharynx is the back of mouthcavity. the tongue moves backwards and upwards to swallow, pushing food into pharynx
Wall of alimentary canal has double layer of muscle :
circular - smooth muscle with fibres arranged in a circle around the organ
longitudinal - smooth muscle with fibres arranged lengthwise along an organ
Peristalsis is waves of muscularcontraction that push food along the alimentary canal
oesophagus is the tube that carries food from the pharynx to the stomach (23 - 25 cm long). as food enters, the circularmuscle behind it contracts to narrow the tube, peristalsis moves the food and is assisted by the secretion of mucus that lubricates inner lining
the liver produces bile
Mucosa is the mucousmembrane that lines the alimentary canal
Mucosa in the stomach is specialised to secretegastricjuice by gastric glands located in gastricpits which are narrow, tube-like structures
Gastricjuice is the digestivejuice secreted by the glands of the stomach. it contains hydrochloricacid, mucus and digestiveenzymes; each being secreted by different types of cells in the gastricpit
pH in the stomach is approximately 2-3 due to the hydrochloricacid. it allows enzyme pepsinogen to convert into pepsin, its active form. cells lining stomach are protected by layer of mucus.
Nutrients are not absorbed into the bloodstream through the stomach because of the thick layer of mucus. however alcohol and other drugs are.
Thickening of circularmuscle at lower end of stomach creates constriction called pyloric sphincter, a ring of smoothmuscle between the stomach and the duodenum which prevents stomach contents moving through unless pushed along by peristalsis
the small intestine is the longest part (6 - 7 metres), but has a small diameter. it receives materials pushed through the pyloricsphincter
the small intestine has three regions :
Duodenum - first part: it is the shortest section at about 25cm, extending from the bottom end of the stomach in a curve around the pancreas. This is where most chemical digestion occurs
Jejunum - middle section: its lining allows for effective absorption of carbohydrates and proteins
Ileum - final part: where vitamin B12, bilesalts and remaining products of digestion are absorbed
the large intestine is 1.5 meters long with a large diameter
large intestine parts :
Caecum - 6cm long. it is the pouch where the small intestine joins to large intestine
Appendix - a small tube attached to caecum
Colon - the longest part with an invertedUshape
Rectum - the last part. semi-solid material is pushed through by peristalsis. As walls stretch, they trigger defecation, relaxing muscles around anus to let faeces out
Anus - the externalopening at end of rectum. Analsphincter is the circularmuscle around anus
the large intestine contains no villi and does not secrete digestivejuices, but its lining does secrete a large amount of mucus
in the largeintestine, most of the water is absorbed, making contents solid. Some bacteria also produce vitamins which is absorbed through walls. Mineralnutrients are also absorbed
faeces is made of water, undigestedfoodmaterial (particularly cellulose), bacteria, bilepigments (gives colour), cells that have broken away from internallining. it passes through the rectum and anus to the exterior