SI Flashcards
three sections
duodenum, jejunum, ileum
duodenum
curves round the head of the pancreas, secretions from the gall bladder and pancreas merge into the hepatopancreatico-ampulla which enter the duodenal papilla. This is guarded by a smooth muscle rung - hepatic-pancreatic sphincter
ileum
terminal section, ends at the ileoceacal valves, controlling flow, preventing back flow
how is it attached
with the stomach at the pyloric sphincter becomes the LI via the ileocaecal valves
what processes occur
chemical digestion is completed
absorption occurs
what absorb fat
lacteals, transporting them along lymph vessels to the thoracic duct where it enters circulation
describe the peritoneum layer
double layer of peritoneum - mesentery attaches to the jejunum and the ileum to the posterior abdominal wall. The attachment creates a fan shape
the large blood vessels and nerves lie on the posterior abdominal wall and branches to the SI pass between the two mesentry layers
mucosal layer
large surface area, with circular folds, villi and microvilli, the circular folds are permanent so don’t smooth out when distended, promoting the mixing of chyme
villi composed of columnar epithelium with microvilli on their free birder throughout the enterocytes are goblet cells interspersed.
capillary network is formed and central lymph capillary
where does the final stages of digestion take place
in the enterocytes before entering the capillaries
what are the intestinal glands
simple tubular glands which are found below the villi, the epithelium migrate up to form the villi walls replacing the cells at the tips which have been rubbed off by the intestinal contents
during migration the epithelial cells produce digestive enzymes which lodge themselves in the microvilli with the intestinal juice.
where are LN found
irregular intervals
solitary lymphoid follicles, are small
at the distal end there is aggregated lymphatic follicles (20 or 30 larger nodes- PEYERS PATCHES)
packed defensive cells which neutralise ingested antigens
functions
peristalsis; para-sympathetic increases waves
intestinal juice secretions via PS
chemical digestion is completed in the enterocytes
protection against microbes by solitary and aggregated follicles
secretion of cholecystokinin and secretin
absorption of nutrients
pancreatic juice
secreted by the endocrine pancreas, enters at the duodenal papilla
slightly alkaline due to the bicarbonate ions
pancreatic lipase and amylase optimum is 8
stimulated by secretin and CCK
acid chyme stimulates hormone production
PJ consists of
water
mineral salts
enzymes: lipas, amylase, nuclease
inactive enzyme precursors: trypsinogen, chymotrypsinogen
protein digestion
trypsinogen and chymotrypsinogen are activated by enterokinase (in microvilli) coverting them into active form, which breaks down proteins to AA
