Flashcards in Small Intestine Deck (27)
what is the small intestine the main site for?
digestion and absorption
what are the 3 parts of the small intestine?
-duodenum – approx. 30 cm
-jejunum – approx. 3.5 m
-ileum – approx. 2.5 m
what does the small intestine receive?
-chyme from stomach
(via the pyloric sphincter)
-pancreatic juice from pancreas
-bile from gall bladder
(both via the sphincter of Oddi)
what does the small intestine secrete?
what does the small intestine move?
Moves remaining residues to the large intestine via the ileocaecal valve
what increases the surface area of the small intestine?
-circular folds (of Kerckring)
-microvilli (the brush border)
what does the small intestine secrete into the blood from endocrine cells within thew mucosa?
what do these peptide hormones do?
-act on G-protein coupled receptors
what are the control mechanisms of secretions in the small intestine?
Distension/irritation, gastrin, CCK, secretin, parasympathetic nerve activity (all enhance), sympathetic nerve activity (decreases)
what does excessive activity of small intestine cause?
what is segmentation?
-“chopping” moves chyme back and forth – very vigorous after a meal (little / none between meals)
-Alternating contraction and relaxation of segments of circular muscle
what initiates segmentation?
small intestine pacemaker cells causing the BER which is continuous. At threshold activates segmentation which in the duodenum is primarily due to distension by entering chyme
what triggers segmentation in the empty ileum?
gastrin from the stomach (gastroileal reflex)
why is the net movement aboral?
Duodenum has frequent segmentation contractions (12 per min), ileum has fewer (9 per min)
what effect does parasympathetic and sympathetic activity have on strength of segmentation?
parasympathetic - enhanced
sympathetic - decreased
what are the two activities that occur in the interdigestive ,or fasting state?
-a few localised contractions
-The migrating motor complex (MMC)
Describe the migrating motor complex (MMC)?
-occurs between meals every 90-120mins
-strong peristaltic contraction passing length of the intestine (stomach ileocaecal valve)
-clears small intestine of debris, mucus and sloughed epithelial cells between meals – ‘housekeeper function’
-inhibited by feeding and vagal activity
-triggered by motilin, suppressed by gastrin and CCK
what are the endocrine pancreatic secretions?
-insulin and glucagon - secreted to blood
what are the exocrine pancreatic secretions?
digestive enzymes (acinar cells), aqueous NaHCO3- solution (duct cells) – secreted to the duodenum collectively as pancreatic juice
what do pancreatic duct cells secrete?
secrete 1 – 2 litre of alkaline (HCO3- - rich) fluid into the duodenum per day
what do duct cells do?
-Neutralises acidic chyme entering the duodenum :
-provides optimum pH for pancreatic enzyme function
-protects the mucosa from erosion by acid
Describe duct cell secretions.
Sodium potassium ATPase – keeps intercellular sodium at a lower value- driving force for sodium to enter cells
-Carbonic anhydrase uses metabolic co2 and water to make carbonic acid (unstable and dissociates into proton and bicarbonate anion) – proton is coupled with sodium inward
-Bicarbonate is is exchanged with chloride, bicarbonate emerges in apical membrane in exchange for chloride but chloride can be recycled , using chloride channel
-Aqueous component of pancreatic juice- is full of bicarbonate
-By neutralizes acid, bicarbonate deactivates pepsin in the chyme protecting mucosa from erosin via acid and pepsin
when are pancreatic enzymes released?
enzymes stored in zymogen granules and released in response to elevated [Ca2+]
Name the proteases.
-procarboxypeptidase A and B
what state are the proteases in the granules?
inactive until they are released from acinar cells which activates trypsin which digests proteins
what enzymes are active in the granules?