Biology 3602A/B Lecture Notes - Lecture 23: Pancreatic Duct, Common Hepatic Duct, Pancreas

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5 Aug 2016
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Chyme travels into the s.i., the duodenum specifically, directly downstream from the stomach
Duodenum receives chyme from the stomach, which is acidic since the stomach secreted HCl,
and also getting secretions from the pancreas
Pancreas we think of as an endocrine organ, but now we look at it as an exocrine organ; one of
the things it secretes is bicarbonate to neutralize the acidity
Enzymes will denature from the acidity, so we need bicarbonate
Also secretes enzymes
Duodenum also receives secretions from the liver; liver secretes bile, stored in the gall bladder,
and from there bile is released into the hepatic duct, into the duodenum
Within the duodenum, you’ll get starches, glycogens, and they can be digested into disacchs by
salivary or pancreatic amylase (diff proteins but work in similar ways)
Closeup view of what the pancreas is doing
There are diff cell types here:
Duct cells synthesize the NaHCO3 solution, which goes to the pancreatic duct into the
duodenum
Acinar cells secrete digestive enzymes go through the pancreatic duct also and into the
duodenum
Endocrine cells (contained in islets of Langerhans) creates hormones such as insulin and
glucagon which go into the bloodstream NOT into the pancreatic duct
Starch has been broken down into disacchs
What happens to the disacchs?
The midgut (jejunum + ileum) has a lot of folds/SA, and if we take a closeup of the folds, there
are finger-like projections called villi
Villi are covered by a lot of cells that has blood vessels and also lymphatic vessels
On the villi are many cells, one of which is the enterocyte for absorption and digestion
Enterocyte has a basolateral membrane and an apical membrane sticking out into the lumen of
the gut
On the apical membrane there are a lot of small folds called microvilli to further increase SA
Bound to the microvilli, facing into the lumen, are disaccharide-digesting enzymes
E.g. if we break down glycogen or starch into the disacch of glucose, which is called maltose,
the maltase bound to the enterocyte microvilli will break that down into 2 glucose molecules
Protein digestion
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