lecture_notes_33_(ta)

Lecture_notes_33(ta - Lecture 33 Gastrointestinal/Digestive Physiology III Pancreas and Liver provide secretions that mix with the contents of the

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Lecture 33: Gastrointestinal/Digestive Physiology III Pancreas and Liver - provide secretions that mix with the contents of the duodenal lumen. ( BOTH ARE CRITICAL FOR PROPER DIGESTIVE FUNCTION ) Pancreas - located behind and below the stomach. The pancreas is a mixed gland that contains both exocrine and endocrine tissue. (Figure 16-18) Exocrine portion – contains 2 cell types ( acinar cells and duct cells ( RELEASES SODIUM BICARB ) ): (1) Acinar cells – release 3 types of enzymes ( proteolytic enzymes ( CONTINUE PROTEIN DIGESTION ) , pancreatic amylase ( CARBOHYDRATE DIGESTION IN SI) , and pancreatic lipase ( FAT DIGESTION ) ): (1) Proteolytic enzymes are important for protein digestion. The 3 major types of proteolytic enzymes are 1) trypsinogen , 2) chymotrypsinogen , and 3) procarboxypeptidase . Each of these is released as an inactive form that is not activated until it reaches the duodenum (to prevent self digestion). Enterokinase – an enzyme in luminal border of the duodenum that converts trypsinogen into trypsin (active form). Trypsin can then autocatalytically trigger further conversion. ( EXAMPLE OF POSITIVE FEEDBACK ) Trypsin inhibitor – is a substance in the pancreas that blocks trypsin in case trypsinogen inadvertently converts to trypsin prematurely ( TO AVOID AUTODIGESTION ” ) Trypsin converts - chymotrypsinogen into chymotrypsin - procarboxypeptidase into carboxypeptidase ( THESE ARE BOTH PROTEIN DIGESTING ENZYMES ) (2) Pancreatic amylase is important for carbohydrate digestion. Pancreatic amylase is secreted as an active form because active amylase can not injure secretory cells. (3) Pancreatic lipase is important for fat digestion. It is the only enzyme secreted in the digestive tract that can digest fat. (2) Duct cells – that release sodium bicarbonate (NaHCO 3 ). All of the pancreatic enzymes work best in an alkaline environment. Duct cells contribute to neutralizing the acidic chyme by releasing sodium bicarbonate
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(NaHCO 3 ). ( RAISE P H, AWAY FROM ACIDIC END ) Endocrine portion - pancreatic secretions are hormonally regulated (Figure 16- 19) Chyme
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This note was uploaded on 05/02/2008 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Winter '08 term at UC Davis.

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Lecture_notes_33(ta - Lecture 33 Gastrointestinal/Digestive Physiology III Pancreas and Liver provide secretions that mix with the contents of the

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