Lecture 6: Secretions of the Small Intestine and Accessory Organs Flashcards
what are the secretions of the small intestine and what do they contain
- intestinal juice (HCO3- and mucus)
- pancreatic juice (digestive enzymes)
- bile (bile salts)
what are the hormones secreted by the small intestine
- secretin
- cholecystokinin
- glucose dependent insulinotrophic peptide (GIP)
what are the secretory cells in the villi
- absorptive enterocytes
- goblet cells
what are the secretory cells in the intestinal glands
- enterocytes secreting isotonic fluid
- entero-endocrine cells
- paneth cells
what are the secretory cells in the duodenum only
Brunner’s glands, which secrete mucus and HCO3-
how quick is epithelial cell turnover
3-6 days
CCK secretion and effect
- I cells
- stimulate pancreatic and gallbladder secretion
secretin secretion and effect
- S cells
- stimulate pancreatic and biliary bicarbonate secretion
GIP secretion and effect
- K cells
- may inhibit acid secretion / stimulate insulin release
what clusters does the pancreas consist of
- 99% exocrine acinar clusters
- 1% endocrine pancreatic islets (islets of langerhans)
what do the exocrine acinar clusters secrete
pancreatic juice containing:
- water
- electrolytes
- sodium bicarbonate
- proenzymes
what do the endocrine pancreatic islets secrete
- glucagon
- insulin
- somatostatin
- pancreatic polypeptide
what do the acinar cells secrete and what do the ducts secrete
acinar: - enzymes - NaCl - fluid duct: - NaHCO3 - fluid
what are the acinar secretions regulated by
- acetylcholine
- cholecystokinin triggered by chyme containing fat and protein products
what are the ductal secretions regulated by
secretin triggered by H+ in highly acidic chyme
what enzyme activates proteolytic enzymes and where is it found
- enterokinase enzyme
- in small intestinal brush border
how is Cl- recycled out of the pancreatic cell
- CTFR chloride channel
- under secretin stimulation
- via cAMP
what is the composition of pancreatic juice with a low secretion rate
electrolyte content similar to that of plasma
what is the composition of pancreatic juice with a high secretion rate
- high in HCO3-
- low Cl-
what happens in cystic fibrosis
- dysfunctional CFTR channel
- ducts become blocked with precipitated enzymes and mucus
- pancreas undergoes fibrosis
- impaired secretion of digestive enzymes
- malabsorption
- patients given oral pancreatic enzyme supplements during meals
what happens in pancreatitis
- pancreatic enzymes are activated within the pancreas
- autodigestion
- most common causes are gallstones and alcohol abuse
which waste products does bile eliminate
- bilirubin
- cholesterol
- drugs
where is bile produced and stored
- produced by hepatocytes
- stored in gallbladder
what are the 3 overall causes of jaundice
- prehepatic
- hepatocellular / congenital
- posthepatic
what happens in pre-hepatic jaundice
- excessive rbc breakdown
- buildup of unconjugated bilirubin
- eg due to haemolytic anaemia
what happens in hepatocellular jaundice
- altered hepatocyte function
- eg Crigler-Najjar syndrome
- absence of enzyme glucoronyl transferase, which normally conjugates bilirubin
- results in increased unconjugated bilirubin
what happens in post-hepatic jaundice
- obstruction to normal bile drainage
- eg due to gallstones
- build up of conjugated bilirubin
what is involved in regulation of bile secretion
- cholecystokinin
- secretin
- minor role of acetylcholine
when is cholecystokinin released and what effect does it have on bile secretion
- released in response to fat content of duodenum
- results in gall bladder contraction
- sphincter of oddi relaxation
when is secretin released and what effect does it have on bile secretion
- released in response to acidic chyme
- results in liver duct secretion of bicarbonate rich watery secretions
what effect does acetylcholine have on bile secretion
- increased bile flow
- increased gallbladder contraction
what are the common causes of gallstones
- excessive water and bile salt reabsorption from bile
- excessive cholesterol in bile (due to high fat diet)
- inflammation of the epithelium
