secretion 2 Flashcards
gallbladder versus liver bile
gall bladder is essentially a concentrated liver bile the mechanism for control is the absorbtion of water, sodium and chloride which leads to a concentrating of bile salts cholesterol, lecithin and bilirubin
cholesterol and lecithin are solubilixed by bile salts
Volume goes from 500 to 50 ml
Cholesterol homeostasis
Hepatic and extrahepatic synthesis= .8g/day
dietarry cholesterol= .2 g/day
input=fecal output
Bile salts
cholesterol is hydroxylated in the liver, to make cholic and chenodeoxycholic acid primary bile acids. in the intestines bacteria further dehydroxylate to deoxycholic acid and litholeic acid and the secndary bile acids are reabsorbed by the liver and are conjugated to glycine and taurine, where they make bile salts.
Bile salts- function to emulsify and decrease surface tension and breaks fat globules into smaller size particles forms micelles (soluble in chyme) and helps absorption of fat breakdown products (FA, MGs, cholesterol
Gallbladder contraction and emptying
bile acids via blood stimulate parenchymal secretion from liver. Secretin stimulates liver ductal secretion. Bile stored in gallbladder. CCK causes gallbladder contractionand relaxation of sphincter of oddi. Vagal timulation causes weak contraction of gall bladder
CCK: fatty foods in duodenum results in release of CCK, gallbladder emyptys within an hour
Secretin: acts on biliary epithelium to produce sodium bicarb to neutralize acids for pancreatic function
gallstones
due to too much absorption of water from bile, too much absorption of bile acids from bile, too much cholesterol, inflammation. Pancreatitis secondary to gall stones. No correlation between amylase or lipase elevation and the severity of acute pancreatitis
Pancreatic insufficiency
Chronic pancreatitis is the most common cause (alcohol). affects both exocrine and endocrine functions
Bilirubin metabolism
macrophages in the spleen break down old RBCs and produce bilirubin from broken down heme. The inderect bilirubin travels into the plasma and binds to albumin making a bilirubin-albumin adduct. UDP glucoronidase in the liver hepatocyte attaches bilirubin to glucoridine. The bilirubin can go then directly into systemic circulation from the hepatocyte and eventually end up in the urine as urobilin OR it can travel in the bile duct from the hepatocyte into the intestine as Urobilinogen. From the intestine it has two paths, first it can end up in th feces (as stercobilin) or in the portal blood where it can go into the systemic circulation and end up in urine as urobilin
elevated indirect (unconjugated) bilirubin- due to increased breakdown of RBC, inability of bilirubin-albumin to be taken up by hepatocytes, inability of hepatocytes to conjugate bilirubin, hepatocyte dysfunction
elevated direct bilirubin- due to biliary obstruction
Small intestine secretions
Brunner’s gland in the duodenum secrete alkaline mucos (protection)
Produced in response to- tactile or irritating stimuli, vagal stimulation, secretin
inhibited by sypathetic stimulation
Crypts of lieberkuhn- contain goblet cells that secrete mucus, and enterocytes that secrete water and electrolytes (1800 ml/day pH 7.5-8)
Peptidases on villi surface break down polypeptides into amino acids
Disaccharides are broken into monosaccharides by sucrase, maltase, isomaltase and lactase
Large intestine secretion
the small intestines have crypts and villi, the large intestines only have crypts
Crypts of lieberkkuhns without villi- for mucus secretion, protects mucosa from excoriation and acid damage, pack stool, antibacterial products
Parasympathetic innervation through pelvic nerves stimulate mucus production
