T1 L8 Secretions of liver, intestines, gallbladder & pancreas Flashcards

Question

What is the mechanism for secretion by the pancreas?

Answer 1

1) Pancreatic enzymes synthesised as inactive proenzymes on ribosomes 2) Transferred into rough ER 3) Move to Golgi complex 4) Form acidic condensing vacuoles 5) Released as zymogen granules 6) Fusion & exocytosis of zymogen granules

Answer 2

Neural or hormonal stimulus causes zymogen granules to move to apical membrane. Fuse with plasma membrane & express their contents into the luminal space by exocytosis Works with intracellular second messenger

Answer 3

Agonists such as: CCK (cholecystokinin) Acetylcholine Secretin

Answer 4

Acetylcholine - binds muscarinic receptors on acing cells. Vasoactive intestinal peptide that increases blood flow & gastrin Cholecystokinin - major agonist released from duodenal I cells when food enters duodenum. Responds to fats, monoglycerides, fatty acids & phenylalanine & tryptophan

Answer 5

Secretin - released by S cells in the duodenum. S cells are stimulates by a low pH as the food enters. Enters blood via duct cells.

Answer 6

pH is rarely low enough to stimulate high levels of secretion CCK & Ach potentiate the action of secretin

Answer 7

1) Na+/k+ pump creates inward directed Na+ gradient across basolateral membrane 2) Na+/K/Cl cotransporter produces net Cl- uptake, driven by Na+ gradient 3) Rise in intracellular K+ results from pump & cotransporter gets shunted by basolateral K+ channels that provide exit pathway for K+. 4) Intracellular accumulation of Cl- establishes electrochemical gradient that drives Cl- secretion into acinar lumen through apical membrane Cl- channels 5) Movement of Cl- into lumen makes the transepithelial voltage more negative, driving Na+ into the lumen via tight junctions

Answer 8

1) Cl- is recycled from the lumen into the cell via CFTR channel 2) Na+ is secreted into the duct lumen 3) Water follows by osmosis to produce a fluid secretion

Answer 9

Ionic composition of pancreatic juice depends on the rate of secretion Greater the rate of secretion the greater the HCO3- levels & the lower the Cl- levels In unstimulated state - flow is low & electrolyte composition is similar to that of plasma In stimulated state - flow rate increases & rise in bicarbonate in the secondary secretion is matched by a reciprocal decline in Cl- ion

Answer 10

Lack of a functional Cl- channel in the luminal membrane resulting in defective ductal fluid secretion Ducts become blocked with precipitated enzyme & mucus which impairs secretion of needed pancreatic enzymes for digestion Pancreas undergoes fibrosis

Answer 11

Oral pancreatic enzyme supplements taken with each meal

Answer 12

Cephalic - 20% Gastric - 10% Intestinal - 70%

Answer 13

Sight, smell, taste of food trigger action potentials Stimulates preganglionic fibres to transmit action potentials to postganglionic fibres Acetylcholine increases primary secretion from acing cells Acetylcholine increases bicarbonate secretion from the duct cells into the intercalated ducts

Answer 14

Peptones in stomach Antrum stimulate gastrin release from G cells. This increases acing secretion. Increase in gastrin release from G cells via vagal peptidergic, postganglionic efferents that stimulate pancreatic acing cells to increase secretion of enzymes via CCK receptor Gastric distention - vago-vagal reflex

Answer 15

Duodenal S cells to increase secretions of secretin, which increases HCO3- secretions from duct cells Monoglycerides, fatty acids & amino acids induce CCK release from duodenal I cells Lipids & proteins trigger vago-vagal reflex that increases pancreatic juice secretions

Answer 16

Zymogens are made in the inactive form Cellular sequestration of zymogens in the membrane-limited vesicles throughout synthesis to the point of exocytosis to avoid contact with acinar cell cytoplasm Activation of zymogens in the small intestine Process depends on conversion of proenzyme trypsinogen to trypsin Pancreas produces trypsin inhibitor to prevent activation of zymogens within pancreas

Answer 17

Pancreatic enzymes are activated within pancreas & surrounding tissue leading to auto digestion of the tissue Epigastric pain radiating from epigastrium to back & is often relieved by leaning forwards Most common causes are gender specific: Gallstones in women Alcohol in men

Answer 18

Provides alkali to neutralise gastric acid Provides bile salts to facilitate absorption of fats Acts as vehicle for the excretion of blood cell breakdown components

Answer 19

Promote emulsification & solubilisation by forming mixed micelles These enhance lipase action & assist in the delivery of digestive products to be absorbed by enterocytes

Answer 20

1) Secreted by hepatocyte canaliculus 2) Undergoes modification in bile ducts 3) Concentrated & stored in gallbladder 4) Excreted into duodenum

Answer 21

Water Ions Bilirubin & biliverdin Bile salts - synthesised from cholesterol

Answer 22

Bile-acid dependent fraction | Bile-acid independent fraction

Answer 23

Made from hepatocytes when sufficient bile acids are available for secretion. Come from cholesterol metabolism which generates cholic acid & chenodeoxycholic acid. Conjugated with taurine or glycine & Na+ to make water-soluble bile salts that are secreted from hepatocytes. In the intestine a small amount of secondary bile acids are formed by bacteria converting a small amount of primary acids.

Answer 24

Produced by duct epithelium by the secretion of water & electrolytes

Answer 25

Minor role of vagus | Major role is from CCK, which is released from the duodenum in the presence of fatty & acidic chyme

Answer 26

Circuit where solutes are secreted by the liver & returned to the liver via intestinal reabsorption

Answer 27

1) Molecules are secreted into the bile by hepatocytes 2) Delivered to the small intestine via the biliary tract 3) Reabsorbed from the small intestine 4) Returned to the liver via the portal venous system to become available again for uptake & secretion by hepatocytes

Answer 28

Bile acid pool isn't large enough to assimilate the lipid content of a typical meal Bile salts & acids are recycled twice each meal & 6-8 times per day 95% of the bile salts that arrive in the intestine are reabsorbed Deconjugated bile salts revert to bile acids

Answer 29

Most are undissociated & reabsorbed by simple diffusion in the jejunum Most primary & secondary bile salts are reabsorbed via Na+ bile salt cotransport when they reach the distal ileum Small amount of bile acid is lost in faecal excretion each day

Answer 30

1) Hepatocytes secrete bile into canaliculi 2) Canaliculi join together & convey hepatic bile toward small terminal ductules at the periphery of liver lobules 3) Bile moves through a sequence of progressively larger ducts in each lobe of the liver & emergences in a hepatic duct 4) Hepatic ducts from each lobe join to form common hepatic duct 5) Cystic duct from gallbladder joins common hepatic duct to form common bile duct

Answer 31

``` Bile salts Bile pigments Cholesterol Lecithin Mucus Electrolytes Isotonic pH ```

Answer 32

Acid-dependent fraction contains bile pigments Excretory function Breakdown of haemoglobin in the spleen produces insoluble bilirubin Hepatocytes conjugate bilirubin & excrete it via bile

Answer 33

It gets covered to urobilinogen for recirculation & excretion via the kidneys. The remainder is lost in the faeces

Answer 34

Accumulation of bilirubin in the blood Impaired uptake by hepatocytes Failure to conjugate bilirubin Seen in hepatitis & cirrhosis

Answer 35

Sac found on underside of the liver Around 10cm long 500-1000ml bile secreted daily from the liver Gallbladder stores & concentrates bile

Answer 36

Haemoglobin breakdown | Intestinal bacteria convert to urobilinogen - brown colour

Answer 37

Common Occurs in several forms from asymptomatic cholelithiasis to biliary colic Different areas of the biliary tract can be involved

Answer 38

Blockage of cystic duct with associated infection of the gallbladder

Answer 39

Blockage of common bile duct

Answer 40

Blockage of common bile duct with associated infection of the bile duct