Secretions lecture 2

Question 1

Secretory Cells

Answer 1

Villi: absorptive enterocytes and mucus secreting goblet cells
Intestinal glands: enterocytes secreting isotonic fluid, enters-endocrine cells, paneth cells
Brunner’s glands in duodenum only

Question 2

Intestinal Juice

Answer 2

1.2 L

Contains electrolytes and water (from enterocytes), lysozyme (Paneth cells), mucus, and alkaline mucus

Question 3

Pancreatic structure

Answer 3

Exocrine pancreas secretes pH 8 secretions and digestive enzymes
99% exocrine acinar clusters: pancreatic juice
1% endocrine pancreatic islets - alpha, beta, delta, F cells

Question 4

Pancreatic Enzymes

Answer 4

Proteolytic - secreted in inactive form
Amylase - hydrolyses starch to di/tri saccharides
Lipases
Nucleases - digest RNA and DNA to nucleic acids
Trypsin inhibitor prevents activation of trypsin to prevent pancreatic digestion

Question 5

Activation of Proteolytic enzymes

Answer 5

Produced as inactive precursors: zymogens
Small intestinal brush border enterokinase enzyme cleaves hexapeptide to form active trypsin from trypsinogen
Trypsin cleaves and activates other proteolytic enzymes
Process prevents pancreatic autodigestion

Question 6

Duct secretion of Sodium Bicarbonate

Answer 6

H+ stimulates secretin
Secretin stimulates HCO3- rich pancreatic juice
Secretion into duct lumen is via Cl-/HCO3- exchange at apical membrane
Cl- recycled out cell via CFTR Cl- channel under secretin stimulation via cAMP
Na+ secreted transcellularly into duct lumen following HCO3- secretion down electrochemical gradient, then water follows

Question 7

Secretory rate

Answer 7

unstimulated - low secretion rate
stimulated - higher secretion rate and rise in HCO3- from ductal cells inversely related to reduced conc of Cl- in pancreatic juice
At all rates, pancreatic is isotonic with plasma

Question 8

Regulation of pancreatic juice secretion

Answer 8

Ach, vaso-vagal gastro-pancreatic reflex, gastrin, secretin, CCK

Question 9

What is pnacreatitis

Answer 9

Inflammatory disease - autodigestion of tissues

Causes: gallstones and alcohol abuse

Question 10

Role of bile

Answer 10

Digestion and absorption of fats

Elimination of waste produces - heme to bilirubin, cholesterol and drugs

Question 11

Synthesis of bile

Answer 11

Synthesised by hepatocytes

Bile drains into the blind ended canaliculi and into bile duct for storage in gall bladder or drainage to duodenum

Question 12

What do liver duct epithelial cells to to bile

Answer 12

Add water, Na+, HCO3- to increase bile volume

In response to secretin

Question 13

What does the gall bladder do to bile

Answer 13

Concentrates

Water and electrolytes are reabsorbed across gall bladder mucosa to concentrate bile salts, bilirubin and cholesterol

Question 14

Regulation of bile secretion

Answer 14

CCK - gall bladder contraction, Sphincter of Oddi relaxation
Secretin - liver ductal secretion of HCO3- and H2O
Vagal and enteric Ach stimulation - bile flow and gall bladder contraction

Question 15

Enterohepatic circulation - bile salt reabsorption

Answer 15

Bile salts secreted into bile and continuously recycled through active reabsorption in ileum
94% salts return via portal vein to drive bile synthesis in liver

Question 16

Gallstones caused by

Answer 16

Excessive water and bile salt reabsorption from bile
Excessive cholesterol in bile - precipitation (high fat diet)
Inflammation of epithelium (low grade chronic infection)