Exocrine Pancreas

Question 1

composition of pancreatic juice

Answer 1

1) water
2) solutes
• Inorganic components
- sodium
- bicarbonate
- chloride

• organic components
Enzymes
- proteolytic
- lipolytic
- amylolytic
-trypsin inhibitor
Mucin

Question 2

functions of pancreatic juice

Answer 2

1. pancreatic secretion contains enzymes that help in digestion of fat, protein and carbohydrate:
   A. for lipid digestion
   • pancreatic lipase - hydrolyses neutral fat into fatty acids and monoglycerides.
   • cholesterol esterase - hydrolysis of cholesterol esters
   • phospholipase - splits FA from phospholipids

B. for protein digestion
• trypsin, chymotrypsin - breaks down proteins into peptides
• carboxypolypeptidase - splits some peptides into individual amino acids

C. for carbohydrate digestion
• Pancreatic amylase - hydrolyses starches, glycogen, and other carbohydrates (except cellulose) to disaccharides and a few triglycerides

Question 3

secretion of pancreatic juice

Answer 3

Although the enzymes of the pancreatic juice are secreted entirely by the acini of the pancreatic glands, the other two important components of pancreatic juice, bicarbonate ions and water, are secreted mainly by the epithelial cells of the ductules and ducts that lead from the acini.

The basic steps in the cellular mechanism for secreting sodium bicarbonate solution into the pancreatic
ductules and ducts are:

1. Carbon dioxide diffuses to the interior of the cell from the blood and, under the influence of carbonic anhydrase, combines with water to form carbonic
   acid (H2CO3). The carbonic acid in turn dissociates into bicarbonate ions and hydrogen ions (HCO3− and
   H+). Then the bicarbonate ions are actively transported in association with sodium ions (Na+) through the luminal border of the cell into the lumen of the
   duct.
2. The hydrogen ions formed by dissociation of carbonic acid inside the cell are exchanged for sodium ions through the blood border of the cell by a secondary active transport process. This supplies the sodium ions (Na+) that are transported through the luminal border
   into the pancreatic duct lumen to provide electrical neutrality for the secreted bicarbonate ions.
3. The overall movement of sodium and bicarbonate ions from the blood into the duct lumen creates an osmotic pressure gradient that causes osmosis of water also into the pancreatic duct, thus forming an almost completely isosmotic bicarbonate solution.

Question 4

regulation of pancreatic secretion

Answer 4

Three basic stimuli are important in causing pancreatic secretion:

1. Acetylcholine, which is released from the parasympathetic vagus nerve endings and from other cholinergic
   nerves in the enteric nervous system
2. Cholecystokinin, which is secreted by the duodenal and upper jejunal mucosa when food enters the small intestine
3. Secretin, which is also secreted by the duodenal and jejunal mucosa when highly acidic food enters the small intestine

The first two of these stimuli, acetylcholine and cholecystokinin, stimulate the acinar cells of the pancreas, causing production of large quantities of pancreatic digestive enzymes but relatively small quantities of water and electrolytes to go with the enzymes. Without the water, most of the enzymes remain temporarily stored in the acini and ducts until more fluid secretion comes along to wash them into the duodenum.

Secretin, in contrast to the first two basic stimuli, stimulates secretion of large quantities of water solution of sodium bicarbonate by the pancreatic ductal epithelium

phases of pancreatic secretion
1. Cephalic Phase:
• mediated by the vagus nerve. (through acetylcholine)
• contributes to 20% of pancreatic secretion
• rich in enzymes. small amount of water and electrolytes.

2. Gastric phase:
   • Another 5-10% of pancreatic enzymes
3. Intestinal phase:
   • when chyme enters the duodenum
   • secretion becomes copious due to secretin.
   • it is also needed for neutralization of acidic chyme

or

Hormonal factors:

1. CCK
2. Secretin
3. Gastrin
4. GRP
5. GIP
6. VIP

Neural factors:

1. parasympathetic: stimulates secretion
2. sympathetic: Inhibitory secretion

Question 5

pancreatic function tests

Answer 5

classification

1. Direct tests
2. Indirect tests (requiring intubation of the duodenum)
3. Indirect Tests (tubeless tests)

Direct tests
• Secretin test
• Cholecystokinin (CCK) test
• Combined secretin and CCK test

Question 6

Cholecystokinin

Answer 6

CCK is a polypeptide hormone. it is secreted from i cells located in upper small intestine in response to fatty foods

It has two receptors: CCK A and CCK B

1. cholecystokinin A receptors are mainly located in the peripheral structures like gall bladder, pancreas, GI tract, etc
2. Cholecystokinin B receptors are present in central structures like brain areas.
3. Cholecystokinin acting on both receptors activates membrane phospholipase C and stimulates production of intracellular IP3 and DAG. IP3 and DAG increase cytosolic calcium concentration.
4. Cholecystokinin increased pancreatic secretion rich in enzymes.