Pancreatic exocrine secretions and control

Question 1

What is the exocrine portion of the pancreas?

Answer 1

Acinar and Duct Cells

Question 2

What is the endocrine portion of the pancreas?

Answer 2

Islets of Langerhans

Question 3

What is the role of acinar cells?

Answer 3

Secrete digestive enzymes (stimulated by CCK) to break down fats, carbohydrates, proetins and nucleic acids

Question 4

What ius the role of duct cells?

Answer 4

Secrete aqueous NaHCO3 solution (stimulated by secretin)

Question 5

Describe the Flow of pancreatic juice.

Answer 5

Ascini (cluster of ascinar cells) contain microvilli that extend into smallest ducts caused the intercalated ducts.

Intercalated ducts lead onto intralobular ducts, lined by cuboidal epithelial cells.

Intralobular ducts lead onto interlobular ducts lined by columnar epithelium and goblet cells.

Interlobular ducts lead onto the pancreatic duct, which enters the duodenum at common bile duct.

Question 6

What happens to pancreatic juices as they flows through the ducts?

Answer 6

Their composition may be changed

Question 7

Describe the composition of pancreatic juices.

Answer 7

1.5L fluid produced a day containing:

• Na+
• HCO3-
• Albumin
• Globulin
• Digestive Enzymes

Question 8

In what form are pancreatic enzymes secreted?

Answer 8

Secreted in an inactive form as zymogens to prevent autodigestion

Question 9

Where are pancreatic enzymes activated?

Answer 9

Duodenum

Question 10

What ions are secreted in the pancreatic juices?

Answer 10

HCO3-
Cl-
SO42-
HPO42-

Na+
K+
Ca2+
Mg2+

Question 11

What is pancreatic fluid secreted by if rate of secretion is low?

Answer 11

Intralobular ducts

Question 12

What effect does secretin have on the pancreas?

Answer 12

Increases output of pancreatic juice rich in bicarbonate ions

decreases output of pancreatic juice rich in chloride ions

also fall in amylase

Question 13

What enzymes are secreted from the pancreas?

Answer 13

3 major types of enxzymes released:

• Proteolytic Enzymes (trypsin, chymotrypsin, carboxypeptidase)
• Amylase
• Lipase

Other enzymes:

• ribonucelase
• deoxyribonuclease

Question 14

What are proteolytic enzymes?

Answer 14

Enzymes that break down proteins

these enzymes are secreted as zymogens to prevent autodigestion

Question 15

How is trypsinogen activated?

Answer 15

Converted to trypsin by enterokinases within the brush border of the duodenum

Question 16

What is the role of amylase?

Answer 16

Enzyme that breaks down carbohydrates, converting polysaccharides to disacchardies

Question 17

What is the role of lipases?

Answer 17

Enzymes that break down lipids, converting triglycerides to fatty acids and glycerol

Question 18

What will pancreatic insufficiency of lipase cause?

Answer 18

lead to malabsorption of fat, causing steatorrhoea

Question 19

What is the Percentage of secreted enzymes that reach the small intestine?

Answer 19

Amylase- 75%
Trypsin- 20%
Lipase- 1%

Question 20

Describe the control of pancreatic secretion.

Answer 20

Neuroendocrine signals

Vagal parasympathetic stimulation
-enhances rate of secretion of enzymes and aqueous components of pancreatic juice

Sympathetic stimulation
-inhibits secretion

Secretin and CCK
-stimulate secretion of pancreatic fluid (enzyme and bicarbonate rich secretion)

Question 21

What are the phases of pancreatic secretion?

Answer 21

1. cephalic phase
2. gastric phase
3. intestinal phase

Question 22

What is the cephalic phase of pancreatic secretion?

Answer 22

Sight/smell food causes vagal stimulation (Ach and VIP) of gastrin release from antrum, which promotes protein rich pancreatic juice

Question 23

What is the Gastric Phase of pancreatic secretion?

Answer 23

Distension causes vagal reflex on fundus or antrum and amino acids/peptides stimulate gastrin release, which promotes enzyme rich pancreatic juice

Question 24

What is the Intestinal Phase of pancreatic secretion?

Answer 24

Under influence of CCK and Secretin, where acidic chyme in the duodenum and jejunum induces secretion of pancreatic juice

Question 25

What are secretin and CCK released by?

Answer 25

Duodenal and jejunal mucosal cells

Question 26

What cells does secretin induce?

Answer 26

Secretin induces pancreatic duct cells to secrete HCO3- rich pancreatic juice Secretin also stimulates production of bile by the liver

Question 27

What cells does CCK induce?

Answer 27

CCK stimulates pancreatic acinar cells to synthesize and release enzyme rich pancreatic juice Also stimulates secretion of concentrated bile from gallbladder for fat absorption by contracting gallbladder and relaxing Sphincter of Oddi to release bile into duodenum

Question 28

What is the effect of cystic fibrosis on the pancreas?

Answer 28

Thick mucus obstructs pancreatic duct, causing pancreatic insufficiency. Consequences are: - severe malabsorption - steatorrhoea - recurrent chest infections - sterility of males (vas deferens fails to develop properly)