PHYS: Pancreatic Secretion

Question 1

What are the two components of exocrine pancreas secretion?

Answer 1

Aqueous component

Enzyme component

Question 2

What is a characteristic of the aqueous component of the pancreatic secretion?

Answer 2

rich in HCO3-

Question 3

What is the function of the aqueous component of the pancreatic secretion?

Answer 3

functions to neutralize the H+ delivered to the duodenum from the stomach to achieve optimal pH for pancreatic enzyme activation

Question 4

What is the function of the enzyme component of the pancreatic secretion?

Answer 4

functions to digest carbohydrates, proteins and lipids into absorbable molecules.

Question 5

How much of the pancreas is considered to be “exocrine”?

Answer 5

around 90%

Question 6

What is the name of the blind end of the branching pancreatic ducts?

Answer 6

acinus

Question 7

What is the acinus lined by?

Answer 7

acinar cells

Question 8

What is the major component of the exocrine pancreas (80%)?

Answer 8

acinar cells

Question 9

What is the role of acinar cells?

Answer 9

secrete the enzymatic portion of the pancreatic secretion

Question 10

What cell type is located at the connection between the acinus and the duct?

Answer 10

centroacinar cells

Question 11

What is the role of the centroacinar cells?

Answer 11

secrete the aqueous portion of the pancreatic secretion (along with ductal cells)

Question 12

What is located at the apical membrane of acinar cells?

Answer 12

multiple zymogen granules (full of pancreatic enzymes)

Question 13

What is the source of sympathetic innervation to the exocrine pancreas?

Answer 13

postganglionic nerves from celiac and superior mesenteric plexuses

Question 14

What is the role of sympathetic innervation to the exocrine pancreas?

Answer 14

inhibits pancreatic secretion

Question 15

What is the source of parasympathetic innervation to the exocrine pancreas?

Answer 15

provided by the vagus nerve—synapse in the enteric nervous system, and postganglionic fibers synapse on exocrine pancreas

Question 16

What is the role of parasympathetic innervation to the exocrine pancreas?

Answer 16

stimulates pancreatic secretion

Question 17

Describe the aqueous component of pancreatic secretions.

Answer 17

isotonic solution of Na+, Cl-, K+, and HCO3-.

Question 18

Flow rate of aqueous pancreatic secretion changes the concentrations of which components?

Answer 18

Cl-

Bicarbonate

Question 19

True or false: the higher the flow rate, the lower the bicarbonate.

Answer 19

FALSE: higher the flow rate, the higher the bicarb

Question 20

What is the role of carbonic anhydrase in the production of aqueous pancreatic secretion?

Answer 20

Carbonic anhydrase combines H2O and CO2 in the pancreatic ductal cell to form bicarbonate + H+.

Question 21

How does the bicarbonate made by carbonic anhydrase get into the pancreatic juice?

Answer 21

This bicarbonate is secreted into pancreatic juice by a HCO3-/Cl- exchanger in the apical membrane

Question 22

How does the H+made by carbonic anhydrase get into the blood?

Answer 22

The H+ is secreted into the blood via the Na+/H+ exchanger in the basolateral membrane. (along the concentration gradient set up by Na+/K+ ATPase)

Question 23

How does Cl- get into the pancreatic juice?

Answer 23

CF membrane regulator

Question 24

What alters the action of the CF membrane regulator?

Answer 24

secretion increases cAMP and leads to Cl- release

Question 25

What is the composition of the enzymatic poriton of the pancreatic secretion?

Answer 25

amylase (carb digestion) lipase (lipid digestion) proteases

Question 26

How do pancreatic enzymes get placed into zymogen granules?

Answer 26

1. Proteins synthesized in the rough ER of the acinar cells. 2. Proteins in the ER lumen bud off as transitional elements 3. TEs fuse on to the Golgi complex and proteins are altered 4. Budding off of Golgi as condensing vacuoles (Cl- and water pumped out to increase concentration of enzymes in the granules) 5. Zymogen granule

Question 27

What is the stimulus for fusion of zymogen granules and exocytosis of enzymes into the lumen?

Answer 27

Ach stimulus→ Ca2+ triggers fusion and exocytosis of enzymes from zymogen granules into the lumen

Question 28

What stimulates the production of the aqueous portion of pancreatic secretion?

Answer 28

stimulated by arrival of H+ in the duodenum

Question 29

What stimulates the production of the enzymatic portion of pancreatic secretion?

Answer 29

products of digestion (small peptides, AAs, FAs)

Question 30

List the 3 phases of pancreatic secretion and their relative contributions to the process.

Answer 30

- Cephalic phase (~20%) - Gastric phase - Intestinal phase (~80%)

Question 31

What type of secretion is produced (mainly) by each phase of pancreatic secretion?

Answer 31

- Cephalic phase (enzymatic) - Gastric phase (enzymatic) - Intestinal phase (enzymatic AND aqueous)

Question 32

What stimulates the cephalic phase?

Answer 32

smell, taste, and conditioning are the stimuli and act through vagus nerve

Question 33

What stimulates the gastric phase?

Answer 33

distention of the stomach is the stimuli and acts through the vagus nerve

Question 34

What type of receptors are present on acinar cells in the pancreas?

Answer 34

Ach

Question 35

How does the intestinal phase of pancreatic secretion lead to the release of enzymatic secretions?

Answer 35

* I cells are stimulated (by presence of AAs, small peptides, and FAs in the stomach) to release CCK→ causes a vagovagal reflex that releases Ach. * Ach binds to muscarinic receptors on acinar cells→stimulates secretion!

Question 36

What type of receptors are present on ductal cells in the pancreas?

Answer 36

secretin

Question 37

How does the intestinal phase of pancreatic secretion lead to the release of aqueous secretions?

Answer 37

* Secretin is released by S cells in response to H+ in the lumen of the intestine * In order to neutralize this acid, secretin stimulates the release of aqueous HCO3- from the ductal cells.

Question 38

What pH is adequate for S cells to get the signal that chyme has arrived from the stomach?

Answer 38

3-4.5

Question 39

What can also lead to secretin release (other than pH of 3-4.5)?

Answer 39

increase the AMOUNT of titratable acid (increased exposure to higher volumes of acid--not necessarily a higher pH)

Question 40

The presence of what amino acid leads to potentiation of the secretin effect on bicarbonate release (leads to peak release of HCO3-)?

Answer 40

phenylalanine

Question 41

What is an example of potentiation in the production of enzymatic secretion from the pancreas?

Answer 41

Secretin and Ach act on two different receptors to stimulate two different pathways that lead to elevated calcium levels and enzyme release from the acinar cells.

Question 42

What is the term for a decreased volume of pancreatic juice and a decrease in level of bicarbonate in the pancreatic juice?

Answer 42

pancreatitis

Question 43

What are the two major factors that lead to pancreatitis?

Answer 43

- Alcoholism | - Blockage of pancreatic duct by gallstones

Question 44

How does blocking pancreatic duct lead to pancreatitis?

Answer 44

enzymes back up and trypsinogen is converted to trypsin→ activates other enzymes→ autodegredation of exocrine pancreas

Question 45

What is the condition characterized by extreme malnutrition with a decreased volume of pancreatic juice (decreased bicarbonate AND enzymes)?

Answer 45

Kwashiorkor

Question 46

What causes Kwashiorkor?

Answer 46

protein synthesis is decreased along with patient being malnourished

Question 47

What is the autosomal recessive condition with lack of Cl- conductance in the apical membrane (faulty synthesis of channel or inability of the cell to put chennel in membrane)?

Answer 47

Cystic fibrosis

Question 48

What effect does CF have on pancreatic secretion?

Answer 48

decreased volume of pancreatic juice (decreased bicarbonate AND enzymes)

Question 49

What is a common symptom between CF and Kwashiorkor?

Answer 49

steatorrhea (no enzymes to break down fat)