Exam 3 (Lecture 9) - Secretory Activities of the Pancreas

Question 1

Is the majority of the pancreas compose of endocrine of exocrine tissue?

Answer 1

Exocrine

Question 2

What cells in the pancreas synthesize digestive enzymes?

Answer 2

Pancreatic acinar cells

Question 3

___________ digesting enzymes are synthesized as zymogens in the same manner as _____________ synthesis in the gastric glands. Why is this important?

Answer 3

1) Protein
2) Pepsinogen

This is important because the enzymes are stored in vesicles (zymogen granules) near the cellular apex.

Question 4

What is the anatomical pathway/function of pancreatic secretions?

Answer 4

1) Acinar cells synthesize large amounts of secretory proteins (digestive enzymes)
- trypsinogen
- chymotrypsin
**Digest protein

  - pancreatic amylase (digests CHOs)
  - pancreatic lipase (digests fat)

2) After synthesis, storage of trypsinogen and chymotrypsin occurs in vesicles (zymogen granules) near the cellular apex (they are activated in the duodenum, where they digest the protein)

3) Upon stimulation, zymogen granules fuse with the plasma membrane and release their contents into the lumen of the gland

4) Zymogens travel through the pancreatic ducts and secretions are added

Question 5

Name the receptors found on the surface of pancreatic acinar, centroacinar, and duct cells. How is each ligand (hormone or neurotransmitter) released?

Answer 5

Receptors:
- ACh
- CCK
- Secretin

Release:
- ACh = Released from nerve endings to stimulate secretion
- CCK = Released from EEC (enteroendocrine cells) in SI > interstitial fluid > bloodstream
- Secretin = Released from EEC in SI > ISF > bloodstream

Question 6

What cell type does CCK stimulate?

Answer 6

Pancreatic acinar cells

Question 7

What cell type does secretin stimulate?

Answer 7

Centroacinar and duct cells

Question 8

What happens when all of the receptors are occupied?

Answer 8

When all receptors are occupied = maximal stimulation of pancreatic secretions

Question 9

Describe how secretin and CCK work together. Is it negative or positive feedback?

Answer 9

CCK increases the action of secretin on centroacinar and duct cells

Secretin increases the action of CCK on acinar cells

Positive feedback

Question 10

Discuss the clinical correlation’s of the pancreatitis case with Beatrice (Beagle).

Answer 10

1) Beatrice ingested an increased amount of fat content
- Increased fat consumption irritates the pancreas = pancreatitis

2) Normally, zymogens (in the zymogen granules) and lysosomes are kept separately from each other

3) During pancreatitis, the zymogen granules and lysosomes fuse, content mixes inside intracellular vacuoles, leading to premature activation of zymogens

4) Abnormal activation of zymogens leads to local damage of pancreatic cells
- Pancreas is mostly made of proteins, so the activation of the zymogens causes the pancreas to digest itself

5) Premature intracellular activation of zymogens causes additional activation of other zymogens, leading to additional pancreatic damage

6) Vomiting

Question 11

Too much of what type of nutrient will give a dog pancreatitis?

Answer 11

Fat

Question 12

What enzyme does the SNAP cPL test measure?

Answer 12

Pancreatic lipase

Question 13

What is the function of plasma protease inhibitors? What occurs if the inhibitors are depleted? What can this lead to?

Answer 13

Plasma protease inhibitors control inflammation
- if depleted, free proteases activate the coagulation, fibrinolytic, and complement cascades
- can lead to shock, disseminated intravascular coagulation (DIC), and death

Question 14

Why would ALP (liver enzyme) be elevated in a dog with pancreatitis?

Answer 14

With pancreatitis, the pancreas is inflamed
- the inflammation can travel up the common bile duct and get into the intrahepatic bile ducts and back
up into the canaliculi
- this then extends into the hepatocytes
- increases the release of ALP into venous blood

Question 15

Why are the segmented neutrophils increased? Why are the bands (immature neutrophils) increased?

Answer 15

These cells are increased because they respond to acute inflammation
- the acute inflammation is due to the pancreatic cell damage by the zymogens

Question 16

Describe how the vomition centers receive afferent signals from four major sources.

Answer 16

1) Visceral afferents from the GI tract
- Vagus or sympathetic nerves
- Signals inform the brain of GI conditions (distention, a very potent stimulus for vomition; and mucosal
irritation

2) Visceral afferents from outside the GI tract
- Includes signals from bile ducts, peritoneum, heart, and other organs
- Bile stone in common bile duct

3) Afferents from extramedullary centers in the brain
- Certain stimuli (odors, fear)
- Vestibular disturbances (motion sickness)
- Cerebral trauma

4) Chemoreceptor trigger zone
- Bilateral sets of centers in the brainstem lying under the floor of the fourth ventricle
- Electrical stimulation of these centers does not induce vomiting, but application of emetic drugs does (if
and only if the vomition centers are intact)
- Chemoreceptor trigger zones function as emetic, chemoreceptors for the vomition centers
- Chemical abnormalities in the body (emetic drugs, uremia, hypoxia, diabetic ketoacidosis) are sensed by
these centers, which then send excitatory signals to the vomition centers
- Most antiemetic drugs act at the level of the chemoreceptor trigger zone

Question 17

Define emetic drug. Define anti-emetic drug. Where to anti-emetic drugs act in the brainstem? Describe how ____________ (type of acid-base imbalance) is caused by vomiting.

Answer 17

1) Emetic drug = stimulates vomiting

2) Anti-emetic drug = inhibits vomiting

3) Chemoreceptor trigger zone

4) Metabolic alkalosis
- Secretions of the stomach are prevented from entering the intestine or are lost from the body (vomiting)
- Blood pH can increase to dangerously high values due to the presence of the HCO3- ions.

Question 18

Observe the normal pancreas and compare with tissue architecture of acute and chronic pancreatitis. Inflammation of the pancreas > premature activation of _____________ > pancreatic tissue damage.

Answer 18

Zymogens