Pancreatic Functions DSA- by learning objectives

Question 1

1. List the four key secretory cells of the pancreatic islets of Langerhans and the primary secretion of each.

Answer 1

Islets of langerhans= the endocrine glands of the pancreas
Beta cells secrete insulin, proinsulin, C peptide, and amylin
Alpha cells secrete glucagon
delta cells secrete somatostatin
F cells secrete pancreatic polypeptide

Question 2

2. Explain how humoral, cell-to-cell, and neural communication methods impact islet cell secretion.

Answer 2

Humoral: blood supply of the islet courses outward from the center, carrying glucose and other secretagogues; cells within a given islet can influence the secretion of other cells. For example, glucagon is a potent insulin secretagogue, insulin modestly inhibits glucagon release, and somatostatin potently inhibits the secretion of both insulin and glucagon (as well as the secretion of growth hormone and other non-islet hormones).

Cell-cell communication: . Both gap and tight junctional structures connect islet cells with one another. Cells within an islet can communicate through gap junctions, which may be important for the regulation of both insulin and glucagon secretion.

Neural: the sympathetic and the parasympathetic divisions of the autonomic nervous system (ANS). Cholinergic stimulation augments insulin secretion. Adrenergic stimulation can have either a stimulatory or inhibitory effect, depending on whether β-adrenergic (stimulatory) or α-adrenergic stimulation (inhibitory) dominates. These three communication mechanisms allow for tight control over the synthesis and secretion of islet hormones.

Question 3

3. Compare the primary metabolic processes which predominate in the fasting and fed states.

Answer 3

When an individual is fasting, the β cell secretes less insulin. When insulin levels decrease, lipids are mobilized from adipose tissue, and amino acids are mobilized from body protein stores within muscle and other tissues. These lipids and amino acids provide fuel for oxidation and serve as precursors for hepatic ketogenesis and gluconeogenesis, respectively. During feeding, insulin secretion increases. Elevated levels of insulin diminish the mobilization of endogenous fuel stores and stimulate carbohydrate, lipid, and amino acid uptake by specific, insulin-sensitive target tissues. In this manner, insulin directs tissues to replenish the fuel reserves that were used during periods of fasting.

Question 4

4. List 8 substances or variables which may act as stimuli for insulin secretion.

Answer 4

Strong: glucose.
Beta cells take up glucose, galactose and mannose –> insulin secretion.

Amino acids: arginine and luecine
keto acids (ketoisocaproate)
ketohexose (fructose)- weak stimulation.

Glucagon- also strong. (weird)

Question 5

5. Identify the seven-step process by which glucose triggers insulin release.

Answer 5

1. Glucose enters the β cell through the GLUT2 glucose transporter by facilitated diffusion Amino acids enter through a different set of transporters.
2. In the presence of glucokinase (the rate-limiting enzyme in glycolysis), the entering glucose undergoes glycolysis and raises [ATP]i by phosphorylating ADP. Some amino acids also enter the citric acid cycle and produce similar changes in [ATP]i and [ADP]i. In both cases, the NADH/NAD+ ratio also would increase.
3. The increased [ATP]i, the increased [ATP]i/[ADP]i ratio, or the elevated [NADH]i/[NAD+]i ratio causes KATP channels to close.
4. Reducing the K+ conductance of the cell membrane causes the β cell to depolarize (i.e., the membrane potential is less negative).
5. This depolarization activates voltage-gated Ca2+ channels
6. The increased Ca2+ permeability leads to increased Ca2+ influx and increased intracellular free Ca2+. This rise in [Ca2+]i additionally triggers Ca2+-induced Ca2+ release
7. The increased [Ca2+]i, perhaps by activation of a Ca2+-calmodulin phosphorylation cascade, ultimately leads to insulin release.

Question 6

6. Evaluate the effects of autonomic influence on insulin secretion, including α-adrenergic, β-adrenergic, and cholinergic stimulation.

Answer 6

beta adrenergic stimulation augments insulin secretion

alpha inhibits it

Question 7

7. Describe the significance of the sympathetic effect on insulin secretion and exercise.

Answer 7

Because postsynaptic csympathetic neurons of the pancreas release norepinephrine, which stimulates alpha more than beta adrenoceptors, sympathetic stimulation through the celiac nerves inhibits insulin secretion.

Question 8

8. Determine the specific effects of insulin on the metabolic processes (not specific biochemical pathways) of the liver, muscle, and adipose tissue.

Answer 8

In liver, insulin promotes storage of glucose as glycogen as well as conversion of glucose to triglycerides. Also promotes storage of fats, fatty acid synthase.

In adipocytes, insulin promotes uptake of glucose and its conversion to triglycerides for storage.

In muscle, insulin promotes uptake of glucose and its storage as glycogen.

Question 9

9. Distinguish between the following metabolic processes and describe the effects of insulin and glucagon on each: glycogen synthesis, glycogenolysis, glycolysis, gluconeogenesis, lipogenesis, lypolysis, protein degradation, and protein synthesis.

Answer 9

still working on this one.

Question 10

10. Summarize the effects of glucagon on the liver.

Answer 10

Glucagon stimulates glycogenolyseis, gluconeogenesis, and ketogenesis.