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GI > 1-21 DSA Pancreatic Function and Carbohydrate Metabolism > Flashcards

1-21 DSA Pancreatic Function and Carbohydrate Metabolism Flashcards

1
Q

What are the 4 secretory cells of the pancreatic islets of Langerhans?

A

alpha
beta
delta
F (cells)

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2
Q

What is the primary secretion of alpha cells of the pancreatic islets of Langerhans?

A

Glucagon

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3
Q

What is the primary secretion of beta cells of the pancreatic islets of Langerhans?

A

Insulin
Proinsulin
C-peptide
Amylin

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4
Q

What is the primary secretion of delta cells of the pancreatic islets of Langerhans?

A

Somatostatin

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5
Q

What is the primary secretion of F cells of the pancreatic islets of Langerhans?

A

pancreatic polypeptide

F cells are AKA pancreatic polypeptide cells

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6
Q

How can humoral factors impact islet cell secretion?

A

Beta cells tend to be in the middle of the islets, with blood supply to the edges (that contain more alpha or delta cells) that is ‘downstream’ of beta cells.

Insulin will act in a paracrine manner on ‘downstream’ cells to modulate their release of hormones - insulin slightly inhibits release of glucagon. Somatostatin inhibits insulin and glucagon.

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7
Q

How can cell-to-cell communication methods impact islet cell secretion? What hormones are affected?

A

Islet cells connected by tight and gap junctions

  • gap jxns allow communication
  • important for regulation of insulin and glucagon secretion
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8
Q

How can neural communication methods impact islet cell secretion?

A

Happens via ANS

Cholinergic - Para
- increases insulin

Adrenergic - Sym

  • goes both ways
  • beta: stimulatory
  • alpha: inhibitory
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9
Q

What metabolic processes predominate in the fasting stage?

A

(Keep in mind that insulin integrates body fuel metabolism in fasting and feeding.)

Fasting:

  • beta cells release less insulin
  • lipids freed from adipocytes
  • AAs are freed from body protein stores

Lipids & AAs provide fuel for oxygenation
- also serve as precursors for hepatic ketogenesis and gluconeogenesis

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10
Q

What metabolic processes predominate in the feeding stage?

A

Increased insulin reduces:
- mobilization of endogenous fuel stores

Increased insulin increases:
- carb, lipid, AA uptake by insulin sensitive target tissues

Insulin directs tissue to replenish fuel reserves used during fasting.
- AKA, a metabolic summary of Christmas break

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11
Q

What substances/variables can trigger insulin release?

A

Glucagon

Depolarizing islet cell membrane

Beta cells taking up:
glucose
galactose
mannose

Weak stimulation from:

  • some AAs - arg and leu
  • small keto acids (alpha ketoisocaproate)
  • ketohexoses (fructoses)

Hormones:

  • CCK
  • Glucagon
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12
Q

What is the 7 step process in which glucose triggers insulin release?

A
  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.
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13
Q

What is the effect of alpha-adrenergic stimulation on on insulin secretion?

A

Inhibits it

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14
Q

What is the effect of beta-adrenergic stimulation on on insulin secretion?

A

Stimulates it

- i.e. isoproterenol

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15
Q

What is the effect of cholinergic stimulation on on insulin secretion?

A

Stimulates it

- ACh from CN X

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16
Q

What is the effect of signalling from the celiac nerves on insulin secretion?

A

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

17
Q

What is the specific effect of insulin on the metabolic processes of the liver?

A

Insulin stimulates formation of glycogen:

  • activates glucokinase and glycogen synthase
  • attenuates glycogen phosphorylase, which normally breaks down glycogen
  • inhibits glucose-6-phosphatase

Insulin promotes conversion of glucose into pyruvate
- also attenuates use of pyruvate and other 3-C molecules for gluconeogenesis

Insulin activates:
glucokinase
phosphofructokinase
pyruvate kinase
pyruvate dehydrogenase
hexose monophosphate shunt
acetyl CoA carboxylase
fatty acid synthase
apoprotein synthesis for VLDLs

Insulin inhibits:

  • gluconeogenesis
  • G-6-Pase
  • glycogen phosphorylase
18
Q

What is the specific effect of insulin on the metabolic processes of adipose tissue?

A

Insulin promotes fat storage
- inhibits oxidation of FAs

Insulin deactivates:
carnitine acyltransferase I - prevents transport of FAs for oxidation

Insulin activates:
malonyl CoA synthesis - inhibits FA transport to mitochondria
fatty acid synthase - generates FAs
creation of triglycerides

19
Q

What is the specific effect of insulin on the metabolic processes of muscle tissue?

A
  1. Insulin potentiates uptake of glucose via GLUT4
    - increases Vmax transport of glucose into mm tissue
  2. Insulin activates hexokinase and glycogen synthase
  3. Insulin increases phosphofructokinase and pyruvate dehydrogenase
  4. Insulin stimulates protein synthesis
    - inhibits degradation/proteolysis
20
Q

What is the effect of insulin and glucagon on glycogen synthesis?

A

Insulin: stimulates

Glucagon: inhibits

21
Q

What is the effect of insulin and glucagon on glycogenolysis?

A

Insulin: inhibits

Glucagon: stimulates

22
Q

What is the effect of insulin and glucagon on glycolysis?

A

Insulin: stimulates.

Glucagon: inhibit

23
Q

What is the effect of insulin and glucagon on gluconeogenesis?

A

Insulin: inhibits

Glucagon: stimulates

24
Q

What is the effect of insulin and glucagon on lipogenesis?

A

Insulin: inhibits

Glucagon: stimulates

25
Q

What is the effect of insulin and glucagon on lipolysis?

A

Insulin: inhibits

Glucagon: stimulates

26
Q

What is the effect of insulin and glucagon on protein degradation?

A

Insulin: inhibits

Glucagon: stimulates

27
Q

What is the effect of insulin and glucagon on protein synthesis?

A

Insulin: stimulates

Glucagon: inhibits

28
Q

What are the main effects of glucagon on the liver?

A

Glucagon is particularly important in stimulating glycogenolysis, gluconeogenesis, and ketogenesis.

GI (26 decks)

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