L30. Physiology - Endocrine Pancreas

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Questions and Answers

Which process is most directly inhibited by the presence of increased levels of glucose-6-phosphate within the hepatocyte?

The transport of glucose across the hepatocyte membrane via GLUT2

The synthesis of glucose from pyruvate

The breakdown of glycogen to glucose-1-phosphate (correct)

The conversion of Fructose-6-phosphate to Fructose-1,6-bisphosphate

In addition to blood glucose levels, what other regulatory mechanism significantly influences insulin secretion during the cephalic phase?

Glucagon release from alpha cells

The sympathetic nervous system

The parasympathetic nervous system (correct)

Incretin production from the gut

The conversion of pyruvate to acetyl CoA in the mitochondria is primarily associated with which metabolic pathway within the hepatocyte?

Lipogenesis following a high carbohydrate meal (correct)

The formation of ketone bodies when fatty acid levels rise.

Gluconeogenesis during periods of fasting.

The breakdown of proteins

How do incretins like GLP1 and GIP enhance insulin secretion?

By acting on the pancreas to increase insulin release after food enters the gut lumen. (B) Signup and view all the answers

Besides insulin directly stimulating lipogenesis, what other direct effect of insulin contributes to increased fatty acid synthesis in hepatocytes?

By promoting increased glucose transport into the cell as substrate for glycolysis (C) Signup and view all the answers

Which of these processes would likely have the most direct negative effect on protein synthesis in a hepatocyte?

Reduced uptake of cellular amino acids (C) Signup and view all the answers

What does the comparison between oral and IV glucose administration demonstrate regarding insulin secretion?

Oral glucose promotes a greater insulin response due to the incretin effect. (A) Signup and view all the answers

What is the primary physiological event that triggers an increase in insulin secretion from β-cells, according to the provided text?

An increase in blood glucose level (B) Signup and view all the answers

What is the most likely effect on lipogenesis if a patient has a genetic defect causing the Carnitine carrier protein to be non-functional?

Lipogenesis will be reduced due to a buildup of fatty acyl-CoA in the cytoplasm (C) Signup and view all the answers

How does administering glucose orally differ from administering it intravenously regarding blood glucose levels and insulin secretion?

Oral glucose leads to a more gradual rise in blood glucose and an enhanced insulin response. (A) Signup and view all the answers

If a drug inhibits GLP1 degradation, what potential impact might this have on insulin secretion?

It would prolong the action of GLP1, thus enhancing postprandial insulin secretion. (B) Signup and view all the answers

What does the phrase 'glucose-stimulated insulin secretion' refer to in the content?

The process where increased blood glucose levels cause increased insulin secretion. (D) Signup and view all the answers

Based on the provided diagram, what is the immediate precursor to the activation of Protein Kinase C (PKC)?

Diacylglycerol (DAG) (A) Signup and view all the answers

According to the diagram, which event directly contributes to an increase in intracellular calcium concentration, [$Ca^{2+}_i$]?

The influx of calcium ions via voltage-gated calcium channels (D) Signup and view all the answers

If a drug were to inhibit the function of diacylglycerol (DAG), what cellular process would most likely be directly affected?

The activation of Protein Kinase C (PKC) (A) Signup and view all the answers

What is the role of the Endoplasmic Reticulum (ER) in the context of this diagram?

To release calcium and increase [$Ca^{2+}_i$] (C) Signup and view all the answers

What process directly leads to the opening of voltage-gated calcium channels that allows for calcium influx?

Binding of neurotransmitters to membrane receptors (D) Signup and view all the answers

How is 'calcium-induced calcium release' represented in the diagram?

The increase in [$Ca^{2+}_i$] after calcium influx through a voltage-gated channel then calcium release from the ER (B) Signup and view all the answers

If a mutation were to prevent the function of Protein Kinase A (PKA), what downstream event depicted would be directly affected?

The release of $Ca^{2+}$ from the ER (C) Signup and view all the answers

Based on the diagram, which of the following is NOT a direct activator of a calcium related process?

Insulin (A) Signup and view all the answers

If a cell were treated with a compound that blocks the voltage-gated calcium channel, what would be the immediate impact on intracellular calcium concentration [$Ca^{2+}_i$] and subsequent calcium release?

Both the influx of calcium through the voltage-gated channel and subsequent calcium release from the ER would be reduced (D) Signup and view all the answers

Which of the following directly promotes the insulin secretion from vesicles?

Arginine (D) Signup and view all the answers

Which process is antagonized by insulin?

Proteolysis (C) Signup and view all the answers

Insulin's influence on electrolyte balance includes which of the following actions?

Increasing cellular uptake of phosphate (C) Signup and view all the answers

Which of these is NOT a primary target tissue for insulin's metabolic effects?

Kidney (C) Signup and view all the answers

Which of the following does NOT stimulate insulin secretion directly?

Glucagon (A) Signup and view all the answers

What is a major action of insulin?

Stimulating anabolism (C) Signup and view all the answers

Which of these is part of insulin's catabolic antagonizing actions?

Suppressing hepatic gluconeogenesis (C) Signup and view all the answers

Which of these is the outcome of insulin action?

Increased cellular uptake of potassium (C) Signup and view all the answers

What do insulin receptor activation and initial steps of the intracellular insulin signaling cascade have in common in its target tissues?

Shared molecular features (B) Signup and view all the answers

Besides fuel sources, which of these also modulates insulin secretion?

Hormones (C) Signup and view all the answers

What is the primary consequence of insulin binding to its receptor?

Conformational change leading to the activation of intrinsic tyrosine kinase. (D) Signup and view all the answers

What is the immediate effect of the activated receptor's tyrosine kinase?

Auto-phosphorylation of tyrosine residues within the receptor. (D) Signup and view all the answers

What is the role of the phosphorylated IRS protein in insulin signaling?

It serves as a docking site for additional intracellular signaling proteins. (D) Signup and view all the answers

What type of protein is the insulin receptor?

A hetero-tetrameric glycoprotein. (B) Signup and view all the answers

Where does insulin specifically bind to the insulin receptor?

On the cysteine-rich domain of the alpha chains. (A) Signup and view all the answers

Which best describes the structure of the insulin receptor?

Two extracellular alpha chains and two membrane-spanning beta chains. (C) Signup and view all the answers

What is a key feature of the beta-chains of the insulin receptor?

They exhibit intrinsic tyrosine kinase activity. (A) Signup and view all the answers

What is the molecular weight of the insulin receptor?

340,000 kD (A) Signup and view all the answers

What is the function of the glycosylation sites on the insulin receptor?

The text does not describe their exact function. (B) Signup and view all the answers

Which of the following events is the last to occur during the early stages of insulin signaling, as described in the content?

Phosphorylation of IRS protein by the tyrosine kinase. (C) Signup and view all the answers

Study Notes

Endocrine Pancreas Session Learning Objectives

Describe the major hormones secreted by the endocrine pancreas and their cell of origin
Describe hormonal, nutritional, and neuronal stimuli for insulin and glucagon secretion
Detail the cellular mechanism by which an increase in blood glucose stimulates insulin secretion in pancreatic beta cells
Describe the primary cellular effects of insulin action in muscle, liver, and adipose tissue
Outline the global effects of insulin action on circulating glucose levels, and how insulin's actions in muscle, liver, and adipose contribute to these effects
Describe the primary cellular effects of glucagon actions on the liver, including receptor and signaling pathways
Describe the global effects of glucagon action on circulating glucose levels, and how muscle, liver, and adipose contribute to these effects

Glucose Homeostasis

The endocrine pancreas regulates nutrient distribution, primarily glucose, through insulin and glucagon.
Glucose levels are maintained around 100 mg/dL.
Insulin is released in response to high blood sugar (e.g., after a meal) and directs tissues to absorb and store glucose.
Glucagon is released during fasting to maintain blood glucose.

Insulin Production from Beta Cells

Insulin is produced in beta cells within the islets of Langerhans.
Insulin is a 51 amino acid polypeptide with two chains (A and B), linked by disulfide bridges.
Proinsulin is initially produced, then converted to insulin and C-peptide.
Insulin:C-peptide is stored in secretory granules.
Insulin is stored as hexameric units of insulin-zinc crystals.

Insulin Action

Insulin acts on many physiological systems, promoting anabolism (building up).
It increases cellular uptake of glucose, fatty acids, and amino acids, converting them to glycogen, triglycerides, and protein.
Insulin suppresses glycogenolysis, lipolysis, and proteolysis.
Insulin decreases hepatic gluconeogenesis.

Glucagon Production from Alpha Cells

Glucagon is produced by alpha cells in the islets of Langerhans.
It's initially produced as proglucagon, which is processed into the active 29 amino acid peptide.
Intestinal L-cells also produce proglucagon, creating incretin hormones GLP-1 and GLP-2.

Glucagon Action

Glucagon acts primarily on the liver.
It stimulates glucose production via gluconeogenesis and glycogenolysis.
It stimulates lipolysis, releasing fatty acids into the bloodstream.
Glucagon secretion is inversely related to glucose levels.

Diabetes

Type 1 diabetes: autoimmune destruction of beta cells, requiring insulin replacement
Type 2 diabetes: insulin resistance or beta cell dysfunction, often associated with obesity and requiring various treatments

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Description

This quiz focuses on the functions and hormonal regulation of the endocrine pancreas, specifically insulin and glucagon. It examines mechanisms of secretion, cellular effects in various tissues, and the overarching influence on glucose levels in the body. Prepare to explore the complex interactions that maintain glucose homeostasis.