Insulin and Glucose Regulation Quiz

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Questions and Answers

What is the name of the glucose transporter that is recruited to the cell surface in skeletal muscle and fat cells in response to insulin?

GLUT 4

Explain the role of insulin in preventing glucose from leaving cells after it enters.

Insulin promotes the rapid phosphorylation of glucose to glucose-6-phosphate once it enters the cell. This phosphorylation prevents the glucose from being transported back out of the cell via the GLUT transporter.

Describe the two main problems that arise from insulin deficiency, and how they affect glucose levels in the body.

Insulin deficiency leads to reduced glucose uptake into tissues, causing energy starvation, and increased glucose release from the liver, leading to hyperglycemia. The combined effect is too little glucose inside cells and too much glucose in the blood.

What is the normal range of plasma glucose levels in mmol/L and mg/dL?

The normal range of plasma glucose levels is 4.4-5.5 mmol/L or 80-100 mg/dL. Signup and view all the answers

What is the primary stimulus for glucagon secretion?

Glucagon is secreted when blood glucose levels fall below 4.4 mmol/L (80 mg/dL). Signup and view all the answers

What is the main target tissue for glucagon, and what effect does glucagon have on this tissue?

The main target tissue for glucagon is the liver. Glucagon stimulates the liver to release glucose into the bloodstream, leading to an increase in blood glucose levels. Signup and view all the answers

Describe two other hormones that act synergistically with glucagon to raise blood glucose levels.

Cortisol and epinephrine, both stress hormones, act synergistically with glucagon to raise blood glucose levels. Signup and view all the answers

How does the endocrine pancreas contribute to fuel homeostasis in the fed and fasted states?

The endocrine pancreas produces insulin and glucagon, which regulate fuel homeostasis in the fed and fasted states, respectively. Insulin promotes glucose uptake and utilization in the fed state, while glucagon stimulates glucose release in the fasted state. Signup and view all the answers

Explain the primary function of insulin in regulating blood glucose levels.

Insulin helps to lower blood glucose levels by promoting the uptake and storage of glucose in muscle and fat cells, as well as inhibiting glucose production by the liver. Signup and view all the answers

What are the two phases of insulin secretion and what is responsible for each?

The first phase of insulin secretion is a rapid burst of preformed insulin from secretory vesicles, lasting 5-15 minutes. The second phase is a more gradual and sustained release of newly synthesized insulin molecules, lasting for about 30 minutes. Signup and view all the answers

Name three major target organs for insulin and briefly describe its effect on each.

The three major target organs for insulin are the liver, skeletal muscle, and adipose tissue (fat). In the liver, insulin promotes glycogen synthesis and inhibits gluconeogenesis. In skeletal muscle, insulin promotes glucose uptake and glycogen synthesis for energy storage. In adipose tissue, insulin stimulates glucose uptake and promotes triglyceride synthesis. Signup and view all the answers

Describe the mechanism by which insulin secretion is initiated by glucose.

Glucose enters pancreatic beta cells through GLUT2 transporters. After entering the cell, glucose is metabolized, leading to an increase in ATP levels. This increased ATP inhibits ATP-sensitive potassium channels, resulting in depolarization of the cell membrane. Depolarization opens voltage-gated calcium channels, allowing calcium to enter the cell. Calcium influx triggers the release of insulin from secretory vesicles into the bloodstream. Signup and view all the answers

Besides glucose, what other factors can stimulate insulin secretion?

Insulin secretion can also be stimulated by increased plasma amino acid levels, as well as by the feed-forward signaling of glucagon-like peptide-1 (GLP-1) from the small intestine. Signup and view all the answers

What is the role of somatostatin in the context of insulin and glucagon secretion?

Somatostatin, secreted by delta cells in the pancreas, acts as a paracrine hormone inhibiting the release of both insulin and glucagon. It helps to fine-tune and regulate the balance of these two hormones in response to various metabolic demands. Signup and view all the answers

What are the four distinct cell types found within the pancreatic islets, and what hormone does each secrete?

The pancreatic islets contain four distinct cell types: beta (β) cells, alpha (α) cells, delta (δ) cells, and PP cells. Beta cells secrete insulin, alpha cells secrete glucagon, delta cells secrete somatostatin, and PP cells secrete pancreatic polypeptide. Signup and view all the answers

Explain the difference between the first and second phases of insulin secretion in terms of the source of insulin.

The first phase of insulin secretion is a rapid release of preformed insulin molecules that were previously stored in secretory vesicles. The second phase involves the release of newly synthesized insulin molecules that are produced in response to the persistent glucose stimulus. Signup and view all the answers

Study Notes

Biochemistry and Nutrition (Regulation of Energy Metabolism)

The course is titled Biochemistry and Nutrition (RNB: 1903)
The topic is the regulation of energy metabolism
Subtopics include:
- The brain and energy metabolism
- Glucagon and insulin (date: 22/10/2021)
- Creatine phosphate
- Creatinine
- Glycogen
- Gluconeogenesis
- Fructose
- Fatty acids
- The Krebs cycles
- Fermentative and aerobic metabolism

Glucagon & Insulin

Insulin is released by pancreatic beta cells when blood sugar is high.
Glucagon is released by pancreatic alpha cells when blood sugar is low.
Exercise lowers blood sugar and stimulates glucagon release.
Eating increases blood sugar, stimulating insulin release.
Adipose cells take up glucose when blood sugar is high.
The liver breaks down glycogen into glucose when blood sugar is low.

Introduction

Insulin and glucagon regulate blood glucose levels.
Glucose from food fuels the body.
Insulin and glucagon work together to maintain blood sugar levels within a normal range.

Learning Outcomes

Students will be able to describe the biological actions of insulin and glucagon.
Students will be able to list the primary target organs of insulin.
Students will be able to identify how insulin affects target organs.
Students will be able to describe how glucagon secretion is controlled.
Students will be able to identify the target organ for glucagon.

Description - Insulin

Pancreatic islets contain different cells that secrete hormones.
Beta cells (approximately 75%) produce insulin.
Alpha cells (approximately 20%) secrete glucagon.
Delta cells produce somatostatin, which inhibits insulin and glucagon secretion.
Insulin is secreted through a process called glucose-stimulated insulin secretion (GSIS).
Insulin secretion is biphasic:
- Initial burst (5-15 minutes) from preformed secretory vesicles.
- Gradual, sustained phase (30 minutes) from newly synthesized molecules.
Insulin has a short half-life (~5 minutes), mostly degraded by the liver and kidneys.
Insulin secretion is also regulated by factors other than glucose, such as amino acids and glucagon-like peptide from the small intestine.
Glucose enters cells via glucose transporters (GLUT).
Glucose is rapidly phosphorylated to glucose-6-phosphate to prevent it from leaving the cell.
There are several glucose transporter families (e.g., GLUT 1, 2, 4).
GLUT 4 is crucial in skeletal muscle and fat cells; insulin promotes its translocation to the surface, increasing glucose uptake.
Normal blood glucose levels are 4.4-5.5 mmol/L (80-100 mg/dL).

Insulin Deficiency

Reduced glucose uptake in tissues (energy starvation).
Increased glucose release from the liver (hyperglycemia).
Consequences:
- Low glucose inside cells.
- High glucose in the blood.

Positive and negative regulation of pancreatic beta-cell secretion

Factors that stimulate insulin secretion:
- Plasma amino acids
- Glucagon-like peptide (GLP-1)
- Parasympathetic nervous system activity
Factors that inhibit or suppress insulin secretion:
- Sympathetic nervous system activity
- Epinephrine

Description - Glucagon

Glucagon is a peptide hormone.
Secreted by pancreatic alpha cells when blood glucose is low (less than 4.4 mmol/L or 80 mg/dL).
Circulates unbound in plasma.
Half-life of 6 minutes.
The primary target of glucagon is the liver.
Glucagon triggers a cascade leading to increased blood glucose by promoting glycogen breakdown and glucose synthesis in the liver.
Glucagon acts synergistically with cortisol and epinephrine to elevate blood glucose levels, especially during stress.

Summary

The endocrine pancreas regulates fuel homeostasis through insulin and glucagon.
Insulin is released in response to high blood glucose levels to promote storage of excess nutrients.
Glucagon is released in response to low blood glucose levels to mobilize stored nutrients.

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Description

Dive into the intricate roles of insulin and glucagon in glucose metabolism. This quiz explores how these hormones function, their effects on different tissues, and the consequences of insulin deficiency. Test your knowledge on glucose transporters and the endocrine pancreas's role in maintaining fuel homeostasis.