Quiz: Hormonal Regulation of Blood Glucose — 11 domande

1. Which pancreatic islet cell type produces and secretes insulin?

A. PP cells

B. α-cells

C. β-cells

D. δ-cells

Answer: (C)

Spiegazione

β-cells are the endocrine cells in the pancreatic islets that produce insulin. α-cells produce glucagon, while δ-cells and PP cells secrete somatostatin and pancreatic polypeptide, respectively.

2. What are the small pancreatic cell clusters called that perform endocrine hormone secretion?

A. Centroacinar cells

B. Ductal cells

C. Islets of Langerhans

D. Acini

Answer: (C)

Spiegazione

The islets of Langerhans are the small clusters of pancreatic cells responsible for hormone production, differentiating them from exocrine cells like acini.

3. What is the main endocrine role of the islets of Langerhans?

A. They produce pancreatic juice for digestion

B. They filter blood and remove old erythrocytes

C. They secrete hormones into the bloodstream

D. They store bile for release into the intestine

Answer: (C)

Spiegazione

The islets of Langerhans are small pancreatic cell clusters that carry out endocrine hormone secretion. Pancreatic juice is an exocrine product, not an islet function.

4. What percentage of the pancreas is made up of the islets of Langerhans?

A. Approximately 2%

B. Approximately 20%

C. Approximately 30%

D. Approximately 10%

Answer: (A)

Spiegazione

The islets of Langerhans constitute about 2% of the pancreas, providing endocrine functions alongside the exocrine tissue.

5. What is the inactive connecting segment removed from proinsulin during maturation?

A. Carboxy-terminal α-chain

B. Signal receptor domain

C. Amino-terminal β-chain

D. C-peptide

Answer: (D)

Spiegazione

C-peptide is the inactive connector within proinsulin that is removed to form mature insulin. The β-chain and α-chain become part of the active hormone.

6. What is the primary purpose of proinsulin processing in the pancreas?

A. To facilitate insulin transport into target tissues

B. To convert inactive proinsulin into active insulin for glucose regulation

C. To produce C-peptide as a byproduct of insulin synthesis

D. To store glucose as glycogen in pancreatic cells

Answer: (B)

Spiegazione

Proinsulin processing converts inactive proinsulin into active insulin, which is essential for glucose regulation. C-peptide is also produced during this process but is not the main purpose of processing.

7. Which statement best describes proinsulin before it is processed?

A. It is an inactive precursor containing β-chain, α-chain, and C-peptide

B. It is already the active hormone that lowers blood glucose

C. It is a single-chain steroid hormone stored in the liver

D. It is a carbohydrate-binding enzyme that digests glucose

Answer: (A)

Spiegazione

Proinsulin is the inactive peptide precursor of insulin and contains three domains: the amino-terminal β-chain, the carboxy-terminal α-chain, and C-peptide. Processing removes the C-peptide to yield active insulin.

8. When does the biphasic insulin release typically occur after a glucose stimulus?

A. Over about 5–15 minutes for the first phase, followed by a prolonged second phase

B. Only during fasting states

C. Immediately within seconds

D. After several hours, during continuous glucose infusion

Answer: (A)

Spiegazione

The biphasic insulin release occurs first with a quick release of pre-formed insulin within about 5–15 minutes, followed by a second, prolonged phase involving new insulin synthesis.

9. How does glucagon secretion differ from insulin secretion in response to plasma glucose levels?

A. Glucagon is secreted when blood glucose is high, whereas insulin is secreted when blood glucose is low.

B. Both hormones are secreted simultaneously regardless of blood glucose levels.

C. Glucagon secretion is stimulated by a decrease in plasma glucose, while insulin secretion is stimulated by an increase in plasma glucose.

D. Glucagon secretion decreases during fasting, while insulin secretion increases during fasting.

Answer: (C)

Spiegazione

Glucagon is primarily secreted when blood glucose levels fall, stimulating glucose release from the liver, whereas insulin secretion is stimulated by elevated blood glucose, promoting glucose uptake and storage.

10. Who is credited with the discovery or formulation of the concept of glucagon as a hormone that raises blood glucose levels?

A. Kunosuke Oka

B. Kimberly M. McDonald

C. Robert M. Allen

D. Edward C. Kendall

Answer: (A)

Spiegazione

Kunosuke Oka was credited with the discovery of glucagon, recognizing its role as a hormone that elevates blood glucose primarily through actions on the liver.

11. What is the primary consequence of insulin up-regulating GLUT-4 expression in insulin-responsive tissues?

A. Inhibition of glucose transport across cell membranes

B. Decreased blood glucose levels independent of cellular uptake

C. Increased cellular glucose uptake

D. Decreased cellular glucose uptake

Answer: (C)

Spiegazione

Insulin up-regulates GLUT-4 expression, which increases the number of glucose transporters on cell membranes, leading to enhanced cellular glucose uptake and a decrease in blood glucose levels.