Endocrinology Practice Questions

Q: At the cellular level the physiological effects of human growth hormone are mediated by?

Insulin-like growth factors. ***Insulin-like growth factors*** - The primary mechanism by which **growth hormone (GH)** exerts its physiological effects is by stimulating the production of **insulin-like growth factors (IGFs)**, particularly **IGF-1**. - **IGF-1** then mediates most of the **growth-promoting actions** of GH on target tissues through the **somatomedin hypothesis**. *Insulin* - **Insulin** is a hormone primarily involved in regulating **glucose metabolism** by promoting glucose uptake and utilization by cells. - While GH can influence **insulin sensitivity**, insulin itself does not mediate the primary growth-promoting effects of GH. *Prolactin* - **Prolactin** is a hormone primarily associated with **lactation** and **mammary gland development**. - It has distinct functions from growth hormone and does not mediate its growth-promoting actions. *Somatotropin* - **Somatotropin** is simply another name for **human growth hormone (hGH)** itself. - The question asks how the effects *of* growth hormone are mediated at the cellular level, implying a **downstream mediator**, not the hormone itself.

Q: Which of the following is true about somatostatin, insulin, and glucagon?

Somatostatin blocks release of insulin and glucagon.. ***Somatostatin blocks release of insulin and glucagon.*** - **Somatostatin** acts as a paracrine inhibitor within the **islets of Langerhans**, suppressing the secretion of both **insulin** from beta cells and **glucagon** from alpha cells. - This inhibitory action helps to modulate and fine-tune nutrient absorption and utilization following a meal, preventing excessive fluctuations in blood glucose levels. *Glucagon blocks insulin and Somatostatin release.* - **Glucagon's primary role** is to raise blood glucose by stimulating **hepatic glucose production**, not to block the release of insulin or somatostatin. - In fact, glucagon can stimulate **somatostatin release**, which then acts to inhibit glucagon secretion, forming a negative feedback loop. *Insulin increases glucagon release.* - **Insulin and glucagon** have opposing roles in glucose regulation; insulin's main function is to lower blood glucose, while glucagon raises it. - High insulin levels typically **suppress glucagon secretion**, as the body needs to lower glucose, not raise it further. *Somatostatin stimulates insulin.* - **Somatostatin** is a potent **inhibitor** of insulin release, not a stimulator. - This inhibitory effect helps to prevent rapid and excessive insulin secretion, which could lead to hypoglycemia.

Q: In surgical stress all hormones are increased except:

Insulin. ***Insulin*** - While other **stress hormones** increase, **insulin** levels typically **decrease** or remain stable due to increased **insulin resistance** during surgical stress. - This physiological response aims to maintain **blood glucose** levels for energy during heightened metabolic demands. *Epinephrine* - **Epinephrine** (adrenaline) is a key **catecholamine** released during surgical stress, leading to a "fight or flight" response. - It increases **heart rate**, **blood pressure**, and promotes **gluconeogenesis** to supply quick energy. *ACTH* - **Adrenocorticotropic hormone (ACTH)** is released from the **pituitary gland** in response to surgical stress. - **ACTH** stimulates the adrenal cortex to produce **cortisol**, a critical stress hormone. *Cortisol* - **Cortisol** levels significantly rise during surgical stress, mediated by **ACTH** release. - It plays a crucial role in **modulating inflammation**, **glucose metabolism**, and maintaining **hemodynamic stability**.

Q: Aldosterone secretion is maximally stimulated by?

Hyperkalemia. ***Hyperkalemia*** - **Hyperkalemia is the most potent direct stimulator** of aldosterone secretion from the zona glomerulosa cells of the adrenal cortex. - Even a small increase in serum potassium (0.1 mEq/L) can significantly increase aldosterone synthesis and secretion. - This is a crucial homeostatic mechanism to promote **renal potassium excretion** via principal cells in the collecting duct, normalizing serum potassium levels. - **Mechanism**: K+ directly depolarizes zona glomerulosa cells → opens voltage-gated Ca2+ channels → increases intracellular Ca2+ → stimulates aldosterone synthesis. *Exogenous steroids* - Exogenous glucocorticoids **suppress the hypothalamic-pituitary-adrenal (HPA) axis** through negative feedback. - They do not stimulate aldosterone secretion; instead, they reduce endogenous corticosteroid production. - Some synthetic steroids may have mineralocorticoid activity themselves, but they don't stimulate endogenous aldosterone. *ACTH* - ACTH has only a **permissive role** in aldosterone secretion, not a primary regulatory role. - While ACTH is required for maintaining the structural integrity of the zona glomerulosa, it is **not the maximal stimulator**. - ACTH primarily regulates **cortisol synthesis** from the zona fasciculata. - The major physiological regulators of aldosterone are **hyperkalemia** and **angiotensin II** (via the renin-angiotensin system). *Hypernatremia* - **Hypernatremia inhibits aldosterone secretion** rather than stimulating it. - Since aldosterone's primary action is to increase sodium reabsorption, elevated sodium levels signal the body to reduce aldosterone to prevent further sodium retention. - This is part of the negative feedback mechanism for sodium homeostasis.

Q: All of the following statements about Insulin like Growth factor - 1 are true, except:

Mainly secreted by the pancreas. ***Mainly secreted by the pancreas*** - **Insulin-like Growth Factor-1 (IGF-1)** is primarily produced by the **liver** in response to **growth hormone (GH)** stimulation, not the pancreas. - While the pancreas does produce some growth factors and hormones, IGF-1 synthesis is predominantly hepatic. *Required for skeletal and cartilage growth* - IGF-1 is a crucial mediator of **growth hormone's effects**, playing a significant role in **linear growth, bone formation**, and **cartilage maintenance**. - It promotes **cell proliferation** and differentiation in various tissues, including bone and cartilage. *Secretion is stimulated by Growth Hormone* - **Growth hormone (GH)** from the pituitary gland stimulates the liver and other tissues to produce IGF-1. - IGF-1 then mediates many of the growth-promoting actions of GH. *Also known as Somatomedin C* - **Somatomedin C** is an older name for **Insulin-like Growth Factor-1 (IGF-1)**. - This term reflects its **growth-promoting actions** and its similarity in structure to **insulin**.

Q: Insulin-mediated transport of glucose is seen in:

Seen in adipose tissue. ***Seen in adipose tissue*** - **Adipose tissue** (fat cells) and muscle cells significantly increase their uptake of glucose in response to **insulin**. - This transport is mediated by **GLUT4 transporters**, which are translocated to the cell membrane upon insulin binding. *Main Mechanism in RBCs* - **Red blood cells (RBCs)** primarily utilize **GLUT1 transporters** for glucose uptake. - **GLUT1** is constitutive and **insulin-independent**, meaning its activity is not regulated by insulin. *All are true* - This option is incorrect because the statement regarding RBCs is false, making the collective "all are true" statement inaccurate. *Via GLUT-2* - **GLUT2** is a primary transporter in the **liver, pancreatic β-cells, intestinal epithelial cells**, and **kidney**. - While it facilitates glucose transport, **GLUT2 is insulin-independent** and has a low affinity but high capacity for glucose, primarily involved in sensing and buffering glucose levels rather than insulin-mediated uptake in peripheral tissues.

Q: Prolactin is synthesized in

Pituitary. ***Pituitary*** - Prolactin is primarily synthesized and secreted by the **lactotroph cells** located in the **anterior pituitary gland**. - Its main function is to stimulate **milk production** (lactation) in mammals. *Thalamus* - The thalamus is a large mass of **gray matter** located in the dorsal part of the diencephalon, primarily involved in relaying **sensory and motor signals**, and the regulation of consciousness and sleep. - It does not have a role in hormone synthesis like prolactin. *Hypothalamus* - The hypothalamus produces **releasing and inhibiting hormones** that regulate the pituitary gland, including **prolactin-inhibiting hormone (PIH)**, which is primarily dopamine. - It does not directly synthesize prolactin itself. *Pineal gland* - The pineal gland is primarily responsible for producing **melatonin**, which regulates **sleep-wake cycles** (circadian rhythm). - It has no role in the synthesis of prolactin.

Q: The blood levels of 1,25 dihydroxycholecalciferol are positively regulated by:-

PTH. ***PTH*** - **Parathyroid hormone (PTH)** is the primary physiological regulator of 1,25-dihydroxycholecalciferol synthesis in the kidneys. - **PTH stimulates the 1-alpha-hydroxylase enzyme**, which converts 25-hydroxycholecalciferol to the active form, 1,25-dihydroxycholecalciferol. *25 OH cholecalciferol* - This is the **precursor molecule** to 1,25-dihydroxycholecalciferol, but its blood level directly reflects overall vitamin D status rather than actively regulating the active form. - While it is the substrate for activated vitamin D, it doesn't directly stimulate its own conversion; rather, **PTH is the key regulator of the conversion process**. *Magnesium* - **Magnesium is a cofactor for many enzymatic reactions**, including those involved in vitamin D metabolism and PTH secretion. - However, it does not directly regulate the blood levels of 1,25-dihydroxycholecalciferol; severe **magnesium deficiency can impair PTH secretion** and action, indirectly affecting vitamin D. *Calcium* - **High blood calcium levels (hypercalcemia) would inhibit PTH release**, thereby negatively regulating 1,25-dihydroxycholecalciferol production. - Conversely, **low calcium levels would stimulate PTH**, which in turn increases 1,25-dihydroxycholecalciferol synthesis to raise calcium levels.

Q: Most metabolically active part in bone is

Cancellous bone. ***Cancellous bone*** - **Cancellous bone** (trabecular/spongy bone) is the **most metabolically active** part of bone due to its **large surface area-to-volume ratio** (approximately 10 times greater than cortical bone). - It has a **high rate of bone turnover** and remodeling, being 8-10 times more active than cortical bone. - Contains abundant **osteoblasts** and **osteoclasts** on trabecular surfaces, making it the primary site for **calcium homeostasis** and rapid response to metabolic demands. - Metabolic bone diseases like **osteoporosis** and **hyperparathyroidism** predominantly affect cancellous bone first due to its high metabolic activity. *Endosteal surface* - The **endosteal surface** (inner lining of cortical bone and trabecular surfaces) is metabolically active with osteoblasts and osteoclasts. - While technically the trabecular surfaces are endosteal surfaces, in clinical teaching, **cancellous bone as a whole** is recognized as the most metabolically active component. - This option represents an anatomical subdivision rather than the structural answer expected in standard physiology. *Cortical bone* - **Cortical bone** (compact bone) is dense and provides structural strength but has **lower metabolic activity** due to its compact structure and smaller surface area. - Remodeling rate is significantly slower (about 1/10th) compared to cancellous bone. - Makes up 80% of skeletal mass but contributes less to metabolic bone turnover. *Periosteal surface* - The **periosteal surface** (outer bone covering) is involved in bone growth in width and fracture repair. - Has osteoblasts and osteoclasts but accounts for a **smaller proportion** of total bone remodeling compared to the extensive trabecular surfaces. - Less metabolically active than cancellous bone overall.

Question 1

At the cellular level the physiological effects of human growth hormone are mediated by?

Accepted Answer

Insulin-like growth factors

Answer

Insulin

Answer

Prolactin

Answer

Somatotropin

Question 2

Which of the following is true about somatostatin, insulin, and glucagon?

Accepted Answer

Somatostatin blocks release of insulin and glucagon.

Answer

Glucagon blocks insulin and Somatostatin release.

Answer

Insulin increases glucagon release.

Answer

Somatostatin stimulates insulin.

Question 3

In surgical stress all hormones are increased except:

Accepted Answer

Insulin

Answer

Epinephrine

Answer

ACTH

Answer

Cortisol

Question 4

Aldosterone secretion is maximally stimulated by?

Accepted Answer

Hyperkalemia

Answer

Exogenous steroids

Answer

ACTH

Answer

Hypernatremia

Question 5

All of the following statements about Insulin like Growth factor - 1 are true, except:

Accepted Answer

Mainly secreted by the pancreas

Answer

Required for skeletal and cartilage growth

Answer

Secretion is stimulated by Growth Hormone

Answer

Also known as Somatomedin C

Question 6

Insulin-mediated transport of glucose is seen in:

Accepted Answer

Seen in adipose tissue

Answer

Main Mechanism in RBCs

Answer

All are true

Answer

Via GLUT-2

Question 7

Prolactin is synthesized in

Accepted Answer

Pituitary

Answer

Thalamus

Answer

Hypothalamus

Answer

Pineal gland

Question 8

During the metabolism of iodine in thyroid synthesis, Wolff-Chaikoff effect is seen due to:

Accepted Answer

Inhibition of organic binding of iodide

Answer

Inhibition of iodide trapping mechanism

Answer

Inhibition of cAMP response of TSH

Answer

Inhibition of proteolysis of Thyroglobulin

Question 9

The blood levels of 1,25 dihydroxycholecalciferol are positively regulated by:-

Accepted Answer

PTH

Answer

25 OH cholecalciferol

Answer

Magnesium

Answer

Calcium

Question 10

Most metabolically active part in bone is

Accepted Answer

Cancellous bone

Answer

Endosteal surface

Answer

Cortical bone

Answer

Periosteal surface

Endocrinology — MCQs

Endocrinology — MCQs

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