Endocrinology Practice Questions

Q: All are true about hormone functions except:

Cortisol regulates plasma volume. ***Cortisol regulates plasma volume*** - While cortisol plays a role in fluid balance by influencing **renal perfusion** and the action of other hormones like ADH, its primary role is not the direct regulation of plasma volume. - **Aldosterone** is the primary hormone directly responsible for regulating plasma volume through its effects on sodium and water reabsorption in the kidneys. *Thyroid hormones regulate metabolism* - **Thyroid hormones** (T3 and T4) are crucial for regulating the body's metabolic rate, influencing factors like energy production, protein synthesis, and cellular oxygen consumption. - They impact the metabolism of **carbohydrates, fats, and proteins**, affecting nearly every cell in the body. *ADH regulates blood osmolality* - **Antidiuretic hormone (ADH)**, also known as vasopressin, primarily regulates blood osmolality by controlling the reabsorption of water in the renal collecting ducts. - It increases the permeability of collecting ducts to water, thus concentrating urine and **reducing plasma osmolality** when it's high. *Insulin regulates blood glucose* - **Insulin** is a key hormone produced by the pancreas that regulates blood glucose levels by facilitating the uptake of glucose into cells for energy or storage. - It plays a crucial role in lowering blood glucose after meals by promoting **glucose utilization** and inhibiting glucose production by the liver.

Q: Organs involved in calcium homeostasis are all except

Lungs. ***Lungs*** - The **lungs** are primarily involved in gas exchange (oxygen and carbon dioxide) and do not play a direct role in the regulation of **calcium homeostasis**. - While other organs contribute to calcium balance through absorption, excretion, or hormone production, the lungs' physiological functions are unrelated to calcium metabolism. *Intestines* - The **intestines**, particularly the small intestine, are crucial for the **absorption of dietary calcium** under the influence of **active vitamin D**. - Without proper intestinal absorption, calcium levels in the body cannot be maintained. *Skin* - The **skin** is essential for the endogenous synthesis of **vitamin D3 (cholecalciferol)** when exposed to ultraviolet B (UVB) radiation. - This **vitamin D3** is then metabolized into active forms that regulate calcium and phosphate levels. *Kidneys* - The **kidneys** play a vital role in calcium homeostasis by **reabsorbing calcium** from the filtrate and excreting excess calcium. - They also hydroxylate calcidiol to form the active hormone **calcitriol** (1,25-dihydroxyvitamin D), which significantly influences calcium levels.

Q: Which of the following anterior pituitary hormones is primarily under inhibitory control of hypothalamus?

Prolactin. ***Prolactin*** - Prolactin secretion is primarily regulated by the **tonic inhibitory control of dopamine** (also known as prolactin-inhibiting hormone, PIH) from the hypothalamus. - Unlike other anterior pituitary hormones, the **absence of hypothalamic input leads to increased prolactin secretion**. *Growth Hormone (GH)* - GH secretion is primarily stimulated by **Growth Hormone-Releasing Hormone (GHRH)** from the hypothalamus and inhibited by **somatostatin** (also known as growth hormone-inhibiting hormone). The predominant control is stimulatory. - While somatostatin inhibits GH, the primary control of GH is considered **stimulatory via GHRH pulsatility**, not tonic inhibition as seen with prolactin. *TSH* - TSH secretion is primarily stimulated by **Thyrotropin-Releasing Hormone (TRH)** from the hypothalamus. - There is no significant tonic inhibitory control from the hypothalamus directly on TSH secretion; rather, it is subject to **negative feedback from thyroid hormones**. *LH and FSH* - Both LH and FSH secretion are primarily stimulated by **Gonadotropin-Releasing Hormone (GnRH)** from the hypothalamus. - GnRH is released in a **pulsatile manner** to stimulate the release of LH and FSH; there is no primary tonic inhibitory control from the hypothalamus.

Q: Increased ratio of insulin to glucagon causes

Hypoglycemia. ***Hypoglycemia*** - An increased insulin-to-glucagon ratio indicates **high insulin levels**, promoting glucose uptake and utilization by cells, which can lead to a drop in blood glucose below normal levels. - High insulin suppresses **hepatic glucose production** (gluconeogenesis and glycogenolysis) and stimulates **glycogenesis**, further lowering blood glucose. *Decreased amino acid synthesis* - **Insulin** is an **anabolic hormone** that promotes protein synthesis, including amino acid incorporation into proteins. - Therefore, an increased insulin-to-glucagon ratio would generally **increase**, not decrease, amino acid synthesis. *Decreased levels of lipoprotein lipase* - **Insulin enhances the activity and synthesis of lipoprotein lipase (LPL)**, particularly in adipose tissue. - This promotes the uptake of fatty acids from circulating lipoproteins into fat cells for storage. *Enhanced lipolysis in adipose tissue* - **Insulin inhibits lipolysis**, the breakdown of triglycerides into fatty acids and glycerol, in adipose tissue. - An increased insulin-to-glucagon ratio would therefore **suppress**, rather than enhance, lipolysis.

Q: Which of the following hormones will be affected most after the change in sex hormone binding globulin?

Testosterone. ***Testosterone*** - **Sex hormone-binding globulin (SHBG)** binds primarily to **testosterone** (and dihydrotestosterone) with **high affinity**. - SHBG has approximately **5 times greater affinity** for testosterone compared to estradiol. - A change in SHBG levels will significantly impact the proportion of **free (biologically active) testosterone** available in the circulation, thus affecting its overall function and measurement. - This makes testosterone the hormone **most affected** by changes in SHBG levels. *Progesterone* - **Progesterone** is primarily bound to **albumin** and **corticosteroid-binding globulin (CBG)**, not SHBG. - Therefore, changes in SHBG would have minimal direct impact on progesterone levels or its bioavailability. *DHEA* - **Dehydroepiandrosterone (DHEA)** is mostly bound to **albumin** in the blood. - Its binding to SHBG is negligible, making changes in SHBG irrelevant to its overall circulating levels or activity. *Estrogen* - **Estrogen (estradiol)** also binds to SHBG, but with **significantly lower affinity** than testosterone (approximately 5-fold less). - While affected by SHBG changes, the impact is less pronounced than on testosterone due to the lower binding affinity and its additional binding to albumin.

Q: A patient is on a low calcium diet for 8 weeks. Which of the following increases to maintain serum calcium levels?

PTH. ***PTH*** - **Parathyroid hormone (PTH)** is the primary regulator of calcium homeostasis and the key hormone that **increases in response to hypocalcemia** (low serum calcium). - In a patient on a low calcium diet for 8 weeks, **PTH secretion increases** to maintain normal serum calcium levels. - PTH acts through three main mechanisms: increasing **bone resorption** (releasing calcium from bone), enhancing renal **calcium reabsorption** in the distal tubule, and stimulating the production of **active vitamin D (1,25-dihydroxycholecalciferol)** which increases intestinal calcium absorption. *Active 24,25 dihydroxy cholecalciferol* - **24,25-dihydroxycholecalciferol** is a relatively **inactive metabolite** of vitamin D and represents a pathway of vitamin D catabolism, not activation. - The **active form** of vitamin D that increases calcium absorption is **1,25-dihydroxycholecalciferol (calcitriol)**, whose production is stimulated by PTH. - This metabolite does **not increase** in response to hypocalcemia as a compensatory mechanism. *Serum phosphate level* - A low calcium diet would **not directly lead to an increase in serum phosphate levels**. - In fact, PTH (which increases in response to low calcium) typically causes a **decrease in serum phosphate** by promoting renal phosphate excretion (phosphaturic effect). - High phosphate levels can actually exacerbate hypocalcemia by forming insoluble calcium-phosphate complexes. *Calcitonin* - **Calcitonin** is released from the thyroid parafollicular cells (C cells) in response to **high serum calcium levels** (hypercalcemia). - It acts to **lower** calcium by inhibiting osteoclast activity and reducing renal calcium reabsorption. - In hypocalcemia (low calcium diet), calcitonin secretion would **decrease, not increase**, making this the opposite of what occurs to maintain calcium homeostasis.

Q: If iodine supplementation in the diet was completely stopped today, thyroid hormone levels in blood will be severely depleted after:

90 days. *7 days* - A 7-day period is too short for thyroid hormone levels to be severely depleted, given the **large iodine reserve** in the thyroid gland. - While daily iodine intake is essential, the body's stores provide a **buffer against acute deficiencies**. *30 days* - While some changes might begin to occur after 30 days, severe depletion of **thyroid hormone levels** is unlikely as the iodine stores are still substantial. - The body's homeostatic mechanisms would continue to draw upon the **thyroid's iodine reserve** during this period. *360 days* - A 360-day period is *too long*; severe depletion of **thyroid hormone levels** would have occurred much earlier. - By this point, the individual would likely be experiencing significant symptoms of **hypothyroidism** due to chronic iodine deficiency. ***90 days*** - The human body has a **significant reserve of iodine** stored in the thyroid gland, primarily within **colloid**. - This stored iodine is sufficient to maintain normal thyroid hormone production for approximately **2 to 4 months** in the absence of dietary intake. - Therefore, **90 days (approximately 3 months)** is when thyroid hormone levels would be severely depleted after complete cessation of iodine supplementation.

Q: Adrenal medulla secretes all EXCEPT:

Cortisol. ***Cortisol*** - **Cortisol** is a **glucocorticoid** hormone primarily secreted by the **adrenal cortex**, not the adrenal medulla. - Its main functions include regulating metabolism, suppressing the immune system, and aiding in stress response. *Epinephrine* - **Epinephrine** (adrenaline) is the primary hormone secreted by the **adrenal medulla**, constituting about 80% of its output. - It plays a crucial role in the **"fight-or-flight" response**, increasing heart rate, blood pressure, and glucose levels. *Norepinephrine* - **Norepinephrine** (noradrenaline) is also secreted by the **adrenal medulla**, making up about 20% of its secretion. - It works alongside epinephrine in the **sympathetic nervous system** to constrict blood vessels and increase alertness. - Norepinephrine also serves as a precursor in the biosynthesis of epinephrine. *Dopamine* - **Dopamine** is an important **neurotransmitter** that also serves as a precursor in the synthesis of norepinephrine and epinephrine. - While dopamine itself is secreted in small amounts by the adrenal medulla, its primary role is generally considered in the central nervous system and as an intermediate in catecholamine synthesis.

Question 1

All are true about hormone functions except:

Accepted Answer

Cortisol regulates plasma volume

Answer

Thyroid hormones regulate metabolism

Answer

ADH regulates blood osmolality

Answer

Insulin regulates blood glucose

Question 2

Organs involved in calcium homeostasis are all except

Accepted Answer

Lungs

Answer

Intestines

Answer

Skin

Answer

Kidneys

Question 3

Which of the following anterior pituitary hormones is primarily under inhibitory control of hypothalamus?

Accepted Answer

Prolactin

Answer

Growth Hormone (GH)

Answer

TSH

Answer

LH and FSH

Question 4

Increased ratio of insulin to glucagon causes

Accepted Answer

Hypoglycemia

Answer

Decreased amino acid synthesis

Answer

Decreased levels of lipoprotein lipase

Answer

Enhanced lipolysis in adipose tissue

Question 5

Which of the following hormones will be affected most after the change in sex hormone binding globulin?

Accepted Answer

Testosterone

Answer

Progesterone

Answer

DHEA

Answer

Estrogen

Question 6

A patient is on a low calcium diet for 8 weeks. Which of the following increases to maintain serum calcium levels?

Accepted Answer

PTH

Answer

Active 24,25 dihydroxy cholecalciferol

Answer

Serum phosphate level

Answer

Calcitonin

Question 7

If iodine supplementation in the diet was completely stopped today, thyroid hormone levels in blood will be severely depleted after:

Accepted Answer

90 days

Answer

7 days

Answer

30 days

Answer

360 days

Question 8

Adrenal medulla secretes all EXCEPT:

Accepted Answer

Cortisol

Answer

Epinephrine

Answer

Norepinephrine

Answer

Dopamine

Question 9

Which of the following is true regarding parathormone (PTH)?

Accepted Answer

Parathormone (PTH) promotes absorption of Ca++ from the intestine

Answer

90% calcium excreted by the glomerulus

Answer

PTH primarily acts on proximal tubule for calcium reabsorption

Answer

PTH promotes action of calcitonin

Question 10

Which of the following statements is not true?

Accepted Answer

The unionized fraction of calcium in the plasma is an important determinant of PTH secretion

Answer

Mg2+ deficiency impairs PTH secretion and can lead to hypocalcemia

Answer

Parathyroid hormone-related protein is responsible for causing hypercalcemia in cancer patients

Answer

Ca2+ influences PTH secretion by acting on a calcium sensor G-protein coupled receptor located in the parathyroid gland

Endocrinology — MCQs

Endocrinology — MCQs

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