Endocrinology Practice Questions

Q: Which of the following is a function of prolactin during lactation?

Decreased estrogen. **Explanation:** The correct answer is **D. Decreased estrogen**. **Mechanism:** Prolactin, primarily known for stimulating milk production (lactogenesis), exerts a potent inhibitory effect on the hypothalamic-pituitary-gonadal (HPG) axis. High levels of prolactin during lactation inhibit the pulsatile release of **Gonadotropin-Releasing Hormone (GnRH)** from the hypothalamus. This suppression leads to a decrease in the secretion of **FSH (Follicle-Stimulating Hormone)** and **LH (Luteinizing Hormone)** from the anterior pituitary. Consequently, the ovaries are not stimulated to produce **estrogen**, leading to a state of temporary hypogonadism known as **lactational amenorrhea**. **Analysis of Incorrect Options:** * **A. Increased FSH:** Prolactin suppresses GnRH, which leads to a *decrease* in FSH levels, not an increase. * **B. Increased libido:** Estrogen and testosterone are key drivers of libido. Since prolactin suppresses these sex steroids, it typically results in *decreased* libido. * **C. Increased testosterone:** In both males and females, hyperprolactinemia inhibits the HPG axis, leading to *decreased* production of testosterone. **Clinical Pearls for NEET-PG:** * **Lactational Amenorrhea Method (LAM):** This physiological suppression of ovulation serves as a natural (though not 100% reliable) form of contraception postpartum. * **Prolactinoma:** In non-lactating patients, a prolactin-secreting tumor presents with galactorrhea, infertility, and decreased bone density (due to chronic low estrogen). * **Dopamine Connection:** Dopamine is the primary "Prolactin-Inhibiting Factor." Drugs that block dopamine (like antipsychotics) can cause hyperprolactinemia.

Q: Pheochromocytoma predominantly secretes which hormone?

Norepinephrine. ### Explanation **Pheochromocytoma** is a catecholamine-secreting tumor derived from the chromaffin cells of the adrenal medulla. **Why Norepinephrine is Correct:** In the normal adrenal medulla, approximately 80% of the secretion is Epinephrine and 20% is Norepinephrine. This is because the enzyme **PNMT** (Phenylethanolamine N-methyltransferase), which converts norepinephrine to epinephrine, is induced by high concentrations of cortisol draining from the adrenal cortex. However, in a **Pheochromocytoma**, the tumor cells often lack sufficient contact with cortical cortisol or lose the ability to express PNMT efficiently. Consequently, the predominant hormone secreted into the circulation is **Norepinephrine**. **Analysis of Incorrect Options:** * **A. Serotonin:** This is primarily secreted by enterochromaffin cells of the GI tract and is the hallmark of Carcinoid Syndrome, not Pheochromocytoma. * **B. Epinephrine:** While secreted by the normal adrenal medulla and some specific pheochromocytomas (especially those associated with MEN 2 syndrome), it is not the *predominant* secretion in sporadic cases. * **D. Dopamine:** Though a precursor in the catecholamine pathway, it is rarely the primary secretion. High dopamine levels are more characteristic of neuroblastomas or extra-adrenal paragangliomas. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 10s:** 10% bilateral, 10% malignant, 10% pediatric, 10% extra-adrenal (Paraganglioma). * **Diagnosis:** Best initial screening test is **24-hour urinary fractionated metanephrines** and VMA. * **Management:** Always give **Alpha-blockers (Phenoxybenzamine)** before Beta-blockers to prevent a hypertensive crisis (unopposed alpha-1 stimulation). * **Associated Syndromes:** MEN 2A, MEN 2B, von Hippel-Lindau (VHL), and NF-1.

Q: Calcitonin is released by:

Parafollicular cells of thyroid. **Explanation:** **Calcitonin** is a 32-amino acid peptide hormone primarily involved in calcium homeostasis. It is synthesized and secreted by the **Parafollicular cells (also known as C-cells)** of the thyroid gland. These cells are neuroendocrine in origin (derived from the neural crest) and are located in the connective tissue between the thyroid follicles. Calcitonin acts to lower plasma calcium levels by inhibiting osteoclast activity and decreasing renal calcium reabsorption, effectively acting as a physiological antagonist to Parathyroid Hormone (PTH). **Analysis of Incorrect Options:** * **B. Chief cells of thyroid:** This is a distractor. Chief cells are found in the **Parathyroid glands**, where they secrete Parathyroid Hormone (PTH), not in the thyroid gland. * **C. Granular cells of adrenal gland:** There are no specific "granular cells" defined as a major secretory unit in the adrenal gland. The adrenal medulla contains Chromaffin cells which secrete catecholamines. * **D. Stratum fasciculata of adrenal gland:** This is the middle layer of the adrenal cortex responsible for secreting **Glucocorticoids** (primarily Cortisol), not calcitonin. **High-Yield Clinical Pearls for NEET-PG:** * **Stimulus for Release:** The primary stimulus for calcitonin secretion is **hypercalcemia**. * **Tumor Marker:** Calcitonin serves as a critical tumor marker for **Medullary Thyroid Carcinoma (MTC)**, which arises from the Parafollicular C-cells. * **Therapeutic Use:** Exogenous calcitonin (often salmon calcitonin) is used clinically to treat Paget’s disease of the bone and severe hypercalcemia. * **Developmental Origin:** While thyroid follicular cells arise from the endoderm (thyroglossal duct), the Parafollicular C-cells originate from the **ultimobranchial body** (derived from the 4th/5th pharyngeal pouches).

Q: Normally, Cortisol levels are maximum at __________ and lowest at ________?

8 am and midnight. ### Explanation **Concept: Circadian Rhythm of Cortisol** The secretion of Cortisol follows a distinct **circadian (diurnal) rhythm**, which is regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus. This rhythm is synchronized with the sleep-wake cycle and exposure to light. 1. **Peak (Maximum):** Cortisol levels begin to rise during the late stages of sleep and reach their **peak around 8:00 AM**. This "morning surge" prepares the body for the stresses of the day by increasing blood glucose and vascular reactivity. 2. **Nadir (Lowest):** Levels gradually decline throughout the day, reaching their **lowest point (nadir) around midnight** (usually 1–2 hours after the onset of sleep). **Analysis of Options:** * **Option D (Correct):** Accurately reflects the physiological peak (8 am) and nadir (midnight) observed in individuals with a standard sleep-wake cycle. * **Option A:** Incorrectly reverses the pattern; 8 pm is near the decline, and early morning is when levels are rising, not at their lowest. * **Option B:** 12 pm (noon) shows declining levels, and while 12 am is the nadir, the peak occurs earlier than noon. * **Option C:** While 8 am is the peak, 8 pm is not the lowest point; levels continue to drop further until midnight. **High-Yield Clinical Pearls for NEET-PG:** * **Cushing Syndrome:** The earliest biochemical sign is the **loss of diurnal variation** (elevated late-night salivary or serum cortisol). * **Diagnostic Timing:** To diagnose adrenal insufficiency (Addison’s), cortisol is measured at **8 am** (when it should be high). To screen for Cushing syndrome, it is measured at **midnight** (when it should be low). * **Stress Factor:** This rhythm can be abolished by physical or psychological stress, which causes persistent ACTH elevation. * **Blindness:** In totally blind individuals, the rhythm may "free-run" (shift) because the SCN lacks light-dark synchronization.

Q: Insulin acts by stimulation of which type of receptor?

Enzymatic receptor. **Explanation:** The insulin receptor belongs to the **Enzymatic receptor** family, specifically the **Receptor Tyrosine Kinase (RTK)** class. It is a heterotetramer consisting of two extracellular alpha-subunits (binding site) and two transmembrane beta-subunits. When insulin binds to the alpha-subunits, it triggers autophosphorylation of the beta-subunits. This activates the intrinsic tyrosine kinase activity, which then phosphorylates **Insulin Receptor Substrates (IRS)**, leading to downstream metabolic effects like glucose uptake via GLUT-4 translocation. **Analysis of Options:** * **A. Ionotropic receptors:** These are ligand-gated ion channels (e.g., Nicotinic ACh receptors) that change membrane potential. Insulin does not directly open an ion channel. * **C. Metabotropic receptors:** These are G-Protein Coupled Receptors (GPCRs) that act via second messengers like cAMP or IP3/DAG (e.g., Glucagon, Epinephrine). Insulin does not utilize G-proteins. * **D. Nuclear receptors:** These are intracellular receptors for lipid-soluble hormones (e.g., Steroids, Thyroid hormone) that act as transcription factors. Insulin is a peptide hormone and cannot cross the lipid bilayer. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4:** The only insulin-dependent glucose transporter, found primarily in skeletal muscle and adipose tissue. * **MAP Kinase Pathway:** Mediates the growth-promoting (mitogenic) effects of insulin. * **PI3-Kinase Pathway:** Mediates the metabolic effects (glucose transport and glycogen synthesis). * **Downregulation:** Chronic hyperinsulinemia (as seen in Type 2 Diabetes) leads to "internalization" of receptors, contributing to insulin resistance.

Q: What causes the increase in endometrial thickness during the post-ovulatory phase?

Progesterone. ### **Explanation** The endometrial cycle is divided into the proliferative phase and the secretory phase. The question refers to the **post-ovulatory phase**, also known as the **Secretory Phase**. **1. Why Progesterone is Correct:** After ovulation, the ruptured follicle transforms into the **Corpus Luteum**, which primarily secretes **Progesterone**. While estrogen causes the initial growth (proliferation), Progesterone is responsible for the further thickening and "maturation" of the endometrium. It induces tortuosity of the endometrial glands, increases vascularity (spiral arteries), and promotes the accumulation of glycogen and lipids. This prepares the lining for the potential implantation of a blastocyst. **2. Why the Other Options are Incorrect:** * **Estrogen:** This is the dominant hormone of the **pre-ovulatory (Proliferative) phase**. It causes the initial regeneration of the endometrium after menstruation by increasing the number of cells (hyperplasia). * **FSH (Follicle-Stimulating Hormone):** Secreted by the anterior pituitary, its primary role is to stimulate the growth of ovarian follicles during the follicular phase. It does not have a direct effect on endometrial thickness. * **LH (Luteinizing Hormone):** The LH surge triggers **ovulation**. While LH maintains the corpus luteum (which then produces progesterone), it is not the direct effector hormone for endometrial changes. ### **High-Yield NEET-PG Pearls:** * **Predominant hormone of Secretory Phase:** Progesterone. * **Predominant hormone of Proliferative Phase:** Estrogen. * **Histological hallmark of the Secretory Phase:** Sub-nuclear vacuolation (the first sign of progesterone effect, appearing ~36–48 hours after ovulation). * **Spiral Arteries:** These develop specifically under the influence of progesterone; their constriction due to progesterone withdrawal leads to menstruation.

Q: Hung up reflex is seen in which of the following conditions?

Hypothyroidism. **Explanation:** The **"Hung-up reflex"** (also known as Woltman’s sign) refers to the delayed relaxation phase of a deep tendon reflex, most commonly elicited in the Achilles tendon. **1. Why Hypothyroidism is correct:** In hypothyroidism, there is a generalized slowing of metabolic processes. The delayed relaxation is not due to a defect in the nerve conduction or the initial contraction phase, but rather a **slowing of the calcium reuptake** by the sarcoplasmic reticulum and a decrease in the rate of cross-bridge cycling in skeletal muscle. This results in a characteristic "slow return" of the limb to its neutral position. While "Myxedema" (Option A) is a severe form of hypothyroidism, "Hypothyroidism" is the broader, standard clinical term used in examinations for this sign. **2. Why other options are incorrect:** * **Hyperthyroidism:** This condition presents with **brisk** or hyperactive reflexes (shortened contraction and relaxation phases) due to increased neuromuscular excitability. * **Pheochromocytoma:** This catecholamine-secreting tumor leads to hypertension and tachycardia. While it may cause tremors or hyperreflexia due to sympathetic overactivity, it does not cause a delayed relaxation phase. **3. Clinical Pearls for NEET-PG:** * **Woltman’s Sign:** Another name for the hung-up reflex; it is considered a highly specific clinical sign for hypothyroidism. * **Other causes of delayed relaxation:** Besides hypothyroidism, it can occasionally be seen in pregnancy, diabetes mellitus, hypothermia, and with the use of beta-blockers. * **Muscle involvement in Hypothyroidism:** Look out for **Hoffmann’s Syndrome** (pseudohypertrophy of muscles associated with hypothyroidism in adults) and **Kocher-Debre-Semelaigne Syndrome** (similar presentation in children).

Question 1

Which of the following is a function of prolactin during lactation?

Accepted Answer

Decreased estrogen

Answer

Increased FSH

Answer

Increased libido

Answer

Increased testosterone

Question 2

Pheochromocytoma predominantly secretes which hormone?

Accepted Answer

Norepinephrine

Answer

Serotonin

Answer

Epinephrine

Answer

Dopamine

Question 3

Calcitonin is released by:

Accepted Answer

Parafollicular cells of thyroid

Answer

Chief cells of thyroid

Answer

Granular cells of adrenal gland

Answer

Stratum fasciculata of adrenal gland

Question 4

Normally, Cortisol levels are maximum at __________ and lowest at ________?

Accepted Answer

8 am and midnight

Answer

8 pm and early morning

Answer

12 pm and 12 am

Answer

8 am and 8 pm

Question 5

Which of the following is NOT an action of calcitriol?

Accepted Answer

Calcitriol increases the excretion of calcium and phosphate through the kidney.

Answer

Calcitriol increases the intestinal absorption of calcium.

Answer

Calcitriol stimulates calcium uptake for deposition as calcium phosphate in the osteoblasts of bone.

Answer

Calcitriol's action is similar to steroid hormones.

Question 6

Glucose-dependent release of insulin is mediated by which mechanism?

Accepted Answer

Cyclic AMP

Answer

Carrier's modulators

Answer

Receptor phosphorylation

Answer

ATP-dependent K+ channel

Question 7

Insulin acts by stimulation of which type of receptor?

Accepted Answer

Enzymatic receptor

Answer

Ionotropic receptor

Answer

Metabotropic receptor

Answer

Nuclear receptor

Question 8

In a transection between the hypothalamus and the anterior pituitary, the production of which hormone remains unaffected?

Accepted Answer

Oxytocin

Answer

Testosterone

Answer

Thyroxine

Answer

Cortisol

Question 9

What causes the increase in endometrial thickness during the post-ovulatory phase?

Accepted Answer

Progesterone

Answer

Estrogen

Answer

Follicle-Stimulating Hormone (FSH)

Answer

Luteinizing Hormone (LH)

Question 10

Hung up reflex is seen in which of the following conditions?

Accepted Answer

Hypothyroidism

Answer

Myxedema

Answer

Hyperthyroidism

Answer

Pheochromocytoma

Endocrinology — MCQs

Endocrinology — MCQs

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