Endocrinology Practice Questions

Q: Prolactin plays an important role in all of the following except:

Milk ejection. **Explanation:** The correct answer is **Milk ejection**, as this process is primarily mediated by **Oxytocin**, not Prolactin. **1. Why Milk Ejection is the correct answer:** Milk ejection (the "let-down reflex") occurs due to the contraction of **myoepithelial cells** surrounding the mammary alveoli. This is triggered by Oxytocin, which is released from the posterior pituitary in response to suckling. Prolactin, conversely, acts on the alveolar epithelium to stimulate the synthesis of milk but does not facilitate its expulsion. **2. Why the other options are incorrect:** * **Development of mammary glands (Mammogenesis):** Prolactin, along with estrogen, progesterone, and growth hormone, is essential for the lobuloalveolar development of the breast during pregnancy. * **Milk secretion (Lactogenesis):** Prolactin is the primary hormone responsible for the initiation and maintenance of milk production. It stimulates the synthesis of milk proteins like casein and lactalbumin. * **Amenorrhoea:** High levels of Prolactin (during lactation or prolactinoma) inhibit the pulsatile release of **GnRH** from the hypothalamus. This leads to decreased FSH and LH, resulting in lactational amenorrhea (a natural form of contraception). **Clinical Pearls for NEET-PG:** * **Prolactin Inhibitory Factor (PIF):** Unlike other anterior pituitary hormones, Prolactin is under tonic **inhibitory** control by **Dopamine**. * **TRH Connection:** Thyrotropin-releasing hormone (TRH) acts as a prolactin-releasing factor; thus, primary hypothyroidism can lead to hyperprolactinemia. * **The "Double O" Rule:** **O**xytoxin causes **O**utflow (ejection), while **P**rolactin causes **P**roduction.

Q: The GnRH (Gonadotrophic Releasing hormone) reaches the anterior pituitary from the hypothalamus along which pathway?

Hypophyseal portal vascular connections. **Explanation:** The hypothalamus and the anterior pituitary (adenohypophysis) are connected via a specialized vascular network known as the **Hypophyseal Portal System**. GnRH is synthesized in the neurons of the arcuate nucleus and preoptic area of the hypothalamus. These neurons terminate at the **median eminence**, where they secrete GnRH into the primary capillary plexus. From here, the hormone travels through the portal veins directly to the secondary capillary plexus in the anterior pituitary to stimulate gonadotrophs (LH and FSH secretion). **Analysis of Options:** * **Hypophyseal portal vascular connections (Correct):** This system allows for the rapid, undiluted transport of hypothalamic hormones directly to their target cells in the anterior pituitary, bypassing systemic circulation. * **Neurological connections (Incorrect):** This describes the **Hypothalamo-hypophyseal tract**, which connects the hypothalamus to the *posterior* pituitary (neurohypophysis) for the transport of Oxytocin and ADH via axons. * **Systemic circulation (Incorrect):** If GnRH entered general circulation, it would be diluted and rapidly degraded by peptidases before reaching the pituitary in effective concentrations. * **Cerebrospinal fluid (Incorrect):** While some hormones are found in CSF, it is not the functional physiological pathway for hypothalamic-pituitary signaling. **High-Yield NEET-PG Pearls:** * **Direction of Flow:** The portal system is a "venous-to-venous" connection. * **Dopamine Exception:** Dopamine (Prolactin Inhibiting Hormone) also uses this portal system; it is the only hypothalamic hormone that primarily exerts inhibitory control. * **Clinical Correlation:** Pituitary stalk transection (e.g., head trauma) leads to a decrease in all anterior pituitary hormones *except* Prolactin, which increases due to the loss of hypothalamic dopamine inhibition.

Q: Which of the following is NOT an effect of estrogen?

Reduces HDL. **Explanation:** The correct answer is **A (Reduces HDL)** because estrogen is fundamentally **cardioprotective**. It improves the lipid profile by increasing "good" cholesterol (HDL) and decreasing "bad" cholesterol (LDL). Therefore, saying estrogen *reduces* HDL is physiologically incorrect. **Mechanism of Action:** Estrogen influences lipid metabolism primarily in the liver. It increases the expression of LDL receptors, leading to enhanced clearance of LDL from the plasma. Simultaneously, it increases the production of Apolipoprotein A-I, which raises HDL levels. **Analysis of Options:** * **B. Reduces LDL:** This is a true effect. Estrogen lowers LDL levels, which is why pre-menopausal women have a lower risk of atherosclerosis compared to men of the same age. * **C. Increases Triglycerides:** This is a true effect. Oral estrogen therapy typically increases plasma triglyceride levels by increasing hepatic synthesis of VLDL. This is a key point to remember for patients with pre-existing hypertriglyceridemia. * **D. Increases HDL:** This is a true effect. Estrogen promotes higher HDL levels, contributing to its protective effect on the cardiovascular system. **NEET-PG High-Yield Pearls:** 1. **Menopause Shift:** After menopause, the decline in estrogen leads to an increase in LDL and a decrease in HDL, significantly increasing the risk of Coronary Artery Disease (CAD). 2. **Route of Administration:** Oral estrogens increase triglycerides more than transdermal patches because of the "first-pass" effect on the liver. 3. **Bone Health:** Estrogen also inhibits osteoclast activity (via OPG/RANKL pathway), which is why its deficiency leads to postmenopausal osteoporosis.

Q: A 50-year-old man presents with a headache and signs of raised intracranial tension. Radiological examination reveals a brain tumor compressing the supraoptic nucleus in the hypothalamus. Which of the following hormones is decreased?

Antidiuretic hormone. ### Explanation The correct answer is **Antidiuretic hormone (ADH)**. #### 1. Why the Correct Answer is Right The hypothalamus contains specific nuclei responsible for the synthesis of posterior pituitary hormones. The **supraoptic nucleus** is primarily responsible for the synthesis of **Antidiuretic Hormone (ADH)**, also known as vasopressin. Once synthesized, ADH travels via the hypothalamo-hypophyseal tract to the posterior pituitary, where it is stored and released. Compression or destruction of the supraoptic nucleus leads to a deficiency in ADH production, clinically manifesting as **Central Diabetes Insipidus**. #### 2. Why the Incorrect Options are Wrong * **ACTH, FSH, and Growth Hormone (Options A, B, and C):** These are **anterior pituitary hormones**. Their secretion is regulated by "releasing hormones" produced in the parvocellular neurons of the hypothalamus (e.g., CRH, GnRH, GHRH). While hypothalamic tumors can affect these, they are not primarily synthesized in the supraoptic nucleus. The supraoptic nucleus is functionally distinct and dedicated to ADH. #### 3. High-Yield NEET-PG Pearls * **Nuclei Mnemonic:** **S**upraoptic = **A**DH (**S-A**); **P**araventricular = **O**xytocin (**P-O**). Note: Both nuclei produce both hormones, but these are the primary associations. * **Lesion Effects:** A lesion in the supraoptic nucleus or the pituitary stalk results in **Permanent Diabetes Insipidus**. However, a lesion restricted only to the posterior pituitary may be transient because ADH can still leak into the systemic circulation from the proximal end of the severed stalk. * **V2 Receptors:** ADH acts on V2 receptors in the late distal tubule and collecting ducts to insert **Aquaporin-2** channels, facilitating water reabsorption.

Q: What are important stimuli for prolactin secretion?

Estrogen. **Explanation:** **1. Why Estrogen is Correct:** Estrogen is a potent stimulator of prolactin secretion. It acts directly on the anterior pituitary to stimulate the hypertrophy and hyperplasia of **lactotrophs** (prolactin-secreting cells). Furthermore, estrogen decreases the sensitivity of lactotrophs to the inhibitory effects of dopamine and directly stimulates the expression of the prolactin gene. This is clinically evident during pregnancy, where rising estrogen levels lead to a significant increase in prolactin levels to prepare the breasts for lactation. **2. Why the Other Options are Incorrect:** * **Dopamine (Option C):** This is the primary **inhibitor** of prolactin. Unlike other anterior pituitary hormones, prolactin is under tonic inhibitory control by dopamine (Prolactin Inhibiting Hormone) secreted from the hypothalamus. * **Insulin (Option A):** While insulin is an anabolic hormone, it does not serve as a primary stimulus for prolactin release. * **Growth Hormone (Option B):** GH and Prolactin are structurally similar (both are somatomammotropins), but GH does not stimulate the secretion of prolactin. **3. High-Yield NEET-PG Clinical Pearls:** * **TRH (Thyrotropin-Releasing Hormone):** In primary hypothyroidism, elevated TRH levels can stimulate lactotrophs, leading to **hyperprolactinemia**. * **Suckling Reflex:** The most important physiological stimulus for prolactin release post-partum. It inhibits dopamine release, thereby "disinhibiting" prolactin secretion. * **Prolactinoma:** The most common secretory tubulointerstitial tumor of the pituitary. * **Drugs:** Dopamine antagonists (e.g., Metoclopramide, Haloperidol) are common causes of drug-induced hyperprolactinemia.

Q: What is the major adrenocortical hormone in the blood?

Cortisol. **Explanation:** The adrenal cortex secretes several steroid hormones, but **Cortisol** is the predominant glucocorticoid and the most abundant adrenocortical hormone in human plasma. **1. Why Cortisol is the correct answer:** In humans, cortisol accounts for approximately **95% of all glucocorticoid activity**. It is secreted at a much higher rate (8–25 mg/day) compared to other steroids. Its high plasma concentration (average 10–20 µg/dL in the morning) and its critical role in glucose metabolism, stress response, and immune modulation make it the "major" hormone of the adrenal cortex. **2. Why the other options are incorrect:** * **Corticosterone (B):** While it has glucocorticoid activity, it is significantly less potent than cortisol in humans. It serves as a major glucocorticoid in rodents, but in humans, it is primarily a precursor in the aldosterone pathway. * **Aldosterone (C):** This is the primary mineralocorticoid. Although it is physiologically vital for sodium and potassium balance, its plasma concentration is extremely low (measured in **nanograms/dL**) compared to cortisol (measured in **micrograms/dL**). * **Deoxycorticosterone (D):** This is a precursor to aldosterone with mild mineralocorticoid activity. It is secreted in trace amounts and does not reach the systemic levels of cortisol. **High-Yield Facts for NEET-PG:** * **Transport:** 90–95% of cortisol is bound to **CBG (Transcortin)**; only the free fraction is biologically active. * **Diurnal Variation:** Cortisol levels peak in the early morning (approx. 8 AM) and are lowest around midnight. * **Potency:** Cortisol has a 1:1 ratio of glucocorticoid to mineralocorticoid activity, whereas Aldosterone has negligible glucocorticoid effect.

Q: Milk ejection is facilitated by:

Oxytocin. **Explanation:** The correct answer is **Oxytocin**. **Mechanism of Milk Ejection:** Milk ejection (the "let-down reflex") is a neuroendocrine reflex. When an infant suckles, sensory receptors in the nipple send signals to the hypothalamus, specifically the **paraventricular and supraoptic nuclei**. This triggers the release of oxytocin from the **posterior pituitary** into the bloodstream. Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli, squeezing milk into the ductal system and out through the nipple. **Analysis of Incorrect Options:** * **A. Prolactin:** While essential for lactation, Prolactin is responsible for **milk production (synthesis)** within the alveolar cells, not its ejection. It is secreted by the anterior pituitary. * **C. Growth Hormone:** GH promotes general tissue growth and has a permissive role in mammary gland development, but it does not acutely trigger milk release. * **D. ACTH:** Secreted by the anterior pituitary, ACTH stimulates the adrenal cortex to release cortisol. It has no direct role in the milk ejection reflex. **High-Yield Clinical Pearls for NEET-PG:** * **The "Love Hormone":** Oxytocin also causes uterine contractions during labor (Ferguson reflex) and aids in uterine involution postpartum. * **Psychological Influence:** The milk ejection reflex can be conditioned; the sound of a baby crying can trigger oxytocin release, while stress or pain can inhibit it via catecholamines. * **Prolactin vs. Oxytocin:** Remember the mnemonic: **P**rolactin **P**roduces, **O**xytocin **O**ozes (ejects). * **Inhibition:** Prolactin secretion is tonically inhibited by **Dopamine** (Prolactin-inhibiting factor).

Question 1

Prolactin plays an important role in all of the following except:

Accepted Answer

Milk ejection

Answer

Development of mammary glands

Answer

Milk secretion

Answer

Amenorrhoea

Question 2

The GnRH (Gonadotrophic Releasing hormone) reaches the anterior pituitary from the hypothalamus along which pathway?

Accepted Answer

Hypophyseal portal vascular connections

Answer

Neurological connections

Answer

Systemic circulation

Answer

Cerebrospinal fluid (CSF)

Question 3

Which of the following is NOT an effect of estrogen?

Accepted Answer

Reduces HDL

Answer

Reduces LDL

Answer

Increases Triglycerides

Answer

Increases HDL

Question 4

Which hormone acts on nuclear receptors?

Accepted Answer

Thyroxine

Answer

Calcitonin

Answer

Glucocorticoids

Answer

Vasopressin

Question 5

In osteogenesis imperfecta, which of the following is defective?

Accepted Answer

Bone collagen

Answer

Phosphate deposition in trabecular bone

Answer

Osteoblasts

Answer

Osteoclasts

Question 6

A 50-year-old man presents with a headache and signs of raised intracranial tension. Radiological examination reveals a brain tumor compressing the supraoptic nucleus in the hypothalamus. Which of the following hormones is decreased?

Accepted Answer

Antidiuretic hormone

Answer

Adrenocorticotropic hormone (ACTH)

Answer

Follicle-stimulating hormone (FSH)

Answer

Growth hormone

Question 7

Insulin sensitivity increases with the following treatments except:

Accepted Answer

Fasting

Answer

Metformin

Answer

Acarbose

Answer

Exercise

Question 8

What are important stimuli for prolactin secretion?

Accepted Answer

Estrogen

Answer

Insulin

Answer

Growth hormone

Answer

Dopamine

Question 9

What is the major adrenocortical hormone in the blood?

Accepted Answer

Cortisol

Answer

Corticosterone

Answer

Aldosterone

Answer

Deoxycorticosterone

Question 10

Milk ejection is facilitated by:

Accepted Answer

Oxytocin

Answer

Prolactin

Answer

Growth hormone

Answer

ACTH

Endocrinology — MCQs

Endocrinology — MCQs

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