Endocrinology Practice Questions

Q: Bone resorption is enhanced by:

PGE2. ### Explanation **Correct Option: C (PGE2)** Prostaglandin E2 (PGE2) is a potent stimulator of bone resorption. It acts primarily by increasing the expression of **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand) on osteoblasts and marrow stromal cells. RANKL then binds to its receptor, RANK, on osteoclast precursors, leading to their differentiation and activation. Additionally, PGE2 inhibits the production of **Osteoprotegerin (OPG)**, a decoy receptor that normally blocks RANKL, further shifting the balance toward bone breakdown. **Analysis of Incorrect Options:** * **A (PGD2):** Primarily involved in allergic and inflammatory responses, smooth muscle contraction, and sleep regulation. It does not play a significant role in bone remodeling. * **B (PGF2α):** Known for its role in luteolysis and uterine contraction. While it may have minor effects on bone cells, it is not the primary prostaglandin associated with bone resorption. * **D (PGI2 - Prostacyclin):** Produced by vascular endothelium, it is a potent vasodilator and inhibitor of platelet aggregation. It generally has an inhibitory effect on osteoclast activity, the opposite of PGE2. **High-Yield Facts for NEET-PG:** * **Mechanism:** PGE2 acts via G-protein coupled receptors (EP receptors), mainly increasing intracellular cAMP. * **Clinical Correlation:** Chronic inflammation (like Periodontitis or Rheumatoid Arthritis) leads to high local PGE2 levels, resulting in localized bone loss. * **NSAIDs Connection:** Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit COX enzymes, reducing PGE2 levels, which is why they can sometimes delay bone healing or be used to manage heterotopic ossification. * **Osteoblast Paradox:** While PGE2 stimulates resorption via RANKL, in certain pulsatile or low-dose conditions, it can also have anabolic (bone-forming) effects. However, in the context of standard physiology and exams, it is the classic mediator of **resorption**.

Q: All of the following cross the plasma membrane except?

Epinephrine. The core concept behind this question is the **solubility of hormones** and the location of their receptors. To cross the lipid bilayer of the plasma membrane, a molecule must be **lipophilic (lipid-soluble)**. ### **Explanation of the Correct Answer** * **A. Epinephrine:** This is a catecholamine derived from the amino acid tyrosine [1]. Epinephrine is **water-soluble (hydrophilic)** and cannot diffuse through the lipid-rich plasma membrane. Therefore, it binds to **G-protein coupled receptors (GPCRs)** located on the cell surface (extracellular receptors) to trigger a second messenger cascade (cAMP) [1]. ### **Why the Other Options are Incorrect** * **B. Thyroxine (T4):** Although derived from tyrosine like epinephrine, thyroid hormones are unique because they are highly lipophilic. They cross the plasma membrane via specific transporters to bind to **intranuclear receptors**. * **C & D. Androstenedione and Estrogen:** These are **steroid hormones** derived from cholesterol [1]. All steroid hormones (including glucocorticoids, mineralocorticoids, and sex steroids) are lipid-soluble and easily diffuse across the plasma membrane to bind to **cytoplasmic or nuclear receptors** [2]. ### **NEET-PG High-Yield Pearls** 1. **Receptor Locations:** * **Cell Surface:** Catecholamines (Epi/NE), Peptides (Insulin, Glucagon), and PTH [1]. * **Cytoplasmic:** Glucocorticoids, Mineralocorticoids, Progesterone. * **Nuclear:** Thyroid hormones (T3/T4), Estrogen, Vitamin D, Retinoic acid. 2. **Mnemonic for Nuclear Receptors:** "**T**ry **V**itamins **A**nd **RE**st" (**T**hroid, **V**itamin D, **A**ldosterone/Steroids, **RE**tinoic acid). 3. **Exception Note:** While thyroid hormones are lipophilic, they primarily use carrier-mediated transport (like MCT8) rather than simple diffusion to enter cells rapidly.

Q: Aldosterone secretion is increased when there is a fall in:

Plasma Na+. **Explanation:** Aldosterone, the primary mineralocorticoid secreted by the **Zona Glomerulosa** of the adrenal cortex, plays a crucial role in maintaining electrolyte balance and blood pressure. **Why Plasma Na+ is correct:** A fall in plasma sodium (**Hyponatremia**) acts as a direct stimulus for aldosterone secretion. More importantly, low sodium levels (often associated with low blood volume) trigger the **Renin-Angiotensin-Aldosterone System (RAAS)**. Decreased sodium delivery to the *macula densa* in the kidney stimulates renin release, leading to increased Angiotensin II, which is the most potent stimulator of aldosterone. Aldosterone then acts on the distal convoluted tubule and collecting ducts to promote **Na+ reabsorption** and water retention. **Analysis of Incorrect Options:** * **A. Plasma K+:** Aldosterone secretion is increased by a **rise** in plasma potassium (Hyperkalemia), not a fall. It functions to excrete excess K+ into the urine. * **C. pH of the plasma:** While aldosterone promotes H+ secretion (acid excretion), plasma pH is not a primary direct regulator of its secretion compared to electrolytes and the RAAS. * **D. Angiotensin II levels:** Aldosterone secretion increases when Angiotensin II levels **rise**, as it is the primary hormonal mediator of the RAAS. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimuli:** The two most important direct stimuli for aldosterone are **Hyperkalemia** and **Angiotensin II**. * **ACTH Role:** ACTH is necessary for aldosterone secretion (permissive action) but plays a minor role in its daily regulation compared to K+ and Angiotensin II. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of Hypertension, Hypokalemia, and Metabolic Alkalosis. * **Atrial Natriuretic Peptide (ANP):** The only major hormone that **inhibits** aldosterone secretion.

Q: All of the following hormones bind to cell surface receptors of the target tissues EXCEPT?

Estrogen. ### Explanation The mechanism of hormone action is determined by the chemical nature of the hormone (solubility). Hormones are broadly classified into **Lipid-soluble** and **Water-soluble** groups. **1. Why Estrogen is the correct answer:** Estrogen is a **steroid hormone** derived from cholesterol. Being lipophilic (lipid-soluble), it easily diffuses through the lipid bilayer of the cell membrane. Therefore, it does not require a cell surface receptor; instead, it binds to **intracellular receptors** (specifically nuclear receptors). The hormone-receptor complex then acts as a transcription factor, binding to DNA to regulate gene expression. **2. Why the other options are incorrect:** * **Thyroid Stimulating Hormone (TSH):** This is a large glycoprotein hormone. Due to its size and water-soluble nature, it cannot cross the cell membrane and must bind to **G-protein coupled receptors (GPCR)** on the cell surface. * **Glucagon:** This is a peptide hormone. Like TSH, it is water-soluble and binds to cell surface **GPCRs**, primarily activating the Adenylyl Cyclase-cAMP pathway. * **Epinephrine:** This is a catecholamine (amino acid derivative). Although small, it is polar and cannot diffuse through the membrane, thus binding to **alpha or beta-adrenergic receptors** on the cell surface. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Intracellular Receptors:** *"PET CAT"* – **P**rogesterone, **E**strogen, **T**estosterone, **C**ortisol, **A**ldosterone, **T**hyroid hormones (T3/T4), and Vitamin D. * **Exception Note:** Although **Thyroid hormones (T3/T4)** are amino acid derivatives, they are lipophilic and use **intracellular (nuclear) receptors**, unlike Epinephrine. * **Fast vs. Slow:** Cell surface receptors (e.g., Epinephrine) usually trigger rapid enzymatic changes, while intracellular receptors (e.g., Estrogen) cause slower, genomic effects.

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.

Question 1

Bone resorption is enhanced by:

Accepted Answer

PGE2

Answer

PGD2

Answer

PGF2

Answer

PGI2

Question 2

All of the following cross the plasma membrane except?

Accepted Answer

Epinephrine

Answer

Thyroxine

Answer

Androstenedione

Answer

Estrogen

Question 3

Aldosterone secretion is increased when there is a fall in:

Accepted Answer

Plasma Na+

Answer

Plasma K+

Answer

pH of the plasma

Answer

Angiotensin II levels

Question 4

All of the following hormones bind to cell surface receptors of the target tissues EXCEPT?

Accepted Answer

Estrogen

Answer

Thyroid stimulating hormone

Answer

Glucagon

Answer

Epinephrine

Question 5

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 6

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 7

Which of the following is NOT an effect of estrogen?

Accepted Answer

Reduces HDL

Answer

Reduces LDL

Answer

Increases Triglycerides

Answer

Increases HDL

Question 8

Which hormone acts on nuclear receptors?

Accepted Answer

Thyroxine

Answer

Calcitonin

Answer

Glucocorticoids

Answer

Vasopressin

Question 9

In osteogenesis imperfecta, which of the following is defective?

Accepted Answer

Bone collagen

Answer

Phosphate deposition in trabecular bone

Answer

Osteoblasts

Answer

Osteoclasts

Question 10

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

Endocrinology — MCQs

Endocrinology — MCQs

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