Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 181: Which of the following hormonal concentrations decreases with age?

A. Parathormone
B. FSH
C. Growth hormone (Correct Answer)
D. Norepinephrine

Explanation: **Explanation:** The correct answer is **Growth Hormone (GH)**. This phenomenon is known as **somatopause**. GH secretion peaks during puberty and undergoes a progressive decline starting in the third decade of life (approximately 14% decrease per decade). This decline is primarily due to decreased hypothalamic GHRH secretion and increased somatostatin tone, contributing to age-related changes like decreased muscle mass (sarcopenia) and increased visceral fat. **Analysis of Options:** * **A. Parathormone (PTH):** PTH levels typically **increase** with age. This is often a secondary response to declining Vitamin D levels, reduced calcium absorption in the gut, and declining renal function in the elderly. * **B. FSH (Follicle-Stimulating Hormone):** FSH levels **increase** significantly with age, particularly in females during menopause. As ovarian follicles deplete, the loss of negative feedback from estrogen and inhibin leads to a compensatory rise in FSH and LH. * **D. Norepinephrine:** Plasma levels of norepinephrine generally **increase** with age due to increased sympathetic nervous system activity and reduced clearance from the synaptic cleft. **High-Yield NEET-PG Pearls:** * **Hormones that Decrease with Age:** Growth Hormone, Melatonin, DHEA (Dehydroepiandrosterone), Testosterone, and Estrogen. * **Hormones that Increase with Age:** PTH, FSH, LH, Norepinephrine, and Vasopressin (ADH). * **Hormones that remain relatively Constant:** Thyroid hormones (T3/T4) and Cortisol (though the circadian rhythm of cortisol may flatten). * **Somatopause Clinical Correlation:** The decline in GH/IGF-1 axis is a major contributor to the "frailty syndrome" in the elderly.

Question 182: Where are the receptors for parathyroid hormone located?

A. Osteoblasts (Correct Answer)
B. Osteoclasts
C. Periosteum
D. Cartilage

Explanation: ### Explanation **1. Why Osteoblasts are the Correct Answer:** The primary target of Parathyroid Hormone (PTH) in the bone is the **osteoblast**. Although PTH’s ultimate physiological effect is to increase bone resorption (releasing calcium into the blood), it does not act directly on osteoclasts. Instead, PTH binds to **PTH-1 receptors (GPCRs)** on osteoblasts. This binding stimulates the expression of **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand) and decreases the secretion of Osteoprotegerin (OPG). The RANKL then binds to RANK receptors on pre-osteoclasts, triggering their maturation into active osteoclasts. Thus, osteoblasts mediate the PTH-induced activation of osteoclasts. **2. Why the Other Options are Incorrect:** * **B. Osteoclasts:** These cells lack PTH receptors. They are stimulated indirectly via the RANK/RANKL pathway initiated by osteoblasts. * **C. Periosteum:** While the periosteum contains osteoprogenitor cells, it is not the primary functional site for PTH-mediated calcium homeostasis. * **D. Cartilage:** PTH-related protein (PTHrP) acts on chondrocytes during endochondral ossification, but the systemic regulation of calcium by PTH specifically targets bone-forming cells (osteoblasts) and the kidneys. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Dual Action:** While continuous high levels of PTH cause bone resorption, **intermittent low doses** of PTH (e.g., Teriparatide) actually stimulate osteoblastic activity and bone formation, making it a treatment for osteoporosis. * **Renal Action:** In the kidneys, PTH increases calcium reabsorption in the **Distal Convoluted Tubule (DCT)** and inhibits phosphate reabsorption in the **Proximal Convoluted Tubule (PCT)** (causing phosphaturia). * **Vitamin D:** PTH stimulates the enzyme **1-alpha-hydroxylase** in the kidneys, converting inactive Vitamin D to its active form, Calcitriol.

Question 183: All of the following statements about adrenal glands are true EXCEPT:

A. Chromaffin granules are seen in pheochromocytoma.
B. The adrenal medulla normally secretes epinephrine in excess of norepinephrine. (Correct Answer)
C. Tumors of the adrenal medulla secrete epinephrine in excess of norepinephrine.
D. The adrenal medulla is not essential for life.

Explanation: **Explanation** The correct answer is **C** (though the prompt indicates B as the key, in standard physiology, Option C is the false statement). Let’s clarify the physiological basis: **1. Why Option C is the "False" Statement (The Correct Answer):** In the **normal adrenal medulla**, the enzyme **PNMT** (Phenylethanolamine-N-methyltransferase) is highly active due to high local cortisol levels, converting norepinephrine to epinephrine. Thus, the normal medulla secretes ~80% epinephrine and 20% norepinephrine. However, in **Pheochromocytoma** (tumors of the adrenal medulla), the reverse is usually true: **Norepinephrine is secreted in excess of epinephrine**. This occurs because these tumors often lack the organized architecture or sufficient PNMT activity to methylate all the produced norepinephrine. **2. Analysis of Other Options:** * **Option A:** Chromaffin granules are the storage vesicles for catecholamines. Their presence is a hallmark histological feature of pheochromocytoma. * **Option B:** This is a **true** statement. Under physiological conditions, epinephrine is the primary hormone (80%) secreted by the adrenal medulla. * **Option D:** This is **true**. While the adrenal **cortex** is essential for life (due to mineralocorticoids/glucocorticoids), the **medulla** is not. The sympathetic nervous system can compensate for the loss of medullary catecholamines. **High-Yield NEET-PG Pearls:** * **PNMT:** The rate-limiting step for epinephrine synthesis; it is induced by **Cortisol**. * **VMA (Vanillylmandelic acid):** The primary urinary metabolite of catecholamines used to screen for pheochromocytoma. * **Rule of 10s:** Pheochromocytoma is 10% bilateral, 10% malignant, 10% extra-adrenal, and 10% pediatric. * **Zuckerkandl’s Organ:** The most common site for extra-adrenal pheochromocytoma (paraganglioma).

Question 184: Which of the following is NOT an endocrine function associated with the kidney?

A. Erythropoietin secretion
B. Natriuretic peptide secretion (Correct Answer)
C. 1,25-dihydroxycholecalciferol formation
D. Renin secretion

Explanation: The kidney is a vital endocrine organ, but it is not the primary source of natriuretic peptides. ### **Why Option B is Correct** **Natriuretic peptides** (specifically ANP and BNP) are primarily secreted by the **heart**. Atrial Natriuretic Peptide (ANP) is secreted by the atrial myocytes, and Brain Natriuretic Peptide (BNP) is secreted by ventricular myocytes in response to stretch (volume overload). While the kidney is the *target* organ for these peptides (where they promote sodium excretion), it does not secrete them. ### **Why Other Options are Incorrect** * **A. Erythropoietin (EPO):** Approximately 90% of EPO is synthesized by the **peritubular interstitial cells** of the renal cortex in response to hypoxia. It stimulates RBC production in the bone marrow. * **C. 1,25-dihydroxycholecalciferol (Calcitriol):** The kidney performs the final, rate-limiting step of Vitamin D activation. The enzyme **1-alpha-hydroxylase** (located in the proximal convoluted tubule) converts 25-hydroxyvitamin D into the active form, Calcitriol. * **D. Renin:** Renin is secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole. It is the initiating enzyme of the Renin-Angiotensin-Aldosterone System (RAAS), crucial for blood pressure regulation. ### **High-Yield NEET-PG Pearls** * **Urodilatin:** A rare natriuretic peptide that *is* produced by the distal tubule, but "Natriuretic Peptide" as a general term refers to the cardiac hormones ANP/BNP. * **Chronic Kidney Disease (CKD):** Patients develop anemia primarily due to **EPO deficiency** and secondary hyperparathyroidism due to **Calcitriol deficiency**. * **Prostaglandins:** The kidney also produces PGE2 and PGI2, which act as local vasodilators to maintain renal blood flow.

Question 185: Sex hormone-binding globulin (SHBG) levels are decreased in which of the following conditions?

A. Hyperthyroidism
B. Increased androgen levels (Correct Answer)
C. Increased estrogen levels
D. Pregnancy

Explanation: **Explanation:** Sex hormone-binding globulin (SHBG) is a glycoprotein produced primarily by the **liver**. It binds to sex steroids (testosterone, DHT, and estradiol) to regulate their bioavailability; only the "free" hormone is biologically active. **Why Option B is Correct:** The synthesis of SHBG in the liver is inhibited by **androgens, insulin, and obesity**. Therefore, in conditions with increased androgen levels (such as PCOS or androgen-secreting tumors), SHBG levels decrease. This creates a clinical "vicious cycle": lower SHBG leads to higher levels of free (active) testosterone, further worsening androgenic symptoms like hirsutism. **Why Other Options are Incorrect:** * **A. Hyperthyroidism:** Thyroid hormones (T3/T4) **stimulate** the hepatic production of SHBG. Thus, SHBG levels are elevated in hyperthyroidism. * **C. Increased Estrogen levels:** Estrogen is a potent stimulator of SHBG synthesis. High estrogen levels increase SHBG, which is why women generally have higher levels than men. * **D. Pregnancy:** This is a state of high endogenous estrogen production, which significantly **increases** SHBG levels (often 5–10 fold). **High-Yield Clinical Pearls for NEET-PG:** * **SHBG Increases in:** Hyperthyroidism, Pregnancy, Oral Contraceptive Pill (OCP) use, Cirrhosis, and Aging (in men). * **SHBG Decreases in:** Hypothyroidism, Obesity, PCOS, Hyperinsulinemia/Type 2 Diabetes, and Acromegaly. * **Clinical Correlation:** In **PCOS**, the combination of high androgens and hyperinsulinemia synergistically suppresses SHBG, making it a key marker for the disease.

Question 186: Inhibin is secreted by which of the following cells?

A. Granulosa cell (Correct Answer)
B. Theca cell
C. Corpus luteum
D. Decidua

Explanation: **Explanation:** **Inhibin** is a glycoprotein hormone that plays a critical role in the negative feedback regulation of the hypothalamic-pituitary-gonadal axis. Its primary function is the **selective inhibition of Follicle-Stimulating Hormone (FSH)** secretion from the anterior pituitary. 1. **Why Granulosa Cells are correct:** In females, Inhibin (specifically Inhibin B) is synthesized and secreted by the **Granulosa cells** of the developing ovarian follicles. As the follicle grows under the influence of FSH, these cells produce more Inhibin, which then feeds back to the pituitary to suppress FSH, preventing the over-stimulation of multiple follicles. (Note: In males, the functional equivalent is the **Sertoli cell**). 2. **Why other options are incorrect:** * **Theca cells:** These cells primarily produce androgens (androstenedione) under the influence of LH, which are then converted to estrogens by granulosa cells. * **Corpus luteum:** While the corpus luteum does secrete **Inhibin A** (along with progesterone and estrogen) during the luteal phase, the classic and primary source of Inhibin in the follicular phase and the most common answer for this physiological concept is the Granulosa cell. * **Decidua:** This is the modified mucosal lining of the uterus during pregnancy; it is involved in maternal-fetal exchange and hormone production (like prolactin), but not the primary secretion of Inhibin. **High-Yield Clinical Pearls for NEET-PG:** * **Inhibin B:** Marker of **ovarian reserve**; produced by small antral follicles. * **Inhibin A:** Produced by the **dominant follicle** and the **Corpus Luteum**. * **Tumor Marker:** Inhibin is a highly specific tumor marker for **Granulosa Cell Tumors** of the ovary. * **Dual Action:** While Inhibin suppresses FSH, **Activin** (also from granulosa cells) stimulates FSH secretion.

Question 187: Prolactin secretion is stimulated by:

A. TRH (Correct Answer)
B. ACTH
C. GnRH
D. Dopamine

Explanation: **Explanation:** Prolactin (PRL) is unique among anterior pituitary hormones because its primary regulation is **inhibitory** rather than stimulatory. Under normal physiological conditions, the hypothalamus exerts a tonic inhibitory influence on prolactin via dopamine. **Why TRH is the correct answer:** Thyrotropin-Releasing Hormone (TRH), primarily known for stimulating TSH, also acts as a potent **prolactin-releasing factor**. In states of primary hypothyroidism, the lack of negative feedback leads to elevated TRH levels. This excess TRH stimulates lactotrophs in the anterior pituitary, leading to hyperprolactinemia. This explains why patients with hypothyroidism may present with galactorrhea or menstrual irregularities. **Analysis of Incorrect Options:** * **ACTH (Adrenocorticotropic Hormone):** This is a hormone secreted *by* the anterior pituitary to stimulate the adrenal cortex; it does not regulate prolactin secretion. * **GnRH (Gonadotropin-Releasing Hormone):** This stimulates the release of LH and FSH. Interestingly, high levels of prolactin actually *inhibit* GnRH secretion, leading to hypogonadism. * **Dopamine:** This is the primary **inhibitor** of prolactin (secreted via the tuberoinfundibular pathway). Drugs that block dopamine (antipsychotics) lead to increased prolactin levels. **NEET-PG High-Yield Pearls:** * **Prolactin Inhibitory Factor (PIF):** Dopamine. * **Prolactin Releasing Factors (PRF):** TRH, VIP (Vasoactive Intestinal Peptide), and Oxytocin. * **Physiological Stimuli:** Suckling (strongest), sleep, stress, and pregnancy (estrogen). * **Clinical Correlation:** Always check TSH levels in a patient with hyperprolactinemia to rule out primary hypothyroidism before considering a prolactinoma.

Question 188: FSH is secreted by which of the following cells?

A. Chromophobes
B. Basophils (Correct Answer)
C. Acidophils
D. Theca interna cells

Explanation: **Explanation:** The anterior pituitary (adenohypophysis) contains cells classified based on their staining properties with hematoxylin and eosin (H&E). **Basophils** are cells that stain with basic dyes and are responsible for secreting the "B-FLAT" hormones: **B**asophils produce **F**SH, **L**H, **A**CTH, and **T**SH. Specifically, FSH (Follicle-Stimulating Hormone) is secreted by **gonadotrophs**, which are a subtype of basophils. **Analysis of Options:** * **Option A (Chromophobes):** These are "color-hating" cells that do not pick up significant stain. They are generally considered to be either resting/degranulated acidophils/basophils or stem cells; they do not actively secrete FSH. * **Option C (Acidophils):** These stain with acidic dyes (eosin) and secrete Growth Hormone (Somatotrophs) and Prolactin (Lactotrophs). A common mnemonic is **"GPA"** (**G**rowth hormone, **P**rolactin are **A**cidophils). * **Option D (Theca interna cells):** These are ovarian cells, not pituitary cells. While they are involved in the reproductive axis, their role is to produce androgens (androstenedione) under the influence of LH, not to secrete FSH. **High-Yield Facts for NEET-PG:** * **Mnemonic for Pituitary Staining:** **"GPA"** (Acidophils: GH, Prolactin) and **"B-FLAT"** (Basophils: FSH, LH, ACTH, TSH). * **PAS Stain:** Basophils are PAS (Periodic Acid-Schiff) positive because the hormones they secrete (FSH, LH, TSH) are glycoproteins. * **Most Numerous Cell Type:** Somatotrophs (Acidophils) are the most abundant cells in the anterior pituitary. * **FSH Function:** In females, it stimulates follicular growth; in males, it acts on Sertoli cells to support spermatogenesis.

Question 189: Where is ADH secreted?

A. Supraoptic nucleus (Correct Answer)
B. Paraventricular nucleus
C. Neurohypophysis
D. Adenohypophysis

Explanation: **Explanation:** The synthesis and release of Antidiuretic Hormone (ADH), also known as Vasopressin, involve a two-step anatomical process. ADH is **synthesized** in the cell bodies of magnocellular neurons located in the hypothalamus and then **secreted** (released) into the bloodstream from the posterior pituitary. * **Why Option A is correct:** While both the Supraoptic (SON) and Paraventricular (PVN) nuclei produce both ADH and Oxytocin, the **Supraoptic nucleus** is the primary site for ADH synthesis (roughly 5/6th of ADH is produced here). In the context of NEET-PG, when forced to choose between the two, SON is the classic answer for ADH. * **Why Option B is incorrect:** The **Paraventricular nucleus** is primarily responsible for the synthesis of **Oxytocin**. Although it produces a small amount of ADH, it is not the principal site. * **Why Option C is incorrect:** The **Neurohypophysis** (Posterior Pituitary) is the site of **storage and release** into the systemic circulation via the inferior hypophyseal artery. It does not synthesize the hormone; it only houses the nerve terminals of the hypothalamo-hypophyseal tract. * **Why Option D is incorrect:** The **Adenohypophysis** (Anterior Pituitary) produces its own hormones (GH, ACTH, TSH, etc.) under the influence of hypothalamic releasing factors, but it has no role in ADH production or secretion. **High-Yield Clinical Pearls:** 1. **V1 Receptors:** Located on vascular smooth muscle (cause vasoconstriction). 2. **V2 Receptors:** Located on the **Principal cells** of the late distal tubule and collecting duct (increase water reabsorption via Aquaporin-2). 3. **Stimulus:** The most potent stimulus for ADH release is an increase in **plasma osmolarity** (detected by osmoreceptors in the OVLT), followed by a decrease in blood volume. 4. **Pathology:** Deficiency of ADH leads to **Central Diabetes Insipidus**, characterized by polyuria and low urine specific gravity.

Question 190: All of the following short stature cases are caused by mechanisms independent of specific defects in the growth hormone axis, except?

A. Gonadal dysgenesis
B. Kasper - Hauser syndrome
C. Laron dwarfism (Correct Answer)
D. Achondroplasia

Explanation: ### Explanation The core of this question lies in distinguishing between short stature caused by **primary skeletal or chromosomal abnormalities** versus those caused by **defects within the Growth Hormone (GH) axis**. **1. Why Laron Dwarfism is the Correct Answer:** Laron dwarfism is a classic example of a defect directly within the GH axis. It is caused by a **mutation in the Growth Hormone Receptor (GHR)**, leading to **GH insensitivity**. In these patients, GH levels are actually high (due to lack of negative feedback), but the body cannot produce **IGF-1** (Insulin-like Growth Factor 1) in response. Because the pathology involves the GH receptor—a specific component of the GH axis—it is the exception in this list. **2. Analysis of Incorrect Options:** * **Gonadal Dysgenesis (Turner Syndrome, 45,XO):** Short stature here is primarily due to the **haploinsufficiency of the SHOX gene** on the X chromosome, which is essential for bone growth. The GH axis is typically intact. * **Kasper-Hauser Syndrome:** This is a psychosocial dwarfism (emotional deprivation). While it can suppress GH secretion temporarily, it is classified as an environmental/psychological cause rather than a primary genetic or structural defect of the GH axis itself. * **Achondroplasia:** This is the most common form of disproportionate short stature. It is caused by a gain-of-function mutation in the **FGFR3 gene**, which inhibits cartilage proliferation at the epiphyseal plate. It is a primary bone dysplasia, independent of GH. **High-Yield NEET-PG Pearls:** * **Laron Dwarfism:** High GH + Low IGF-1. Treatment is recombinant IGF-1 (Mecasermin). * **African Pygmies:** They have normal GH levels but a partial defect in GH receptors, leading to low IGF-1 levels. * **Levi-Lorain Dwarfism:** A historical term for isolated GH deficiency (Low GH + Low IGF-1). * **SHOX Gene:** Located on the pseudoautosomal region of X and Y chromosomes; its absence is the most common cause of short stature in Turner Syndrome.

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