Endocrinology Practice Questions

Q: What is the primary source of human chorionic gonadotropin (HCG)?

Syncytiotrophoblast. **Explanation:** The primary source of **Human Chorionic Gonadotropin (hCG)** is the **Syncytiotrophoblast**, the outer, multinucleated layer of the trophoblast that invades the uterine wall. 1. **Why Syncytiotrophoblast is correct:** Shortly after implantation (around day 8 post-fertilization), the syncytiotrophoblast begins secreting hCG. This hormone is crucial for maintaining the **corpus luteum**, ensuring the continued secretion of progesterone to support the pregnancy until the placenta takes over steroidogenesis (the luteal-placental shift). 2. **Why other options are incorrect:** * **Cytotrophoblast:** This is the inner, single-cell layer of the trophoblast. While it acts as a precursor to the syncytiotrophoblast, its primary endocrine product is **CRH (Corticotropin-Releasing Hormone)** and GnRH, not hCG. * **Langhan’s layer:** This is simply another name for the **Cytotrophoblast**. These cells are prominent in early pregnancy but thin out as gestation progresses. * **Chorionic villi:** While the villi as a whole produce hormones, the term refers to the entire structural unit (comprising the syncytium, cytotrophoblast, and mesoderm). The specific cellular source within the villi is the syncytiotrophoblast. **High-Yield Clinical Pearls for NEET-PG:** * **Doubling Time:** In early pregnancy, hCG levels double every **48–72 hours**. * **Peak Levels:** hCG levels peak at **8–10 weeks** of gestation and then decline to a lower plateau. * **Structure:** hCG is a glycoprotein with two subunits. The **$\alpha$-subunit** is identical to LH, FSH, and TSH; the **$\beta$-subunit** is unique and is what pregnancy tests detect. * **Clinical Marker:** Pathologically high levels are seen in **Hydatidiform mole** and **Choriocarcinoma**, while low levels for gestational age may indicate an ectopic pregnancy or impending abortion.

Q: What is the average reproductive lifespan of an ovum?

12-24 hours. **Explanation:** The reproductive lifespan of an ovum refers to the period during which it remains viable for fertilization after ovulation. Once the secondary oocyte is released from the Graafian follicle, it enters the fallopian tube. Its fertilizability is strictly time-limited, typically lasting **12 to 24 hours**. If fertilization does not occur within this window, the ovum undergoes degeneration and is phagocytosed. **Analysis of Options:** * **A (6-12 hours):** This is too short. While the ovum is most "fertile" immediately after ovulation, it remains viable for up to a full day. * **B (12-24 hours):** **Correct.** Standard physiological texts (like Guyton and Ganong) define the window of oocyte viability as roughly 24 hours, though its peak quality declines after 12 hours. * **C (24-36 hours):** This exceeds the typical functional lifespan of a human ovum. Beyond 24 hours, the zona pellucida and ooplasm undergo changes that prevent successful sperm penetration. * **D (3 days):** This is incorrect for the ovum but is the approximate lifespan of **spermatozoa** within the female reproductive tract (which can survive 48–72 hours). **High-Yield Clinical Pearls for NEET-PG:** * **Fertilization Site:** Occurs specifically in the **Ampulla** of the fallopian tube. * **Meiotic State:** At the time of ovulation, the ovum is arrested in **Metaphase of Meiosis II**. Meiosis II is only completed *after* fertilization (triggered by sperm entry). * **The Fertile Window:** Because sperm survives longer (3 days) than the ovum (1 day), the "fertile window" for intercourse is usually considered to be 3 days before ovulation to 1 day after.

Q: In which organ is the maximum synthesis of fat (lipogenesis) observed?

Liver. **Explanation:** The correct answer is **Liver (Option A)**. In humans, the liver is the primary site for **de novo lipogenesis (DNL)**. This process involves the conversion of excess dietary carbohydrates (glucose) into fatty acids, which are then esterified into triglycerides. These triglycerides are packaged into Very Low-Density Lipoproteins (VLDL) and transported via the bloodstream to peripheral tissues for storage. **Why other options are incorrect:** * **Adipose tissue (Option B):** While adipose tissue is the primary site for fat **storage**, its contribution to de novo fatty acid synthesis in humans is significantly lower (approximately 10-20%) compared to the liver. In many other mammals (like rodents), adipose tissue is a major site of synthesis, which often leads to confusion. * **Intestine (Option C):** The intestine is primarily involved in the absorption of dietary fats and the assembly of **chylomicrons**, rather than the large-scale synthesis of new fatty acids from glucose. * **Muscle (Option D):** Muscles primarily utilize fatty acids for energy (beta-oxidation) or store small amounts as intramyocellular lipids; they do not perform significant lipogenesis. **High-Yield NEET-PG Pearls:** * **Rate-limiting enzyme:** Acetyl-CoA Carboxylase (ACC), which requires **Biotin** as a cofactor. * **Key Stimulator:** Insulin (promotes lipogenesis in the fed state). * **Key Inhibitor:** Glucagon and Epinephrine. * **Cellular Location:** Lipogenesis occurs in the **Cytosol**, whereas Beta-oxidation occurs in the Mitochondria. * **End product:** The primary end product of the Fatty Acid Synthase (FAS) complex is **Palmitate** (a 16-carbon saturated fatty acid).

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: The reabsorption of sodium chloride in the proximal convoluted tubules is increased by hormones secreted from which part of the adrenal gland?

Adrenal cortex. **Explanation:** The correct answer is **Adrenal cortex**. The reabsorption of sodium chloride (NaCl) in the proximal convoluted tubule (PCT) is primarily stimulated by **Angiotensin II** and **Glucocorticoids** (like Cortisol). While Aldosterone (a mineralocorticoid) acts mainly on the distal parts of the nephron, the adrenal cortex secretes both Cortisol (from the Zona Fasciculata) and Aldosterone (from the Zona Glomerulosa). Cortisol has a permissive effect on sodium reabsorption in the PCT, and Angiotensin II (part of the RAAS axis involving adrenal hormones) directly stimulates the Na+/H+ exchanger in the PCT to increase NaCl and water reabsorption. **Analysis of Incorrect Options:** * **Anterior Pituitary:** Secretes trophic hormones like ACTH, which stimulates the adrenal cortex, but it does not directly secrete hormones that act on PCT sodium reabsorption. * **Posterior Pituitary:** Secretes ADH (Vasopressin), which increases water reabsorption in the collecting ducts via Aquaporin-2 channels, not NaCl in the PCT. * **Adrenal Medulla:** Secretes catecholamines (Epinephrine/Norepinephrine). While they influence hemodynamics, they are not the primary hormonal regulators of PCT sodium reabsorption. **NEET-PG High-Yield Pearls:** * **PCT Fact:** Approximately 65-70% of filtered sodium is reabsorbed in the PCT, regardless of hormonal status (obligatory reabsorption). * **Angiotensin II:** This is the most potent hormone increasing sodium reabsorption in the **Proximal Tubule**. * **Aldosterone:** Acts on the **Principal cells** of the Late Distal Tubule and Collecting Duct to reabsorb Na+ and secrete K+. * **ANP (Atrial Natriuretic Peptide):** The only major hormone that *decreases* NaCl reabsorption in the tubule to lower blood pressure.

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: Which of the following statements about Histamine is true?

All of the above. **Explanation:** Histamine is a biogenic amine that acts as a potent chemical mediator in various physiological and pathological processes. * **Option A (Mast Cells):** Histamine is primarily synthesized and stored in the granules of **mast cells** and **basophils**. Upon IgE-mediated stimulation (Type I Hypersensitivity), these cells degranulate, releasing histamine into the surrounding tissue. * **Option B (Gastric Acid):** In the stomach, histamine is released by **Enterochromaffin-like (ECL) cells**. It binds to **H2 receptors** on gastric parietal cells, activating the proton pump via the cAMP pathway to increase gastric acid secretion. This is the physiological basis for using H2-blockers (e.g., Ranitidine) in peptic ulcer disease. * **Option C (Arousal and BP):** In the CNS, histaminergic neurons originate in the **tuberomammillary nucleus** of the hypothalamus and are essential for maintaining **wakefulness/arousal** (which is why first-generation antihistamines cause sedation). Peripherally, histamine causes significant **vasodilation** (via H1 and H2 receptors), which can lead to a fall in blood pressure, most notably during anaphylaxis. **Clinical Pearls for NEET-PG:** * **Triple Response of Lewis:** Characterized by Red spot (capillary dilation), Flare (arteriolar dilation), and Wheal (exudation/edema) upon intradermal histamine injection. * **Receptors:** H1 (Allergy/Gq), H2 (Gastric acid/Gs), H3 (Presynaptic/Gi), H4 (Chemotaxis). * **Histamine Synthesis:** Derived from the amino acid **L-histidine** via the enzyme histidine decarboxylase.

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

What is the primary source of human chorionic gonadotropin (HCG)?

Accepted Answer

Syncytiotrophoblast

Answer

Cytotrophoblast

Answer

Langhan's layer

Answer

Chorionic villi

Question 2

What is the average reproductive lifespan of an ovum?

Accepted Answer

12-24 hours

Answer

6-12 hours

Answer

24-36 hours

Answer

3 days

Question 3

In which organ is the maximum synthesis of fat (lipogenesis) observed?

Accepted Answer

Liver

Answer

Adipose tissue

Answer

Intestine

Answer

Muscle

Question 4

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 5

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 6

The reabsorption of sodium chloride in the proximal convoluted tubules is increased by hormones secreted from which part of the adrenal gland?

Accepted Answer

Adrenal cortex

Answer

Anterior pituitary

Answer

Posterior pituitary

Answer

Adrenal medulla

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 of the following statements about Histamine is true?

Accepted Answer

All of the above

Answer

Is found in mast cells

Answer

Increases gastric acid secretion

Answer

Related to arousal and blood pressure

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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