Endocrinology Practice Questions

Q: All of the following are true regarding prolactin agonists EXCEPT:

Dopamine stimulates prolactin production. **Explanation:** The correct answer is **C (Dopamine stimulates prolactin production)** because it is a false statement. In human physiology, prolactin is unique among anterior pituitary hormones because its primary regulation is via **tonic inhibition**, not stimulation. 1. **Why Option C is the Correct Answer (The False Statement):** Dopamine, secreted by the tuberoinfundibular pathway of the hypothalamus, acts on **D2 receptors** of the lactotrophs in the anterior pituitary to **inhibit** the release of prolactin. Therefore, dopamine is also known as Prolactin-Inhibiting Hormone (PIH). It does not stimulate production. 2. **Analysis of Other Options:** * **Option A & B:** These are true. Prolactin’s primary physiological role is **lactogenesis** (milk production). It prepares the mammary glands during pregnancy and stimulates milk synthesis after childbirth in response to suckling. * **Option D:** This is true. As established, dopamine is the primary physiological inhibitor of prolactin. **Clinical Pearls for NEET-PG:** * **Prolactin Regulation:** While dopamine inhibits it, **TRH (Thyrotropin-Releasing Hormone)** stimulates prolactin release. This explains why patients with primary hypothyroidism (high TRH) often present with hyperprolactinemia. * **Drug-Induced Hyperprolactinemia:** Drugs that block D2 receptors (e.g., Antipsychotics like Haloperidol or Metoclopramide) lead to increased prolactin levels, causing galactorrhea and amenorrhea. * **Prolactinoma Treatment:** Dopamine agonists (e.g., **Cabergoline**, Bromocriptine) are the first-line treatment for prolactin-secreting tumors. * **Feedback:** Prolactin inhibits its own secretion by stimulating dopamine release (short-loop negative feedback) and inhibits GnRH, leading to lactational amenorrhea.

Q: The antimullerian hormone is secreted by?

Sertoli cells. **Explanation:** Anti-Müllerian Hormone (AMH), also known as Müllerian Inhibiting Substance (MIS), is a glycoprotein belonging to the TGF-β superfamily. Its primary physiological role occurs during male fetal development. **1. Why Sertoli Cells are Correct:** In males, AMH is secreted by the **fetal Sertoli cells** starting around the 8th week of gestation. Its critical function is to cause the regression of the Müllerian ducts (paramesonephric ducts), which would otherwise develop into the uterus, fallopian tubes, and upper vagina. Without AMH, every fetus would develop female internal reproductive organs. **2. Why the Other Options are Incorrect:** * **Granulosa Cells:** While AMH is produced by granulosa cells in postnatal females (used clinically to measure ovarian reserve), the classic physiological context of AMH in embryology—and the primary answer in most exams—focuses on its role in male sexual differentiation via Sertoli cells. * **Leydig Cells:** These cells secrete **Testosterone**, which is responsible for the stabilization and development of the Wolffian ducts (mesonephric ducts) into the male internal genitalia (epididymis, vas deferens, seminal vesicles). They do not produce AMH. **Clinical Pearls for NEET-PG:** * **Persistent Müllerian Duct Syndrome (PMDS):** Occurs due to a deficiency of AMH or a mutation in its receptor. Result: A genotypic male (46,XY) with normal male external genitalia but possessing a uterus and fallopian tubes. * **Ovarian Reserve Marker:** In adult females, AMH levels are proportional to the number of primordial follicles and are used to predict response to IVF. * **Gene Location:** The gene for AMH is located on **Chromosome 19**.

Q: Intracellular receptors are present for which of the following substances?

All of the above. **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Hormones that are **lipid-soluble (lipophilic)** can easily diffuse through the lipid bilayer of the cell membrane to bind with **intracellular receptors**, whereas water-soluble hormones bind to cell surface receptors. 1. **Estrogen:** As a steroid hormone derived from cholesterol, it is lipophilic. It binds to intracellular receptors (specifically **Type I nuclear receptors**) in the cytoplasm or nucleus, which then act as transcription factors to alter gene expression. 2. **Vitamin D:** Although often classified as a vitamin, it functions as a steroid hormone (Calcitriol). It binds to the **Vitamin D Receptor (VDR)**, a nuclear receptor, to regulate calcium homeostasis. 3. **Thyroxine (T4/T3):** Despite being derived from the amino acid tyrosine, thyroid hormones are unique because they are lipophilic. They enter the cell via carrier-mediated transport and bind to **Type II nuclear receptors** already located on the DNA. Since all three substances utilize intracellular/nuclear receptors to exert their physiological effects, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Cytoplasmic Receptors:** Primarily used by Glucocorticoids and Mineralocorticoids. * **Nuclear Receptors:** Primarily used by Estrogen, Progesterone, Testosterone, Thyroid hormones (T3/T4), and Retinoic acid. * **Mnemonic for Intracellular Receptors:** **"PET TV"** (Progesterone, Estrogen, Testosterone, Thyroid hormones, Vitamin D/A). * **Speed of Action:** Hormones acting via intracellular receptors have a **slow onset** (hours to days) but **long duration** of action because they require new protein synthesis.

Q: What is the primary role of calcitonin in calcium regulation?

To lower serum calcium levels. **Explanation:** **Calcitonin** is a peptide hormone secreted by the **parafollicular cells (C-cells)** of the thyroid gland. Its primary physiological role is to act as a "calcium-lowering" hormone, serving as a physiological antagonist to Parathyroid Hormone (PTH). **Why Option A is correct:** Calcitonin lowers serum calcium levels primarily through two mechanisms: 1. **Bone:** It directly inhibits **osteoclast** activity, thereby reducing bone resorption and the release of calcium into the blood. 2. **Kidneys:** It increases the urinary excretion of calcium by inhibiting renal tubular reabsorption. **Why the other options are incorrect:** * **Option B:** Increasing serum calcium is the primary function of **Parathyroid Hormone (PTH)** and **Vitamin D (Calcitriol)**. * **Options C & D:** While calcitonin does promote phosphaturia (decreasing serum phosphate), its **primary** and most significant regulatory role is defined by its effect on calcium homeostasis. PTH also decreases phosphate levels, but it is the dominant regulator of phosphate balance compared to calcitonin. **NEET-PG High-Yield Pearls:** * **Marker for Medullary Thyroid Carcinoma (MTC):** Calcitonin serves as a specific tumor marker for the diagnosis and post-operative monitoring of MTC. * **The "Escape" Phenomenon:** The hypocalcemic effect of calcitonin is short-lived because osteoclasts eventually become desensitized to it (downregulation of receptors). * **Therapeutic Use:** Due to its ability to inhibit osteoclasts, exogenous calcitonin is used clinically in the treatment of **Paget’s disease**, severe hypercalcemia, and postmenopausal osteoporosis. * **Stimulus:** The primary stimulus for calcitonin secretion is an increase in plasma calcium concentration.

Q: After bilateral vasectomy, which of the following substances will be deficient?

None. **Explanation:** The correct answer is **D. None**. The fundamental concept here is the anatomical site of a vasectomy relative to the accessory sex glands. A vasectomy involves the ligation and excision of a small portion of the **vas deferens**. This procedure prevents the transport of spermatozoa from the epididymis to the ejaculatory ducts, resulting in **azoospermia**. However, it does not affect the production or secretion of seminal fluid from the accessory glands, as these glands enter the reproductive tract distal to the site of ligation. **Why the other options are incorrect:** * **A. Fructose:** Produced by the **seminal vesicles**. Since the seminal vesicles empty into the ejaculatory duct (distal to the vasectomy site), fructose levels in the semen remain normal. * **B. Prostaglandins:** Also primarily secreted by the **seminal vesicles**. They remain present in the ejaculate post-vasectomy. * **C. Fibrinolysin:** Secreted by the **prostate gland**. The prostatic secretions contribute to the bulk of the ejaculate and enter the prostatic urethra; thus, they are unaffected by a vasectomy. **High-Yield Facts for NEET-PG:** * **Ejaculate Composition:** Approximately 60% of semen volume comes from the seminal vesicles, 30% from the prostate, and only 10% from the vas deferens (sperm and fluid). Post-vasectomy, the volume of ejaculate decreases only marginally. * **Hormonal Status:** Vasectomy does not affect Leydig cell function; therefore, **serum Testosterone, LH, and FSH levels remain normal.** * **Post-Vasectomy Semen Analysis:** Sterility is not immediate. Patients must use contraception until two consecutive semen analyses show zero sperm count (usually after 12–20 ejaculations or 3 months).

Q: The kidney secretes all of the following hormones except:

Vasopressin. **Explanation:** The correct answer is **Vasopressin (Antidiuretic Hormone/ADH)**. While the kidney is the primary *target organ* for Vasopressin, it does not synthesize or secrete it. Vasopressin is synthesized in the **supraoptic and paraventricular nuclei of the hypothalamus** and is secreted into the bloodstream by the **posterior pituitary gland (neurohypophysis)**. **Analysis of Options:** * **Renin (Option A):** Secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole in response to low blood pressure or low sodium delivery. It is the rate-limiting enzyme of the Renin-Angiotensin-Aldosterone System (RAAS). * **Erythropoietin (Option B):** Produced by **interstitial cells (peritubular capillaries)** in the renal cortex. It stimulates RBC production in the bone marrow in response to hypoxia. * **1,25-Dihydroxycholecalciferol (Option D):** Also known as **Calcitriol** (active Vitamin D). The kidney contains the enzyme **1-alpha-hydroxylase** (in the proximal convoluted tubule), which converts 25-hydroxyvitamin D into its active form. **NEET-PG High-Yield Pearls:** 1. **Thrombopoietin:** While primarily produced in the liver, a small amount is also synthesized in the kidney. 2. **Prostaglandins:** The kidney produces PGE2 and PGI2, which act as local vasodilators to maintain renal blood flow. 3. **Kinins:** The renal kallikrein-kinin system produces bradykinin, a potent vasodilator. 4. **Gluconeogenesis:** During prolonged fasting, the kidney is a major site of glucose production, contributing up to 20-25% of systemic glucose.

Q: Which of the following statements regarding growth hormone is incorrect?

It lowers blood sugar levels if present in excess.. **Explanation:** **1. Why Option A is the correct (incorrect statement):** Growth Hormone (GH) is a **diabetogenic hormone**. It does not lower blood sugar; instead, it increases it. GH antagonizes the action of insulin, decreases glucose uptake by peripheral tissues (like muscle and adipose tissue), and increases hepatic glucose production (gluconeogenesis). Chronic excess of GH, as seen in acromegaly, can lead to "pituitary diabetes." **2. Analysis of other options:** * **Option B:** GH is strongly **anabolic**. It promotes amino acid uptake and protein synthesis in muscles and organs, leading to a positive nitrogen balance. * **Option C:** In healthy individuals, dopamine stimulates GH release. However, in patients with GH-secreting **pituitary adenomas** (Acromegaly), dopaminergic agonists (like Bromocriptine or Cabergoline) paradoxically **suppress** GH secretion. This is a classic high-yield physiological shift used in medical management. * **Option D:** While GH has some direct effects (like lipolysis), most of its growth-promoting actions (skeletal and cartilage growth) are mediated by **IGF-1 (Somatomedin C)**, which is primarily produced in the liver. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolic effects:** GH is Lipolytic (increases FFA), Diabetogenic (hyperglycemic), and Anabolic (protein sparer). * **Stimulators of GH:** Hypoglycemia, fasting, sleep (Stage 3 & 4), exercise, and Arginine. * **Inhibitors of GH:** Hyperglycemia, Somatostatin, and IGF-1 (via negative feedback). * **Diagnosis:** The gold standard for diagnosing Acromegaly is the failure to suppress GH levels below 1 ng/mL following an **Oral Glucose Tolerance Test (OGTT)**.

Q: Plasma ACTH levels are typically highest between which hours?

4 AM and 10 AM. ### Explanation **Concept: The Diurnal Rhythm of the HPA Axis** The secretion of Adrenocorticotropic Hormone (ACTH) and Cortisol follows a distinct **circadian (diurnal) rhythm**, which is synchronized with the sleep-wake cycle. This rhythm is regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus, which controls the pulsatile release of Corticotropin-Releasing Hormone (CRH). **Why Option B is Correct:** ACTH levels begin to rise during the late stages of sleep, peaking just before or shortly after awakening. In individuals with a standard sleep pattern (sleeping at night, awake during the day), the highest plasma concentrations occur between **4 AM and 10 AM** (typically peaking around 6 AM to 8 AM). This surge prepares the body for the metabolic demands of the day. **Why Other Options are Incorrect:** * **Options A, C, and D:** These represent periods of the day when ACTH levels are either declining or at their nadir. ACTH and Cortisol levels gradually decline throughout the afternoon and evening, reaching their **lowest point (nadir) around midnight** (usually between 10 PM and 2 AM). --- ### High-Yield Clinical Pearls for NEET-PG: * **Diagnostic Timing:** Because of this diurnal variation, a single random cortisol measurement is often clinically useless. To diagnose **Cushing’s Syndrome**, we look for the *loss* of this rhythm (e.g., elevated late-night salivary cortisol). * **Stress Response:** While the basal rhythm is fixed, acute physical or emotional stress can override this cycle, causing rapid spikes in ACTH at any time. * **Feedback Mechanism:** ACTH is inhibited by Cortisol via negative feedback. In **Addison’s Disease** (Primary Adrenal Insufficiency), ACTH levels are pathologically high at all times due to the lack of cortisol feedback. * **Shift Workers:** The diurnal rhythm is not innate; it takes about 1–2 weeks to shift if an individual changes their sleep-wake schedule (e.g., night shift work).

Question 1

All of the following are true regarding prolactin agonists EXCEPT:

Accepted Answer

Dopamine stimulates prolactin production

Answer

Associated with lactation

Answer

Stimulates milk production after childbirth

Answer

Dopamine inhibits prolactin production

Question 2

The antimullerian hormone is secreted by?

Accepted Answer

Sertoli cells

Answer

Granulosa cells

Answer

Leydig cells

Answer

None of the above

Question 3

Intracellular receptors are present for which of the following substances?

Accepted Answer

All of the above

Answer

Estrogen

Answer

Vitamin D

Answer

Thyroxine

Question 4

What is the primary role of calcitonin in calcium regulation?

Accepted Answer

To lower serum calcium levels

Answer

To increase serum calcium levels

Answer

To decrease serum phosphate levels

Answer

To increase serum phosphate levels

Question 5

After bilateral vasectomy, which of the following substances will be deficient?

Accepted Answer

None

Answer

Fructose

Answer

Prostaglandin

Answer

Fibrinolysin

Question 6

The kidney secretes all of the following hormones except:

Accepted Answer

Vasopressin

Answer

Renin

Answer

Erythropoietin

Answer

1,25-Dihydroxycholecalciferol

Question 7

In a male newborn, adrenogenital syndrome (congenital hyperplasia of the adrenal glands) is most often associated with which of the following?

Accepted Answer

Persistent paramesonephros (Mullerian ducts)

Answer

Normal appearing genitalia

Answer

Hypoglycemia

Answer

Pseudohermaphroditism

Question 8

Which of the following statements regarding growth hormone is incorrect?

Accepted Answer

It lowers blood sugar levels if present in excess.

Answer

It has a strong anabolic action.

Answer

Dopaminergic agonists depress its release in pituitary adenomas.

Answer

Its action is mediated by IGF-1.

Question 9

Gastric tetany is due to:

Accepted Answer

Decreased calcium absorption

Answer

Increased intestinal acidity

Answer

Vagal hyperactivity

Answer

Increased calcium sequestration

Question 10

Plasma ACTH levels are typically highest between which hours?

Accepted Answer

4 AM and 10 AM

Answer

4 PM and 8 PM

Answer

10 AM and 3 PM

Answer

10 AM and 2 PM

Endocrinology — MCQs

Endocrinology — MCQs

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