Endocrinology Practice Questions

Q: Which of the following inhibits prolactin secretion?

Bromocriptine. **Explanation:** The regulation of prolactin is unique among anterior pituitary hormones because it is under **predominant tonic inhibition** by the hypothalamus. The primary Prolactin Inhibiting Factor (PIF) is **Dopamine**, which acts on D2 receptors of the lactotrophs. **Why Bromocriptine is correct:** **Bromocriptine** is a potent **Dopamine (D2) receptor agonist**. By mimicking the action of endogenous dopamine, it directly inhibits the synthesis and secretion of prolactin from the anterior pituitary. It is the clinical gold standard for treating hyperprolactinemia and prolactinomas. **Analysis of Incorrect Options:** * **A. Dopamine antagonist:** These drugs (e.g., Metoclopramide, Haloperidol) block the inhibitory effect of dopamine, leading to **increased** prolactin levels (hyperprolactinemia) and potentially causing galactorrhea. * **B. GABA:** While GABA can have minor inhibitory effects on prolactin in some experimental models, it is not the primary physiological regulator. In the context of standard physiology and NEET-PG, Dopamine is the definitive inhibitor. * **C. Neurophysin:** These are carrier proteins for Oxytocin (Neurophysin I) and ADH (Neurophysin II). They are involved in the transport of posterior pituitary hormones and have no role in prolactin regulation. **High-Yield Clinical Pearls for NEET-PG:** * **TRH (Thyrotropin-Releasing Hormone):** Acts as a potent prolactin-releasing factor. This explains why patients with **primary hypothyroidism** (high TRH) often present with secondary hyperprolactinemia. * **Prolactin & GnRH:** High prolactin levels inhibit the pulsatile release of GnRH, leading to infertility and amenorrhea. * **Suckling Reflex:** Inhibits dopamine release, thereby disinhibiting prolactin to promote milk production.

Q: Which of the following is NOT a mechanism of action of insulin?

Inhibition of Na+K+ATPase. **Explanation:** The correct answer is **C (Inhibition of Na+K+ATPase)** because insulin actually **stimulates** the Na+K+ATPase pump, rather than inhibiting it. **Why Option C is correct:** Insulin increases the activity and number of Na+K+ATPase pumps on cell membranes (especially in skeletal muscle and adipose tissue). This leads to an increased influx of Potassium ($K^+$) into the cells and an efflux of Sodium ($Na^+$). This mechanism is clinically significant as it can lead to hypokalemia, which is why insulin is used in the emergency management of hyperkalemia. **Why the other options are incorrect:** * **Option A (Tyrosine kinase-beta cell stimulation):** The insulin receptor is a heterotetramer with intrinsic **Tyrosine Kinase** activity. When insulin binds to the alpha subunits, it causes autophosphorylation of the beta subunits, triggering the intracellular signaling cascade. * **Option B (Incorporation of GLUT-4):** Insulin promotes the translocation of **GLUT-4** (glucose transporter) from intracellular vesicles to the plasma membrane in skeletal muscle and adipose tissue, facilitating glucose uptake. * **Option D (Hexokinase stimulation):** Insulin enhances glucose utilization by inducing and activating key glycolytic enzymes, including **Hexokinase** (and Glucokinase in the liver), to trap glucose inside the cell as Glucose-6-Phosphate. **High-Yield NEET-PG Pearls:** * **GLUT-4** is the only insulin-dependent glucose transporter. * Insulin causes a **"Shift" of Potassium** into cells; always monitor $K^+$ levels when administering an insulin drip for DKA. * **Anabolic effects:** Insulin stimulates protein synthesis, glycogen synthesis (Glycogen Synthase), and lipogenesis, while inhibiting gluconeogenesis and ketogenesis.

Q: Which of the following is an amine hormone?

Thyroxine. **Explanation:** Hormones are chemically classified into three main categories: **Amines, Peptides/Proteins, and Steroids.** **Thyroxine (T4)** is the correct answer because it is an **amine hormone**. Amine hormones are derivatives of the amino acid **Tyrosine**. This group includes thyroid hormones (T3, T4) and catecholamines (Epinephrine, Norepinephrine, and Dopamine). Although derived from tyrosine, thyroid hormones are unique because they are lipophilic and act on intracellular receptors, unlike catecholamines which are hydrophilic. **Analysis of Incorrect Options:** * **Insulin:** This is a **peptide hormone** consisting of 51 amino acids arranged in two chains (A and B) linked by disulfide bridges. * **Glucocorticoids (e.g., Cortisol):** These are **steroid hormones** derived from cholesterol. They are produced in the adrenal cortex and are lipid-soluble. * **Parathyroid Hormone (PTH):** This is a **polypeptide hormone** (84 amino acids) secreted by the chief cells of the parathyroid gland. **High-Yield NEET-PG Pearls:** 1. **Tyrosine Derivatives:** Remember the "T" rule—Tyrosine gives rise to **T**hyroid hormones and **T**ransmitters (Catecholamines). 2. **Tryptophan Derivative:** **Melatonin** and Serotonin are derived from the amino acid Tryptophan (frequently tested). 3. **Receptor Location:** Most amine and peptide hormones bind to cell surface receptors, but **Thyroid hormones** are the notable exception—they bind to **nuclear receptors**. 4. **Steroid Mnemonic:** All hormones from the Adrenal Cortex, Gonads, and Corpus Luteum are steroids (plus Vitamin D).

Q: Capacitation of sperms occurs in which of the following locations?

Uterus. **Explanation:** **Capacitation** is the final physiological maturation process that spermatozoa must undergo to gain the ability to fertilize an oocyte. While sperms are morphologically mature and motile upon leaving the male reproductive tract, they are functionally "decapacitated" by inhibitory factors in the seminal fluid. **Why Uterus is Correct:** Capacitation occurs within the **female reproductive tract** (primarily the uterus and fallopian tubes). The process involves the removal of cholesterol and glycoproteins from the sperm cell membrane, leading to increased calcium permeability. This triggers **hyperactivation** (whiplash-like tail movement) and prepares the sperm for the **acrosome reaction** upon contact with the zona pellucida. It typically takes 5–7 hours. **Why Incorrect Options are Wrong:** * **Seminiferous Tubules:** This is the site of **spermatogenesis** (production of immature sperms). Sperms here are non-motile and incapable of fertilization. * **Epididymis:** This is the site where sperms undergo **morphological maturation** and gain progressive motility. However, they remain inhibited by decapacitation factors. * **Vas Deferens:** This serves primarily as a storage and transport conduit for mature sperms prior to ejaculation. **High-Yield NEET-PG Pearls:** 1. **Site of Fertilization:** Usually the **Ampulla** of the fallopian tube. 2. **Acrosome Reaction:** Occurs only *after* capacitation, triggered by binding to **ZP3 receptors** on the zona pellucida. 3. **Key Ion:** **Calcium ($Ca^{2+}$)** influx is the critical trigger for both hyperactivation and the acrosome reaction. 4. **In Vitro Fertilization (IVF):** In lab settings, capacitation must be induced artificially using specific media to mimic the female tract environment.

Q: A patient has a goiter associated with high plasma levels of both TRH and TSH. Her heart rate is elevated. This patient most likely has which condition?

A hypothalamic tumor secreting large amounts of TRH. ### Explanation **Concept Overview:** The diagnosis of thyroid disorders relies on understanding the **Hypothalamic-Pituitary-Thyroid (HPT) axis** and the principle of **negative feedback**. Normally, high levels of thyroid hormones (T3/T4) inhibit the release of TRH from the hypothalamus and TSH from the anterior pituitary. **Why Option B is Correct:** In this patient, both **TRH and TSH are elevated**. This indicates a "top-down" pathology. A **hypothalamic tumor** secreting TRH will overstimulate the pituitary to produce TSH. High TSH, in turn, overstimulates the thyroid gland, causing **goiter** (hyperplasia) and excessive T3/T4 production. The elevated heart rate (tachycardia) is a clinical manifestation of the resulting hyperthyroidism. **Why Other Options are Incorrect:** * **A. Endemic Goiter:** Caused by iodine deficiency. While TSH is high (due to lack of feedback inhibition), T3/T4 levels are low, and TRH is usually not the primary driver measured in this context. * **C. Pituitary Tumor (TSH-oma):** While this would cause high TSH and high T3/T4, the high circulating thyroid hormones would **suppress** the hypothalamus via negative feedback, leading to **low TRH** levels. * **D. Graves' Disease:** This is an autoimmune condition where TSH-receptor antibodies (TRAb) stimulate the thyroid. Because T3/T4 levels are very high, both **TRH and TSH would be suppressed (low)**. **NEET-PG High-Yield Pearls:** * **Secondary Hyperthyroidism:** High T3/T4 with high TSH (usually a pituitary adenoma). * **Tertiary Hyperthyroidism:** High T3/T4 with high TSH and high TRH (hypothalamic origin). * **Primary Hyperthyroidism:** High T3/T4 with low TSH (e.g., Graves', Toxic Multinodular Goiter). * **Wolff-Chaikoff Effect:** Reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.

Q: ACTH secretion is highest during which part of the day?

Morning. **Explanation:** The secretion of **ACTH (Adrenocorticotropic Hormone)** and its downstream product, **Cortisol**, follows a distinct **Diurnal (Circadian) Rhythm**. This rhythm is regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus, which controls the release of Corticotropin-Releasing Hormone (CRH). **Why Morning is Correct:** ACTH levels begin to rise during the late stages of sleep and reach their **peak (nadir) between 6:00 AM and 9:00 AM**. This surge prepares the body for the physiological stresses of waking and the day's activities by increasing blood glucose levels and metabolic activity. **Why Other Options are Incorrect:** * **Noon:** Levels begin to decline steadily after the morning peak. * **Evening:** ACTH levels continue to drop throughout the afternoon and evening. * **Night:** ACTH and Cortisol reach their **lowest levels (trough)** shortly after the onset of sleep, typically around **midnight**. **High-Yield NEET-PG Pearls:** 1. **Pulsatile Secretion:** ACTH is secreted in pulses; however, the frequency and amplitude of these pulses are highest in the early morning. 2. **Clinical Correlation:** To diagnose **Cushing’s Syndrome**, we look for the loss of this diurnal rhythm (e.g., elevated late-night salivary cortisol). 3. **Stress Override:** While the circadian rhythm is the primary regulator, acute physical or emotional stress can override this cycle, causing a spike in ACTH at any time of day. 4. **Shift Workers:** The rhythm is not fixed to clock time but to the sleep-wake cycle; it takes about 1–2 weeks for the rhythm to shift after a change in sleep patterns.

Q: Where are the alpha-estrogen receptors located?

Nuclear receptors in breast. **Explanation:** Estrogen receptors (ERs) are members of the **nuclear receptor superfamily** of intracellular transcription factors. Estrogen, being a lipid-soluble steroid hormone, diffuses across the cell membrane to bind with these receptors. Upon binding, the receptor-ligand complex translocates to the nucleus (if not already present), binds to Estrogen Response Elements (EREs) on DNA, and regulates gene transcription. **Why Option B is Correct:** There are two main subtypes of estrogen receptors: **ER-alpha (ERα)** and **ER-beta (ERβ)**. ERα is the predominant subtype found in the **breast** (specifically mammary epithelium) and the uterus. Its activation is responsible for the proliferative effects of estrogen in these tissues. **Analysis of Incorrect Options:** * **Options A & C:** While a small fraction of estrogen receptors (GPER) are membrane-bound for rapid non-genomic signaling, the classic alpha-estrogen receptors are fundamentally classified as **nuclear receptors**. * **Option D:** While ERα is present in the ovaries (theca cells), **ER-beta (ERβ)** is the predominant isoform found in the granulosa cells of the ovaries. **High-Yield NEET-PG Pearls:** * **Location Summary:** ERα is primarily in the breast, uterus, and liver; ERβ is primarily in the ovaries, prostate, and colon. * **Clinical Correlation:** ERα status is a critical biomarker in breast cancer; ER-positive tumors are candidates for endocrine therapies like **Tamoxifen** (a SERM). * **Mechanism:** Steroid receptors (Estrogen, Progesterone, Testosterone) are typically **Type I nuclear receptors**, whereas Thyroid and Vitamin D receptors are **Type II** (already bound to DNA).

Question 1

Which of the following inhibits prolactin secretion?

Accepted Answer

Bromocriptine

Answer

Dopamine antagonist

Answer

GABA

Answer

Neurophysin

Question 2

Which of the following is NOT a mechanism of action of insulin?

Accepted Answer

Inhibition of Na+K+ATPase

Answer

Tyrosine kinase-beta cell stimulation

Answer

Incoporation of GLUT-4 into cells

Answer

Hexokinase stimulation

Question 3

Which of the following is an amine hormone?

Accepted Answer

Thyroxine

Answer

Insulin

Answer

Glucocorticoid

Answer

Parathyroid hormone (PTH)

Question 4

Capacitation of sperms occurs in which of the following locations?

Accepted Answer

Uterus

Answer

Seminiferous tubules

Answer

Epididymis

Answer

Vas deferens

Question 5

A patient has a goiter associated with high plasma levels of both TRH and TSH. Her heart rate is elevated. This patient most likely has which condition?

Accepted Answer

A hypothalamic tumor secreting large amounts of TRH

Answer

An endemic goiter

Answer

A pituitary tumor secreting large amounts of TSH

Answer

Graves' disease

Question 6

Parasympathetic stimulation of nerves innervating the islets of the pancreas will:

Accepted Answer

Increase secretion of insulin from B cells

Answer

Have no effect

Answer

Decrease secretion of insulin from B cells

Answer

Increase secretion of glucagon from B cells

Question 7

Which of the following hormones stimulates increased testosterone production by ovaries in PCOD?

Accepted Answer

Luteinizing Hormone

Answer

Estrogen

Answer

Follicle-stimulating Hormone

Answer

Inhibin

Question 8

ACTH secretion is highest during which part of the day?

Accepted Answer

Morning

Answer

Noon

Answer

Evening

Answer

Night

Question 9

What is the Chvostek sign?

Accepted Answer

Twitching of circumoral muscles on tapping of the facial nerve

Answer

Involuntary blink on tapping of the facial nerve

Answer

Inability to open the eye on tapping of the facial nerve

Answer

Inability to close the eye on tapping of the facial nerve

Question 10

Where are the alpha-estrogen receptors located?

Accepted Answer

Nuclear receptors in breast

Answer

Membrane receptors in breast

Answer

Membrane receptors in ovaries

Answer

Nuclear receptors in ovaries

Endocrinology — MCQs

Endocrinology — MCQs

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