Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 741: All of the following act on cell membrane receptors except:

A. TSH
B. Insulin
C. Cortisol (Correct Answer)
D. FSH

Explanation: ***Cortisol*** - **Cortisol** is a **steroid hormone** which is **lipophilic** and can freely diffuse across the cell membrane to bind to **intracellular receptors** in the cytoplasm or nucleus. - Its mechanism of action involves altering gene transcription and protein synthesis, which is characteristic of steroid hormones acting on intracellular receptors. *TSH* - **Thyroid-stimulating hormone (TSH)** is a **glycoprotein hormone** that binds to specific **G protein-coupled receptors** on the surface of thyroid follicular cells. - This binding initiates a signaling cascade that stimulates thyroid hormone production and release. *Insulin* - **Insulin** is a **peptide hormone** that primarily acts by binding to and activating **tyrosine kinase receptors** on the cell surface of target cells like muscle, adipose, and liver cells. - This binding triggers a phosphorylation cascade leading to glucose uptake and metabolic regulation. *FSH* - **Follicle-stimulating hormone (FSH)** is a **glycoprotein hormone** that acts by binding to **G protein-coupled receptors** located on the surface of target cells in the gonads (granulosa cells in females, Sertoli cells in males). - Its binding activates intracellular signaling pathways that regulate reproductive functions, such as follicular development and spermatogenesis.

Question 742: Which of the following is the principal steroid secreted by the fetal adrenal cortex?

A. Dehydroepiandrosterone (Correct Answer)
B. Progesterone
C. Corticosterone
D. Cortisol

Explanation: ***Dehydroepiandrosterone*** - The **fetal adrenal cortex**, particularly the **fetal zone**, is highly active in synthesizing **steroid hormones**, with **dehydroepiandrosterone (DHEA)** being its principal secretion. - **DHEA** serves as a crucial precursor for **estrogen synthesis** in the placenta, which is essential for maintaining pregnancy. *Progesterone* - **Progesterone** is primarily synthesized by the **placenta** during pregnancy and by the **corpus luteum** in the early stages; it is not the main steroid secreted by the fetal adrenal cortex. - While progesterone is important for maintaining uterine quiescence, its production by the fetal adrenal gland is minimal compared to its placental synthesis. *Corticosterone* - **Corticosterone** is a glucocorticoid mainly produced by the adult adrenal cortex, and its synthesis in the fetal adrenal gland is less significant compared to DHEA. - In humans, **cortisol** is the primary glucocorticoid, while corticosterone is more prominent in rodents. *Cortisol* - **Cortisol** is the main glucocorticoid produced by the adult adrenal cortex, playing roles in stress response and metabolism, but it is not the principal steroid secreted by the fetal adrenal cortex. - While the fetal adrenal gland does produce some cortisol, its primary function is **DHEA** production for placental estrogen synthesis.

Question 743: Prolactin inhibiting substance is:

A. Adrenaline
B. Dopamine (Correct Answer)
C. Thyroxine
D. ACTH

Explanation: ***Dopamine*** - **Dopamine** acts as the primary **prolactin-inhibiting hormone (PIH)**, tonically suppressing prolactin release from the anterior pituitary. - It binds to **D2 receptors** on lactotroph cells, reducing prolactin synthesis and secretion. *Adrenaline* - **Adrenaline** (epinephrine) is primarily involved in the "fight or flight" response, affecting heart rate, blood pressure, and metabolism. - While it can indirectly influence pituitary hormones, it is not considered the primary prolactin-inhibiting substance. *Thyroxine* - **Thyroxine (T4)** is a thyroid hormone that regulates metabolism, growth, and development. - There is no direct role of thyroxine as a prolactin-inhibiting substance. *ACTH* - **Adrenocorticotropic hormone (ACTH)** stimulates the adrenal glands to produce cortisol. - It does not directly inhibit prolactin secretion.

Question 744: The suckling reflex:

A. Increases the release of dopamine from the arcuate nucleus
B. Increases placental lactogen secretion
C. Triggers the release of oxytocin by stimulating the supraoptic nuclei
D. Has afferent neuronal and efferent hormonal components (Correct Answer)

Explanation: ***Correct: Has afferent neuronal and efferent hormonal components*** - The **suckling reflex** is a classic **neuroendocrine reflex** with both neural and hormonal components. - **Afferent pathway**: Mechanoreceptors in the nipple send sensory signals via **spinal nerves** to the hypothalamus. - **Efferent pathway**: Hormonal responses include **oxytocin release** (milk ejection) and **prolactin release** (milk production). - This represents the complete physiological description of the suckling reflex mechanism. *Incorrect: Triggers the release of oxytocin by stimulating the supraoptic nuclei* - While partially true, this is **anatomically imprecise**. - Oxytocin for milk ejection is primarily synthesized in the **paraventricular nuclei**, not the supraoptic nuclei. - The **supraoptic nucleus** primarily produces **vasopressin (ADH)**, though both nuclei produce some oxytocin. - This option is too specific and emphasizes the wrong nucleus. *Incorrect: Increases the release of dopamine from the arcuate nucleus* - The suckling reflex **decreases dopamine release** from the arcuate nucleus (tuberoinfundibular neurons). - Since dopamine acts as **prolactin-inhibiting factor (PIF)**, decreased dopamine leads to **increased prolactin secretion**. - This disinhibition mechanism is essential for milk production during lactation. *Incorrect: Increases placental lactogen secretion* - **Human placental lactogen (hPL)** is secreted by the **placenta during pregnancy**, not postpartum. - It prepares mammary glands during pregnancy but does not respond to suckling. - After delivery, the placenta is expelled and hPL secretion ceases.

Question 745: Which of the following is not seen after removal of testis in an adult?

A. Decrease FSH (Correct Answer)
B. Impotence
C. Loss of libido
D. Muscle weakness

Explanation: ***Decrease FSH*** - Removal of the testes (orchiectomy) in an adult leads to a **decrease in testosterone production** and the **loss of inhibin B**, which normally suppress FSH secretion. - This reduction in negative feedback on the pituitary gland results in a **marked rise in FSH and LH levels**, not a decrease. - Therefore, "decrease FSH" is **NOT seen** after testicular removal - FSH actually **increases**. *Impotence* - The testes are the primary site of **testosterone production**, which is crucial for erectile function. - Their removal substantially reduces testosterone, leading to **erectile dysfunction (impotence)**. *Loss of libido* - **Testosterone** plays a vital role in maintaining sexual desire and libido in males. - Orchiectomy causes a significant drop in testosterone, leading to a **marked decrease or loss of libido**. *Muscle weakness* - **Testosterone** has anabolic effects, promoting muscle growth and strength. - Its removal leads to a chronic state of **hypogonadism**, often resulting in **muscle atrophy and weakness** over time.

Question 746: Which of the following is the primary physiological stimulus for prolactin release?

A. Increased sleep duration
B. Reduction in dopamine levels
C. Elevated blood glucose levels
D. Nipple stimulation (Correct Answer)

Explanation: ***Nipple stimulation*** - **Nipple stimulation** (e.g., during breastfeeding or suckling) is the **primary physiological stimulus** for prolactin release. - It activates neural pathways from the nipple to the hypothalamus, which **inhibit dopamine release**. - Since dopamine acts as **prolactin-inhibiting hormone (PIH)**, reduced dopamine leads to **disinhibition** of prolactin secretion from the anterior pituitary lactotroph cells. - This is the most clinically important mechanism for maintaining lactation. *Increased sleep duration* - Prolactin levels do exhibit a **circadian rhythm** with elevated levels during sleep (nocturnal surge). - However, sleep is not considered a primary or acute stimulus for prolactin release. - **Suckling/nipple stimulation** and **stress** are much more potent stimuli. *Reduction in dopamine levels* - This represents the **biochemical mechanism** underlying prolactin release rather than a physiological stimulus. - Dopamine from the hypothalamus tonically **inhibits** prolactin secretion. - Various physiological stimuli (like nipple stimulation, stress, or pregnancy) work by reducing dopamine tone. - When asking for a "stimulus," we refer to the **initiating event** (e.g., suckling), not the intermediate biochemical step. *Elevated blood glucose levels* - **Elevated blood glucose** primarily stimulates **insulin release** from pancreatic beta cells. - There is no direct physiological link between blood glucose and prolactin secretion. - Prolactin is not involved in glucose homeostasis.

Question 747: Appetite is stimulated by all except

A. Neuropeptide Y
B. Agouti related peptide
C. Melanocyte concentrating hormone
D. Melanocyte stimulating hormone (Correct Answer)

Explanation: ***Melanocyte stimulating hormone*** - **Alpha-melanocyte stimulating hormone (α-MSH)** is a catabolic hormone that acts to reduce appetite and increase energy expenditure. - It is an **anorexigenic peptide** that suppresses feeding by binding to central melanocortin receptors, primarily MC4R. *Neuropeptide Y* - **Neuropeptide Y (NPY)** is a potent **orexigenic peptide** that stimulates appetite and food intake. - It plays a crucial role in regulating energy balance and is increased during fasting states. *Agouti related peptide* - **Agouti-related peptide (AgRP)** is a strong **orexigenic peptide** that increases food intake. - It acts as an **antagonist** at the MC3R and MC4R melanocortin receptors, counteracting the appetite-suppressing effects of α-MSH. *Melanocyte concentrating hormone* - **Melanin-concentrating hormone (MCH)** is an **orexigenic neuropeptide** that stimulates feeding behavior. - It is primarily expressed in the lateral hypothalamus and plays a significant role in promoting appetite and weight gain.

Question 748: Systemic factor which is responsible for bone remodeling :

A. Cytokines (e.g., IL-1, IL-6)
B. Prostaglandin E2 (PGE2)
C. PTH (Correct Answer)
D. Transforming Growth Factor-beta (TGF-β)

Explanation: ***PTH*** - **Parathyroid hormone (PTH)** is a major systemic regulator of bone remodeling, primarily influencing **calcium and phosphate homeostasis**. - High levels of PTH, particularly prolonged or continuous elevation, stimulate **osteoclasts** directly or indirectly, leading to increased **bone resorption**. *Cytokines (e.g., IL-1, IL-6)* - These are primarily **local humoral factors** that regulate bone remodeling in a specific area, often in response to inflammation or injury. - While they can influence bone metabolism, their action is generally more localized, unlike the widespread systemic effects of PTH. *Prostaglandin E2 (PGE2)* - **PGE2** is another **local mediator** involved in bone remodeling, produced by various cells including osteoblasts and osteocytes. - It plays a role in both bone formation and resorption depending on concentration and context, but its effects are typically paracrine or autocrine rather than systemic endocrine control. *Transforming Growth Factor-beta (TGF-β)* - **TGF-β** is a potent **local growth factor** stored within the bone matrix and released during bone resorption. - It regulates proliferation and differentiation of osteoblasts and osteoclasts, primarily acting as a local regulator of bone formation and repair rather than a systemic hormone.

Question 749: A middle aged man noticed that he can no longer fit in his shoes and that his jaw was protruding and phalanges were enlarged. These effects are likely to be mediated by

A. TRH
B. ACTH
C. TGF Beta
D. IGF-1 (Correct Answer)

Explanation: ***IGF-1*** - The described symptoms (increased shoe size, jaw protrusion, enlarged phalanges) are characteristic of **acromegaly**, a condition caused by excessive growth hormone (GH) secretion in adults. - **Insulin-like Growth Factor 1 (IGF-1)** is primarily responsible for mediating the growth-promoting effects of GH on various tissues, leading to the clinical manifestations seen in this patient. *TRH* - **Thyrotropin-releasing hormone (TRH)** stimulates the release of thyroid-stimulating hormone (TSH) from the pituitary, which in turn regulates thyroid hormone production. - Excess TRH would lead to hyperthyroidism symptoms like weight loss, heat intolerance, and tachycardia, not acromegalic features. *ACTH* - **Adrenocorticotropic hormone (ACTH)** stimulates the adrenal glands to produce cortisol. - Excessive ACTH causes **Cushing's syndrome**, characterized by central obesity, moon facies, striae, and muscle weakness, which are different from the presented symptoms. *TGF Beta* - **Transforming growth factor beta (TGF-beta)** is a pleiotropic cytokine involved in cell growth, differentiation, apoptosis, and immune regulation. - While it plays a role in tissue remodeling and fibrosis, it is not the direct mediator of the generalized growth and skeletal changes seen in acromegaly.

Question 750: The hormone which helps in milk secretion:

A. FSH
B. Oxytocin
C. Growth hormone
D. Prolactin (Correct Answer)

Explanation: **Prolactin** - **Prolactin** is the primary hormone responsible for **milk production** (lactogenesis) in the mammary glands after childbirth. - It stimulates the alveolar cells to synthesize and secrete milk components. *FSH* - **Follicle-stimulating hormone (FSH)** is involved in the development of **ovarian follicles** and **sperm production**, not milk secretion. - Its main actions are on the gonads to regulate reproductive cycles. *Oxytocin* - **Oxytocin** is responsible for **milk ejection** (milk let-down reflex), causing contraction of myoepithelial cells, but it does not directly stimulate milk production. - It also plays a role in uterine contractions during labor. *Growth hormone* - **Growth hormone (GH)** primarily promotes **growth** and **metabolism** throughout the body. - While it can have some metabolic effects that indirectly support lactation, it is not the main hormone for milk *secretion* itself.

Practice by Chapter

Principles of Endocrine Regulation

Practice Questions

Hypothalamus and Pituitary Gland

Practice Questions

Thyroid Physiology

Practice Questions

Adrenal Cortex and Medulla

Practice Questions

Pancreatic Hormones and Glucose Metabolism

Practice Questions

Calcium and Phosphate Homeostasis

Practice Questions

Growth Hormone and Growth Factors

Practice Questions

Endocrine Regulation of Metabolism

Practice Questions

Hormone Receptors and Signaling

Practice Questions

Assessment of Endocrine Function

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free