Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 751: Following organs/tissues have proven endocrine function/capability except

A. Salivary gland (Correct Answer)
B. Adipocytes
C. Stomach
D. Heart

Explanation: ***Salivary gland*** - Salivary glands are primarily **exocrine glands**, producing saliva which contains enzymes and lubricants for digestion. - While they contribute to oral health, they do not have a recognized **endocrine function** of secreting hormones directly into the bloodstream to regulate distant organs. *Adipocytes* - **Adipocytes** (fat cells) are known to have significant **endocrine function**, secreting hormones like **leptin**, adiponectin, and resistin, which play roles in metabolism, appetite regulation, and inflammation. - These hormones act on various target tissues throughout the body, influencing energy homeostasis and insulin sensitivity. *Stomach* - The stomach contains specialized cells that secrete various hormones, such as **gastrin**, ghrelin, somatostatin, and histamine. - **Gastrin** stimulates gastric acid secretion, while **ghrelin** promotes hunger, demonstrating its important endocrine role in digestion and appetite regulation. *Heart* - The heart, particularly the atria, produces and secretes **atrial natriuretic peptide (ANP)**. - **ANP** acts as a hormone to regulate blood pressure and fluid balance by promoting sodium and water excretion by the kidneys.

Question 752: Prolactin levels are highest in which of the following?

A. After 24 hrs of ovulation
B. After nipple stimulation (Correct Answer)
C. After 24 hours of parturition
D. Just before parturition

Explanation: ***After nipple stimulation*** - Nipple stimulation is a powerful physiological stimulus for **prolactin release** from the anterior pituitary. - This reflex is essential for **lactation** and milk let-down, as suckling signals directly enhance prolactin secretion. *After 24 hrs of ovulation* - Prolactin levels do not peak significantly 24 hours after ovulation; while some fluctuation occurs during the menstrual cycle, the highest levels are not seen at this time. - **Luteinizing hormone (LH)** and **follicle-stimulating hormone (FSH)** are the primary hormones exhibiting surges related to ovulation. *After 24 hours of parturition* - While prolactin levels are elevated throughout the third trimester and immediately postpartum, they tend to **decline somewhat** if breastfeeding is not initiated within the first 24-48 hours. - Post-partum, prolactin levels are primarily sustained by **frequent nipple stimulation** from breastfeeding. *Just before parturition* - Prolactin levels are **chronically elevated** during the third trimester of pregnancy, but the **acute highest surge** or peak is typically in response to specific triggers like nipple stimulation, rather than just the state of being immediately pre-partum. - High prolactin during late pregnancy prepares the breasts for lactation but is not necessarily the **absolute peak** that nipple stimulation can elicit.

Question 753: Serum prolactin levels are highest

A. 24 hrs after parturition
B. REM sleep
C. In actively lactating mothers
D. During third trimester of pregnancy (Correct Answer)

Explanation: ***Correct: During third trimester of pregnancy*** - **Serum prolactin levels reach their absolute highest** during the **third trimester of pregnancy**, rising progressively from normal levels (5-25 ng/mL) to peak values of **200-400 ng/mL** near term. - This represents the **highest physiological prolactin levels** observed in humans. - Despite these high levels, **lactation does not occur** during pregnancy because **estrogen and progesterone** block prolactin's action on mammary tissue. - The high prolactin prepares the breast for lactation but milk secretion is inhibited until delivery. *Incorrect: 24 hrs after parturition* - After delivery, prolactin levels actually begin to **decline** from their pregnancy peak, though they remain elevated (around 200 ng/mL). - While **lactogenesis II** (copious milk production) begins 24-72 hours postpartum, this is due to the **removal of estrogen/progesterone inhibition**, not because prolactin levels peak at this time. - The confusion arises from conflating **functional milk production** with **peak hormone levels**. *Incorrect: REM sleep* - Prolactin exhibits **circadian variation** with nocturnal rise during sleep, peaking in early morning hours. - However, these sleep-related peaks (typically 25-40 ng/mL) are **much lower** than pregnancy levels. - This physiological variation is unrelated to reproductive function. *Incorrect: In actively lactating mothers* - During established lactation, basal prolactin levels gradually decline over weeks to months. - Each **suckling episode** causes transient prolactin surges (2-10 fold increase), but these peaks are still **lower than third trimester levels**. - By 6 months postpartum, basal prolactin may return near pre-pregnancy levels despite continued lactation.

Question 754: Which hormone has permissive role in puberty?

A. GH
B. Leptin (Correct Answer)
C. GnRH
D. Insulin

Explanation: ***Leptin*** - **Leptin** acts as a permissive signal that informs the hypothalamus about the body's **nutritional status** and energy reserves. - A certain threshold level of **leptin**, reflecting adequate body fat, is generally required for the initiation and progression of puberty. *GH* - **Growth hormone (GH)** is crucial for overall somatic growth during childhood and adolescence, but it does not directly trigger the onset of puberty. - While GH is important for the pubertal growth spurt, it acts primarily in an anabolic role rather than initiating the reproductive axis. *GnRH* - **Gonadotropin-releasing hormone (GnRH)** is the primary neurohormone that directly initiates and drives puberty by stimulating the pituitary. - However, GnRH is the *driver* of puberty rather than a *permissive* factor, meaning its pulsatile release is the direct trigger for the reproductive cascade. *Insulin* - **Insulin** is involved in glucose metabolism and energy homeostasis throughout the body. - While good metabolic health is indirectly important for puberty, insulin does not play a direct permissive role in initiating the pubertal process like leptin does.

Question 755: Which of the following hormone crosses the plasma membrane for its action?

A. Insulin
B. Epinephrine
C. Thyroxine (Correct Answer)
D. Glucagon

Explanation: ***Thyroxine*** - **Thyroxine (T4)** and **triiodothyronine (T3)** are **lipid-soluble** thyroid hormones. - Due to their lipid solubility, they can freely cross the **plasma membrane** and bind to intracellular receptors. *Insulin* - **Insulin** is a **peptide hormone** and is **water-soluble**. - It binds to specific **cell-surface receptors** on the plasma membrane, initiating a signaling cascade without entering the cell. *Epinephrine* - **Epinephrine (adrenaline)** is a **catecholamine** and is **water-soluble**. - It acts on **G protein-coupled receptors** on the cell surface, triggering intracellular secondary messengers. *Glucagon* - **Glucagon** is a **peptide hormone** that is **water-soluble**. - Like insulin, it binds to specific **cell-surface receptors** (G protein-coupled receptors) to exert its effects.

Question 756: In females, the adrenal glands are the exclusive source for secretion of?

A. Testosterone
B. Estrogen
C. Progesterone
D. DHEAS (Correct Answer)

Explanation: ***DHEAS*** - **Dehydroepiandrosterone sulfate (DHEAS)** is almost exclusively produced by the **adrenal glands** in both males and females. - Its levels are often used as a marker of **adrenal androgen production**, making it unique in terms of its exclusive adrenal source in women. *Testosterone* - While the adrenal glands produce small amounts of androgens, the primary source of **testosterone** in females is the **ovaries** and peripheral conversion of adrenal precursors. - Testes are the primary source in males, and it is not exclusively from the adrenal glands in females. *Estrogen* - **Estrogen** is primarily produced by the **ovaries** in females, particularly estradiol. - Peripheral conversion of androgens in adipose tissue also contributes to estrogen levels, and the adrenal glands do not secrete significant amounts directly. *Progesterone* - **Progesterone** is predominantly produced by the **corpus luteum** in the ovary after ovulation and by the placenta during pregnancy. - The adrenal glands produce only minor amounts of progesterone.

Question 757: Maximum steroid produced by fetal adrenal:

A. Progesterone
B. DHEA-S (Correct Answer)
C. Corticosterone
D. Cortisol

Explanation: ***DHEA-S*** - The fetal adrenal gland, particularly the **fetal zone**, is highly developed and specialized in producing large amounts of **dehydroepiandrosterone sulfate (DHEA-S)**. - DHEA-S serves as a crucial precursor for **estrogen synthesis** in the placenta during pregnancy. *Progesterone* - While essential for maintaining pregnancy, **progesterone** is primarily produced by the **placenta**, not the fetal adrenal gland. - The fetal adrenal gland lacks the enzyme **3β-hydroxysteroid dehydrogenase** in its fetal zone, limiting its ability to convert DHEA to progesterone. *Corticosterone* - **Corticosterone** is a glucocorticoid, but it is not the primary or maximum steroid produced by the fetal adrenal gland. - The fetal adrenal gland focuses more on **androgen precursors** necessary for feto-placental estrogen production. *Cortisol* - Although the fetal adrenal gland does produce some **cortisol**, its production significantly increases towards late gestation for organ maturation, it is not the **maximum steroid** produced throughout fetal development, especially compared to DHEA-S. - The pathway for cortisol synthesis is not as prominent in the fetal zone as the pathway for **DHEA-S**.

Question 758: All of the following are true about the adrenal gland EXCEPT:

A. Zona fasciculata secretes cortisol
B. Medulla produces mineralocorticoids (Correct Answer)
C. Zona glomerulosa produces aldosterone
D. Zona reticularis secretes androgens

Explanation: ***Medulla produces mineralocorticoids*** - The **adrenal medulla** primarily produces **catecholamines** (epinephrine and norepinephrine), not mineralocorticoids. - **Mineralocorticoids** (like aldosterone) are secreted by the **zona glomerulosa** in the adrenal cortex. *Zona fasciculata secretes cortisol* - The **zona fasciculata** is the middle and largest layer of the adrenal cortex. - Its primary function is the secretion of **glucocorticoids**, mainly **cortisol**, which is crucial for stress response and metabolism. *Zona glomerulosa produces aldosterone* - The **zona glomerulosa** is the outermost layer of the adrenal cortex. - It is responsible for producing **mineralocorticoids**, with **aldosterone** being the most significant. *Zona reticularis secretes androgens* - The **zona reticularis** is the innermost layer of the adrenal cortex, adjacent to the medulla. - It primarily secretes **adrenal androgens** (like DHEA and androstenedione), which are precursors to sex hormones.

Question 759: Which hormone does not play a significant role in utero growth?

A. Insulin
B. Cortisol
C. Growth hormone (Correct Answer)
D. Thyroid hormone

Explanation: ***Growth hormone*** - **Growth hormone (GH)** plays a crucial role in postnatal growth, but its direct impact on fetal growth is considered minor, as the **fetal pituitary gland** is not fully mature. - Fetal growth is primarily regulated by other factors like **insulin**, **insulin-like growth factors (IGFs)**, and nutrient supply. *Insulin* - **Insulin** is a major anabolic hormone in utero, promoting nutrient uptake and storage, leading to **fetal growth and glycogen synthesis**. - **Fetal hyperinsulinemia**, often seen in maternal diabetes, can lead to **macrosomia**. *Cortisol* - **Cortisol** is essential for **fetal lung maturation** and the development of several organ systems, thus indirectly influencing overall fetal viability and growth. - While high levels can potentially inhibit growth, physiological levels are crucial for normal development. *Thyroid hormone* - **Thyroid hormone** is critical for normal **fetal brain development** and skeletal maturation. - **Congenital hypothyroidism** can lead to significant developmental delays and poor growth.

Question 760: Which hormone inhibits appetite by acting on hypothalamus?

A. Ghrelin
B. Leptin (Correct Answer)
C. Cortisol
D. Insulin

Explanation: ***Leptin*** - **Leptin** is a hormone produced by fat cells that acts on the hypothalamus to signal **satiety** and inhibit appetite. - Higher levels of leptin typically indicate sufficient energy stores, leading to reduced food intake and increased energy expenditure. *Ghrelin* - **Ghrelin** is primarily produced by the stomach and is known as the "**hunger hormone**" because it stimulates appetite, rather than inhibiting it. - Its levels rise before meals and fall after eating, signaling the brain to initiate food consumption. *Cortisol* - **Cortisol** is a steroid hormone produced by the adrenal glands, often associated with stress response, and can actually stimulate appetite, particularly for high-calorie foods. - It does not primarily function as an appetite-inhibiting hormone acting on the hypothalamus. *Insulin* - **Insulin** is a hormone produced by the pancreas that regulates blood glucose levels; while it can have some short-term effects on satiety, its primary role is not long-term appetite inhibition in the hypothalamus. - High insulin can initially suppress appetite, but chronically elevated insulin can sometimes contribute to **insulin resistance** and increased food intake.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Adrenal Cortex and Medulla

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Pancreatic Hormones and Glucose Metabolism

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Calcium and Phosphate Homeostasis

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Growth Hormone and Growth Factors

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Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

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Assessment of Endocrine Function

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