Endocrinology Practice Questions

Q: Prolactin is synthesized in

Pituitary. ***Pituitary*** - Prolactin is primarily synthesized and secreted by the **lactotroph cells** located in the **anterior pituitary gland**. - Its main function is to stimulate **milk production** (lactation) in mammals. *Thalamus* - The thalamus is a large mass of **gray matter** located in the dorsal part of the diencephalon, primarily involved in relaying **sensory and motor signals**, and the regulation of consciousness and sleep. - It does not have a role in hormone synthesis like prolactin. *Hypothalamus* - The hypothalamus produces **releasing and inhibiting hormones** that regulate the pituitary gland, including **prolactin-inhibiting hormone (PIH)**, which is primarily dopamine. - It does not directly synthesize prolactin itself. *Pineal gland* - The pineal gland is primarily responsible for producing **melatonin**, which regulates **sleep-wake cycles** (circadian rhythm). - It has no role in the synthesis of prolactin.

Q: The blood levels of 1,25 dihydroxycholecalciferol are positively regulated by:-

PTH. ***PTH*** - **Parathyroid hormone (PTH)** is the primary physiological regulator of 1,25-dihydroxycholecalciferol synthesis in the kidneys. - **PTH stimulates the 1-alpha-hydroxylase enzyme**, which converts 25-hydroxycholecalciferol to the active form, 1,25-dihydroxycholecalciferol. *25 OH cholecalciferol* - This is the **precursor molecule** to 1,25-dihydroxycholecalciferol, but its blood level directly reflects overall vitamin D status rather than actively regulating the active form. - While it is the substrate for activated vitamin D, it doesn't directly stimulate its own conversion; rather, **PTH is the key regulator of the conversion process**. *Magnesium* - **Magnesium is a cofactor for many enzymatic reactions**, including those involved in vitamin D metabolism and PTH secretion. - However, it does not directly regulate the blood levels of 1,25-dihydroxycholecalciferol; severe **magnesium deficiency can impair PTH secretion** and action, indirectly affecting vitamin D. *Calcium* - **High blood calcium levels (hypercalcemia) would inhibit PTH release**, thereby negatively regulating 1,25-dihydroxycholecalciferol production. - Conversely, **low calcium levels would stimulate PTH**, which in turn increases 1,25-dihydroxycholecalciferol synthesis to raise calcium levels.

Q: Most metabolically active part in bone is

Cancellous bone. ***Cancellous bone*** - **Cancellous bone** (trabecular/spongy bone) is the **most metabolically active** part of bone due to its **large surface area-to-volume ratio** (approximately 10 times greater than cortical bone). - It has a **high rate of bone turnover** and remodeling, being 8-10 times more active than cortical bone. - Contains abundant **osteoblasts** and **osteoclasts** on trabecular surfaces, making it the primary site for **calcium homeostasis** and rapid response to metabolic demands. - Metabolic bone diseases like **osteoporosis** and **hyperparathyroidism** predominantly affect cancellous bone first due to its high metabolic activity. *Endosteal surface* - The **endosteal surface** (inner lining of cortical bone and trabecular surfaces) is metabolically active with osteoblasts and osteoclasts. - While technically the trabecular surfaces are endosteal surfaces, in clinical teaching, **cancellous bone as a whole** is recognized as the most metabolically active component. - This option represents an anatomical subdivision rather than the structural answer expected in standard physiology. *Cortical bone* - **Cortical bone** (compact bone) is dense and provides structural strength but has **lower metabolic activity** due to its compact structure and smaller surface area. - Remodeling rate is significantly slower (about 1/10th) compared to cancellous bone. - Makes up 80% of skeletal mass but contributes less to metabolic bone turnover. *Periosteal surface* - The **periosteal surface** (outer bone covering) is involved in bone growth in width and fracture repair. - Has osteoblasts and osteoclasts but accounts for a **smaller proportion** of total bone remodeling compared to the extensive trabecular surfaces. - Less metabolically active than cancellous bone overall.

Q: Insulin secretion is decreased by:

Adrenaline. ***Adrenaline*** - **Adrenaline** (epinephrine) stimulates **alpha-2 adrenergic receptors** on pancreatic beta cells, which inhibits insulin secretion. - This mechanism is important during **stress** or **hypoglycemia** to prevent excessive insulin release and support glucose mobilization. *Vagal stimulation* - **Vagal stimulation** (parasympathetic nervous system) generally **increases** insulin secretion. - This effect is mediated by the release of **acetylcholine**, which acts on muscarinic receptors on beta cells. *Glucagon* - While glucagon's primary role is to **increase blood glucose**, it can also directly **stimulate insulin secretion** under certain physiological conditions. - This serves as a feedback loop to prevent excessive hyperglycemia following glucagon-mediated glucose release. *Glucose* - **Glucose** is the primary physiological stimulus for **insulin secretion**. - High blood glucose levels directly activate pancreatic beta cells, leading to insulin release to lower blood glucose.

Q: Due to fear which of the following hormones increases rapidly?

Epinephrine. ***Epinephrine*** - **Epinephrine**, also known as adrenaline, is a hormone and neurotransmitter involved in the **"fight or flight" response** to stress, fear, or excitement. - When faced with fear, the **adrenal medulla** releases epinephrine, leading to rapid physiological changes like increased heart rate, blood pressure, and energy availability to prepare the body for immediate action. *Growth hormones* - **Growth hormone (GH)** primarily regulates growth, metabolism, and body composition. - While stress can influence GH secretion, a rapid increase in direct response to acute fear is not its primary function. *Thyroid hormone* - **Thyroid hormones (T3 and T4)** regulate metabolism, energy balance, and body temperature over a longer term. - Their primary role is not in the immediate, rapid physiological response to acute fear. *Corticosteroid* - **Corticosteroids**, such as cortisol, are released in response to stress, but their increase is typically more prolonged than the instant surge of epinephrine. - They play a role in modulating immune response and metabolism during stress but are not responsible for the immediate "fight or flight" reactions.

Q: The primary action of leptin is:

To decrease food intake. ***To decrease food intake*** - **Leptin** is a hormone primarily produced by **adipocytes (fat cells)** that acts on the hypothalamus to signal satiety and reduce hunger. - Higher levels of leptin indicate ample energy stores, leading to a **decrease in food intake** and an increase in energy expenditure. *To increase food intake* - This is the opposite of leptin's primary action; instead, hormones like **ghrelin** are known to increase food intake. - Leptin's role is to regulate long-term energy balance by **reducing appetite**. *To increase gastric contraction* - **Gastric contractions** are primarily regulated by neural and other hormonal signals (e.g., motilin, gastrin), not leptin. - Leptin's main target is the central nervous system to influence overall **appetite control**. *To increase intestinal motility* - Intestinal motility is primarily influenced by the **enteric nervous system** and hormones such as **serotonin** and **motilin**. - Leptin's action is more focused on **central regulation of satiety** rather than direct effects on gut movement.

Q: Which of the following statements regarding prolactin levels is true?

Sleep - Increased prolactin. ***Sleep - Increased prolactin*** - Prolactin secretion is **pulsatile** and highest during **nocturnal sleep**, peaking around 4-5 AM. - This physiological increase occurs regardless of sleep onset and is a normal diurnal rhythm. *Hyperthyroidism - Increased prolactin* - **Hyperthyroidism** typically causes **decreased prolactin levels** due to altered dopaminergic tone and thyroid hormone effects on pituitary lactotrophs. - Conversely, **hypothyroidism**, particularly primary hypothyroidism, can lead to **increased prolactin** due to elevated TRH stimulating prolactin secretion. *Organic seizure - normal prolactin* - An **organic seizure** (e.g., tonic-clonic seizure) usually causes an **acute, significant elevation in prolactin** levels postictally. - This transient rise in prolactin can be a valuable diagnostic marker to differentiate epileptic seizures from non-epileptic events. *Psychogenic seizure - Decreased prolactin* - **Psychogenic non-epileptic seizures (PNES)** typically result in **normal or slightly decreased prolactin** levels after the event. - This is a key diagnostic differentiator from true epileptic seizures, which show postictal prolactin elevation.

Q: The function of which of the following is increased by an elevated parathyroid hormone concentration:

Osteoclasts. ***Osteoclasts*** - **Parathyroid hormone (PTH)** primarily acts to increase serum calcium levels by stimulating **osteoclasts**, leading to bone resorption and release of calcium and phosphate into the bloodstream. - While PTH does not directly act on osteoclasts, it binds to receptors on osteoblasts, which then release factors that activate osteoclasts. *Action of osteoblasts only* - PTH indirectly affects **osteoblasts** by binding to their receptors, but this action primarily leads to **RANKL expression**, which then stimulates osteoclast activity, not a direct increase in osteoblastic bone formation. - Chronic elevation of PTH, as seen in primary hyperparathyroidism, can paradoxically lead to a net loss of bone mass due to increased osteoclastic activity. *Phosphate reabsorptive pathways in the renal tubules* - PTH actually **decreases reabsorption of phosphate** in the renal tubules, leading to phosphaturia. This helps to prevent calcium-phosphate precipitation by lowering serum phosphate levels while raising calcium. - This is a key mechanism by which PTH increases serum calcium—by both mobilizing it from bone and reducing its renal excretion, while simultaneously promoting renal phosphate excretion. *Hepatic formation of 25-hydroxycholecalciferol* - The **liver** is responsible for the hydroxylation of vitamin D3 (cholecalciferol) to **25-hydroxycholecalciferol (calcidiol)**, a process that is not directly regulated by PTH. - PTH primarily stimulates the **kidneys** to convert 25-hydroxycholecalciferol to its active form, **1,25-dihydroxyvitamin D (calcitriol)**, which then enhances intestinal calcium absorption.

Q: Function of leptin is:

Reduce food intake. ***Reduce food intake*** - **Leptin** is a hormone secreted by **adipose tissue** that signals **satiety** to the brain, which leads to a reduction in energy intake and increased expenditure. - It acts on the **hypothalamus** to inhibit the production of neuropeptides that stimulate appetite and to stimulate the production of neuropeptides that suppress appetite. *Stimulation of AgRP* - **Agouti-related peptide (AgRP)** is a neuropeptide that **promotes feeding** and reduces energy expenditure. - Leptin's function is to **inhibit, not stimulate**, AgRP expression and activity, thus suppressing appetite. *Decrease lipolysis* - Leptin generally acts to **increase lipolysis** and lipid oxidation in peripheral tissues, rather than decrease it. - This action helps to reduce fat stores and increase energy expenditure, aligning with its role in weight regulation. *All of the options* - This option is incorrect because leptin's primary role is to **reduce food intake**, and it **inhibits AgRP** and generally **increases lipolysis**, contrary to the other choices. - Therefore, not all the listed functions are accurate descriptions of leptin's actions.

Question 1

Prolactin is synthesized in

Accepted Answer

Pituitary

Answer

Thalamus

Answer

Hypothalamus

Answer

Pineal gland

Question 2

During the metabolism of iodine in thyroid synthesis, Wolff-Chaikoff effect is seen due to:

Accepted Answer

Inhibition of organic binding of iodide

Answer

Inhibition of iodide trapping mechanism

Answer

Inhibition of cAMP response of TSH

Answer

Inhibition of proteolysis of Thyroglobulin

Question 3

The blood levels of 1,25 dihydroxycholecalciferol are positively regulated by:-

Accepted Answer

PTH

Answer

25 OH cholecalciferol

Answer

Magnesium

Answer

Calcium

Question 4

Most metabolically active part in bone is

Accepted Answer

Cancellous bone

Answer

Endosteal surface

Answer

Cortical bone

Answer

Periosteal surface

Question 5

Insulin secretion is decreased by:

Accepted Answer

Adrenaline

Answer

Vagal stimulation

Answer

Glucagon

Answer

Glucose

Question 6

Due to fear which of the following hormones increases rapidly?

Accepted Answer

Epinephrine

Answer

Growth hormones

Answer

Thyroid hormone

Answer

Corticosteroid

Question 7

The primary action of leptin is:

Accepted Answer

To decrease food intake

Answer

To increase food intake

Answer

To increase gastric contraction

Answer

To increase intestinal motility

Question 8

Which of the following statements regarding prolactin levels is true?

Accepted Answer

Sleep - Increased prolactin

Answer

Hyperthyroidism - Increased prolactin

Answer

Organic seizure - normal prolactin

Answer

Psychogenic seizure - Normal prolactin

Question 9

The function of which of the following is increased by an elevated parathyroid hormone concentration:

Accepted Answer

Osteoclasts

Answer

Action of osteoblasts only

Answer

Phosphate reabsorptive pathways in the renal tubules

Answer

Hepatic formation of 25-hydroxycholecalciferol

Question 10

Function of leptin is:

Accepted Answer

Reduce food intake

Answer

Stimulation of AgRP

Answer

Decrease lipolysis

Answer

All of the options

Endocrinology — MCQs

Endocrinology — MCQs

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