NEET-PG 2013 - Physiology Practice Questions

Q: Which of the following hormones is not stored in cells?

Cortisol. ***Cortisol*** - Cortisol is a **steroid hormone** that is synthesized from **cholesterol** on demand and is **not stored** in secretory vesicles or elsewhere within cells. - Being **lipophilic**, it diffuses freely across cell membranes immediately after synthesis. - Its release is regulated by the **hypothalamic-pituitary-adrenal (HPA) axis**, with synthesis and immediate secretion occurring upon stimulation. *Insulin* - Insulin is a **peptide hormone** synthesized as **proinsulin** and then cleaved into active insulin. - It is **stored in secretory granules** within pancreatic beta cells, allowing for rapid release in response to elevated blood glucose. *Thyroxine* - Thyroxine (T4) is a **thyroid hormone** that is synthesized from tyrosine and iodine. - It is **stored extracellularly** within the thyroid gland's follicles as part of a large protein called **thyroglobulin**. - Unlike cortisol (which is never stored), thyroxine has a **substantial storage pool** that can last weeks, though the storage is extracellular rather than intracellular. *Renin* - Renin is an **enzyme** produced by the **juxtaglomerular cells** of the kidney. - It is **stored in secretory granules** within these cells and released in response to decreased renal perfusion pressure or sympathetic stimulation.

Q: Which hormone acts on JAK-STAT kinase receptor?

GH. ***GH*** - **Growth Hormone (GH)** binds to a **cytokine receptor** that lacks intrinsic tyrosine kinase activity and instead signals through associated **JAK-STAT kinases**. - This binding leads to **JAK phosphorylation**, which then phosphorylates and activates **STAT proteins**, regulating gene expression. *TSH* - **Thyroid-stimulating hormone (TSH)** acts on a **G protein-coupled receptor** to stimulate thyroid hormone production and release. - Its signaling pathway primarily involves the activation of **adenylyl cyclase** and increases in **cAMP**, not the JAK-STAT pathway. *Thyroxine* - **Thyroxine (T4)** is a **thyroid hormone** that primarily acts by binding to **intracellular nuclear receptors**, which then regulate gene transcription. - It directly influences gene expression, rather than signaling through cell surface receptors and kinase pathways like JAK-STAT. *FSH* - **Follicle-stimulating hormone (FSH)**, like TSH, signals through a **G protein-coupled receptor** on target cells in the gonads. - This activation primarily leads to an increase in **intracellular cAMP levels** to mediate its effects on gamete production and hormone synthesis.

Q: What is the half-life of the thyroid hormone triiodothyronine (T3)?

1 day. ***1 day*** - The **half-life of T3 (triiodothyronine)** is approximately **1 day (24 hours)**, making its biological effects relatively rapid compared to T4. - This shorter half-life contributes to its quicker onset and offset of action. *8 hours* - While reflecting a relatively short duration, **8 hours** is not the accepted half-life for T3. - This value is too short for T3, which has a more sustained biological effect. *6 hours* - A half-life of **6 hours** is too short for T3, which has a more sustained effect than such a rapid clearance would suggest. - This would imply a much faster metabolic turnover than observed clinically. *10 days* - **10 days** is longer than the actual **half-life of T4 (thyroxine)**, which is approximately **7 days**. - T4 serves as a prohormone and is more extensively protein-bound, contributing to its prolonged presence in circulation compared to T3.

Q: Thyroid hormone binds to which receptor ?

Nuclear. ***Nuclear*** - Thyroid hormones, being **lipid-soluble**, readily diffuse across the **cell membrane** to bind to receptors located in the nucleus. - This binding directly influences **gene expression** and protein synthesis, mediating the hormone's effects. *Membrane* - Membrane receptors typically bind **water-soluble hormones** (e.g., peptide hormones, catecholamines) that cannot freely cross the cell membrane. - These interactions usually trigger a **second messenger cascade** within the cell. *Cytoplasmic* - While some **steroid hormones** bind to cytoplasmic receptors which then translocate to the nucleus, thyroid hormones bind directly to nuclear receptors. - Cytoplasmic receptors are located in the **cytosol** before their ligand-induced translocation. *None of the options* - This option is incorrect, as thyroid hormones have a specific and well-defined receptor location. - The direct action on **gene regulation** necessitates a nuclear receptor.

Q: Which of the following does not stimulate growth hormone (GH) release?

Free fatty acids. ***Free fatty acids*** - High levels of **free fatty acids** in the bloodstream inhibit growth hormone (GH) secretion. - This occurs through a **negative feedback loop** at the level of the hypothalamus and pituitary gland. *Fasting* - **Fasting** (especially prolonged) is a potent stimulus for GH release, helping to mobilize fat stores and maintain **glucose homeostasis**. - During fasting, ghrelin levels increase, which further promotes GH secretion. *Exercise* - **Physical exercise** is a well-known physiological stimulus for GH release, contributing to muscle growth and repair. - The intensity and duration of exercise can influence the magnitude of GH secretion. *Stress* - Various forms of **stress**, including physical (e.g., trauma, surgery) and psychological stress, stimulate GH release. - This response is mediated in part by the **sympathetic nervous system** and increased cortisol levels.

Q: Which hormone increases with age?

Parathormone. ***Parathormone*** - **Parathormone (PTH)** levels in the blood tend to increase with age, often due to a decline in renal function and reduced vitamin D synthesis, leading to compensatory hyperparathyroidism. - This age-related increase in PTH can contribute to **bone demineralization** and an increased risk of osteoporosis. *GH* - **Growth hormone (GH)** levels generally **decrease with age**, leading to a condition known as somatopause. - Reduced GH contributes to changes in body composition, such as increased adiposity and decreased lean muscle mass, as well as reduced bone density. *Prolactin* - **Prolactin** levels typically remain relatively stable or may slightly decrease with age in men, while in women they can fluctuate due to hormonal changes like menopause but do not show a consistent increase with age. - High prolactin levels are often associated with specific pathological conditions like **prolactinomas** rather than normal aging. *Insulin* - While **insulin resistance** often increases with age, leading to higher fasting insulin levels in some individuals, the overall picture of insulin secretion can be complex and is often influenced by factors such as diet, exercise, and genetics rather than solely age. - A *decline in pancreatic beta-cell function* with age can also lead to impaired insulin secretion in some elderly individuals, complicating the simple relationship between age and insulin levels.

Q: What is the critical closing pressure in the context of capillary physiology?

Pressure below which capillaries close. ***Pressure below which capillaries close*** - The **critical closing pressure** is the lowest pressure at which blood can flow through a capillary. - When the luminal pressure falls below this threshold, the capillary collapses due to **extrinsic tissue pressure** and intrinsic vascular tone. *Arterial pressure minus venous pressure* - This calculation represents the **arteriovenous pressure gradient**, which drives blood flow through a vascular bed. - It does not directly define the point at which capillaries collapse. *Capillary pressure minus venous pressure* - This difference primarily influences filtration and reabsorption of fluids across the capillary wall. - It is not directly related to the **critical closing pressure** of the capillaries. *None of the options* - This is incorrect as one of the provided options accurately defines the **critical closing pressure**.

Q: When blood pressure falls below 40 mm Hg, which mechanism of regulation is working?

CNS ischemic reflex. ***CNS ischemic reflex*** - The **CNS ischemic reflex** is activated when blood pressure falls below 60 mmHg, with maximal activation below 40 mmHg, indicating severe ischemia in the brain's vasomotor center. - This reflex elicits an intense **sympathetic vasoconstriction** and cardiac stimulation to prioritize blood flow to the brain even at the expense of other organs. *Chemoreceptor response* - The chemoreceptor reflex is primarily activated by a decrease in **arterial pO2**, an increase in **pCO2**, or a decrease in **pH**. - While it can increase blood pressure, it is not the primary or most profound regulatory mechanism specifically triggered by extremely low blood pressure (below 40 mmHg) to prevent brain ischemia. *Baroreceptor response* - **Baroreceptors** are most sensitive to changes in blood pressure within the normal to moderately hypotensive range (e.g., 60-180 mmHg). - At very low pressures (below 40-50 mmHg), baroreceptors become **less sensitive** or "saturated," and their effectiveness in raising blood pressure significantly diminishes. *None of the options* - This option is incorrect because the **CNS ischemic reflex** specifically functions as a powerful, last-ditch mechanism to maintain cerebral blood flow during severe hypotension which is a life saving reflex during conditions like hemorrhage.

Q: All are true about baroreceptors, except?

Stimulated when BP decreases. ***Stimulated when BP decreases*** - Baroreceptors are **stretch receptors** located in the walls of the carotid sinus and aortic arch. - They are stimulated by an **increase in blood pressure (BP)**, which causes stretching of the arterial walls, not by a decrease. *Afferents are through sino-aortic nerves* - This statement is **true**. Afferent impulses from the carotid sinus baroreceptors travel via the **glossopharyngeal nerve (IX)**, and those from the aortic arch baroreceptors travel via the **vagus nerve (X)**. - These nerves collectively form the **sino-aortic nerves** that relay information to the brainstem. *Stimulation causes increased vagal discharge* - This statement is **true**. When baroreceptors are stimulated by **increased BP**, they send signals to the cardiovascular center in the medulla. - This leads to increased **parasympathetic (vagal) outflow** to the heart, causing a decrease in heart rate and contractility, and inhibition of sympathetic outflow. *Stimulate nucleus ambiguus* - This statement is **true**. The **nucleus ambiguus** is a brainstem nucleus that contains the cell bodies of preganglionic parasympathetic neurons that contribute to the vagus nerve. - Baroreceptor stimulation leads to activation of the nucleus ambiguus, thereby increasing **vagal output** to the heart.

Question 1

Which of the following hormones is not stored in cells?

Accepted Answer

Cortisol

Answer

Thyroxin

Answer

Renin

Answer

Insulin

Question 2

Which hormone acts on JAK-STAT kinase receptor?

Accepted Answer

GH

Answer

TSH

Answer

Thyroxine

Answer

FSH

Question 3

Which of the following statements about thyroid hormone receptors is correct?

Accepted Answer

They are intracellular receptors that mediate gene transcription after binding with T3 or T4, but their primary action is through T3.

Answer

They directly bind to thyrotropin-releasing hormone (TRH)

Answer

They directly bind to thyroid-stimulating hormone (TSH)

Answer

They cause nuclear transcription after binding with T4

Question 4

What is the half-life of the thyroid hormone triiodothyronine (T3)?

Accepted Answer

1 day

Answer

8 hours

Answer

6 hours

Answer

10 days

Question 5

Thyroid hormone binds to which receptor ?

Accepted Answer

Nuclear

Answer

Membrane

Answer

Cytoplasmic

Answer

None of the options

Question 6

Which of the following does not stimulate growth hormone (GH) release?

Accepted Answer

Free fatty acids

Answer

Exercise

Answer

Fasting

Answer

Stress

Question 7

Which hormone increases with age?

Accepted Answer

Parathormone

Answer

GH

Answer

Prolactin

Answer

Insulin

Question 8

What is the critical closing pressure in the context of capillary physiology?

Accepted Answer

Pressure below which capillaries close

Answer

Arterial pressure minus venous pressure

Answer

Capillary pressure minus venous pressure

Answer

None of the options

Question 9

When blood pressure falls below 40 mm Hg, which mechanism of regulation is working?

Accepted Answer

CNS ischemic reflex

Answer

Chemoreceptor response

Answer

Baroreceptor response

Answer

None of the options

Question 10

All are true about baroreceptors, except?

Accepted Answer

Stimulated when BP decreases

Answer

Stimulation causes increased vagal discharge

Answer

Stimulate nucleus ambiguus

Answer

Afferents are through sino-aortic nerves

NEET-PG 2013 — Physiology