After injecting testosterone in a hypoandrogenic male, which of the following occurs ?
In the breast, lactiferous ducts are formed under the influence of which hormone?
What does spermiogenesis refer to?
Which of the following does not stimulate growth hormone (GH) release?
What is the half-life of the thyroid hormone triiodothyronine (T3)?
Plasma volume is measured by ?
Most common type of calcium channels of skeletal muscles is?
What is the effect of moderate exercise on cerebral blood flow?
What is the primary function of the 'patch-clamp' technique in electrophysiology?
Ossicles of middle ear are responsible for which of the following ?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 71: After injecting testosterone in a hypoandrogenic male, which of the following occurs ?
- A. Decreased LH secretion
- B. Decreased FSH secretion (Correct Answer)
- C. Increased spermatogenesis
- D. None of the options
Explanation: ***Decreased FSH secretion*** - Exogenous testosterone administration leads to **negative feedback** on the hypothalamic-pituitary-gonadal axis, suppressing **GnRH** release, which in turn decreases both **LH** and **FSH** secretion. - FSH suppression is particularly clinically significant because it results in **inhibition of spermatogenesis**, which is a key consideration when using testosterone replacement therapy. - The decrease in FSH, combined with reduced **intratesticular testosterone** (due to LH suppression), impairs Sertoli cell function and sperm production. *Decreased LH secretion* - **This also occurs** with exogenous testosterone administration due to negative feedback on the hypothalamus and pituitary. - Testosterone primarily suppresses **LH** through direct negative feedback at the hypothalamic-pituitary level. - However, in the context of this question focusing on the consequences in a hypoandrogenic male receiving testosterone, the **FSH suppression** and its impact on spermatogenesis is the more clinically emphasized outcome. - **Note:** Both LH and FSH decrease; this question likely emphasizes FSH due to its role in fertility concerns with testosterone therapy. *Increased spermatogenesis* - This is **incorrect**. Exogenous testosterone actually **suppresses spermatogenesis** through multiple mechanisms: - Decreased **FSH** (essential for Sertoli cell function) - Decreased **intratesticular testosterone** concentration (despite high systemic levels) - The high local testosterone concentration within the seminiferous tubules (30-100x serum levels) cannot be achieved by systemic testosterone alone. *None of the options* - This is incorrect because exogenous testosterone administration clearly causes **suppression of gonadotropins** (both LH and FSH) through well-established negative feedback mechanisms.
Question 72: In the breast, lactiferous ducts are formed under the influence of which hormone?
- A. Progesterone
- B. LH
- C. FSH
- D. Estrogen (Correct Answer)
Explanation: ***Estrogen*** - **Estrogen** plays a primary role in the development and branching of the **lactiferous ducts** in the breast. - It stimulates the proliferation of ductal epithelial cells, contributing to the growth of the duct system. *Progesterone* - **Progesterone** is primarily responsible for the development of the **lobuloalveolar system** and secretory differentiation within the breast. - While essential for lactation, its main function is not duct formation but rather the maturation of secretory units. *LH* - **Luteinizing hormone (LH)** is crucial for ovulation and the formation of the **corpus luteum** in the ovaries. - It has no direct role in the structural development of the lactiferous ducts in the breast. *FSH* - **Follicle-stimulating hormone (FSH)** is essential for the growth and maturation of **ovarian follicles**. - It does not directly influence the formation or development of lactiferous ducts in the breast.
Question 73: What does spermiogenesis refer to?
- A. Formation of spermatozoa from spermatogonia
- B. Formation of spermatozoa from spermatids (Correct Answer)
- C. Formation of spermatids from spermatocytes
- D. Formation of secondary spermatocytes from primary spermatocytes
Explanation: ***Formation of spermatozoa from spermatids*** - **Spermiogenesis** is the final stage of spermatogenesis, involving the remarkable transformation of a round **spermatid** into a motile, mature **spermatozoon**. - This process includes crucial morphological changes such as the formation of the **acrosome**, condensation of the nucleus, development of the flagellum, and shedding of excess cytoplasm. *Formation of spermatozoa from spermatogonia* - This describes the entire process of **spermatogenesis**, which begins with **spermatogonia** and encompasses multiple stages including mitosis, meiosis, and spermiogenesis. - While it's the ultimate outcome, it doesn't specifically define the detailed transformation from spermatid to sperm. *Formation of spermatids from spermatocytes* - This stage refers to **meiosis II**, where **secondary spermatocytes** undergo division to produce **spermatids**. - Spermatids are precursors to spermatozoa and still require significant morphological changes to become mature sperm. *Formation of secondary spermatocytes from primary spermatocytes* - This describes **meiosis I**, where a **primary spermatocyte** divides to form two **secondary spermatocytes**. - This step reduces the chromosome number by half but doesn't involve the final morphological changes seen in spermiogenesis.
Question 74: Which of the following does not stimulate growth hormone (GH) release?
- A. Exercise
- B. Free fatty acids (Correct Answer)
- C. Fasting
- D. Stress
Explanation: ***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.
Question 75: What is the half-life of the thyroid hormone triiodothyronine (T3)?
- A. 8 hours
- B. 1 day (Correct Answer)
- C. 6 hours
- D. 10 days
Explanation: ***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.
Question 76: Plasma volume is measured by ?
- A. Inulin
- B. Evans blue (Correct Answer)
- C. D2O
- D. Mannitol
Explanation: ***Evans blue*** - **Evans blue** is a dye that binds to plasma proteins and **does not readily cross capillary membranes**, making it an effective tracer for measuring plasma volume. - After intravenous injection, its concentration can be measured to calculate the dilution space, which corresponds to the **plasma volume**. *Inulin* - **Inulin** is a polysaccharide primarily used to measure the **glomerular filtration rate (GFR)** because it is freely filtered by the glomeruli and neither reabsorbed nor secreted by the renal tubules. - It distributes into the **extracellular fluid compartment** and is not confined to the plasma, making it unsuitable for plasma volume measurement. *Mannitol* - **Mannitol** is an osmotic diuretic that distributes in the **extracellular fluid (ECF)**, it is generally used for its osmotic effects to reduce edema or intracranial pressure. - Due to its distribution beyond the plasma compartment, it is not used directly to measure **plasma volume**. *D20* - **D2O (deuterium oxide)**, or heavy water, is used to measure **total body water (TBW)** as it distributes throughout all fluid compartments of the body. - It does not selectively remain within the plasma compartment, making it unsuitable for measuring **plasma volume** alone.
Question 77: Most common type of calcium channels of skeletal muscles is?
- A. N-type
- B. T-type
- C. R-type
- D. L-type (Correct Answer)
Explanation: ***L type*** - **L-type calcium channels**, also known as **dihydropyridine receptors (DHPRs)**, are the predominant type of calcium channel found in skeletal muscle. - In skeletal muscle, they serve as voltage sensors that **mechanically link** to ryanodine receptors (RyRs) on the sarcoplasmic reticulum to trigger calcium release without significant calcium influx from the extracellular space. *N-type* - **N-type calcium channels** are primarily found in **neurons** and play a crucial role in neurotransmitter release at synapses. - They are not the primary calcium channels involved in skeletal muscle excitation-contraction coupling. *T-type* - **T-type calcium channels** are low-voltage activated channels found in various excitable cells, including cardiac muscle and neurons, where they contribute to **pacemaker activity** and repetitive firing. - They are not the main calcium channels responsible for excitation-contraction coupling in skeletal muscle. *R-type* - **R-type calcium channels** are found in various neural cells and are involved in diverse functions, including **synaptic transmission**, but their precise physiological role is less clearly defined compared to other types. - These channels are not the primary calcium entry pathways in skeletal muscle and do not play a significant role in its contraction.
Question 78: What is the effect of moderate exercise on cerebral blood flow?
- A. Decreases
- B. Initially decreases then increases
- C. Increases (Correct Answer)
- D. Does not change
Explanation: ***Increases*** - Moderate exercise leads to an **increase in systemic arterial pressure** and an increase in **cardiac output**, which often results in a moderate increase in cerebral blood flow. - This increase is also attributed to **vasodilation of cerebral arteries** in response to metabolic demands and changes in blood gas levels during exercise. *Decreases* - A decrease in cerebral blood flow is generally associated with conditions leading to **hypoperfusion** or **severe vasoconstriction**, which are not typical effects of moderate exercise. - While extreme exercise could potentially cause some transient vasoconstriction, moderate exercise typically has the opposite effect due to compensatory mechanisms. *Initially decreases then increases* - There is generally no physiological mechanism by which moderate exercise would cause an initial decrease in cerebral blood flow followed by an increase. - Cerebral autoregulation usually maintains a stable blood flow, and the overall trend with moderate exercise is an increase. *Does not change* - While **cerebral autoregulation** aims to keep cerebral blood flow stable over a range of blood pressures, moderate exercise often pushes parameters (like CO2 levels and systemic pressure) enough to cause a measurable, albeit modest, **increase in blood flow**. - The brain's metabolic demand also increases during exercise, necessitating an increased blood supply.
Question 79: What is the primary function of the 'patch-clamp' technique in electrophysiology?
- A. To record facilitated diffusion
- B. To record osmotic pressure around semipermeable membrane
- C. To record RMP
- D. To record ionic currents through single or multiple ion channels (Correct Answer)
Explanation: ***To record ionic currents through single or multiple ion channels*** - The **patch-clamp technique** uses a microscopic glass pipette to form a tight seal with a cell membrane, allowing direct measurement of electrical currents flowing through individual or multiple **ion channels**. - This method is crucial for understanding the biophysical properties of **ion channels**, including their opening and closing kinetics, conductance, and sensitivity to various stimuli. *To record facilitated diffusion* - **Facilitated diffusion** is a passive transport process involving carrier proteins, which does not generate measurable electrical currents directly recorded by patch clamp. - While ion channels can facilitate diffusion, the patch-clamp technique specifically measures the **ionic current** generated by their activity, not the overall diffusive movement itself. *To record osmotic pressure around semipermeable membrane* - **Osmotic pressure** refers to the pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. - The patch-clamp technique is designed to measure electrical phenomena, not **osmotic pressure** or water movement across membranes. *To record RMP* - While the patch-clamp technique can be used in a **whole-cell configuration** to measure the **resting membrane potential (RMP)**, its primary and most distinctive function is to resolve **single ion channel activity**. - Other, simpler electrophysiological methods can also measure RMP, but patch-clamp excels at the high-resolution study of **ionic currents** through specific channels.
Question 80: Ossicles of middle ear are responsible for which of the following ?
- A. Amplification of sound intensity
- B. Reduction of sound intensity
- C. Protecting the inner ear
- D. Reduction of impedance for sound transmission (Correct Answer)
Explanation: ***Reduction of impedance for sound transmission*** - The ossicles (malleus, incus, and stapes) act as a **lever system** to match the impedance between the air-filled outer ear and the fluid-filled inner ear. - This impedance matching ensures that maximum sound energy is transferred to the cochlea, preventing significant **sound reflection**. *Amplification of sound intensity* - While the ossicles do slightly amplify the sound pressure, their primary role is not extensive amplification but rather **impedance matching**. - The amplification achieved is a byproduct of efficient energy transfer, rather than a direct goal of increasing sound intensity for its own sake. *Reduction of sound intensity* - This function is primarily attributed to the **acoustic reflex**, where the middle ear muscles contract to stiffen the ossicular chain in response to loud sounds. - The primary function of the ossicles themselves is to transmit sound efficiently, not to reduce intensity under normal conditions. *Protecting the inner ear* - While the **acoustic reflex** (involving middle ear muscles attached to the ossicles) offers some protection against very loud sounds by stiffening the ossicular chain, this is a separate, reflexive mechanism. - The intrinsic structure and primary mechanical function of the ossicles are centered on efficient sound transmission, not direct physical protection of the inner ear.