Growth hormone level is highest during
Insensible water loss per day is ?
Which of the following factors increases the rate of particle diffusion across the cell membrane?
Gas exchange in tissues takes place at?
From the given pressure-volume curve, identify the end-diastolic volume (EDV) and end-systolic volume (ESV), then calculate the ejection fraction using the formula EF = (EDV - ESV)/EDV × 100%.
Which of the following factors increases stroke volume?
A man slept with his head over his forearm. The next morning, he complains of tingling and numbness over the forearm. If this were primarily due to hypoxia affecting nerve fibers, which of the following statements about nerve fiber sensitivity to hypoxia is correct?
Transducin is a protein found in:
Substance that is completely reabsorbed from the kidney?
Which structure of the eye has the maximum refractive power?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 71: Growth hormone level is highest during
- A. Sleep (Correct Answer)
- B. Hypoglycemia
- C. Fasting
- D. Exercise
Explanation: ***Sleep*** - Growth hormone (GH) secretion is **pulsatile**, with the largest and most consistent pulses occurring during **slow-wave sleep** (deep sleep). - This nocturnal surge contributes significantly to the overall daily GH output and is crucial for growth and metabolic regulation. *Hypoglycemia* - While **hypoglycemia** is a potent stimulus for GH release, it is an acute stress response rather than a state where GH levels are consistently highest. - The body's primary response to hypoglycemia is to raise blood glucose, and while GH helps, it is not the peak physiological secretion time. *Fasting* - **Prolonged fasting** can increase GH secretion as a mechanism to mobilize fat stores and conserve glucose. - However, the peak levels due to fasting are generally less pronounced than the dramatic surge observed during deep sleep. *Exercise* - **Vigorous exercise** can acutely stimulate GH release, particularly with sustained effort. - This increase is typically transient and not as high or consistently cyclical as the secretion during nocturnal sleep.
Question 72: Insensible water loss per day is ?
- A. 100 ml
- B. 1000 ml (Correct Answer)
- C. 700 ml
- D. 300 ml
Explanation: ***1000 ml*** - **Insensible water loss** occurs through the skin (evaporation) and respiratory tract (exhalation) without conscious perception. - The typical daily insensible water loss in an adult is approximately **800-1000 ml/day**. - **Breakdown**: Skin evaporation (~400-500 ml) + Respiratory tract (~300-400 ml) = **~900-1000 ml total**. - **1000 ml** is the standard value cited in major physiology textbooks (Guyton & Hall, Ganong) and is the most commonly accepted answer for NEET PG examinations. *100 ml* - This value is significantly **lower** than the actual insensible water loss, which occurs continuously throughout the day. - Such a low volume would imply negligible evaporation and respiratory loss, which is not physiologically accurate. *300 ml* - While greater than 100 ml, 300 ml is still **far below** the typical range for daily insensible water loss. - This amount represents only about one-third of the actual insensible losses from the skin and respiratory system combined. *700 ml* - Although this value is sometimes mentioned in literature, it is at the **lower end** of the physiological range. - The more widely accepted standard value for insensible water loss in a healthy adult under normal conditions is **900-1000 ml/day**. - 700 ml would underestimate the normal daily insensible losses.
Question 73: Which of the following factors increases the rate of particle diffusion across the cell membrane?
- A. Decreasing the lipid solubility of the substance
- B. Increasing the size of the opening in the cell membrane
- C. Maintaining a concentration gradient across the membrane (Correct Answer)
- D. Increasing the size of the particle
Explanation: ***Maintaining a concentration gradient across the membrane*** - **Diffusion** is the net movement of particles from an area of higher concentration to an area of lower concentration, driven by the **concentration gradient**. - A steeper gradient means a larger difference in concentration, leading to a faster rate of net diffusion until equilibrium is reached. - According to **Fick's Law**, the rate of diffusion is directly proportional to the concentration gradient across the membrane. *Decreasing the lipid solubility of the substance* - The cell membrane is primarily composed of a **lipid bilayer**, meaning that substances with **higher lipid solubility** can more easily pass through it via simple diffusion. - Decreasing lipid solubility would **hinder** the substance's ability to cross the membrane, thus slowing down or preventing diffusion. *Increasing the size of the opening in the cell membrane* - While increasing channel or pore diameter can increase diffusion rate for **channel-mediated transport**, this option is less comprehensive than maintaining a concentration gradient. - The concentration gradient is the **primary driving force** for diffusion across all types of membrane transport (simple diffusion through lipid bilayer, channel-mediated, and carrier-mediated). - Channel size is relevant only for specific facilitated diffusion pathways, not for general particle diffusion. *Increasing the size of the particle* - **Smaller particles** generally diffuse faster than larger particles because they have higher diffusion coefficients and can more easily navigate through the membrane. - According to the **Stokes-Einstein equation**, diffusion rate is inversely proportional to particle size. - Increasing particle size would therefore **decrease** the rate of diffusion.
Question 74: Gas exchange in tissues takes place at?
- A. Artery
- B. Capillary (Correct Answer)
- C. Vein
- D. Venules
Explanation: ***Capillary*** - **Capillaries** are the smallest and most numerous blood vessels, with very thin walls (only one cell thick), which facilitates the efficient exchange of gases, nutrients, and waste products between blood and tissues. - Their extensive network ensures close proximity to nearly every cell in the body, maximizing the surface area and minimizing the diffusion distance for **gas exchange**. *Artery* - Arteries carry **oxygenated blood** away from the heart to the tissues but have thick, muscular walls designed for high pressure and transport, not for direct exchange with tissues. - They branch into smaller arterioles, which then lead to capillaries, making them a conduit rather than an exchange site. *Vein* - Veins carry **deoxygenated blood** back to the heart from the tissues and have relatively thin walls compared to arteries but are still too thick for efficient gas exchange. - They primarily serve as blood return vessels and reservoirs. *Venules* - Venules are small blood vessels that merge from capillaries and eventually combine to form veins; they primarily function in collecting blood from capillary beds. - While slightly more permeable than larger veins, their main role is still collection and transport, not the extensive gas exchange facilitated by capillaries.
Question 75: From the given pressure-volume curve, identify the end-diastolic volume (EDV) and end-systolic volume (ESV), then calculate the ejection fraction using the formula EF = (EDV - ESV)/EDV × 100%.
- A. 40%
- B. 50%
- C. 55%
- D. 60% (Correct Answer)
Explanation: ***60%*** - From the pressure-volume loop, the **end-diastolic volume (EDV)** is the volume at point 'a', which is **130 mL**. - The **end-systolic volume (ESV)** is the volume at point 'd', which is **50 mL**. - Using the formula EF = (EDV - ESV) / EDV × 100% = (130 mL - 50 mL) / 130 mL × 100% = 80 mL / 130 mL × 100% = **61.5%**, which rounds to **60%** (the closest option). *40%* - To obtain an ejection fraction of 40%, the ESV would need to be higher, or the EDV lower, than what is indicated by the points 'a' and 'd' on the graph. - (130 - ESV) / 130 = 0.40 => 130 - ESV = 52 => ESV = 78 mL. This isn't consistent with the graph. *50%* - An ejection fraction of 50% would mean that the heart ejected half of its EDV. - (130 - ESV) / 130 = 0.50 => 130 - ESV = 65 => ESV = 65 mL. This value for ESV is not depicted at point 'd'. *55%* - For an ejection fraction of 55%, the calculation would yield a different ESV than what is presented in the curve. - (130 - ESV) / 130 = 0.55 => 130 - ESV = 71.5 => ESV = 58.5 mL. This is not the ESV at point 'd'.
Question 76: Which of the following factors increases stroke volume?
- A. Increased end-diastolic and end-systolic volumes
- B. Decreased end-diastolic and end-systolic volumes
- C. Increased end-diastolic volume and decreased end-systolic volume (Correct Answer)
- D. Decreased end-diastolic volume and increased end-systolic volume
Explanation: ***Increased end-diastolic volume and decreased end-systolic volume*** - **Stroke volume (SV)** is calculated as **End-Diastolic Volume (EDV)** minus **End-Systolic Volume (ESV)**. Therefore, increasing the volume before contraction while decreasing the volume after contraction will maximize the ejected blood. - A higher **EDV** signifies greater **preload** (more blood filling the ventricle), and a lower **ESV** indicates more complete ejection of blood, often due to increased **contractility** or decreased **afterload**. *Increased end-diastolic and end-systolic volumes* - While an **increased EDV** would tend to increase stroke volume, an **increased ESV** suggests that the heart is ejecting less blood per beat, which would decrease stroke volume. - The combined effect makes it less likely to unequivocally increase stroke volume, as the increase in ESV might offset or even surpass the effect of increased EDV. *Decreased end-diastolic and end-systolic volumes* - Both a **decreased EDV** (less filling) and a **decreased ESV** (more complete ejection) work against each other in terms of stroke volume calculation. - If **EDV** decreases, there's less blood to eject, and if the decrease in **EDV** is proportionally larger than the decrease in **ESV**, stroke volume will decrease. *Decreased end-diastolic volume and increased end-systolic volume* - A **decreased EDV** means less blood is available for ejection, reducing preload and the amount of blood the heart can pump. - An **increased ESV** means the heart is ejecting less blood with each beat, indicating reduced contractility or increased afterload, both of which would decrease stroke volume.
Question 77: A man slept with his head over his forearm. The next morning, he complains of tingling and numbness over the forearm. If this were primarily due to hypoxia affecting nerve fibers, which of the following statements about nerve fiber sensitivity to hypoxia is correct?
- A. A fibers are most sensitive to hypoxia, followed by B fibers, and C fibers are least sensitive.
- B. All nerve fibers are equally sensitive to hypoxia.
- C. B fibers are most sensitive to hypoxia, followed by A fibers, and C fibers are least sensitive.
- D. C fibers are most sensitive to hypoxia, followed by B fibers, and A fibers are least sensitive. (Correct Answer)
Explanation: ***C fibers are most sensitive to hypoxia, followed by B fibers, and A fibers are least sensitive.*** - **C fibers**, being **unmyelinated** and having relatively small diameters, are more dependent on aerobic metabolism and are therefore most susceptible to the effects of **hypoxia**. - **B fibers** are lightly myelinated and have intermediate sensitivity, while **A fibers** are heavily myelinated and are the most resistant to hypoxia. *All nerve fibers are equally sensitive to hypoxia.* - Nerve fibers vary significantly in their **myelination status** and **metabolic demands**, which directly influences their sensitivity to hypoxia. - This statement is incorrect because nerve fibers exhibit a **differential sensitivity** to metabolic disturbances like hypoxia. *A fibers are most sensitive to hypoxia, followed by B fibers, and C fibers are least sensitive.* - This statement is incorrect as it reverses the actual order of sensitivity; **A fibers** are the **most resistant** to hypoxia due to their high myelination and larger diameter. - **C fibers** are the most sensitive due to their lack of myelin and smaller diameter, making them more vulnerable to metabolic compromise. *B fibers are most sensitive to hypoxia, followed by A fibers, and C fibers are least sensitive.* - This option is incorrect because **C fibers** are known to be the most sensitive to hypoxia, not the least sensitive. - The order presented here misrepresents the sensitivity of nerve fibers to oxygen deprivation.
Question 78: Transducin is a protein found in:
- A. Glomerulus
- B. Retina (Correct Answer)
- C. Skeletal muscle
- D. Adrenal medulla
Explanation: ***Retina*** - **Transducin** is a **G-protein** crucial for **phototransduction** in the retina. - It plays a key role in the cascade that converts light signals into electrical impulses within **rod** and **cone photoreceptor cells**. *Glomerulus* - The **glomerulus** is a capillary network in the **kidney** responsible for filtering blood. - Its primary proteins are involved in filtration barriers, such as **podocin** and **nephrin**, not transducin. *Skeletal muscle* - **Skeletal muscle** contains proteins like **actin**, **myosin**, and **troponins** for contraction. - Transducin is not involved in muscle contraction or skeletal muscle function. *Adrenal medulla* - The **adrenal medulla** produces **catecholamines** like epinephrine and norepinephrine. - Proteins in this gland are involved in hormone synthesis, storage, and release, not light perception.
Question 79: Substance that is completely reabsorbed from the kidney?
- A. Na+
- B. K+
- C. Urea
- D. Glucose (Correct Answer)
Explanation: ***Glucose*** - In a healthy individual, **virtually all filtered glucose** is reabsorbed in the proximal convoluted tubule via **sodium-glucose cotransporters (SGLTs)**. - This complete reabsorption ensures that this vital energy source is conserved and not excreted in the urine. *Na+* - While a large proportion of filtered **Na+** is reabsorbed to maintain fluid and electrolyte balance, not all of it is reabsorbed; some is excreted in urine. - The reabsorption of Na+ is **regulated** by hormones like **aldosterone** to fine-tune its excretion based on the body's needs. *K+* - **K+** undergoes both reabsorption and secretion in different parts of the nephron, and its excretion is tightly regulated. - Net reabsorption of K+ is not complete; its handling ensures appropriate plasma levels are maintained for muscle and nerve function. *Urea* - Approximately **50% of filtered urea undergoes reabsorption** in the renal tubules, while the other half is excreted. - Urea reabsorption is important for generating the **medullary osmotic gradient**, which is essential for concentrating urine, but it is never completely reabsorbed.
Question 80: Which structure of the eye has the maximum refractive power?
- A. Anterior surface of lens
- B. Posterior surface of lens
- C. Anterior surface of cornea (Correct Answer)
- D. Posterior surface of cornea
Explanation: ***Anterior surface of cornea*** - The **cornea** accounts for approximately two-thirds of the eye's total refractive power due to the large difference in refractive index between air and the corneal tissue. - The **anterior surface of the cornea** is the primary site of light refraction as light enters the eye from the air. *Anterior surface of lens* - The **lens** contributes significantly to accommodation, but its overall refractive power is less than that of the cornea in the unaccommodated state. - The change in refractive index between the aqueous humor and the lens is less pronounced compared to the air-cornea interface. *Posterior surface of lens* - The **posterior surface of the lens** also contributes to the focusing power of the lens, but its curvature and refractive index difference are typically less than the anterior surface of the cornea. - Its contribution to total refractive power is secondary to the anterior corneal surface and the anterior lens surface. *Posterior surface of cornea* - The **posterior surface of the cornea** has a much smaller refractive power compared to the anterior surface due to the smaller difference in refractive index between the cornea and the aqueous humor. - This interface does contribute to refraction but is not the primary focusing component.