UPSC-CMS 2025 — Physiology

Q: Consider the following statements regarding respiratory function in old age: I. There is increasing ventilation-perfusion mismatch II. There is increased ventilatory response to hypoxia and hypercapnia III. There is a decline in maximum oxygen uptake leading to reduction in cardiorespiratory reserve IV. There is decline in the Forced Expiratory Volume to Forced Vital Capacity ratio (FEV1/FVC) by around 0.2% per year after the forties Which of the statements given above are correct?

I, III and IV. ***I, III and IV*** - With aging, there is a **loss of elastic recoil** in the lungs and a structural decrease in **alveolar surface area**, leading to increased **ventilation-perfusion (V/Q) mismatch** as gravity-dependent areas collapse. - The **maximum oxygen uptake (VO2 max)** declines with age due to reduced cardiac output and skeletal muscle mass, thus decreasing **cardiorespiratory reserve**. The **FEV1/FVC ratio** also decreases by approximately **0.2% per year** after age 40 because of reduced elastic recoil and increased airway collapsibility. *I, II and IV* - While statement I and IV are correct, statement II is incorrect because the **ventilatory response to hypoxia and hypercapnia** actually **decreases** with age. - Older adults have a blunted response to changes in oxygen and carbon dioxide levels, making them more susceptible to respiratory compromise. *II, III and IV* - Statement II is incorrect as the **ventilatory response to hypoxia and hypercapnia decreases** with age, not increases. - Statements III and IV accurately describe the decline in **maximum oxygen uptake** and the **FEV1/FVC ratio** with aging. *I, II and III* - Statement II is incorrect; the **ventilatory response to hypoxia and hypercapnia is diminished** in older adults. - Statements I and III correctly identify increased **ventilation-perfusion mismatch** and decreased **maximum oxygen uptake** as age-related changes in respiratory function. [Practice more Physiology PYQs on OnCourse]

Q: Which one of the following correctly denotes the inheritance pattern of cystic fibrosis?

Autosomal Recessive. ***Autosomal Recessive*** - Cystic fibrosis is an **autosomal recessive** disorder, meaning an individual must inherit **two copies** of the defective gene (one from each parent) to develop the condition. - Parents who are **carriers** (having one normal and one defective gene) typically do not show symptoms but can pass the gene to their children. *X-linked Dominant* - In **X-linked dominant** inheritance, a single copy of a mutated gene on the X chromosome is sufficient to cause the disorder. - This pattern would show common inheritance in females and often more severe phenotypes in males, which is not characteristic of cystic fibrosis. *Autosomal Dominant* - **Autosomal dominant** disorders require only **one copy** of a mutated gene on a non-sex chromosome for the disease to manifest. - If cystic fibrosis were autosomal dominant, affected individuals would typically have an affected parent, and the disease would be much more prevalent than observed. *X-linked Recessive* - **X-linked recessive** disorders primarily affect males, as they have only one X chromosome. Females are typically carriers and less severely affected. - Cystic fibrosis affects males and females nearly equally, which rules out an X-linked recessive inheritance pattern. [Practice more Physiology PYQs on OnCourse]

Q: Good measure of systemic perfusion on ABG is:

Lactate and / or the base deficit. ***Lactate and / or the base deficit*** - **Lactate** is a direct indicator of **anaerobic metabolism**, which occurs when tissue oxygen supply is insufficient to meet demand, reflecting poor systemic perfusion. - **Base deficit** (or base excess) quantifies the overall metabolic acid-base status and is sensitive to changes in unmeasured anions like lactate, making it a good marker of **tissue hypoperfusion** and metabolic acidosis. *Bicarbonate* - While bicarbonate reflects the body's primary **buffer system**, changes in bicarbonate can be influenced by both respiratory and metabolic processes and thus are not as specific a marker for systemic perfusion as lactate or base deficit. - A low bicarbonate often indicates **metabolic acidosis**, but it doesn't pinpoint the cause as precisely as lactate, which directly reflects anaerobic metabolism. *PCO2* - **PCO2** primarily reflects the **ventilatory status** and respiratory component of acid-base balance. - While extreme changes can indirectly affect perfusion (e.g., hypercapnia leading to vasodilation), it is not a direct or reliable measure of **systemic tissue perfusion**. *pH* - **pH** indicates the overall acid-base balance but is a **composite measure** influenced by both respiratory (PCO2) and metabolic (bicarbonate, lactate) factors. - It does not specifically isolate **perfusion deficits** as clearly as lactate or base deficit, which directly reflect metabolic responses to tissue hypoxia. [Practice more Physiology PYQs on OnCourse]

Q: Which of the following are functions of the gall bladder? I. Reservoir for bile II. Production of bile III. Secretion of mucus IV. Concentration of bile Select the correct answer using the code given below :

I, III and IV. ***I, III and IV (Correct)*** - The gallbladder **stores bile** produced by the liver, acting as a reservoir (I) until it's needed for digestion. - It **concentrates bile** 5-20 fold (IV) by absorbing water and electrolytes through its epithelium. - The gallbladder epithelium **secretes mucin** (III), which forms a protective mucous layer. - The gallbladder does **NOT produce bile** (II) - this is exclusively a function of hepatocytes in the liver. *II, III and IV (Incorrect)* - This option incorrectly includes bile production (II), which is **not a function of the gallbladder**. - The **liver produces bile**; the gallbladder only stores and concentrates it. - While III and IV are correct functions, the inclusion of II makes this option wrong. *I, II and III (Incorrect)* - This option incorrectly states that the gallbladder produces bile (II), which is a **hepatic function**. - Additionally, it omits bile concentration (IV), which is one of the **primary functions** of the gallbladder. - Only I and III are correct in this combination. *I, II and IV (Incorrect)* - This option incorrectly includes bile production (II) as a gallbladder function. - The gallbladder's actual roles are **storage (I), concentration (IV), and mucus secretion (III)** - not bile production. [Practice more Physiology PYQs on OnCourse]

Q: Which of the following conditions CAN BE transmitted as a recessive, sex-linked trait? I. Retinitis pigmentosa II. Colour blindness III. Cystic fibrosis IV. Duchenne muscular dystrophy Select the correct answer using the code given below :

I, II and IV. ***I, II and IV*** - All three conditions listed—**Retinitis Pigmentosa**, **Colour Blindness**, and **Duchenne Muscular Dystrophy**—can be inherited as recessive, **sex-linked traits**. - **Sex-linked inheritance** primarily refers to genes located on the **X chromosome**; males are more frequently affected because they have only one X chromosome. *II, III and IV* - This option incorrectly includes **Cystic Fibrosis**, which is an **autosomal recessive disorder**, not a sex-linked trait. - While **Colour Blindness** and **Duchenne Muscular Dystrophy** are sex-linked, their grouping with an autosomal condition makes this option incorrect. *I, II and III* - This option also incorrectly includes **Cystic Fibrosis** as a sex-linked trait. - **Retinitis Pigmentosa** and **Colour Blindness** can be sex-linked, but the inclusion of **Cystic Fibrosis** renders the entire option incorrect. *I, III and IV* - This option incorrectly includes **Cystic Fibrosis**; it is an **autosomal recessive condition**, not sex-linked. - Although **Retinitis Pigmentosa** and **Duchenne Muscular Dystrophy** are correctly identified as conditions that can be sex-linked, the incorrect inclusion of **Cystic Fibrosis** makes this option wrong. [Practice more Physiology PYQs on OnCourse]

5 Previous Year Questions with Answers & Explanations

Questions

Consider the following statements regarding respiratory function in old age: I. There is increasing ventilation-perfusion mismatch II. There is increased ventilatory response to hypoxia and hypercapnia III. There is a decline in maximum oxygen uptake leading to reduction in cardiorespiratory reserve IV. There is decline in the Forced Expiratory Volume to Forced Vital Capacity ratio (FEV1/FVC) by around 0.2% per year after the forties Which of the statements given above are correct?

Which one of the following correctly denotes the inheritance pattern of cystic fibrosis?

Good measure of systemic perfusion on ABG is:

Which of the following are functions of the gall bladder? I. Reservoir for bile II. Production of bile III. Secretion of mucus IV. Concentration of bile Select the correct answer using the code given below :

Which of the following conditions CAN BE transmitted as a recessive, sex-linked trait? I. Retinitis pigmentosa II. Colour blindness III. Cystic fibrosis IV. Duchenne muscular dystrophy Select the correct answer using the code given below :

UPSC-CMS 2025 - Physiology UPSC-CMS Practice Questions and MCQs

Question 1: Consider the following statements regarding respiratory function in old age: I. There is increasing ventilation-perfusion mismatch II. There is increased ventilatory response to hypoxia and hypercapnia III. There is a decline in maximum oxygen uptake leading to reduction in cardiorespiratory reserve IV. There is decline in the Forced Expiratory Volume to Forced Vital Capacity ratio (FEV1/FVC) by around 0.2% per year after the forties Which of the statements given above are correct?

A. I, III and IV (Correct Answer)
B. I, II and IV
C. II, III and IV
D. I, II and III

Explanation: ***I, III and IV*** - With aging, there is a **loss of elastic recoil** in the lungs and a structural decrease in **alveolar surface area**, leading to increased **ventilation-perfusion (V/Q) mismatch** as gravity-dependent areas collapse. - The **maximum oxygen uptake (VO2 max)** declines with age due to reduced cardiac output and skeletal muscle mass, thus decreasing **cardiorespiratory reserve**. The **FEV1/FVC ratio** also decreases by approximately **0.2% per year** after age 40 because of reduced elastic recoil and increased airway collapsibility. *I, II and IV* - While statement I and IV are correct, statement II is incorrect because the **ventilatory response to hypoxia and hypercapnia** actually **decreases** with age. - Older adults have a blunted response to changes in oxygen and carbon dioxide levels, making them more susceptible to respiratory compromise. *II, III and IV* - Statement II is incorrect as the **ventilatory response to hypoxia and hypercapnia decreases** with age, not increases. - Statements III and IV accurately describe the decline in **maximum oxygen uptake** and the **FEV1/FVC ratio** with aging. *I, II and III* - Statement II is incorrect; the **ventilatory response to hypoxia and hypercapnia is diminished** in older adults. - Statements I and III correctly identify increased **ventilation-perfusion mismatch** and decreased **maximum oxygen uptake** as age-related changes in respiratory function.

Question 2: Which one of the following correctly denotes the inheritance pattern of cystic fibrosis?

A. X-linked Dominant
B. Autosomal Recessive (Correct Answer)
C. Autosomal Dominant
D. X-linked Recessive

Explanation: ***Autosomal Recessive*** - Cystic fibrosis is an **autosomal recessive** disorder, meaning an individual must inherit **two copies** of the defective gene (one from each parent) to develop the condition. - Parents who are **carriers** (having one normal and one defective gene) typically do not show symptoms but can pass the gene to their children. *X-linked Dominant* - In **X-linked dominant** inheritance, a single copy of a mutated gene on the X chromosome is sufficient to cause the disorder. - This pattern would show common inheritance in females and often more severe phenotypes in males, which is not characteristic of cystic fibrosis. *Autosomal Dominant* - **Autosomal dominant** disorders require only **one copy** of a mutated gene on a non-sex chromosome for the disease to manifest. - If cystic fibrosis were autosomal dominant, affected individuals would typically have an affected parent, and the disease would be much more prevalent than observed. *X-linked Recessive* - **X-linked recessive** disorders primarily affect males, as they have only one X chromosome. Females are typically carriers and less severely affected. - Cystic fibrosis affects males and females nearly equally, which rules out an X-linked recessive inheritance pattern.

Question 3: Good measure of systemic perfusion on ABG is:

A. Bicarbonate
B. Lactate and / or the base deficit (Correct Answer)
C. PCO2
D. pH

Explanation: ***Lactate and / or the base deficit*** - **Lactate** is a direct indicator of **anaerobic metabolism**, which occurs when tissue oxygen supply is insufficient to meet demand, reflecting poor systemic perfusion. - **Base deficit** (or base excess) quantifies the overall metabolic acid-base status and is sensitive to changes in unmeasured anions like lactate, making it a good marker of **tissue hypoperfusion** and metabolic acidosis. *Bicarbonate* - While bicarbonate reflects the body's primary **buffer system**, changes in bicarbonate can be influenced by both respiratory and metabolic processes and thus are not as specific a marker for systemic perfusion as lactate or base deficit. - A low bicarbonate often indicates **metabolic acidosis**, but it doesn't pinpoint the cause as precisely as lactate, which directly reflects anaerobic metabolism. *PCO2* - **PCO2** primarily reflects the **ventilatory status** and respiratory component of acid-base balance. - While extreme changes can indirectly affect perfusion (e.g., hypercapnia leading to vasodilation), it is not a direct or reliable measure of **systemic tissue perfusion**. *pH* - **pH** indicates the overall acid-base balance but is a **composite measure** influenced by both respiratory (PCO2) and metabolic (bicarbonate, lactate) factors. - It does not specifically isolate **perfusion deficits** as clearly as lactate or base deficit, which directly reflect metabolic responses to tissue hypoxia.

Question 4: Which of the following are functions of the gall bladder? I. Reservoir for bile II. Production of bile III. Secretion of mucus IV. Concentration of bile Select the correct answer using the code given below :

A. II, III and IV
B. I, II and III
C. I, II and IV
D. I, III and IV (Correct Answer)

Explanation: ***I, III and IV (Correct)*** - The gallbladder **stores bile** produced by the liver, acting as a reservoir (I) until it's needed for digestion. - It **concentrates bile** 5-20 fold (IV) by absorbing water and electrolytes through its epithelium. - The gallbladder epithelium **secretes mucin** (III), which forms a protective mucous layer. - The gallbladder does **NOT produce bile** (II) - this is exclusively a function of hepatocytes in the liver. *II, III and IV (Incorrect)* - This option incorrectly includes bile production (II), which is **not a function of the gallbladder**. - The **liver produces bile**; the gallbladder only stores and concentrates it. - While III and IV are correct functions, the inclusion of II makes this option wrong. *I, II and III (Incorrect)* - This option incorrectly states that the gallbladder produces bile (II), which is a **hepatic function**. - Additionally, it omits bile concentration (IV), which is one of the **primary functions** of the gallbladder. - Only I and III are correct in this combination. *I, II and IV (Incorrect)* - This option incorrectly includes bile production (II) as a gallbladder function. - The gallbladder's actual roles are **storage (I), concentration (IV), and mucus secretion (III)** - not bile production.

Question 5: Which of the following conditions CAN BE transmitted as a recessive, sex-linked trait? I. Retinitis pigmentosa II. Colour blindness III. Cystic fibrosis IV. Duchenne muscular dystrophy Select the correct answer using the code given below :

A. II, III and IV
B. I, II and IV (Correct Answer)
C. I, II and III
D. I, III and IV

Explanation: ***I, II and IV*** - All three conditions listed—**Retinitis Pigmentosa**, **Colour Blindness**, and **Duchenne Muscular Dystrophy**—can be inherited as recessive, **sex-linked traits**. - **Sex-linked inheritance** primarily refers to genes located on the **X chromosome**; males are more frequently affected because they have only one X chromosome. *II, III and IV* - This option incorrectly includes **Cystic Fibrosis**, which is an **autosomal recessive disorder**, not a sex-linked trait. - While **Colour Blindness** and **Duchenne Muscular Dystrophy** are sex-linked, their grouping with an autosomal condition makes this option incorrect. *I, II and III* - This option also incorrectly includes **Cystic Fibrosis** as a sex-linked trait. - **Retinitis Pigmentosa** and **Colour Blindness** can be sex-linked, but the inclusion of **Cystic Fibrosis** renders the entire option incorrect. *I, III and IV* - This option incorrectly includes **Cystic Fibrosis**; it is an **autosomal recessive condition**, not sex-linked. - Although **Retinitis Pigmentosa** and **Duchenne Muscular Dystrophy** are correctly identified as conditions that can be sex-linked, the incorrect inclusion of **Cystic Fibrosis** makes this option wrong.