Cardiovascular System

To solve the problem, we need to describe the physiological meanings of (a) Residual Volume and (b) Stroke Volume, which are important parameters in the study of respiratory and cardiovascular systems respectively.

(a) Residual Volume:

Definition:
Residual Volume (RV) is the amount of air that remains in the lungs after a person has exhaled as forcefully and completely as possible.

Explanation:
- Even after a maximal expiration, some air remains trapped in the alveoli to prevent lung collapse.
- This volume is essential for continuous gas exchange between breaths.
- On average, the residual volume in an adult is about 1200 mL.

Importance:

• Maintains alveolar inflation and functional efficiency of the lungs.
• Prevents the collapse of the lungs by keeping them partially inflated.

(b) Stroke Volume:

Definition:
Stroke Volume (SV) is the amount of blood pumped by the left ventricle of the heart in one contraction.

Explanation:
- It is a key component of cardiac output and reflects the heart’s pumping efficiency.
- Stroke volume depends on factors like heart size, contractility, and venous return.
- The average stroke volume in a healthy adult is about 70 mL per beat.

Importance:

• Indicates the effectiveness of the heart in circulating blood.
• Helps determine overall cardiovascular fitness and cardiac output (CO = SV × Heart Rate).

Final Answer:
(a) Residual Volume is the air left in the lungs after maximum exhalation (about 1200 mL), essential for preventing lung collapse.
(b) Stroke Volume is the volume of blood ejected by the heart in one beat (about 70 mL), indicating the efficiency of the heart’s pumping action.