Problem 97 - Objective Biology for NEET

Question

During cardiac cycle each ventricle pumps out about \(70 \mathrm{~mL}\) of blood which is called (a) Stroke volume (b) Cardiac output (c) Tidal volume (d) Residual volume

Step-by-Step Solution

Answer

The correct answer is (a) Stroke Volume.

Step 1: Understand the Given Terms

Let's analyze each choice individually: \n(a) Stroke volume: This is the quantity of blood that the left ventricle ejects into the aorta with each contraction (heartbeat). \n(b) Cardiac output: This is the volume of blood pumped by the heart in one minute. It can be calculated by the product of stroke volume and heart rate. \n(c) Tidal volume: This term is used in respiratory physiology, and it refers to the volume of air breathed in or out during a normal breath. \n(d) Residual volume: This also refers to lungs and is the amount of air that remains in the lungs even after the most forceful expiration.

Step 2: Match the Definition

From the definitions provided in step 1, it is clear that the term that refers to the volume of blood pumped out by each ventricle during each heartbeat is the stroke volume.

Key Concepts

Stroke Volume

Stroke volume is a fundamental concept in understanding heart function and cardiac health. It represents the amount of blood that the left ventricle ejects into the aorta with each contraction, or heartbeat. A typical value for stroke volume is around 70 milliliters per heartbeat, but it can vary based on an individual's size, health, and activity level.

Factors affecting stroke volume include preload, afterload, and myocardial contractility. Preload refers to the degree of stretch of the heart muscle before contraction, which is influenced by the blood volume returning to the heart. Afterload is the resistance the left ventricle must overcome to circulate blood, while myocardial contractility is the strength of the heart's contraction itself.

Understanding and measuring stroke volume is crucial in the medical field, as it can indicate the heart's efficiency and health. For instance, low stroke volume may be indicative of heart failure or cardiomyopathy.

Cardiac Output

When we discuss 'cardiac output,' we are referring to the volume of blood the heart pumps to the body in one minute. It's a key measurement for assessing the heart's pumping capacity and overall circulatory health. To calculate cardiac output, we need two values: stroke volume and heart rate. The formula is as follows:
\[ \text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate} \]
For an average adult at rest, this typically amounts to about 5 liters per minute. However, during intense exercise, cardiac output can increase significantly as the body demands more oxygen and nutrients for the muscles at work. Regular monitoring of cardiac output is vital in clinical settings, especially to manage conditions like heart failure, where cardiac output is often reduced.

Respiratory Physiology

Respiratory physiology delves into how our bodies take in oxygen and expel carbon dioxide, essential for cellular metabolism and overall functioning. It involves the study of air movement, blood gas transport, and the mechanics of breathing.

A crucial term in this domain is 'tidal volume,' which is the amount of air inhaled or exhaled with each normal breath, typically about 500 milliliters for a healthy adult. Another term is 'residual volume,' the air remaining in the lungs after a forceful exhalation, ensuring that the lungs do not collapse and that gas exchange can continue even between breaths.

Comprehension of these concepts is foundational for professions such as respiratory therapy, critical care medicine, and exercise physiology, where managing patients' ventilatory needs is often a matter of life or death.