Problem 163 - Objective Biology for NEET

Question

Assertion: Body has the ability to alter cardiac output. Reason: Body has the ability to alter the stroke volume as well as the heart rate.

Step-by-Step Solution

Answer

Yes, the assertion is correct, and the reason is valid. The body does have the ability to alter cardiac output, and it does this by altering stroke volume and heart rate.

Step 1: Definition of Terms

First, understand the terms referred in the exercise. Cardiac output is the volume of blood that the heart pumps per minute. It is determined by two factors: Stroke Volume (the amount of blood pumped by the heart in one beat) and Heart Rate (the number of heart beats per minute). So, Cardiac Output = Stroke Volume x Heart Rate.

Step 2: Evaluating the Assertion

The assertion states that the body has the ability to alter cardiac output. This is medically accurate. The body can adjust both the stroke volume and the heart rate in response to various factors, thus ALTERING the cardiac output.

Step 3: Evaluating the Reason

The reason provided is that the body can alter the stroke volume as well as the heart rate. This is indeed correct. For instance, during exercise, the body increases the heart rate and stroke volume to increase the cardiac output ensuring more oxygenated blood is delivered to the muscles.

Step 4: Making the Connection

The reason provided directly supports the assertion. Because the body can independently adjust both stroke volume and heart rate, it can, therefore, control cardiac output. In summary, the assertion is correct and the reason provided is a valid explanation and supportive of the assertion.

Key Concepts

Stroke Volume

When we talk about stroke volume, we are referring to the amount of blood the heart ejects with each beat. This fundamental aspect of cardiovascular physiology plays a vital role in determining how efficiently the heart can supply blood throughout the body. The average adult stroke volume is about 70 milliliters per heartbeat.

The body's ability to alter stroke volume makes it possible to respond to different physiological demands. For instance, during exercise, the stroke volume can increase as the heart pumps more forcefully. This ensures that more oxygen-rich blood reaches the muscles.

• Stroke volume depends on the heart's contractility, the volume of venous return (preload), and arterial pressure (afterload).
• Increased stroke volume means more blood is effectively circulating, which is crucial for meeting elevated physical demands.

As stroke volume changes, it directly impacts cardiac output, showcasing its importance in cardiovascular physiology.

Heart Rate

Heart rate is simply the number of times the heart beats per minute. It is a continuous, dynamic measure that the body can adjust to meet changing circumstances. The typical resting heart rate for adults falls between 60 and 100 beats per minute (bpm).

During physical activities, the body increases the heart rate, allowing for higher cardiac output and ensuring that tissues receive sufficient oxygen and nutrients. Conversely, a lower heart rate at rest may indicate an efficiently functioning heart that doesn't need to beat as frequently to maintain adequate blood flow.

• The heart rate is influenced by factors such as physical activity, stress, hormonal signals, and sleep.
• Heart rate can be altered by both the sympathetic and parasympathetic nervous systems.

By adjusting the heart rate, the body plays a crucial role in regulating overall cardiac output and maintaining homeostasis.

Cardiovascular Physiology

Cardiovascular physiology deals with the study of the heart and blood vessels, focusing on how they work together to circulate blood throughout the body. This complex system ensures that every cell receives enough oxygen and nutrients while helping to remove waste products.

A key concept in cardiovascular physiology is cardiac output, which is the heart's ability to pump blood effectively. It is determined by the interplay between stroke volume and heart rate. During various activities or conditions, the cardiovascular system can adjust these factors to maintain balance and meet the body's needs.

• The autonomic nervous system plays a critical part in regulating cardiovascular responses.
• Other components include blood pressure regulation, vascular resistance, and the oxygen-carrying capacity of blood.

Understanding cardiovascular physiology helps us appreciate how vital the dynamic adjustments in stroke volume and heart rate are for sustaining life and adapting to ever-changing bodily demands.