Regulation Of Cardiac Activity

Let's evaluate each statement regarding the components of an ECG:

P is the contraction of only the left atria:

• This statement is incorrect. The P wave represents the depolarization of both atria (left and right). It does not specifically represent the contraction of only the left atrium. The contraction of the atria occurs after depolarization, but the P wave represents depolarization, not contraction.

QRS complex represents ventricular contraction:

• This statement is correct. The QRS complex represents the depolarization of the ventricles, which leads to ventricular contraction.

T is the end of systole:

• This statement is correct. The T wave represents ventricular repolarization, which occurs towards the end of the systole (contraction phase of the heart).

P is the contraction of both atria:

• This statement is correct. As mentioned earlier, the P wave represents the depolarization of both atria, which leads to their contraction.

The incorrect statement is A.

The correct answer is (A) : P is the contraction of only left atria..

Cardiac Output (CO) is defined as the volume of blood pumped out by each ventricle per minute. It is calculated by multiplying the Heart Rate (HR) by the Stroke Volume (SV).

The formula is:

We are given the following values:

• Heart Rate (HR) = 70 beats/minute
• Stroke Volume (SV) = 55 ml/beat

Now, substitute these values into the formula:

Therefore, the cardiac output of the individual is 3850 ml per minute.

Comparing this result with the given options:

• 3750 ml
• 125 ml
• 3850 ml
• None of the above

The correct option is 3850 ml.

Here is the solution for the question on the conducting system of the human heart:

Step 1: Understanding the Components of the Conducting System The conducting system of the heart includes specialized tissues responsible for the propagation of electrical impulses, which regulate heartbeats:

• SAN (Sinoatrial Node): The natural pacemaker of the heart, located in the right atrium.
• AVN (Atrioventricular Node): Located at the junction of the atria and ventricles, it delays the impulse before it passes to the ventricles.
• Bundle of His: A bundle of fibers that conducts the impulse from the AVN to the ventricles.
• Interventricular Septum: A wall between the two ventricles.

Step 2: Identify the Labels in the Diagram By referring to the structure of the heart's conducting system:

• P corresponds to the Interventricular septum.
• Q corresponds to the AVN.
• R corresponds to the Bundle of His.
• S corresponds to the SAN.

The correct answer is (B) : p-SAN, q-AVN, r-Bundle of His, s-Interventricular septum.

Identify the given information:

• Stroke Volume (SV) of an adult healthy human = 70 mL/beat
• Identify the required information:
  • Cardiac Output (CO) in one hour (Lit/hour)
• Recall the definition and formula for Cardiac Output:
  • Cardiac Output (CO) is the volume of blood pumped by the heart per unit time.
  • The formula for Cardiac Output per minute is:
• Assume a standard Heart Rate (HR):
  • The question asks for a healthy adult, but doesn't provide the heart rate. A typical resting heart rate for a healthy adult is approximately 72 beats per minute. We will use this standard value.
  • HR = 72 beats/minute
• Calculate the Cardiac Output per minute:
• Convert Cardiac Output from mL/minute to Lit/hour:
  • First, convert mL/minute to mL/hour. There are 60 minutes in an hour.
  • Next, convert mL/hour to Lit/hour. There are 1000 mL in 1 Liter.

The correct answer is (D) : 302.4 Lit/hour.