Question

Given below are two statements:
Statement (I): Two specific types of cardiac action potentials exist (fast response and slow response) in different regions of cardiac muscles.
Statement (II): Highest blood pressure is observed in veins, the capacitance vessel.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Remember that blood pressure drops continuously along the systemic circulation:
\[ \text{Aorta} > \text{Arteries} > \text{Arterioles} > \text{Capillaries} > \text{Veins} > \text{Vena Cava} \] Arterioles are the primary site of systemic vascular resistance, causing the steepest drop in pressure.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This problem addresses cardiovascular physiology, comparing the electrophysiology of different cardiac cells with the pressure gradients that drive blood flow through the systemic circulation.

Step 2: Detailed Explanation:
Let us analyze both statements:

Statement (I): Cardiac muscle cells exhibit two distinct types of action potentials based on their location and channel kinetics:
1.Fast-response action potentials: Occur in working myocardial cells (atria and ventricles) and Purkinje fibers. They have a rapid depolarization phase (Phase 0) driven by fast voltage-gated sodium channels.
2.Slow-response action potentials: Occur in the pacemaker nodes (Sinoatrial and Atrioventricular nodes). They lack fast sodium channels, and their depolarization phase is slower, driven by L-type calcium channels.
Thus, Statement (I) iscorrect.

Statement (II): Blood flows down a pressure gradient from high-pressure vessels to low-pressure vessels.
The highest blood pressure is observed in theaorta and large arteries (the conduit vessels) during ventricular systole (\(\sim 120 \text{ mmHg}\) in humans, varying by species).
As blood flows through arterioles, capillaries, and finally into the venules and veins, the pressure drops significantly.
In the vena cava (veins, which act as capacitance vessels holding up to 60-70% of blood volume), the pressure is extremely low, approaching \(\approx 0 \text{ to } 5 \text{ mmHg}\).
Therefore, stating that veins have the highest blood pressure is incorrect. Thus, Statement (II) isincorrect.
Therefore, Statement (I) is correct but Statement (II) is incorrect.

Step 3: Final Answer:
The correct option is (C).