Question

Which of the following statement(s) regarding the cardiac system is/are correct? (i) Human heart is an ectodermal derivative. (ii) Mitral valve guards the opening between the right atrium and left ventride. (iii) SAN is located on the left upper comer of the right atrium. (iv) Stroke volume \(\times\) Heart rate \(=\) Cardiac output (a) (i) only (b) (i) and (ii) (c) (ii) and (iii) (d) (iv) only

Short answer

Statement (iv) is correct.

Step-by-step solution

Evaluate statement (i)

Assess the development of the human heart in the embryo. The heart develops from the mesoderm, not the ectoderm. Hence, statement (i) is incorrect.

Evaluate statement (ii)

Examine the mitral valve's position. The mitral valve separates the left atrium from the left ventricle, not between the right atrium and left ventricle. Therefore, the statement (ii) is incorrect.

Evaluate statement (iii)

Identify the location of the Sinoatrial Node (SAN). The SAN is indeed located on the right upper corner of the right atrium and not the left. Therefore, the statement (iii) is incorrect.

Evaluate statement (iv)

Analyze the formula for cardiac output. Cardiac output is indeed the product of stroke volume and heart rate. Therefore, statement (iv) is correct.

Key concepts

Human Heart Embryological Origin

Understanding the embryological origin of the human heart is key for a robust foundation in cardiac anatomy and physiology. The heart begins to form early in embryonic development from the mesoderm, one of the three primary germ layers. Specifically, it originates from the cardiogenic area of the mesoderm, which develops into the endocardial heart tubes. These tubes fuse to form a singular primitive heart tube, which eventually differentiates and folds to give rise to the various structures of the heart.

Contrary to statement (i) from the exercise, the heart is not an ectodermal derivative. The ectoderm forms structures such as the skin and nervous system. The mesodermal origin of the heart is critical because it lays the framework for the development of the cardiac muscle, endothelial linings, and connective tissues. This embryonic process showcases the intricate journey from a simple tube to a complex four-chambered heart, which will support the circulatory system throughout an individual's life.

Mitral Valve Anatomy

The mitral valve, also known as the bicuspid valve, is a vital component of the heart's anatomy. It is located between the left atrium and left ventricle. Its primary function is to allow blood to flow from the left atrium into the left ventricle and to prevent backflow as the ventricle contracts.

Structure of the Mitral Valve

The mitral valve consists of two leaflets or cusps — an anterior and a posterior cusp. These cusps are connected to the papillary muscles in the ventricle by the chordae tendineae, which resemble heartstrings. When the left atrium contracts, the valve opens, permitting blood to move into the left ventricle. As the ventricle contracts, the valve leaflets close tightly to prevent the reverse flow of blood.

To clarify the confusion in statement (ii) of the exercise, the mitral valve does not guard the opening between the right atrium and left ventricle; that role is played by the tricuspid valve. The accurate understanding of the mitral valve's structure and function is imperative to grasp pathophysiological conditions such as mitral valve prolapse or regurgitation.

Sinoatrial Node

The sinoatrial node (SAN), commonly referred to as the heart's natural pacemaker, is a small mass of cardiac tissue that initiates the electrical impulses leading to heart contractions. It is located in the right upper corner of the right atrium, near the entrance of the superior vena cava. The SAN's pivotal position ensures that it can successfully trigger the atria to contract, sending blood into the ventricles.

Function of the Sinoatrial Node

The autonomous rhythmic impulses generated by the SAN spread across the atria and reach the atrioventricular node. From there, they travel along the conducting fibers to the ventricles, causing them to contract. This organized sequence of contractions results in the efficient pumping of blood throughout the body. Statement (iii) in the exercise misleadingly locates the SAN in the left corner of the right atrium. However, from an anatomical and functional perspective, it is imperative to properly understand the exact location and role of the SAN to comprehend the mechanisms of arrhythmias and the effects of certain medications on heart rhythm.

Cardiac Output Calculation

Cardiac output is a measurement of the heart's efficiency, representing the volume of blood the heart pumps in one minute. The formula for calculating cardiac output is the product of heart rate and stroke volume:
\[ Cardiac\text{ } Output \text{ }(CO) = Heart\text{ } Rate \text{ }(HR) \times Stroke\text{ } Volume \text{ }(SV) \]

Understanding Cardiac Output

Heart rate refers to the number of times the heart beats per minute, whereas stroke volume is the amount of blood pumped out of the left ventricle with each beat. Factors like physical activity, stress, and various pathological conditions can influence both the heart rate and stroke volume, thereby altering cardiac output.

It is critical to understand the interplay between these factors in clinical settings, especially when dealing with cardiac diseases. Clear comprehension of the cardiac output formula thus allows us to appreciate how the heart adapts to both physiological and pathological demands. Statement (iv) in the exercise is the only correct one, highlighting the essential concept of cardiac output calculation.