Structure and function of heart Questions in English

(D) Based on the anatomical diagram of the human heart,the vessel labeled '$X$' is the Superior Vena Cava.
It is the large vein that carries deoxygenated blood from the upper parts of the body (head,neck,and arms) into the right atrium of the heart.
The other options are incorrect because:
- Pulmonary veins carry oxygenated blood from the lungs to the left atrium.
- The Inferior Vena Cava carries deoxygenated blood from the lower parts of the body to the right atrium.
- Coronary veins drain blood from the heart muscle itself into the coronary sinus.

(D) Bradycardia is a condition characterized by a slower than normal heart rate.
In a healthy adult, the normal resting heart rate typically ranges from $60$ to $100$ beats per minute.
When the heart rate falls below $60$ beats per minute, it is clinically defined as bradycardia.
Therefore, the correct option is $D$.

(D) The $AV$ (atrioventricular) valves, which include the tricuspid valve and the mitral (bicuspid) valve, are anchored to the papillary muscles of the ventricular walls by fibrous cords known as $Chordae \text{ } tendineae$.
These structures prevent the valves from inverting into the atria during ventricular contraction (systole).

(D) The inner surface of the ventricles is not smooth but contains irregular muscular ridges known as $trabeculae$ $carneae$.
These ridges help in the contraction of the ventricles and prevent the suction effect of the blood against the ventricular walls.
$Chordae$ $tendinae$ are the fibrous cords that attach the valves to the papillary muscles.
$Papillary$ $muscles$ are conical projections from the ventricular walls that anchor the $chordae$ $tendinae$.
$Interventricular$ $septum$ is the wall that separates the left and right ventricles.

(B) The human heart contains specialized cardiac musculature called nodal tissue.
$1$. The $SA$ Node (Sino-atrial node) is present in the right upper corner of the right atrium.
$2$. The $AV$ Node (Atrio-ventricular node) is located in the lower left corner of the right atrium,close to the atrio-ventricular septum.
$3$. The $AV$ bundle continues from the $AV$ node and passes through the atrio-ventricular septa.
$4$. Purkinje fibres are specialized muscle fibres that arise from the $AV$ bundle and spread throughout the ventricular musculature.
Therefore,the correct answer is $AV$ Node.

(D) The discovery of blood circulation was made by $William \ Harvey$ in the year $1628$. He demonstrated that blood circulates throughout the body in a closed system,pumped by the heart. Therefore,the correct option is $D$.

(C) The correct answer is $C$.
During a cardiac cycle,two prominent heart sounds are produced.
The first heart sound,known as 'lub',is produced due to the closure of the atrioventricular valves (tricuspid and bicuspid valves) at the beginning of ventricular systole.
The second heart sound,known as 'dub',is produced due to the closure of the semilunar valves at the beginning of ventricular diastole.
Therefore,the sequence of sounds is the closure of bicuspid and tricuspid valves followed by the closure of semilunar valves.

(B) The correct option is $(B)$.
In the human heart's conducting system:
$p$ represents the Sino-Atrial Node $(SAN)$,which is located in the right atrium.
$q$ represents the Atrio-Ventricular Node $(AVN)$,located near the base of the interatrial septum.
$r$ represents the Bundle of His,which originates from the $AVN$ and passes through the interventricular septum.
$s$ represents the Interventricular septum,the wall separating the two ventricles.

(A) Pure (oxygenated) blood from the lungs is carried back to the heart by the pulmonary veins,which empty into the left auricle (atrium).
From there,the blood moves to the left ventricle to be pumped to the rest of the body.

(B) The correct answer is $B$.
The sinoatrial $(SA)$ node,often referred to as the natural pacemaker of the heart,is located in the right atrium.
It generates rhythmic electrical impulses that initiate each heartbeat.
These impulses spread through the heart muscle,causing the atria to contract and setting the pace for the heart rate,thereby maintaining the frequency of heartbeats.