Structure and function of heart Questions in English

(C) The pacemaker,also known as the $SA$ node (Sinoatrial node),is a specialized cluster of cells located in the right atrium of the heart.
It acts as the natural pacemaker because it has the ability to generate electrical impulses spontaneously.
These electrical impulses spread through the heart muscle,causing it to contract in a rhythmic manner.
Therefore,the primary function of the pacemaker is to initiate and regulate the rate of the heartbeat.

(A) The heart valves (specifically the atrioventricular valves) are connected to the papillary muscles by fibrous cords known as $Chordae \ tendineae$.
These structures prevent the valves from prolapsing into the atria during ventricular contraction (systole).
Therefore,the correct option is $A$.

(C) The heart rate of an infant is significantly higher than that of an adult.
For a two-month-old infant,the normal resting heart rate typically ranges from $100$ to $160$ beats per minute.
Since all options except $C$ suggest values lower than or equal to $72/min$ (which is the average adult resting heart rate),the only correct choice is $C$,which represents a rate greater than $72/min$.

(A) The heart rate of children is generally higher than that of adults. As a person grows from childhood to adulthood,the heart size increases,and the stroke volume (the amount of blood pumped per beat) also increases. Consequently,the heart does not need to beat as frequently to maintain the required cardiac output,leading to a lower resting heart rate in adults compared to children.

(D) The heart produces two main sounds during each cardiac cycle,known as 'lub' and 'dub'.
$1$. The first heart sound,'lub',is produced during the closure of the atrioventricular valves (the bicuspid and tricuspid valves) at the beginning of ventricular systole.
$2$. The second heart sound,'dub',is produced during the closure of the semilunar valves at the beginning of ventricular diastole.
Therefore,the 'lub' sound is associated with the closure of both the bicuspid and tricuspid valves.

(C) The cardiac cycle produces two primary heart sounds,'$LUB$' and '$DUB$'.
$1$. The first heart sound,'$LUB$',is produced by the closure of the atrioventricular valves (tricuspid and mitral valves) at the beginning of ventricular systole.
$2$. The second heart sound,'$DUB$',is produced by the closure of the semilunar valves (aortic and pulmonary valves) at the beginning of ventricular diastole.
Therefore,the '$DUB$' sound is associated with the closure of the semilunar valves.

(D) The heart is myogenic,meaning its rhythmic contraction is initiated by specialized cardiac muscles.
The $SA$ node (Sinoatrial node) is located in the right upper corner of the right atrium.
It acts as the natural pacemaker of the heart because it has the highest rate of depolarization and generates the electrical impulses that set the rhythm of the heart contraction.
Therefore,the $SA$ node is known as the pacemaker.

(A) The heart is myogenic,meaning its rhythmic contractions are initiated by specialized cardiac muscle cells.
The $SA$ (Sinoatrial) node,located in the right atrium,acts as the natural pacemaker of the heart.
It generates electrical impulses that spread through the heart,initiating and maintaining the rhythmic contraction of the cardiac muscle.
Therefore,the $SA$ node is responsible for initiating and maintaining the heartbeat.

(C) The Cords of Billroth,also known as splenic cords,are found in the red pulp of the spleen. These cords consist of a network of reticular fibers and cells (macrophages and lymphocytes) that separate the splenic sinuses. They play a crucial role in filtering the blood by removing old or damaged red blood cells.

(C) In the human circulatory system, arteries typically carry oxygenated blood away from the heart to the rest of the body.
However, the $Pulmonary$ artery is an exception.
It carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation.
Therefore, the correct answer is $C$.

(B) In a fetus, the $Ductus arteriosus$ is a blood vessel that connects the pulmonary artery to the proximal descending aorta.
It allows blood to bypass the non-functional fetal lungs, as the fetus receives oxygenated blood from the placenta.
After birth, this vessel typically closes and becomes the $Ligamentum arteriosum$.
$Foramen ovale$ is an opening in the atrial septum of the fetal heart, not the connection between the pulmonary artery and the aorta.

(A) The heart consists of four chambers: two atria and two ventricles. The ventricles have thicker walls than the atria because they are responsible for pumping blood out of the heart. Among the two ventricles, the $Left \text{ ventricle}$ has the thickest muscular wall. This is because it must generate enough pressure to pump oxygenated blood through the entire systemic circulation to all parts of the body.

(D) The '$Bundle$ of $His$' (also known as the atrioventricular bundle) is a collection of specialized cardiac muscle fibers.
These fibers are responsible for conducting electrical impulses from the atrioventricular $(AV)$ node to the ventricles of the heart.
Therefore,they are modified cardiac muscle cells that facilitate the rhythmic contraction of the heart.

(D) The heart rate of an animal is generally inversely proportional to its body size. Smaller animals have a higher metabolic rate and a faster heart rate to maintain their body temperature and meet their physiological demands. Among the given options,the mouse is the smallest animal and therefore exhibits the highest heart rate compared to the elephant,whale,and human.

(B) The tricuspid valve is a heart valve that prevents backflow of blood from the right ventricle to the right atrium. In humans,this valve is located between the right atrium and the right ventricle. While frogs have a three-chambered heart with a single ventricle,they do not possess a tricuspid valve in the same anatomical sense as mammals. Therefore,among the given options,the tricuspid valve is a characteristic feature of the human heart.

(B) William Harvey $(1578-1657)$ is widely recognized as the 'Father of Physiology'.
He is best known for his pioneering work in describing the systemic circulation and properties of blood being pumped to the body by the heart.
His landmark book,'Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus',published in $1628$,fundamentally changed the understanding of the circulatory system.

(A) The circulation of blood in the human body was first described and demonstrated by the English physician $William \ Harvey$ in $1628$. He published his findings in the book titled '$Exercitatio \ Anatomica \ de \ Motu \ Cordis \ et \ Sanguinis \ in \ Animalibus$'. This discovery fundamentally changed the understanding of the cardiovascular system.

(A) $Purkinje$ fibers are specialized conducting fibers located within the subendocardial layer of the heart's ventricular walls.
They are part of the cardiac conduction system and are responsible for transmitting electrical impulses from the $AV$ node to the ventricular myocardium,ensuring coordinated contraction of the heart.

(B) The $Spleen$ is known as the 'graveyard of RBCs' because it removes old and damaged erythrocytes from circulation. Additionally, it acts as a large reservoir of erythrocytes, storing a significant volume of blood that can be released into the circulation during emergencies or physical stress.

(C) The spleen is a large,bean-shaped organ that acts as a filter for the blood.
It is primarily known as a large reservoir for erythrocytes (red blood cells).
In addition to storing red blood cells,it also acts as a graveyard for old and damaged red blood cells and plays a significant role in the immune system by storing lymphocytes and filtering pathogens from the blood.

(A) The spleen is a bean-shaped organ located in the upper left part of the abdomen. It acts as a reservoir for red blood cells (RBCs) and also serves as a graveyard for old and damaged RBCs. It filters the blood and plays a significant role in the immune system by storing lymphocytes and macrophages.

(B) The Blue Whale $(Balaenoptera musculus)$ is the largest animal known to have ever existed. Due to its massive body size,which can reach up to $30 \ m$ in length and weigh up to $190 \ tonnes$,it requires a very large heart to pump blood throughout its body. The heart of a Blue Whale is roughly the size of a bumper car and weighs approximately $180 \ kg$ to $200 \ kg$.

(B) $1$. Statement $P$ is true: Both birds (Aves) and mammals possess a four-chambered heart,which allows for complete separation of oxygenated and deoxygenated blood.
$2$. Statement $Q$ is true: In mammals,the systemic aorta (aortic arch) curves to the left side,whereas in birds,it curves to the right side.
$3$. Conclusion: While both statements are scientifically correct,the four-chambered heart is a structural feature of the heart itself,whereas the direction of the aortic arch is a specific anatomical characteristic of the systemic circulation. Therefore,the four-chambered heart is not the reason for the left-sided aortic arch. Thus,$P$ is not the correct explanation of $Q$.

(C) The correct answer is $(C)$.
The heart of a frog is myogenic, which means the heartbeat originates from the specialized cardiac muscle cells rather than from nervous impulses.
Because the heart is myogenic, it is also autoexcitable, meaning it can generate its own electrical impulses to initiate contraction.
Due to these properties, the heart continues to beat outside the body as long as it receives an adequate supply of oxygen, nutrients, and $ATP$ to sustain the metabolic activity of the cardiac muscle cells.

(A) The blood pressure in the pulmonary artery is higher than that in the pulmonary vein.
$1$. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs.
$2$. The pulmonary vein carries oxygenated blood from the lungs to the left atrium.
$3$. Since the pulmonary artery is closer to the pumping action of the heart (right ventricle) and the pulmonary vein is a venous vessel returning blood to the heart,the pressure in the artery is significantly higher than in the vein.

(A) : The temporary rise in blood pressure during the contraction of the heart is called systolic pressure,and the temporary fall in blood pressure during the relaxation of the heart is called diastolic pressure.
Blood pressure is expressed as the ratio of the systolic pressure over the diastolic pressure.
For a healthy resting adult person,the average systolic/diastolic pressures are $120/80 \ mmHg$.
The aorta is directly supplied by the left ventricle; thus,the blood pressure in the aorta is highest during the systole of the left ventricle.
During this phase,the left ventricle contracts and pushes blood into the aorta.

(B) The correct answer is $B$.
'Bundle of His' is a specialized part of the cardiac conduction system in the human heart.
It consists of a bundle of nodal fibres,also known as the atrioventricular bundle ($AV$ bundle).
This bundle continues from the atrioventricular node $(AVN)$ and passes through the atrioventricular septa.
It emerges on the top of the interventricular septum and immediately divides into a right and left bundle.
These branches give rise to minute fibres throughout the ventricular musculature of the respective sides,which are called Purkinje fibres.
Together,these structures form the 'Bundle of His',which is essential for the rhythmic contraction of the heart.

(D) : The tricuspid valve is located between the right atrium and the right ventricle of the human heart. It consists of three cusps that regulate the flow of blood from the atrium to the ventricle.
When the right ventricle contracts to pump blood into the pulmonary artery,the tricuspid valve closes to prevent the backflow of blood into the right atrium.
The chordae tendinae are fibrous cords that anchor the valve cusps to the papillary muscles,ensuring the valve remains closed during ventricular systole.
If the chordae tendinae are partially non-functional,the valve may not close properly,leading to regurgitation of blood into the right atrium.
Consequently,the volume of blood effectively pumped into the pulmonary artery will be reduced.

(B) The correct answer is $B$. Blood flows from the post caval (inferior vena cava) into the right atrium during its diastolic phase due to a pressure gradient. The pressure in the right atrium is lower than the pressure in the post caval vein,which facilitates the passive movement of blood into the heart chamber.

(D) The heart acts as a pump that maintains a continuous flow of blood through the circulatory system.
In a healthy human heart,the volume of blood pumped by the right ventricle into the pulmonary circulation must equal the volume of blood pumped by the left ventricle into the systemic circulation to maintain homeostasis.
This principle is known as the $Frank-Starling$ law of the heart,which ensures that the output of both ventricles is balanced.
Therefore,at any given moment,the quantity of blood present in each chamber is essentially the same,as the heart functions as a closed-loop system where the stroke volume of the left and right sides is equal.

(A) During ventricular systole,the pressure inside the ventricles increases significantly.
This pressure rise causes the atrioventricular valves (Tricuspid and Bicuspid) to close to prevent backflow of blood into the atria.
Simultaneously,the high pressure forces the Semilunar valves (located at the base of the aorta and pulmonary artery) to open,allowing blood to be ejected from the ventricles into the systemic and pulmonary circulations.
Therefore,the correct answer is the Semilunar valve.

(A) The heart produces two main sounds during each cardiac cycle,commonly referred to as 'lub' and 'dub'.
$1$. The first heart sound,'$S_1$' or 'lub',is produced by the closure of the atrioventricular valves (bicuspid and tricuspid valves) at the beginning of ventricular systole.
$2$. The second heart sound,'$S_2$' or 'dub',is produced by the closure of the semi-lunar valves at the end of ventricular systole.
$3$. Therefore,the first sound is associated with the closure of the bicuspid and tricuspid valves.

(D) The human heart is $myogenic$,meaning the heartbeat originates from specialized muscle cells rather than external nerve impulses.
It contains specialized $nodal$ $tissue$ (the $SA$ node and $AV$ node) which acts as a pacemaker.
These nodal tissues are capable of generating $action$ $potentials$ (electric stimuli) that initiate and regulate the rhythmic contraction of the heart.
Therefore,all the given statements are correct.

(A) The heart is myogenic,meaning the heartbeat is initiated by specialized cardiac muscle cells.
Specifically,the impulse for the heartbeat originates in the Sinoatrial $(S.A.)$ node,which is located in the right atrium.
Because the $S.A.$ node sets the rhythm of the heart,it is known as the pacemaker of the heart.

(A) The $SAN$ (Sino-atrial node), also known as the pacemaker of the heart, is a specialized patch of nodal tissue present in the right upper corner of the right atrium.
It is capable of generating action potentials without any external stimuli (auto-rhythmic).
The rate of impulse generation by the $SAN$ is approximately $70-75$ times per minute, which corresponds to the normal heart rate of a healthy adult.

(C) The heart's conducting system consists of the $SA$ node,$AV$ node,Bundle of His,and Purkinje fibers.
While all these components are capable of generating action potentials (auto-excitability),the $SA$ node is the primary pacemaker.
This is because the $SA$ node possesses the highest inherent rate of depolarization,approximately $70-75$ beats per minute.
Since it reaches the threshold for an action potential faster than any other part of the conducting system,it initiates the heartbeat and sets the rhythm for the rest of the heart.

(C) The $SA$ node (sinoatrial node) acts as the pacemaker of the heart, initiating the electrical impulse.
When this action potential reaches the $AV$ node (atrioventricular node), there is a physiological delay of approximately $0.1$ seconds.
This delay is crucial because it ensures that the atria have sufficient time to complete their contraction (atrial systole) and empty their blood contents into the ventricles before the ventricles begin to contract.
If this delay did not occur, the atria and ventricles might contract simultaneously, which would significantly reduce the efficiency of blood pumping.

(C) The heart is myogenic, meaning its rhythmic contraction is initiated by a specialized nodal tissue.
The $SAN$ (Sino-Atrial Node) is located in the right upper corner of the right atrium.
It is known as the pacemaker of the heart because it has the highest rate of depolarization and generates the action potential first, which then spreads through the heart to initiate contraction.

(B) The correct answer is $B$.
Statement $A$ is correct: Semilunar valves are located at the base of the aorta and pulmonary artery to prevent backflow of blood into the ventricles.
Statement $B$ is incorrect: Bicuspid (mitral) and tricuspid valves are connected by chordae tendineae to the papillary muscles of the ventricular wall,not to the wall of the artery.
Statement $C$ is correct: The sinoatrial $(SA)$ node is situated in the upper right corner of the right atrium.
Statement $D$ is correct: The atrioventricular node $(AVN)$ is located in the lower left corner of the right atrium,close to the atrioventricular septum.

(B) The $SAN$ (Sino-Atrial Node) is a specialized patch of tissue present in the right upper corner of the right atrium.
It has the unique ability to generate action potentials without any external stimuli (auto-rhythmic).
It generates the maximum number of action potentials ($70-75$ per minute) compared to other parts of the heart's conduction system.
Because it initiates and maintains the rhythmic contractile activity of the heart,it is known as the natural pacemaker of the heart.

(C) The bundle of His is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the atrioventricular $(AV)$ node to the point of the apex of the fascicular branches.
These branches then further divide into a network of fine fibers known as Purkinje fibres,which spread throughout the ventricular myocardium to initiate ventricular contraction.

(B) Cardiac muscles are specialized muscle tissues found only in the heart.
They are structurally striated like skeletal muscles but function independently of conscious control.
Therefore,they are classified as involuntary muscles because they contract automatically without conscious effort.

(D) The heart of a frog is myogenic,meaning the heartbeat originates from specialized muscle cells within the heart itself rather than from nervous impulses.
Because the heart is myogenic,it is also self-excitable,allowing it to continue beating for a short period even after being removed from the body,provided it is kept in a suitable physiological saline solution.
Statement $(i)$ is a fact about frogs but does not explain why the heart continues to beat.
Statement $(ii)$ is incorrect as frogs have a closed circulatory system.
Therefore,statements $(iii)$ and $(iv)$ are the correct reasons for the observed phenomenon.

(B) The human heart has four chambers: two atria and two ventricles.
$1$. The tricuspid valve is a three-flap valve located between the right atrium and the right ventricle.
$2$. Its primary function is to prevent the backflow of blood from the right ventricle into the right atrium during ventricular systole.
$3$. The bicuspid or mitral valve is located between the left atrium and the left ventricle.
$4$. Therefore,the correct option is $B$.

(B) The $Celiac$ $artery$ (also known as the $Celiac$ $trunk$) is the first major branch of the abdominal aorta.
It divides into three main branches: the left gastric artery,the common hepatic artery,and the splenic artery.
Therefore,the splenic artery arises from the celiac artery.

(A) The heart produces two primary sounds during the cardiac cycle,often described as 'lubb' and 'dubb'.
$1$. The first heart sound,'lubb',is associated with the closure of the atrioventricular valves (tricuspid and bicuspid valves) at the beginning of ventricular systole.
$2$. The second heart sound,'dubb',is associated with the closure of the semilunar valves (aortic and pulmonary valves) at the beginning of ventricular diastole.
Therefore,the 'dubb' sound is produced by the closure of the semilunar valves.

(C) The heart's rhythmic contraction is initiated by a specialized patch of cardiac muscle fibers called the $SA$ node (Sinoatrial node).
It is located in the right upper corner of the right atrium.
Because it generates the action potential that sets the pace for the heart's contraction,it is known as the natural pacemaker of the heart.