Structure and function of heart Questions in English

(B) The pulmonary trunk (or pulmonary artery) is the vessel that carries deoxygenated blood from the heart to the lungs for oxygenation.
It originates from the $Right \text{ ventricle}$ of the heart.
Blood is pumped from the $Right \text{ ventricle}$ through the pulmonary valve into the pulmonary trunk, which then divides into the left and right pulmonary arteries.

(C) The heart is protected by a double-walled membranous bag known as the $Pericardium$,which encloses the pericardial fluid. This fluid helps in reducing friction during the contraction and relaxation of the heart.

(A) The mitral valve,also known as the bicuspid valve,is located between the left atrium and the left ventricle in the mammalian heart.
It prevents the backflow of blood from the left ventricle into the left atrium during ventricular systole.
Therefore,it regulates the flow of oxygenated blood between the left atrium and the left ventricle.

(B) The cardiac muscle fibers are unique because they have a long refractory period.
During each cardiac cycle,the heart undergoes a period of relaxation known as diastole.
Even though the heart beats continuously,the duration of diastole (relaxation phase) is sufficient for the cardiac muscle to recover and replenish its oxygen and nutrient supplies.
This period of rest between beats prevents the accumulation of fatigue-inducing metabolites,allowing the heart to function throughout an individual's life without tiring.

(A) Blood enters the heart from the veins into the atria due to atrial diastole (relaxation of the atria). During atrial diastole,the pressure in the atria decreases,creating a suction effect that draws blood from the vena cava and pulmonary veins into the right and left atria,respectively. Therefore,the correct answer is $A$.

(B) The heart contains four main valves that ensure the unidirectional flow of blood.
$1$. The $Tricuspid$ $valve$ is located between the right atrium and the right ventricle.
$2$. The $Bicuspid$ $(Mitral)$ $valve$ is located between the left atrium and the left ventricle.
$3$. The $Pulmonary$ $semilunar$ $valve$ is located at the opening of the right ventricle into the pulmonary artery.
$4$. The $Aortic$ $semilunar$ $valve$ is located at the opening of the left ventricle into the aorta.
Therefore, the valve between the right ventricle and the pulmonary artery is the $Semilunar$ $valve$.

(B) The cardiac impulse originates at the $SA$ node (Sinoatrial node),which acts as the natural pacemaker of the heart.
From the $SA$ node,the impulse travels through the internodal pathways to the $AV$ node (Atrioventricular node).
The $AV$ node is located in the lower left corner of the right atrium near the interatrial septum.
At the $AV$ node,the cardiac impulse is delayed for approximately $0.1$ seconds.
This delay is crucial because it allows the atria to complete their contraction and empty their blood into the ventricles before the ventricles begin to contract.

(C) In the human circulatory system, arteries are defined as blood vessels that carry blood away from the heart. Generally, systemic arteries carry oxygenated blood to various body tissues. However, the $Pulmonary$ artery is an exception because it carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation.

(C) myogenic heart is a heart where the heartbeat is initiated by specialized muscle cells rather than nerve impulses.
In vertebrates,including mammals like the elephant,the heart is myogenic.
In contrast,invertebrates like the cockroach and leech possess a neurogenic heart,where the heartbeat is controlled by the nervous system.
Therefore,among the given options,the elephant has a myogenic heart.

$(C)$ Cardiac output is defined as the volume of blood pumped by each ventricle per minute.
It is calculated by the formula: $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$.
In a healthy individual, the average stroke volume is approximately $70 \, mL$ and the average heart rate is $72 \, \text{beats/min}$.
Therefore, $\text{Cardiac Output} = 70 \, mL \times 72 \, \text{beats/min} \approx 5040 \, mL/min$, which is approximately $5 \, L/min$.

(A) The $foramen$ $ovale$ is an opening in the fetal heart that allows blood to bypass the non-functional fetal lungs by flowing directly from the right atrium to the left atrium.
After birth,as the lungs begin to function,this opening closes and becomes a depression known as the $fossa$ $ovalis$.
The $fossa$ $ovalis$ is located on the interatrial $septum$,which is the wall separating the right and left atria of the heart.

(B) The pacemaker of the human heart is the $Sino-Atrial$ $Node$ $(SAN)$.
It is a specialized patch of nodal tissue located in the right upper corner of the right atrium.
It is responsible for initiating and maintaining the rhythmic contractile activity of the heart.

(D) The pericardial fluid is secreted by the serous layer of the pericardium,specifically the visceral layer (also known as the epicardium) and the parietal layer of the serous pericardium. This fluid acts as a lubricant,reducing friction between the heart and the surrounding tissues during cardiac contractions.

(C) The $pulmonary \text{ veins}$ are responsible for transporting oxygenated blood from the lungs to the left atrium of the heart.
Unlike most veins in the body which carry deoxygenated blood, the pulmonary veins are unique because they carry oxygen-rich blood.
- $Superior \text{ vena cava}$ and $inferior \text{ vena cava}$ carry deoxygenated blood to the right atrium.
- $Pulmonary \text{ artery}$ carries deoxygenated blood from the right ventricle to the lungs.

(C) Myocardial infarction (heart attack) occurs when blood flow to a part of the heart muscle is blocked, usually by a blood clot. The $Left Anterior Descending (LAD)$ artery is the most frequently occluded vessel, often referred to as the 'widow-maker' artery because its blockage leads to extensive damage to the left ventricle, which is the primary pumping chamber of the heart.

(B) The bundle of His (also known as the atrioventricular bundle) is a collection of heart muscle cells specialized for electrical conduction.
It originates from the atrioventricular node $(AVN)$,which is located in the lower left corner of the right atrium near the interatrial septum.
From the $AVN$,the bundle of His passes through the atrioventricular septum to enter the interventricular septum,where it divides into right and left bundle branches to conduct impulses to the ventricles.

(B) 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 node $(AVN)$ to the ventricles of the heart.
Therefore,it is a network of muscle fibers located in the ventricular wall that facilitates the contraction of the ventricles.

(D) The first heart sound,'$Lubb$',is produced by the closure of the $tricuspid$ and $bicuspid$ (mitral) valves at the beginning of ventricular systole.
The second heart sound,'$Dupp$',is produced by the closure of the $semilunar$ valves (aortic and pulmonary valves) at the beginning of ventricular diastole.
Therefore,the characteristic '$Lubb-Dupp$' sounds are caused by the sequential closure of these valves.

(C) The heart of a frog is myogenic. The pacemaker of the frog's heart is the $Sinus \text{ } venosus$. It is a thin-walled, triangular chamber that receives deoxygenated blood from the body and initiates the heartbeat.

(D) The heart contains four main valves that ensure the unidirectional flow of blood.
$1$. The $Tricuspid$ $valve$ is located between the right atrium and the right ventricle.
$2$. The $Mitral$ $valve$ (or $Bicuspid$ $valve$) is located between the left atrium and the left ventricle.
$3$. The $Pulmonary$ $semilunar$ $valve$ is located between the right ventricle and the pulmonary artery.
$4$. The $Aortic$ $semilunar$ $valve$ is located between the left ventricle and the aorta.
Therefore, the correct answer is the $Tricuspid$ $valve$.

(C) The heart produces two primary sounds during the cardiac cycle: '$LUB$' 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 end of ventricular systole.
Therefore,the '$DUB$' sound is heard when the semilunar valves close.

(B) The $Spleen$ is a secondary lymphoid organ that receives oxygenated blood via the $Splenic$ artery,which branches directly from the $Celiac$ trunk of the $Aorta$. Unlike the $Lungs$ (which receive deoxygenated blood from the $Pulmonary$ artery) or the $Liver$ (which receives a significant portion of deoxygenated blood via the $Hepatic$ portal vein),the $Spleen$ is primarily supplied by arterial blood.

(C) During fetal development, the $ductus arteriosus$ is a blood vessel that connects the pulmonary artery to the aorta, allowing blood to bypass the non-functional fetal lungs.
After birth, as the lungs begin to function, the $ductus arteriosus$ constricts and closes.
This closed, fibrous remnant of the vessel is known as the $ligamentum arteriosum$.

(A) The human heart is described as $Myogenic$ because the heartbeat is initiated by a specialized patch of modified heart muscle cells called the $Sinoatrial$ $(SA)$ node,which acts as a natural pacemaker.
Unlike neurogenic hearts (found in many invertebrates),where the heartbeat is initiated by nerve impulses from a ganglion,the myogenic heart generates its own electrical impulses independently of the nervous system.

(B) Cardiac muscles are specialized involuntary muscles found in the heart.
They exhibit rhythmic contraction and relaxation throughout the life of an organism.
These muscles are structurally striated like skeletal muscles but functionally behave like smooth muscles because they are involuntary.
Crucially,cardiac muscles are highly resistant to fatigue due to the presence of a large number of mitochondria and a rich blood supply,which ensures a continuous supply of oxygen and nutrients.
Therefore,they contract quickly and rhythmically without getting fatigued.

(B) Purkinje fibers are specialized conducting fibers located within the subendocardial layer of the heart's ventricular walls.
They are responsible for transmitting electrical impulses from the atrioventricular $(AV)$ node to the ventricular myocardium,ensuring coordinated contraction of the heart ventricles.

(C) Purkinje fibers are specialized conducting fibers composed of electrically excitable cells.
They are located in the inner ventricular walls of the heart,just beneath the endocardium.
These fibers conduct cardiac action potentials more quickly and efficiently than any other cells in the cardiac conduction system.
This rapid conduction allows the heart's conduction system to create synchronized contractions of the ventricles,which is essential for maintaining a consistent heart rhythm and effective blood pumping.

(A) In the embryonic development of the human heart,the sinus venosus is a primitive structure that receives venous blood. During the process of heart development,the sinus venosus gets incorporated into the wall of the right atrium. This incorporation forms the smooth-walled part of the right atrium,known as the sinus venarum,while the original embryonic right atrium forms the pectinate muscles. Therefore,the sinus venosus merges with the right atrium.

(A) Valves are specialized structures that ensure the unidirectional flow of blood or lymph.
$1$. In vertebrates,valves are present in the heart (between atria and ventricles,and at the base of major arteries) and in veins to prevent backflow.
$2$. Valves are also present in the lymphatic system of vertebrates to maintain the flow of lymph.
$3$. In many invertebrates,the circulatory system (often open type) also contains valves within the heart or ostia to regulate hemolymph flow.
Therefore,valves are found in the heart and blood vessels of both vertebrates and invertebrates,as well as in the lymphatic system of vertebrates.

(B) In the human circulatory system,the right ventricle receives deoxygenated blood from the right atrium.
Upon contraction of the right ventricle,this deoxygenated blood is pumped into the pulmonary artery.
The pulmonary artery carries this blood to the lungs for oxygenation.
Therefore,the correct destination for blood pumped by the right ventricle is the lungs.

(B) The tricuspid valve is an atrioventricular valve located between the right atrium and the right ventricle of the heart. It consists of three flaps (cusps) that prevent the backflow of blood from the right ventricle into the right atrium during ventricular systole.

(D) Purkinje fibers are specialized conducting fibers located within the subendocardial surface of the ventricular walls of the heart.
They are part of the cardiac conduction system and are responsible for transmitting electrical impulses from the $AV$ node to the ventricular myocardium,which triggers ventricular contraction.

(B) The pacemaker of the heart is the $Sinoatrial$ $node$ $(SAN)$.
It is a specialized patch of cardiac muscle fibers located in the wall of the right atrium,near the opening of the superior vena cava.
It is responsible for initiating and maintaining the rhythmic contractile activity of the heart,hence it is called the natural pacemaker.

(B) The human heart contains four valves that ensure unidirectional blood flow.
$1$. The $Bicuspid$ valve,also known as the $Mitral$ valve,is located between the left atrium and the left ventricle.
$2$. The $Tricuspid$ valve is located between the right atrium and the right ventricle.
$3$. The $Semilunar$ valves are located at the openings of the pulmonary artery and the aorta.
Therefore,the correct location for the bicuspid valve is between the left atrium and the left ventricle.

(B) In the human heart,the right atrium receives deoxygenated blood from the body through two major veins: the superior vena cava and the inferior vena cava. These vessels collectively drain into the right atrium. Therefore,the correct answer is the vena cava.

(B) The $Pulmonary \text{ vein}$ is unique because it is the only vein in the adult human body that carries oxygenated blood from the lungs to the left atrium of the heart.
While the $Pulmonary \text{ artery}$ carries deoxygenated blood to the lungs, the $Coronary \text{ artery}$ and $Cerebral \text{ artery}$ carry oxygenated blood to the heart muscle and brain respectively, but the blood in the $Pulmonary \text{ vein}$ has the highest oxygen concentration as it has just been freshly oxygenated in the lungs.

(D) The human heart consists of four chambers: two atria and two ventricles.
The atria receive blood,while the ventricles pump blood out of the heart.
The left ventricle is responsible for pumping oxygenated blood to the entire body through the systemic circulation.
Because it must generate enough pressure to overcome the systemic resistance and reach all parts of the body,the muscular wall of the left ventricle is significantly thicker than that of the other three chambers.

(B) The valve located between the left atrium and the left ventricle is known as the $Mitral$ valve (also called the bicuspid valve).
This valve allows blood to flow from the left atrium into the left ventricle but prevents it from flowing back.
The tricuspid valve is located between the right atrium and the right ventricle.

(A) The tricuspid valve is located between the right atrium and the right ventricle.
Its primary function is to prevent the backflow of blood from the right ventricle into the right atrium during ventricular systole.
If the tricuspid valve becomes non-functional due to damage to the chordae tendineae,blood will leak back into the right atrium during ventricular contraction.
Consequently,less blood will be pumped into the pulmonary artery,which carries deoxygenated blood to the lungs for oxygenation.
Therefore,the flow of blood into the pulmonary artery will be reduced.

(D) Cardiac output is defined as the volume of blood pumped by each ventricle per minute.
It is calculated as the product of stroke volume (approximately $70 \, ml$) and heart rate (approximately $72 \, \text{beats/min}$), which equals approximately $5040 \, ml$ or $5 \, L$ per minute.
The body has the ability to alter the cardiac output through the autonomic nervous system and hormonal regulation to meet metabolic demands.
Therefore, the statement that the body has no ability to alter cardiac output is incorrect.

(D) The heart rate of a rabbit is significantly higher than that of a human. On average,the heart rate of an adult rabbit ranges from $120$ to $150$ beats per minute. This high metabolic rate is characteristic of small mammals.

(C) Cardiac output is defined as the volume of blood pumped out by each ventricle per minute.
In a healthy individual, the stroke volume is approximately $70 \ mL$ and the average heart rate is $72$ beats per minute.
Therefore, Cardiac Output = Stroke Volume $\times$ Heart Rate.
Cardiac Output = $70 \ mL \times 72 \ \text{beats/min} = 5040 \ mL \approx 5 \ \text{liters/min}$.
Thus, it refers to the volume of blood pumped by the left ventricle per minute.

(C) The first successful human-to-human heart transplant was performed by Dr. Christiaan Barnard on December $3$,$1967$,at Groote Schuur Hospital in Cape Town,South Africa. The patient was Louis Washkansky.

(B) The first heart sound is known as '$Lub$'.
It is produced by the closure of the atrioventricular valves (tricuspid and bicuspid valves) at the beginning of ventricular systole.
This closure prevents the backflow of blood into the atria when the ventricles start to contract.
Therefore,the correct option is $B$.

(C) The heart produces two primary sounds during each cardiac cycle,known as '$Lubb$' and '$Dupp$'.
$1$. The first heart sound,'$Lubb$',is produced by the closure of the atrioventricular valves,which are the mitral (bicuspid) and tricuspid valves,at the beginning of ventricular systole.
$2$. The second heart sound,'$Dupp$',is produced by the closure of the semilunar valves (pulmonary and aortic valves) at the beginning of ventricular diastole.
Therefore,the first heart sound is associated with the closure of the mitral and tricuspid valves.

(A) The heart contains specialized valves that ensure the unidirectional flow of blood.
Specifically,the valve located between the right atrium and the right ventricle is the $Tricuspid$ $valve$.
It consists of three muscular flaps or cusps that prevent the backflow of blood from the right ventricle into the right atrium during ventricular systole.
In contrast,the $Bicuspid$ $valve$ (or $Mitral$ $valve$) is located between the left atrium and the left ventricle.

(A) The electrical impulse for the heartbeat originates at the $S.A.$ node (Sinoatrial node),which acts as the pacemaker.
This impulse travels to the $A.V.$ node (Atrioventricular node).
From the $A.V.$ node,the impulse is transmitted to the Bundle of His and then spreads throughout the ventricular musculature via the Purkinje fibers.
The Purkinje fibers are responsible for the rapid conduction of the electrical impulse,which triggers the contraction of the ventricles.

(B) The heart of a healthy adult human typically beats at an average rate of $72$ to $75$ beats per minute.
This range falls within the standard physiological range of $70-80$ beats per minute.
Therefore,option $B$ is the correct answer.

(A) The human heart has four chambers: two atria and two ventricles.
$1$. The tricuspid valve is a flap of tissue that prevents backflow of blood.
$2$. It is situated between the right atrium and the right ventricle.
$3$. Its primary function is to ensure that blood flows in only one direction from the right atrium into the right ventricle during atrial contraction.
Therefore,the correct option is $A$.

(A) The heart sounds are produced by the closure of heart valves.
$1$. The first heart sound,'$lub$',is produced by the closure of the atrioventricular valves (tricuspid and bicuspid 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.