Structure and function of heart Questions in English

(A) Purkinje fibers are specialized cardiac muscle fibers that are located in the inner ventricular walls of the heart,just beneath the endocardium in a space called the subendocardium.
Although they are derived from cardiac muscle cells,they are specialized for rapid conduction of electrical impulses throughout the ventricles,which allows for coordinated ventricular contraction.
Therefore,they are essentially modified muscular tissues.

(A) In the human circulatory system,oxygenated blood is returned from the lungs to the heart via the pulmonary veins.
These veins empty the oxygenated blood into the left atrium.
During atrial systole (atrial contraction),the blood is pushed from the left atrium into the left ventricle through the bicuspid (mitral) valve.
Therefore,the circulation of oxygenated blood occurs from the left atrium to the left ventricle during atrial systole.

(C) The heart sounds are produced by the closing of the heart valves.
$1$. The first heart sound,'$lubb$',is produced by the closure of the atrioventricular $(AV)$ valves (tricuspid and bicuspid valves) at the beginning of ventricular systole.
$2$. The second heart sound,'$dubb$',is produced by the closure of the semilunar valves at the beginning of ventricular diastole.
Therefore,both sounds are associated with the closing of valves.

(C) The first heart sound,commonly known as '$Lubb$',is produced during the cardiac cycle.
It occurs at the beginning of ventricular systole.
This sound is caused by the sudden closure of the atrioventricular $(AV)$ valves (tricuspid and bicuspid valves) due to the increase in ventricular pressure.

(C) The correct matching is as follows:
$1$. Superior Vena Cava $(a)$ brings deoxygenated blood from the upper body parts to the right atrium $(s)$.
$2$. Inferior Vena Cava $(b)$ brings deoxygenated blood from the lower body parts to the right atrium $(r)$.
$3$. Pulmonary Artery $(c)$ carries deoxygenated blood from the heart towards the lungs $(p)$.
$4$. Pulmonary Vein $(d)$ carries oxygenated blood from the lungs towards the heart $(q)$.
Therefore, the correct sequence is $a-s, b-r, c-p, d-q$.

(D) The mitral valve (also known as the bicuspid valve) is located between the left atrium and the left ventricle of the heart.
It is attached to the papillary muscles of the left ventricle by fibrous cords known as $Chordae$ $tendineae$.
These structures prevent the valve leaflets from prolapsing into the atrium during ventricular contraction (systole).

(D) The heartbeat is myogenic in humans. The sequence of conduction is as follows:
$1$. The impulse originates at the $SA$ (Sinoatrial) node,which acts as the pacemaker.
$2$. From the $SA$ node,the impulse spreads to the $AV$ (Atrioventricular) node.
$3$. From the $AV$ node,it travels through the Bundle of $His$ (Atrioventricular bundle).
$4$. Finally,it is distributed to the ventricular musculature via the Purkinje fibers.
Therefore,the correct sequence is: $SA$ node $\rightarrow$ $AV$ node $\rightarrow$ Bundle of $His$ $\rightarrow$ Purkinje fibers.

(B) In the human circulatory system, the $Pulmonary \text{ vein}$ is unique because it is the only vein that carries oxygenated (pure) blood from the lungs to the left atrium of the heart.
Conversely, the $Pulmonary \text{ artery}$ carries deoxygenated blood from the heart to the lungs.
The $Renal \text{ vein}$ carries deoxygenated blood away from the kidneys, and the $Hepatic \text{ portal vein}$ carries nutrient-rich but deoxygenated blood from the digestive tract to the liver.
Therefore, the correct option is $B$.

(B) neurogenic heart is a type of heart where the heartbeat is initiated by nerve impulses generated by a ganglion (a cluster of nerve cells) located near the heart. This is a characteristic feature of most invertebrates,such as annelids and arthropods. In contrast,vertebrates (like humans,rats,and rabbits) possess a myogenic heart,where the heartbeat is initiated by specialized muscle cells (the sinoatrial node). Therefore,the correct option is $B$.

(B) The heart produces two main sounds during the cardiac cycle,commonly described as 'lub' and 'dub'.
The first heart sound,known as '$S_1$' or 'lub',is produced by the closure of the atrioventricular valves (tricuspid and bicuspid/mitral valves) at the beginning of ventricular systole.
The second heart sound,known as '$S_2$' or 'dub',is produced by the closure of the semilunar valves at the end of ventricular systole.

(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 node ($AV$ node) to the ventricles of the heart,ensuring coordinated contraction. Therefore,it is a group of modified muscle fibers.

(D) The $SA$ node (Sinoatrial node) is a specialized bundle of cardiac muscle fibers located in the right atrium of the heart.
It is known as the natural pacemaker of the heart because it generates electrical impulses that initiate and regulate the rhythmic contraction of the heart muscle.
These impulses spread through the heart,causing it to beat at a regular rate.

(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 option is $C$.

(C) Purkinje fibers are specialized cardiac muscle fibers that conduct electrical impulses from the atrioventricular $(AV)$ node to the ventricular myocardium.
These fibers are distributed throughout the ventricular walls.
When the electrical impulse reaches the Purkinje fibers,it triggers the simultaneous contraction of both the right and left ventricles,ensuring efficient blood pumping into the pulmonary artery and the aorta.

(C) The human heart contains four valves that ensure the unidirectional flow of blood.
$1$. 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.

(C) The normal heart rate for a two-month-old infant typically ranges from $100$ to $160$ beats per minute.
Since $100$ to $160$ is significantly greater than $72$,the correct option is $> 72/min$.

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

(A) 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 in a space called the subendocardium.
Although they are modified cardiac muscle cells,they are specialized for rapid conduction of electrical impulses throughout the ventricles,which allows the heart to contract in a synchronized manner.
Therefore,they are essentially specialized muscular fibers.

(B) The pulmonary vein is a unique blood vessel in the human circulatory system.
Unlike other veins in the body that carry deoxygenated blood,the pulmonary veins carry oxygenated blood.
These veins transport oxygen-rich blood from the lungs back to the left atrium of the heart.
Therefore,the correct description is that it carries oxygenated blood from the lungs to the heart.

(B) The human heart contains two specialized nodal tissues:
$1$. The $Sino-atrial$ $node$ $(SAN)$, located in the right upper corner of the right atrium.
$2$. The $Atrio-ventricular$ $node$ $(AVN)$, located in the lower left corner of the right atrium close to the $atrio-ventricular$ septum.
These nodes are responsible for generating and conducting the electrical impulses that initiate the heartbeat.

(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 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 $5 \, Litres/min$.

(A) In humans,oxygenated blood is carried from the lungs to the heart via the pulmonary veins.
During atrial diastole,the left atrium receives this oxygenated blood.
During atrial systole,the left atrium contracts,pushing the oxygenated blood into the left ventricle through the bicuspid (mitral) valve.
Therefore,the circulation of oxygenated blood occurs from the left atrium to the left ventricle during atrial systole.

(B) Heart murmurs are abnormal sounds produced by turbulent blood flow within the heart.
These sounds are typically caused by defective or damaged heart valves that do not close properly (regurgitation) or do not open fully (stenosis).
Therefore,heart murmurs are a clinical indicator of valvular heart disease.

(A) The $Foramen \text{ } ovale$ is an opening in the interatrial septum of the fetal heart that allows blood to bypass the non-functional fetal lungs.
After birth, this opening closes and becomes the $Fossa \text{ } ovalis$.
Therefore, the remnant of this structure is located in the interatrial septum.

(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 cardiac cycle involves two primary heart sounds,$Lubb$ and $Dupp$.
$1$. The first heart sound,$Lubb$ $(S1)$,is produced due to the simultaneous closure of the atrioventricular valves,which are the bicuspid (mitral) valve and the tricuspid valve,at the beginning of ventricular systole.
$2$. The second heart sound,$Dupp$ $(S2)$,is produced due to the closure of the semilunar valves (aortic and pulmonary valves) at the end of ventricular systole.
Therefore,the $Lubb$ sound is produced by the closure of both the bicuspid and tricuspid valves.

(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 is non-functional,blood will regurgitate (flow back) into the right atrium during ventricular contraction. This reduces the volume of blood pumped into the pulmonary artery,which carries deoxygenated blood to the lungs for oxygenation. Therefore,the immediate effect is a reduction in the flow of blood into the pulmonary artery.

(A) The mitral valve,also known as the bicuspid valve,is located between the left atrium and the left ventricle of the heart.
It acts as a one-way valve that prevents the backflow of blood from the left ventricle into the left atrium during ventricular contraction (systole).
Therefore,it regulates the flow of blood from the left atrium into the left ventricle.

(D) The cardiac muscle is unique because it is myogenic and possesses a long refractory period.
During the cardiac cycle,the heart undergoes a period of relaxation known as diastole.
This period of diastole provides the heart muscle with sufficient time for rest and recovery,allowing it to replenish oxygen and nutrients and remove metabolic waste,thereby preventing fatigue despite continuous activity throughout life.

(D) The heart is enclosed by a double-walled membranous bag called the pericardium,which contains the pericardial fluid.
This fluid is secreted by the serous layer of the pericardium,specifically the inner visceral layer (epicardium) and the outer parietal layer.
Its primary function is to reduce friction between the heart walls and the surrounding tissues during the contraction and relaxation of the heart.

(B) Cardiac muscles are the muscles of the heart.
They exhibit striations (light and dark bands) under a microscope,similar to skeletal muscles,hence they are striated.
However,their contraction is not under the conscious control of the organism,meaning they are involuntary.
Therefore,cardiac muscles are striated and involuntary.

(A) Cardiac muscles are specialized muscle cells that contract rhythmically throughout an individual's life without fatigue.
To support this continuous activity,they require a constant and high supply of $ATP$ (Adenosine Triphosphate).
Therefore,cardiac muscle fibers contain a significantly higher number of mitochondria compared to skeletal muscle fibers to facilitate aerobic respiration and meet the high energy demands.

(A) The heart of a mammal is myogenic.
In a myogenic heart,the heartbeat is initiated by a specialized group of muscle cells called the sinoatrial node ($SA$ node) or pacemaker,which is located within the heart muscle itself.
This is in contrast to a neurogenic heart,where the heartbeat is initiated by nerve impulses from the central nervous system.

(D) The post caval vein, also known as the $Inferior Vena Cava$, carries deoxygenated blood from the lower parts of the body to the right atrium of the heart.
At the point where the $Inferior Vena Cava$ enters the right atrium, there is a fold of the endocardium known as the $Eustachian valve$.
This valve prevents the backflow of blood into the vein during the contraction of the atrium in the embryonic stage, though it becomes non-functional in adults.

(D) The Eustachian valve is a fold of endocardium found in the right atrium of the heart.
It is located at the opening of the inferior vena cava into the right atrium.
During fetal development,it helps direct oxygenated blood from the inferior vena cava towards the foramen ovale,allowing it to bypass the non-functional fetal lungs.
Therefore,the correct option is $D$.

(B) The cardiac impulse originates in the $SA$ (Sinoatrial) node,which acts as the natural pacemaker of the heart.
From the $SA$ node,the impulse spreads to the $AV$ (Atrioventricular) node.
From the $AV$ node,the impulse travels through the Bundle of $His$ (Atrioventricular bundle).
Finally,the impulse is distributed throughout the ventricular musculature by the Purkinje fibers.
Therefore,the correct sequence is: $SA$ node $\rightarrow$ $AV$ node $\rightarrow$ Bundle of $His$ $\rightarrow$ Purkinje fibers.

(C) The human heart is myogenic,meaning the heartbeat is initiated by specialized 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 muscle,causing it to contract and initiating the heartbeat.
Therefore,the $SA$ node is responsible for initiating the heartbeat.

(A) The heart is myogenic,meaning the heartbeat is initiated by a specialized patch of cardiac muscle fibers called the $S.A.$ (Sinoatrial) node.
It 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 impulse that stimulates the heart to contract.

(D) The heart is myogenic,meaning it can generate its own electrical impulses.
The $SA$ node (Sinoatrial node) is known as the pacemaker of the heart because it has the highest rate of spontaneous depolarization and generates action potentials without any external stimulus.
While the $AV$ node and Purkinje fibers also possess autorhythmicity,the $SA$ node initiates the impulse that sets the rhythm for the entire heart.

(B) The heart's natural pacemaker is the Sinoatrial $(SA)$ node,which is located in the right atrium.
It generates electrical impulses that initiate the heartbeat and regulate the rhythm of the heart.
An artificial pacemaker is implanted to perform the same function as the $SA$ node when the natural pacemaker fails to maintain a normal heart rate.
Therefore,the function of an artificial pacemaker is similar to that of the $SA$ node.

(D) The heart consists of four chambers: two atria and two ventricles.
The atria are receiving chambers and have relatively thin walls.
The ventricles are pumping chambers and have thicker walls than the atria.
Among the two ventricles,the left ventricle has the thickest wall because it must pump oxygenated blood to the entire body through the systemic circulation,which requires high pressure.
Therefore,the left ventricle is the chamber with the thickest wall.

(D) The heart wall is composed of three distinct layers:
$1$. Epicardium: The thin,outer protective layer.
$2$. Myocardium: The thick,middle muscular layer responsible for contraction.
$3$. Endocardium: The thin,smooth inner lining of the heart chambers.
Since all three layers constitute the heart wall,the correct option is $D$.

(C) The $SA$ node (Sinoatrial node) is a specialized patch of cardiac muscle fibers located in the right atrium of the heart.
It is known as the natural pacemaker because it has the ability to generate action potentials spontaneously at a higher rate than any other part of the heart.
These electrical impulses initiate the contraction of the heart muscle,thereby regulating the heartbeat.

(C) Papillary muscles are specialized muscles located in the ventricles of the heart.
They are attached to the atrioventricular valves (tricuspid and mitral valves) via fibrous cords known as chordae tendineae.
Their primary function is to prevent the inversion or prolapse of these valves into the atria during ventricular systole (contraction).
By contracting,they pull on the chordae tendineae,ensuring the valves remain tightly closed and preventing the backflow of blood.

(B) The human heart wall consists of three layers: the epicardium (outer),the myocardium (middle),and the endocardium (inner).
The myocardium is composed of cardiac muscle tissue,which is responsible for the contraction and relaxation of the heart.
Because it contains thick layers of cardiac muscle,the myocardium is the thickest layer of the heart wall,providing the necessary strength for pumping blood throughout the body.

(B) heart murmur is an abnormal sound heard during the cardiac cycle,typically described as a whooshing or swishing noise.
It is caused by turbulent blood flow within or near the heart.
This turbulence is most commonly caused by defective heart valves,such as stenosis (narrowing) or regurgitation (leaking),which prevent the valves from closing or opening properly.

(B) The $Systemic$ $heart$ refers to the left atrium and the left ventricle of the heart in higher vertebrates (like mammals and birds).
This part of the heart receives oxygenated blood from the lungs via the pulmonary veins and pumps it into the systemic circulation (the rest of the body) through the aorta.
In contrast,the right side of the heart is often referred to as the $Pulmonary$ $heart$ because it pumps deoxygenated blood to the lungs.

(C) The posterior vena cava (inferior vena cava) enters the right atrium of the mammalian heart.
This opening is guarded by a fold of the endocardium known as the $Eustachian$ $valve$.
This valve is functional during embryonic development to direct oxygenated blood from the inferior vena cava towards the foramen ovale,but it becomes non-functional or vestigial in adults.

(A) Among the given options,the giraffe ($Giraffa$ $camelopardalis$) possesses the largest heart. $A$ giraffe's heart can weigh up to $11$ to $12$ $kg$ and is approximately $60$ $cm$ long. This large size is an evolutionary adaptation required to pump blood against gravity up its long neck to reach the brain.

(A) Papillary muscles are specialized muscles located in the ventricles of the heart in mammals,including humans and rabbits.
They are attached to the atrioventricular valves (tricuspid and mitral valves) via the chordae tendineae.
Their primary function is to prevent the prolapse of these valves into the atria during ventricular contraction (systole).