Structure and function of heart Questions in English

(A) The circulation of blood in the human body was discovered by William Harvey in the year $1628$. He demonstrated that blood is pumped by the heart and circulates through the body in a closed system.

(B) The heart is a mesodermally derived organ.
It is situated in the thoracic cavity,in the mediastinum space between the two lungs,and is slightly tilted to the left.

(N/A) The tricuspid valve is located at the opening 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.

(B) The valve that guards the opening between the left atrium and the left ventricle is called the Mitral valve.
It is also known as the bicuspid valve because it consists of two cusps or flaps.
This valve prevents the backflow of blood from the left ventricle into the left atrium during ventricular systole.

(B) The valves in the heart allow the flow of blood only in one direction,i.e.,from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta.
These valves prevent any backward flow of blood,ensuring efficient circulation throughout the body.

(B) Our heart normally beats $70-75$ times in a minute (average $72$ beats $min^{-1}$).

(N/A) Cardiac output is defined as the volume of blood pumped by each ventricle per minute. It is calculated by multiplying the stroke volume (the amount of blood pumped by each ventricle per beat) by the heart rate (the number of beats per minute). The formula is: $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$.

(B) The heart is called myogenic because its rhythmic contractions are initiated and regulated by specialized cardiac muscle cells known as nodal tissue (e.g.,$SA$ node).
Unlike neurogenic hearts,which require nerve impulses from the central nervous system to contract,the myogenic heart generates its own electrical impulses intrinsically.
This nodal tissue possesses properties of both muscle and nerve cells,allowing the heart to maintain its beat even when disconnected from the nervous system.

(N/A) Purkinje fibres: These are specialized cardiac muscle fibres that conduct electrical impulses from the $AV$ node to the ventricular myocardium. They are located in the subendocardial surface of the ventricular walls.
$(b)$ Bundle of His: This is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the $AV$ node to the point of the apex of the fascicular branches. It is located in the interventricular septum of the heart.

(N/A) The time gap allows the ventricles to remain relaxed while the action potential travels from the sino-atrial $(SA)$ node to the ventricles. This delay ensures that the atria complete their contraction (atrial systole) and empty their blood into the ventricles before the ventricles begin to contract. This maximizes ventricular filling,thereby increasing cardiac output.

(D) The four primary types of tissues in the human body are epithelial,connective,muscular,and nervous tissues.
An organ is a structure composed of two or more types of tissues working together to perform a specific function.
The heart is a complex organ that contains all four types of tissues:
$1$. Epithelial tissue: Lines the inner chambers (endocardium) and outer surface (epicardium) of the heart.
$2$. Connective tissue: Forms the valves,fibrous skeleton,and blood vessels within the heart.
$3$. Muscular tissue: The cardiac muscle (myocardium) is responsible for the pumping action.
$4$. Nervous tissue: The nodal tissue ($SA$ node,$AV$ node) and nerve fibers regulate the heart rate and conduction system.

(B) The human circulatory system,also known as the blood vascular system,consists of a muscular chambered heart,a network of closed branching blood vessels,and blood,which is the fluid that is circulated.
Therefore,the correct components are the heart,the network of branched blood vessels,and the blood.

(B) The heart is a mesodermal organ,which means it originates from the mesoderm layer during embryonic development.
It is located in the thoracic cavity,specifically in the mediastinum,between the two lungs.
It is slightly tilted towards the left side.
The size of the human heart is approximately that of a clenched fist.
Therefore,the statement that the heart is situated in the abdominal cavity is incorrect,as it is located in the thoracic cavity.

(C) The human heart is a four-chambered organ consisting of two atria and two ventricles.
Anatomically,the atria are the upper receiving chambers,while the ventricles are the lower pumping chambers.
Because the ventricles are responsible for pumping blood to the entire body (left ventricle) and the lungs (right ventricle),they possess much thicker muscular walls and a larger overall volume capacity compared to the atria.
Therefore,the ventricles are larger than the atria.

(B) The heart is enclosed in a double-walled sac called the $Pericardium$.
This membrane protects the heart,anchors it within the chest cavity,and prevents overfilling with blood.
$Peritoneum$ is the lining of the abdominal cavity.
$Pleura$ is the membrane surrounding the lungs.
$Perimetrium$ is the outer layer of the uterus.

(B) The heart structure consists of various septa that separate its chambers:
$1$. The $P$. Interatrial septum is a thin muscular wall that separates the right and left atria.
$2$. The $Q$. Interventricular septum is a thick wall that separates the right and left ventricles to withstand higher pressure.
$3$. The $R$. Atrioventricular septum is a thick fibrous tissue that separates the atria from the ventricles,containing the valves.
Therefore,the correct matching is $P-II, Q-III, R-I$.

(D) The human heart contains four main valves that ensure unidirectional blood flow:
$1$. Tricuspid valve: Located between the right atrium and the right ventricle.
$2$. Bicuspid (Mitral) valve: Located between the left atrium and the left ventricle.
$3$. Aortic semilunar valve: Located at the base of the aorta,separating it from the left ventricle.
$4$. Pulmonary semilunar valve: Located at the base of the pulmonary artery,separating it from the right ventricle.
Comparing these with the options,option $D$ correctly identifies all these locations.

(A) In the provided diagram of the human heart:
- Label $P$ points to the papillary muscles,which are muscular projections in the ventricles that attach to the chordae tendineae.
- Label $Q$ points to the myocardium (cardiac muscle layer).
- Label $R$ points to the chordae tendineae.
- Label $S$ points to the endocardium or the inner wall of the ventricle.
Therefore,the correct label for papillary muscles is $P$.

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

(D) The $SA$ node (Sino-atrial node) is located in the upper right corner of the right atrium.
It acts as the natural pacemaker of the heart.
The $AV$ node (Atrio-ventricular node) is located in the lower left corner of the right atrium,close to the atrio-ventricular septum.
Therefore,the correct option is $D$.

(A) The $SA$ node (Sinoatrial node) is known as the pacemaker of the heart. It is a specialized patch of cardiac muscle fibers located in the right atrium that possesses the property of self-excitation. It generates an action potential spontaneously without any external neural or hormonal stimulus,which initiates the heartbeat.

(A) The $SA$ node (Sinoatrial node) is a specialized patch of tissue present in the right upper corner of the right atrium. It is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Because it generates the maximum number of action potentials per minute ($70-75$ per minute) and controls the heart rate,it is known as the natural pacemaker of the heart.

(A) The $SA$ node (Sinoatrial node) is known as the 'pacemaker' of the heart. It is often referred to as the 'heart of the heart' because it initiates the rhythmic electrical impulses that cause the heart to contract,thereby setting the pace for the entire cardiac cycle.

(C) The human heart is a myogenic organ that initiates its own rhythmic contractions.
In a healthy adult,the normal heart rate at rest is typically between $70$ and $75$ beats per minute,with an average value often cited as $72$ beats per minute.
Therefore,the correct range is $70-75$ beats per minute.

(A) Cardiac output is defined as the volume of blood pumped out by each ventricle per minute.
It is calculated by multiplying the stroke volume (the volume of blood pumped by each ventricle per cardiac cycle, which is approximately $70 \ mL$) by the heart rate (the number of heartbeats per minute, which is approximately $72$ beats per minute).
Therefore, $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate} \approx 70 \ mL \times 72 \ \text{beats/min} \approx 5040 \ mL$ or $5 \ L$ per minute.

(C) The stroke volume is the volume of blood pumped by each ventricle per beat,which is approximately $70 \text{ mL}$.
Cardiac output is the volume of blood pumped by each ventricle per minute.
It is calculated as: $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$.
Assuming an average heart rate of $72 \text{ beats/min}$,$\text{Cardiac Output} = 70 \text{ mL} \times 72 = 5040 \text{ mL}$ (or approximately $5 \text{ L}$).
Therefore,the correct values are $70 \text{ mL}$ for stroke volume and $5040 \text{ mL}$ for cardiac output.

(C) The heart sounds,specifically the '$lub$' and '$dub$' sounds,are produced by the closure of the heart valves during the cardiac cycle.
These sounds are low-frequency vibrations that can be heard by a physician using a medical instrument called a stethoscope.
$A$ sphygmomanometer is used to measure blood pressure,and a spirometer is used to measure lung capacity.
Therefore,the correct instrument for listening to heart sounds is the stethoscope.

(A) The cardiac cycle involves two primary heart sounds:
$1$. The first heart sound,'$lub$',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,'$dub$',is produced by the closure of the semilunar valves at the beginning of ventricular diastole.
Therefore,the correct sequence is: $Lub$ = Closure of $AV$ valves,$Dub$ = Closure of semilunar valves.

(A) The $Stethoscope$ is a medical instrument used for auscultation, or listening to the internal sounds of an animal or human body, such as the heart and lungs.
$Sphygmomanometer$ is used to measure blood pressure.
$Spirometer$ is used to measure the volume of air inspired and expired by the lungs.
$Barometer$ is used to measure atmospheric pressure.

(B) William Harvey is credited with the discovery of the systemic circulation of blood in the human body. In his landmark work,'Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus' published in $1628$,he demonstrated that blood is pumped throughout the body by the heart.

(D) The correct answer is option $D$ $(E-C-A-D-B)$.
The conduction system of the heart follows a specific pathway to ensure coordinated contraction:
$1$. The action potential originates at the $SA$ node $(E)$.
$2$. It travels to the $AV$ node $(C)$.
$3$. From the $AV$ node,it passes to the $AV$ bundle $(A)$.
$4$. The $AV$ bundle divides into right and left bundle branches $(D)$.
$5$. Finally,the impulse spreads through the Purkinje fibres $(B)$ to the ventricular myocardium.

(B) The heart produces two main sounds during each cardiac cycle, which can be heard through a stethoscope.
$1$. The first heart sound is known as '$Lubb$'. It 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 is known as '$Dub$'. It is produced by the closure of the semilunar valves at the end of ventricular systole.
Therefore, the first heart sound is the '$Lubb$' sound produced at the beginning of ventricular systole.

(C) Cardiac output is defined as the volume of blood pumped by the left ventricle into the aorta per minute.
It is calculated by multiplying the stroke volume (the amount of blood pumped per beat,approximately $70 \ mL$) by the heart rate (number of beats per minute,approximately $72 \ beats/min$).
Thus,the average cardiac output is approximately $5000 \ mL$ or $5 \ L$ per minute.

(C) The human heart is composed of cardiac muscle,but it also contains connective tissue (valves,chordae tendineae,fibrous skeleton) and specialized nodal tissue. Thus,statement $A$ is incorrect as the heart is not made entirely of cardiac muscle.
Statement $B$ refers to the Sino-Atrial Node $(SAN)$,which is located in the right upper corner of the right atrium and acts as the pacemaker.
Statement $C$ is incorrect because the Atrio-Ventricular Node $(AVN)$ is located in the lower left corner of the right atrium,but it generates action potentials at a rate of $40-60 \text{ min}^{-1}$,not $70-75 \text{ min}^{-1}$.
Statement $D$ is correct as nodal tissue is auto-excitable.

(D) The $SA$ node (Sinoatrial node) is a specialized bundle of cardiac muscle fibers located in the wall of the right atrium.
Specifically,it is situated in the upper lateral wall of the right atrium,near the opening of the superior vena cava.
It acts as the natural pacemaker of the heart,initiating the electrical impulses that lead to cardiac contraction.

(B) During the cardiac cycle,ventricular systole refers to the contraction of the ventricles.
As the ventricles contract,the ventricular pressure rises significantly.
This increase in pressure forces the $AV$ (tricuspid and bicuspid) valves to close to prevent the backflow of blood into the atria.
Consequently,the correct answer is the closure of tricuspid and bicuspid valves.

(B) Statement $I$ is incorrect because the heart sound $Dub$ (or $S2$) is produced by the closure of the semilunar valves at the beginning of ventricular diastole.
Statement $II$ is incorrect because the heart sound $Lubb$ (or $S1$) is produced by the closure of the atrioventricular valves at the beginning of ventricular systole,not during atrial systole.
Therefore,both statements are incorrect.

(A) The correct matching is as follows:
$1$. Eustachian valve $(i)$ guards the opening of the inferior vena cava $(c)$.
$2$. Thebesian valve $(ii)$ guards the opening of the coronary sinus $(d)$.
$3$. Mitral valve $(iii)$ is located at the left atrioventricular aperture $(b)$.
$4$. Semilunar valve $(iv)$ guards the opening of the pulmonary aorta and the aorta $(a)$.
Therefore,the correct sequence is $i-c, ii-d, iii-b, iv-a$.

(D) The $Thebesian$ valve (also known as the valve of the coronary sinus) guards the opening of the coronary sinus into the right atrium. The opening of the postcaval vein (inferior vena cava) is guarded by the $Eustachian$ valve. Therefore,option $D$ is the mismatched pair.

(A) The bicuspid (mitral) and tricuspid valves are atrioventricular valves that prevent the backflow of blood into the atria during ventricular systole.
These valves are anchored to the papillary muscles of the ventricular walls by tough,inelastic,collagenous cords known as $Chordae \ tendinae$.
These structures ensure that the valves do not invert into the atria when the ventricles contract under high pressure.

(C) $i$. The visceral layer of the serous pericardium,also known as the epicardium,forms the outermost layer of the heart wall. Thus,Statement $I$ is correct.
$ii$. The epicardium is a thin layer composed of simple squamous epithelium and connective tissue,not a thick layer of cardiac muscles. The thick layer of cardiac muscles is called the myocardium. Thus,Statement $II$ is incorrect.

(B) The $SA$ Node (Sinoatrial node) is known as the natural pacemaker of the human heart because it initiates the rhythmic electrical impulses that determine the heart rate.
The $AV$ Node (Atrioventricular node) acts as a pace setter or relay station that delays the impulse slightly to allow for ventricular filling.
Therefore,the $SA$ Node sets the pace,and the $AV$ Node regulates the transmission of that pace.

(D) The heart is enclosed in a double-walled membranous sac called the pericardium.
The pericardium consists of two main layers: the outer fibrous pericardium and the inner serous pericardium.
The serous pericardium is further divided into two layers: the parietal layer (outer) and the visceral layer (inner),which is also known as the epicardium.
The pericardial cavity is the space between the parietal and visceral layers of the serous pericardium.
This cavity is filled with pericardial fluid,which reduces friction between the heart walls during contraction and relaxation.

(B) The first heart sound, '$Lub$', is produced by the closure of the atrioventricular $(AV)$ valves (tricuspid and bicuspid valves) at the beginning of ventricular systole.
Option '$B$' is incorrect because the '$Lub$' sound is not caused by the closure of the Thebesian valve (which is a valve of the coronary sinus).
Option '$A$' is correct as the second heart sound, '$Dub$', is caused by the closure of the semilunar valves.
Option '$C$' and '$D$' are correct statements regarding the clinical measurement of blood pressure using a sphygmomanometer.

(B) The $Mediastinum$ is the central compartment of the thoracic cavity,located between the two lungs. The heart is situated within this space.
$Rathke's$ pouch is an embryonic precursor to the anterior pituitary gland.
$Median$ eminence is a part of the hypothalamus.
$Sella$ turcica is a bony depression in the sphenoid bone that houses the pituitary gland.

(B) The heart has specific valves to ensure unidirectional blood flow.
$1$. The $Aorta$ and $Pulmonary \text{ artery}$ (Pulmonary aorta) have semilunar valves at their base to prevent backflow of blood into the ventricles.
$2$. The $Inferior \text{ vena cava}$ and $Superior \text{ vena cava}$ enter the right atrium without any valves.
$3$. The $Pulmonary \text{ veins}$ enter the left atrium without any valves.
$4$. Among the given options, the $Pulmonary \text{ vein}$ is the correct answer as it lacks a valve at its junction with the left atrium.

(A) During fetal development,the $foramen \ ovale$ is an opening in the inter-atrial (inter-auricular) septum that allows blood to bypass the non-functional fetal lungs.
After birth,this opening closes and becomes a depression known as the $fossa \ ovalis$.
The term $foramen \ ovale$ refers to the embryonic aperture itself,while the remnant is technically the $fossa \ ovalis$. Given the options provided,$foramen \ ovale$ (often misspelled as $foramen \ ovalis$ in some contexts) is the structure being referred to as the embryonic aperture.

(D) Purkinje fibers are specialized conducting cells located in the subendocardial layer of the heart's ventricles.
They are part of the cardiac conduction system,which transmits electrical impulses from the atrioventricular $(AV)$ bundle to the ventricular myocardium.
This conduction ensures the synchronized contraction of the ventricles,which is essential for the rhythmic and efficient pumping of blood throughout the body.

(D) The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle and opens into the Right atrium.
Similarly,the pulmonary veins are responsible for carrying oxygenated blood from the lungs and opening into the Left atrium.

(C) neurogenic heart is a type of heart where the heartbeat is initiated by nerve impulses generated by a specialized group of nerve cells (ganglia) located near the heart.
In contrast,a myogenic heart (found in humans) initiates its own heartbeat through specialized muscle cells.
Since the stimulus for contraction in a neurogenic heart originates from nerve cells,it is transmitted via nerve fibres.
Therefore,the correct option is $C$.