Cardiac cycle Questions in English

(B) Systole refers to the phase of contraction of the heart chambers.
In the cardiac cycle,the term 'systole' generally refers to ventricular systole,where the ventricles contract to pump blood into the aorta and pulmonary artery.
Auricles (atria) and ventricles do not contract simultaneously; they contract in a coordinated sequence to ensure efficient blood flow.
Therefore,the auricles and ventricles contract separately during the cardiac cycle.

(D) The term $diastole$ refers to the relaxation phase of the heart chambers. Therefore,$ventricular$ $diastole$ specifically refers to the period when the ventricles are in a state of relaxation. During this phase,the pressure inside the ventricles decreases,allowing them to fill with blood from the atria.

(C) The cardiac cycle involves a sequence of events where the atria contract first,followed by the ventricles. The atrial systole lasts for approximately $0.1\,\text{seconds}$. The electrical impulse generated by the $SA$ node causes atrial contraction,and there is a slight delay (about $0.1\,\text{seconds}$) at the $AV$ node before the impulse reaches the ventricles to initiate ventricular contraction. Therefore,ventricular contraction is preceded by atrial contraction by approximately $0.1\,\text{seconds}$.

(C) The Fick principle states that the total uptake of (or release of) a substance by an organ is the product of the blood flow to the organ and the arteriovenous concentration difference of the substance.
In the case of oxygen,the Fick equation is used to calculate cardiac output $(CO)$:
$CO = \frac{\text{Oxygen consumption}}{\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content}}$.
Therefore,the Oxygen-Fick method is a standard clinical procedure used to measure cardiac output.

(C) During the cardiac cycle,atrial contraction (atrial systole) occurs at the end of ventricular diastole. This contraction forces the remaining blood into the ventricles. The pressure in the atria increases by approximately $6-8 \, mm\,Hg$ during this phase to facilitate the final filling of the ventricles.

(D) The end diastolic volume $(EDV)$ is the volume of blood in the ventricles at the end of diastole (relaxation phase),just before contraction begins.
In a healthy adult,the $EDV$ is approximately $120\,ml$.
After the ventricular systole,the volume of blood remaining in the ventricles is called the end systolic volume $(ESV)$,which is approximately $50\,ml$.
The difference between $EDV$ and $ESV$ gives the stroke volume,which is $120\,ml - 50\,ml = 70\,ml$.

(D) Diastole refers to the relaxation phase of the heart chambers. During ventricular diastole,the ventricles relax,which allows the pressure inside them to decrease. This drop in pressure causes blood to flow from the atria into the ventricles. Simultaneously,during atrial diastole,blood from the vena cava and pulmonary veins enters the atria. Therefore,the primary event during diastole is the filling of the heart chambers with blood.

(B) The cardiac cycle involves two primary heart sounds,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 (tricuspid and bicuspid/mitral valves) at the beginning of ventricular systole.
$2$. The second heart sound,'$S_2$' or 'dub',is produced by the closure of the semilunar valves (aortic and pulmonary valves) at the end of ventricular systole.
Therefore,the first heart sound is associated with the closure of the tricuspid and bicuspid valves.

(A) The cardiac cycle consists of a sequence of events that occur during one heartbeat.
$1$. Atrial systole: The atria contract,forcing blood into the ventricles.
$2$. Ventricular systole: The ventricles contract,pumping blood into the aorta and pulmonary artery.
$3$. Joint diastole: Both the atria and ventricles are in a relaxed state,allowing the heart to fill with blood again.
Therefore,the correct sequence is Atrial systole $\rightarrow$ Ventricular systole $\rightarrow$ Joint diastole.

(C) Cardiac output is defined as the volume of blood pumped out by each ventricle per minute.
In a healthy adult, the stroke volume is approximately $70 \ mL$ and the heart rate is about $72$ beats per minute.
Therefore, Cardiac Output = Stroke Volume $\times$ Heart Rate.
Cardiac Output = $70 \ mL \times 72 \ \text{beats/min} \approx 5000 \ mL$ or $5 \ L$ per minute.
Thus, it refers to the volume of blood pumped by the left ventricle per minute.

(D) The cardiac output is defined as the volume of blood pumped out by each ventricle per minute and is calculated as the product of stroke volume and heart rate ($70 \ mL \times 72 \ \text{beats/min} \approx 5000 \ mL$ or $5 \ L$).
Option $A$ is correct as the average stroke volume is $70 \ mL$.
Option $B$ is correct as cardiac output = stroke volume $\times$ heart rate.
Option $C$ is correct as this is the definition of cardiac output.
Option $D$ is incorrect because the body has the ability to alter the stroke volume as well as the heart rate, and thereby the cardiac output, to meet the physiological demands of the tissues.

(C) Ventricular diastole is the phase of the cardiac cycle where the ventricles relax.
$1$. As the ventricles relax,the ventricular pressure drops significantly.
$2$. Due to the drop in pressure,the blood in the arteries (aorta and pulmonary artery) attempts to flow back into the ventricles.
$3$. This backflow causes the semilunar valves to close,which produces the second heart sound (dub).
$4$. Therefore,the closure of semilunar valves is a characteristic event during the early phase of ventricular diastole.

(A) The rhythmic contraction and relaxation of the heart constitute the cardiac cycle.
$1$. The contraction phase of the heart,specifically the ventricles or atria,is known as $Systole$.
$2$. The relaxation phase of the heart is known as $Diastole$.
Therefore,the contraction of the heart is called $Systole$.

(D) Joint diastole is the phase of the cardiac cycle where all four chambers of the heart (two atria and two ventricles) are in a relaxed state.
During this phase,the tricuspid and bicuspid (mitral) valves open,allowing blood to flow from the atria into the ventricles.
Simultaneously,the semilunar valves remain closed to prevent the backflow of blood from the arteries into the ventricles.
Therefore,all the given statements are correct.

(D) The cardiac cycle produces two main sounds,often described as 'lub' and 'dup'.
$1$. The first heart sound,'lub',is associated with the closure of the atrioventricular $(AV)$ valves.
$2$. The second heart sound,'dup',is associated with the closure of the semilunar valves.
$3$. This closure occurs at the end of ventricular systole,preventing the backflow of blood from the pulmonary artery and aorta into the ventricles.
Therefore,the correct option is $(d)$.

(C) The cardiac cycle refers to the sequence of events that occur during one complete heartbeat.
In a healthy human adult,the heart beats approximately $72$ times per minute.
To calculate the duration of one cardiac cycle,we divide $60$ seconds by the heart rate ($72$ beats per minute).
Duration $= 60 / 72 = 0.833$ seconds,which is approximately $0.8$ seconds.
Therefore,the correct duration of a cardiac cycle is $0.8$ seconds.

(D) During the cardiac cycle,two primary heart sounds are produced.
$1$. The first heart sound,'$Lubb$',is associated with the closure of the atrioventricular $(AV)$ valves.
$2$. The second heart sound,'$Dupp$',is produced when the semilunar valves close at the beginning of ventricular diastole.
This closure prevents the backflow of blood from the pulmonary artery and aorta into the ventricles,marking the end of ventricular systole.

(C) Cardiac output is defined as the volume of blood pumped by each ventricle per minute. It is calculated as the product of stroke volume and heart rate.
Stroke volume is the amount of blood pumped by the ventricle in one beat,which is the difference between the end-diastolic volume $(EDV)$ and the end-systolic volume $(ESV)$.
Given: $EDV = 100 \; mL$,$ESV = 50 \; mL$.
Stroke volume = $EDV - ESV = 100 \; mL - 50 \; mL = 50 \; mL$.
Cardiac output = $5 \; L = 5000 \; mL$.
Formula: $\text{Cardiac output} = \text{Stroke volume} \times \text{Heart rate}$.
$5000 \; mL = 50 \; mL \times \text{Heart rate}$.
Heart rate = $5000 / 50 = 100$ beats per minute.

(N/A) cardiac cycle is defined as the sequential events in the heart that occur from the beginning of one heartbeat to the beginning of the next. It consists of three main stages: atrial systole, ventricular systole, and joint diastole.
Cardiac output is defined as the volume of blood pumped out by each ventricle per minute. It is calculated by the product of stroke volume and heart rate ($Cardiac Output = Stroke Volume \times Heart Rate$).

(N/A) Systole and Diastole

Systole	Diastole
$(1)$ It is the contraction of the heart chambers to drive blood into the aorta and the pulmonary artery.	$(1)$ It is the relaxation of the heart chambers between two contractions. During diastole, the chambers are filled with blood.
$(2)$ Systole decreases the volume of the heart chambers and forces the blood out of them.	$(2)$ Diastole brings the heart chambers back into their original sizes to receive more blood.

(N/A) The heart beats about $72$ times in a minute. It acts as a pump, and its events show regular sequential patterns. This is called the cardiac cycle.
The contraction phase of the heart is called systole, and the relaxation phase is called diastole.
The following phases are observed during the cardiac cycle:
$(i)$ Initially, all four chambers are in a state of joint diastole.
$(ii)$ The tricuspid and bicuspid valves are open. Blood from the pulmonary veins and vena cava flows into the left and right ventricles, respectively.
$(iii)$ The semilunar valves are closed at this stage. The $SAN$ generates an action potential which stimulates both the atria to undergo simultaneous contraction (atrial systole). This increases the flow of blood into the ventricles by about $30\%$.
$(iv)$ The action potential is conducted to the ventricular side by the $AVN$ and $AV$ bundle, from where the bundle of $HIS$ transmits it through the entire ventricular musculature.
$(v)$ This causes ventricular muscles to contract (ventricular systole), while the atria undergo relaxation (diastole), coinciding with the ventricular systole. Ventricular systole causes the closure of tricuspid and bicuspid valves, which prevents the backflow of blood into the atria.
$(vi)$ As ventricular pressure increases further, the semilunar valves guarding the pulmonary artery and the aorta are forced open, allowing the blood in the ventricles to flow through these vessels into the circulatory pathways.
$(vii)$ The ventricles now relax (ventricular diastole), and the ventricular pressure falls, causing the closure of semilunar valves, which prevents the backflow of blood into the ventricles.
$(viii)$ Now, the bicuspid and tricuspid valves are pushed open by the pressure in the atria exerted by the blood which was being emptied into them by veins.
$(ix)$ The ventricles and atria are now again in a relaxed (joint diastole) state. This process repeats in this order continuously.

Time period	Atria	Ventricles
$0.10 \, s$	Systole	Diastole
$0.30 \, s$	Diastole	Systole
$0.40 \, s$	Diastole	Diastole

The heart beats $72$ times per minute. From this, it can be deduced that the duration of a cardiac cycle is $0.8 \, s$.
During a cardiac cycle, each ventricle pumps out approximately $70 \, ml$ of blood, which is called the stroke volume.
The stroke volume multiplied by the heart rate (number of beats per minute) gives the cardiac output. Therefore, the cardiac output is defined as the volume of blood pumped out by each ventricle per minute and averages $5000 \, ml$ or $5 \, L$ in a healthy person. The cardiac output of an athlete is much higher than that of an ordinary person.

(A) Diagram $A$: The atria are filling with blood from the venae cavae and pulmonary veins,while the atrioventricular valves are closed. This indicates that the atria are in a relaxed state,known as atrial diastole.
Diagram $B$: The atria are contracted,and the bicuspid and tricuspid valves are open,allowing blood to flow into the ventricles. This state is called atrial systole.
Diagram $C$: The semilunar valves are open,and blood is being pumped into the pulmonary artery and aorta. This occurs due to the contraction of the ventricles,a state known as ventricular systole.

(B) Cardiac output is 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 $70 \; mL$ per beat and the average heart rate is $72$ beats per minute.
Therefore,$\text{Cardiac output} = 70 \; mL/\text{beat} \times 72 \; \text{beats/minute} = 5040 \; mL/\text{minute}$,which is approximately $5 \; L/\text{minute}$.

(B) The cardiac cycle in a normal person takes about $0.8$ seconds.
This cycle consists of atrial systole ($0.1$ seconds), ventricular systole ($0.3$ seconds), and joint diastole ($0.4$ seconds).
Thus, the total duration of one complete cardiac cycle is $0.1 + 0.3 + 0.4 = 0.8$ seconds.

(A) The cycle of events which occurs in a single heartbeat is called the cardiac cycle. It involves the contraction and relaxation of the heart muscle.
$1$. Systole: When blood is ejected from the heart due to contraction.
$2$. Diastole: When the chambers of the heart are filled with blood. It is also called relaxation.

(C) The first heart sound '$Lubb$' is produced by the closure of the atrioventricular $(AV)$ valves.
This event occurs at the beginning of ventricular systole.
When the ventricles begin to contract,the intraventricular pressure rises rapidly,exceeding the atrial pressure.
This pressure difference forces the $AV$ valves (tricuspid and bicuspid) to close,preventing the backflow of blood into the atria.
The vibration caused by the sudden closure of these valves creates the low-pitched '$Lubb$' sound.

(A) The cardiac cycle begins with atrial systole (not shown),followed by ventricular filling,ventricular systole,and ventricular diastole.
Diagram $B$ shows atrial diastole and ventricular filling (blood flowing from atria to ventricles).
Diagram $A$ shows ventricular systole (ventricles contracting,blood being pumped into arteries).
Diagram $C$ shows ventricular diastole (ventricles relaxing,blood filling from atria).
The correct sequence of these stages in the cardiac cycle is $B$ (atrial diastole/ventricular filling) $\rightarrow$ $A$ (ventricular systole) $\rightarrow$ $C$ (ventricular diastole).
Therefore,the correct sequence is $B, A, C$.

(D) The human heart beats approximately $72$ times per minute under normal resting conditions.
Since one heartbeat corresponds to one cardiac cycle, $72$ cardiac cycles are performed per minute.
To calculate the duration of one cardiac cycle: $60 \, \text{seconds} / 72 \, \text{beats} \approx 0.8 \, \text{seconds}$ per cycle.

(D) During a cardiac cycle,each ventricle pumps out approximately $70 \; mL$ of blood,which is known as the stroke volume.
Cardiac output is defined as the volume of blood pumped by each ventricle per minute.
Cardiac output = Stroke volume $\times$ Heart rate (number of beats per minute).
Given that the average stroke volume is $70 \; mL$ and the average heart rate is $72$ beats per minute:
Cardiac output = $70 \; mL \times 72 = 5040 \; mL/min$,which is approximately $5 \; L/min$.

(B) The cardiac cycle lasts for $0.8$ seconds.
The closure of the semilunar valves marks the beginning of ventricular diastole.
The closure of the $AV$ valves marks the beginning of ventricular systole.
The time interval between the closure of the semilunar valves and the closure of the $AV$ valves represents the duration of ventricular diastole.
In a standard cardiac cycle,ventricular diastole lasts for $0.5$ seconds.

(B) cardiac cycle consists of a sequential series of events in the heart.
Based on the provided diagram,the sequence of events is as follows:
$1$. Auricular systole $(0.1 \ s)$: The atria contract,forcing blood into the ventricles.
$2$. Ventricular systole $(0.3 \ s)$: The ventricles contract,pumping blood into the aorta and pulmonary artery.
$3$. Complete cardiac diastole or joint diastole $(0.4 \ s)$: Both the atria and ventricles are in a relaxed state,allowing the heart to fill with blood.
Therefore,the correct sequence is Auricular systole - Ventricular systole - Complete cardiac diastole.

(B) The total duration of a normal cardiac cycle is $0.8 \; \text{seconds}$.
Ventricular systole (contraction phase) lasts for $0.3 \; \text{seconds}$.
Ventricular diastole (relaxation phase) is calculated by subtracting the ventricular systole duration from the total cardiac cycle duration.
Therefore, ventricular diastole = $0.8 \; \text{seconds} - 0.3 \; \text{seconds} = 0.5 \; \text{seconds}$.

(C) The Assertion is incorrect because isovolumetric systole is the phase where the volume of blood in the ventricles remains constant,and it does not cause the opening of semilunar valves. The semilunar valves open only when the intraventricular pressure exceeds the pressure in the aorta and pulmonary artery,which occurs during the ventricular ejection phase,not the isovolumetric phase.
During isovolumetric systole,both the $AV$ valves (tricuspid and bicuspid) and the semilunar valves are closed. The ventricles contract,leading to a rapid increase in intraventricular pressure without any change in blood volume. Therefore,the Reason is correct.

(N/A) The cardiac cycle refers to the sequential events in the heart which are cyclically repeated. It includes the contraction (systole) and relaxation (diastole) of both the atria and the ventricles. The heart beats approximately $72$ times per minute,and each beat represents one complete cardiac cycle,which lasts for about $0.8$ seconds.

(B) During joint diastole,all four chambers of the heart are in a relaxed state. In this phase,the tricuspid and bicuspid valves are open,allowing blood to flow freely from the atria into the ventricles.
Option $A$ is incorrect because the valves open due to the pressure gradient created by atrial relaxation and ventricular filling,not just contraction.
Option $C$ is incorrect because increased ventricular pressure causes the closing of the atrioventricular valves,while the semilunar valves open.
Option $D$ is incorrect because the $SA$ node,not the $AVN$,is the pacemaker that initiates the action potential for atrial contraction.

(B) During the cardiac cycle,the atria undergo contraction (atrial systole) while the ventricles are in diastole.
This atrial systole forces the remaining blood from the atria into the ventricles.
This process contributes an additional $30\%$ of blood flow into the ventricles,as $70\%$ of the blood flows passively into the ventricles before the atrial contraction occurs.
Therefore,the correct answer is $30\%$.

(A) In the context of the cardiac cycle,the term $Systole$ refers to the phase of contraction of the heart muscles,specifically the atria or ventricles.
Conversely,the term $Diastole$ refers to the phase of relaxation of the heart muscles,allowing the chambers to fill with blood.
Therefore,$P$ corresponds to $Contraction$ and $Q$ corresponds to $Relaxation$.

(A) The cardiac cycle refers to the sequence of events that occur during one complete heartbeat.
In a healthy human adult,the heart beats approximately $72$ times per minute.
To calculate the duration of one cardiac cycle,we divide $60$ seconds by the heart rate ($72$ beats per minute).
Duration = $60 / 72 = 0.833$ seconds,which is approximately $0.8$ seconds.

(B) Stroke volume is defined as the volume of blood pumped out by each ventricle of the heart during a single cardiac cycle.
On average, the stroke volume in a healthy human is approximately $70 \ mL$.
In contrast, the volume of blood pumped out by the heart in one minute is known as cardiac output, which is calculated as the product of stroke volume and heart rate ($70 \ mL \times 72 \ \text{beats/min} \approx 5000 \ mL$ or $5 \ L$).

(C) In a standard cardiac cycle of $0.8$ seconds,the durations of the various stages are as follows:
$1$. Atrial systole: $0.1$ seconds.
$2$. Ventricular systole: $0.3$ seconds.
$3$. Joint diastole (also known as ventricular diastole or relaxation phase): $0.4$ seconds.
Since $0.4$ seconds is the longest duration among these,the joint diastole stage is the longest.

(C) In the cardiac cycle diagram:
$1$. '$a$' represents atrial systole (contraction of atria), which contributes about $25\%$ of the blood to the ventricles.
$2$. '$b$' represents ventricular systole (contraction of ventricles).
$3$. '$c$' and '$d$' represent the joint diastole (relaxation of both atria and ventricles), during which about $75\%$ of the blood flows passively from the atria into the ventricles.
Therefore, option '$c$' is the correct statement.

(D) The duration of one cardiac cycle in a healthy human heart is approximately $0.8$ seconds.
To find the number of cycles completed in $30$ seconds,we divide the total time by the duration of one cycle.
Number of cycles = $\frac{\text{Total time}}{\text{Duration of one cycle}} = \frac{30 \text{ s}}{0.8 \text{ s}} = 37.5$.
However,in standard biological calculations for heart rate,if we assume an average heart rate of $72$ beats per minute,then in $30$ seconds,the heart completes $36$ beats.
Thus,$36$ double circulations are completed in $30$ seconds.

(A) The total duration of a single cardiac cycle is $0.8$ seconds.
In a cardiac cycle,the ventricular systole lasts for $0.3$ seconds.
The ventricular diastole is the period during which the ventricles relax and fill with blood.
Therefore,the duration of ventricular diastole is calculated as: $0.8 \text{ s} - 0.3 \text{ s} = 0.5 \text{ s}$.

(A) The duration of a single cardiac cycle is approximately $0.8$ seconds.
In this cycle, atrial systole (contraction of the atria) lasts for about $0.1$ seconds.
Following this, ventricular systole lasts for $0.3$ seconds, and the joint diastole (relaxation of both atria and ventricles) lasts for $0.4$ seconds.
Therefore, the correct duration for atrial systole is $0.1$ seconds.

(A) Cardiac output is the volume of blood pumped by each ventricle per minute.
Formula: $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$.
Given: $\text{Stroke Volume} = 70 \ mL$,Average $\text{Heart Rate} = 72 \ \text{beats/minute}$.
Cardiac output per minute = $70 \ mL \times 72 = 5040 \ mL/minute = 5.04 \ L/minute$.
To find the cardiac output in one hour $(60 \ \text{minutes})$:
$\text{Cardiac Output per hour} = 5.04 \ L/minute \times 60 \ \text{minutes} = 302.4 \ L/hour$.
Therefore,the correct option is $A$.

(C) Cardiac output is defined as the volume of blood pumped by the heart per minute.
It is calculated by multiplying the stroke volume $(SV)$,which is the volume of blood ejected by the ventricle during each contraction,by the heart rate $(HR)$,which is the number of heart beats per minute.
The formula is: $\text{Cardiac Output} (CO) = SV \times HR$.
Given: Stroke volume $(SV)$ = $55 \ mL$ and Heart rate $(HR)$ = $70 \ \text{beats/min}$.
Therefore,$\text{Cardiac Output} = 55 \times 70 = 3850 \ mL$.

(A) The stroke volume $(SV)$ is the volume of blood pumped out by each ventricle during each cardiac cycle.
It is calculated using the formula: $SV = EDV - ESV$.
Given:
End-diastolic volume $(EDV)$ = $120 \ mL$
End-systolic volume $(ESV)$ = $50 \ mL$
Therefore,$SV = 120 \ mL - 50 \ mL = 70 \ mL$.
Thus,the correct option is $A$.