Cardiac Cycle
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What are the two main types of blood circulation described in the cardiac cycle?
Pulmonary circulation and systemic circulation.
What is pulmonary circulation?
The flow of deoxygenated blood from the right side of the heart to the lungs for oxygenation, then back to the left side of the heart.
Where does deoxygenated blood enter the heart?
Through the superior and inferior vena cava into the right atrium.
Which valve does blood pass through from the right atrium to the right ventricle?
The tricuspid valve.
How does blood leave the right ventricle on its way to the lungs?
Through the pulmonary arteries.
What type of valve is the pulmonary valve?
A semilunar valve with three cusps.
Where does oxygenated blood from the lungs enter the heart?
The left atrium.
Which valve does blood pass through from the left atrium to the left ventricle?
The mitral (bicuspid) valve.
How does oxygenated blood leave the left ventricle?
It is pumped into the aorta for distribution around the body.
What is systemic circulation?
The flow of oxygenated blood from the left side of the heart through the aorta to body tissues.
Which arteries provide the blood supply to the heart muscle?
The right coronary artery and left coronary artery.
Where do the right and left coronary arteries arise from?
The aorta.
What is the course of the right coronary artery described in the slides?
It passes towards the right margins of the heart and extends to the posterior aspect, supplying the heart.
What happens to the left coronary artery after it arises from the aorta?
After a short distance, it divides into two branches that supply the heart.
Where does blood from the coronary arteries go after passing through the heart's capillary network?
It enters the cardiac veins.
Where does the coronary sinus empty?
Into the right atrium.
What does the word 'sulcus' mean?
A groove.
What is the average heart rate stated in the cardiac-cycle slides?
About 70â72 beats per minute.
How long does one cardiac cycle last according to the slides?
About 0.8 seconds.
How many stages make up one cardiac cycle?
Three stages: atrial systole, ventricular systole and joint diastole.
What is atrial systole?
The stage in which both atria contract simultaneously.
How long does atrial systole last?
About 0.1 seconds.
Where does blood move during atrial systole?
From the right atrium to the right ventricle and from the left atrium to the left ventricle.
What happens to prevent backflow during atrial systole?
The atrioventricular valves prevent blood from flowing backwards.
What is ventricular systole?
The stage in which both ventricles contract simultaneously.
How long does ventricular systole last?
About 0.3 seconds.
Where does ventricular contraction begin?
At the apex of the heart.
Which valves close as ventricular contraction begins?
The tricuspid and bicuspid (mitral) valves close.
What is the state of the semilunar valves at the start of ventricular systole?
They are initially closed.
Why do the ventricles initially contract as closed chambers?
The atrioventricular valves have closed and the semilunar valves are still closed.
When do the semilunar valves open during ventricular systole?
As the force of contraction reaches near the base of the heart.
Where does blood travel during ventricular systole?
From the right ventricle to the lungs and from the left ventricle to the body.
What is joint diastole?
The stage when all four chambers of the heart relax.
How long does joint diastole last?
About 0.4 seconds.
What happens to the semilunar valves during joint diastole?
They close.
What happens to blood flow during joint diastole?
Blood flows from the vessels into the atria and freely from the atria into the ventricles.
Approximately what proportion of the ventricles fills during joint diastole?
About 75%.
Approximately what proportion of ventricular filling occurs during atrial systole?
About 25%.
What is cardiac output?
The amount of blood ejected from a ventricle in one minute.
What is stroke volume?
The amount of blood ejected from each ventricle with every contraction.
What average stroke volume is given in the slides?
75 mL.
What heart-rate range is used in the cardiac-output example?
70â80 beats per minute.
What is the equation for cardiac output?
Cardiac output = stroke volume à heart rate.
What happens in the arteries when the ventricles contract?
Blood is pumped into arteries that are already filled with blood, causing them to distend.
What produces the arterial pulse?
The distension of arteries when blood is ejected by the contracting ventricles.
How does pulse rate relate to heart rate?
The pulse rate is equal to the heart rate; each heartbeat produces one pulse impulse.
Where can the arterial pulse commonly be felt?
At the radial artery, by placing a finger over it.
Name the pulse points listed in the slides.
Temporal, carotid, brachial, radial, femoral, popliteal, posterior tibial and pedal arteries.
Is the apical pulse an arterial pulse point?
No. It is assessed by listening to the left ventricle contracting with a stethoscope.
What does 'myogenic' mean in relation to the human heart?
The heartbeat originates within the heart muscle rather than requiring an external nervous or hormonal stimulus.
Which structure is identified as the originator of the heartbeat?
The sinoatrial (SA) node.
Where is the SA node located?
In the wall of the right atrium near the opening of the superior vena cava.
What is another name for the SA node?
The natural pacemaker of the heart.
What happens when the impulse spreads from the SA node?
It spreads through the atria and initiates atrial contraction.
Which structure receives the impulse from the SA node and conducts it onwards?
The atrioventricular (AV) node.
Where is the AV node located?
Embedded in the interatrial septum just above the junction of the atria and ventricles.
What structure arises from the AV node?
The atrioventricular bundle, also called the Bundle of His.
Where does the Bundle of His travel?
It enters the interventricular septum.
What happens to the Bundle of His in the interventricular septum?
It divides into right and left bundle branches.
Where do the right and left bundle branches travel?
Down the interventricular septum.
What arises from the bundle branches?
Purkinje fibres.
Where do Purkinje fibres travel?
They pass to the outer wall of the ventricles and travel back towards the base of the heart.
What is the role of the heart's specialised myocardial conducting cells?
They can initiate contractions without external nervous or hormonal stimulation.
How can the autonomic nervous system affect the heart?
It can influence the heart's conducting pathways and alter heart rate.
What effect do sympathetic neurons have on heart rate?
They increase heart rate.
What effect do parasympathetic neurons have on heart rate?
They decrease heart rate.
Which nerve carries parasympathetic fibres to the heart?
The vagus nerve.
What effect does exercise have on heart rate?
It increases heart rate.
What effect does elevated temperature have on heart rate?
It increases heart rate.
How do thyroid hormones T3 and T4 affect heart rate?
Increased levels of T3 and T4 increase heart rate.
How does adrenaline affect heart rate?
Adrenaline increases heart rate.
Where is adrenaline secreted from, according to the slides?
The adrenal medulla.
What difference in heart rate between sexes is stated in the slides?
The slides state that females have a faster heartbeat than males.
How can medicines affect heart rate?
Many medicines can increase heart rate.
Name other factors listed as affecting heart rate.
Emotion, stress and depression, among other factors.
What are the three durations of the cardiac-cycle stages given in the slides?
Atrial systole: 0.1 s; ventricular systole: 0.3 s; joint diastole: 0.4 s.
How does the total duration of the three cardiac-cycle stages relate to one heartbeat?
0.1 + 0.3 + 0.4 seconds = 0.8 seconds.
What is the route of blood through the right side of the heart and lungs?
Venae cavae â right atrium â tricuspid valve â right ventricle â pulmonary valve/pulmonary arteries â lungs.
What is the route of blood from the lungs through the left side of the heart to the body?
Lungs â pulmonary veins â left atrium â mitral valve â left ventricle â aortic valve/aorta â body.
What is the difference between pulmonary and systemic circulation?
Pulmonary circulation carries blood between the heart and lungs; systemic circulation carries blood between the heart and the rest of the body.
Which chamber receives blood returning from the body?
The right atrium.
Which chamber pumps blood to the lungs?
The right ventricle.
Which chamber receives oxygenated blood returning from the lungs?
The left atrium.
Which chamber pumps blood into the aorta?
The left ventricle.