Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

all events are associated with one heartbeat
atria contract while the ventricles relax
followed by
atrial relaxation and ventricular contraction

Question 2

What is the relaxation period?

Answer 2

end of a heartbeat where all of the chambers are in diastole
the pressure in the ventricles fall and therefore aortic and pulmonary valves close

Question 3

What is isometric relaxation?

Answer 3

mitral and tricuspid closed no change in blood volume

Question 4

What is ventricular filling?

Answer 4

rapid ventricular filling: AV valves open, blood pours from atria into the ventricles passively
diastasis: only small volume entered
atrial systole pumps one 20-30% of EDV
aortic and pulmonary valves remain shut

Question 5

Ventricular Systole

Answer 5

near the end of ventricular systole, ventricles depolarise and ventricular contraption begins
AV valves pushed closed by blood so blood won’t be pushed back into the atria
AV valves are closed
isometric contraction occurs
ventricular ejection occurs when pressure in ventricles open aortic and pulmonary valves

Question 6

What is cardiac output?

Answer 6

SV x HR

amount ejected in a minute with one beat x HR in one minute

Question 7

stroke volume

Answer 7

amount of blood ejected in one beat

Question 8

EDV

Answer 8

amount of blood at the end of diastole

total volumes passes through the lungs and systemic circulation in one minute

Question 9

What does the body have to do if it requires more oxygen during exercise?

Answer 9

increase output, HR, number of contractions and SV

elite athletes can increase cardiac output by 7-8 times

Question 10

Age related changes

Answer 10

decreased maximal CO
changes in nodal conducting cells so conduction slows down
decreased elasticity of fibrous Skelton so ventricles can’t stretch as much

Question 11

What governs regulation of stroke volume?

Answer 11

preload
contractility
afterload

Question 12

causes of preload

Answer 12

regurgitation of cardiac valves
heart failure
hypervolemia

Question 13

causes of after load

Answer 13

increased hypertension
vasoconstriction
increased after load and cardiac workload
muscle will hypertrophy and the ventricle will dilate

Question 14

Regulation of heart rate

Answer 14

automatic control-SA node has auto rhythmic rate of 90-120 but at rest parasympathetic effect predominates ad lower HR to 70-75

sympathetic and parasympathetic output usually balance

Question 15

Sympathetic output

Answer 15

increased HR

Question 16

Parasympathetic

Answer 16

decreased HR and slows down depolarisation of SA node

Question 17

How are chemicals regulated?

Answer 17

adrenal medula produces arenaline and noradrenaline which increases HR and contraiclity
thyroid hormone- tachycardia
Ions: increased K and Na decrease HR and contractility

Question 18

Why do babies have an increased HR?

Answer 18

ventricles can’t increase SV because they are stiff and can’t dilate

Question 19

Preload

Answer 19

The stretch of the heart before contraction
A bigger preload on the cardiac muscle fibres prior to contraction increases their force of contraction
The higher the filling the stage (diastole) the higher the force and stretch during systole
A decreased HR allows for more filling time of the ventricles which increases SV
A high HR (more than 160bpm) doesn’t allow enough time to fill the ventricles so decreases SV

Question 20

Contractility

Answer 20

Strength of contraction of individual muscle fibres
strength of contraction at a given preload
+ve inotropic substances- will make the heart contract more effectively and needed for regulating atrial diastole of heart
-ve inotropic substances decrease SV and contraction

Question 21

Afterload

Answer 21

pressure to overcome before blood is pumped out of the ventricles
pressure in the aorta and pulmonary artery need to be exceeded
increased afterload, decreases SV so more blood remains in the ventricle at the end f systole
high pressure will decrease SV