The cardiac cycle

That happens in systole and diastole

Systole : heart chambers contract and heart pumps the blood

Diastole: heart chambers relax and the heart fills

Where is the SA node found?

Near the opening of the superior vena cava

What causes the A and C wave

A: increase in atrial pressure

C: mitral valve closes

What causes V wave?

Atrial pressure increasing due to blood from pulmonary vein

What causes the X descent and dichrotic notch?

X descent: atrial pressure initially decreases as atrial base is being pulled down as the ventricles contract

Dichrotic notch: Aortic valve closes

Stroke volume =

End diastolic volume - end systolic volume

What is the EDV and ESV ?

EDV: volume of blood in the ventricle just before contracting (how full it is at the end of diastole)

ESV:the lowest volume of blood in the ventricle during the cardiac cycle (how much blood is left over after a contraction)

What factors can increase the heart rate (positive chronotropic)

• sympathetic nervous system

• Hormones (T3,T4)

• Increases Ca²+ levels

What factors can decrease the heart rate (negative chronotropic)

• parasympathetic nervous system

• Decrease in K+ levels

• Decrease in Ca2+ levels

How do chemoteceptors cause an increase in heart rate?

** found in the middle all of the aorta and carotid artery

• respiration causes an increase in CO2 → decrease in pH

• Increase frequency of impulses sent to the medulla via the SNS

• Increase of impulses sent to the SAN

How do baroreceprtoes cause an decrease heart rate?

** found in the wall of the aorta ans carotid artery

1. Receptors stretch with increased bp

2. Send more impulses to the medulla via PSNS

3. less frequency of impulses to the SAN

What is the order of conduction in the heart?

1. SA node

2. AV node

3. Common bundle

4. Bundle (bundle of his)

5. Purkinje fibres

What is stoke volume affected by?

• preload

• Contractility

• Afterload

What is preload?

Amount of stretch of ventricles in diastole

** increases stroke volume

What is preload affected by?

• Heart contacts → increased venous return → increase in EDV → increases preload

• Respiratory pump: increases thoracic volume → decreased pressure + decreases abdominal volume → increases pressure : blood flows high to low pressure

• Venous tone

• Gravity decreases preload

What is frank atsrlings law of contractility?

The more the heart stretches the more it contracts (as the heart fills and stretches the harder it pumps our blood)

What factors increases contractility ?

• sympathetic nervous system (noradrenaline)

• Hormones (T3/4, glucagon)

• Drugs

What factors decrease contractility ?

• beta blockers

• Calcium channel blockers

• High K+/ Na+/ H+

What is afterload?

The amount of resistance needed to be overcome by the ventricles to pump blood to the aorta

** decreases SV

What increases after load?

• semilunar valve damage

• Increased vascular resistance

1. A wave

2. C wave

3. X descent

4. V wave

In what order do the valves open and close?

1. Mitral valve closes

2. Aortic valve opens

3. Aortic valve closes

4. Mitral valve opens

The cardiac cycle

1. atrial systole: atria contract → arial pressure > ventricular → the mitral valve opens remaining blood flows into the ventricle (ESV)

2. Isovolumetric contraction: ventricles contract → ventricular pressure > atrial → mitral valve closes → S1 sound

3. Ejection stage: ventricular pressure > pressure in aortic → aortic valve opens

4. Isovolumetric relaxation: ventricular presure < aortic → aortic valve closes → S2 sound

5. Atrial systole/Ventricular diastole: atria fills → atrial pressure > venticular → mitral valve opens and the ventricles start to fill