Lecture 4 - Cardiac Cycle

Question 1

what are systole and diastole ?

Answer 1

Systole - contraction and ejection of blood from the ventricles

Diastole - Relaxation and filling of ventricles

Question 2

outline the flow of blood within the heart

Answer 2

it is two pumps acting in series
the output of the left and right sides must be equal over time

the systemic circulation ( body) is at a high pressure
the pulmonary system (lungs) is at a low pressure

atria are priming pumps for the ventricles

deoxy blood from body enters the right atrium via the superior and inferior Vena Cava

it passes through the tricuspid valve into the right ventricle - contraction sends blood into pulmonary artery - via the pulmonary valve

oxy blood returns from pulmonary system via 2 superior and 2 inferior Pulmonary veins into the left atrium

passes into left ventricle (far thicker, to pump blood with more force hence higher pressure) via the mitral valve

• oxy blood is pumped past the aortic valve into the aorta, where it is carried into the body

Question 3

what does 120/80 mean ?

Answer 3

120 would be the systolic pressure

80 is the diastolic pressure

Question 4

explain the specialisations of the heart muscle cells ?

cardiac myocytes

Answer 4

Has gap junctions between cells, allow for rapid communication. this is what allows the heart to have a synchronised beat

the cells will contract in response to an action potential, caused due to a rise in intracellular Calcium

Cardiac cells action potential is relatively long single contraction - 280 ms

Valve cusps are pushed open to allow blood
flow and close together to seal and prevent
backflow.

• Cusps of mitral and tricuspid valves attach
to papillary muscles via chordae tendineae.
Prevents inversion of valves on systole.

Question 5

outline the conduction system of the heart

Answer 5

Pacemaker cells in the sinoatrial node generate an AP

Activity spreads over atrial system and contractions occur

reaches the Atrioventricular node - delays signal for 120 ms (ensure the heart beats in order)

signal travels through the bundle of his, down the purkinjie fibers - will travel down to the apex, and then up the walls of the ventricles

ventricles will contract from apex upward, forcing blood through outflow valves

Question 6

what are the 7 phases of the cardiac cycle ?

Answer 6

1. Atrial Contraction
2. Isovolumetric Contraction
3. Rapid Ejection
4. Reduced Ejection
5. Isovolumetric Relaxation
6. Rapid Filling
7. Reduced Filling

Question 7

sketch or describe all the parts of a wiggers diagram

explain what happens at each point

Answer 7

check against your notes

Question 8

stroke volume = ?

Answer 8

SV = End diastolic volume (EDV) - End Systolic Volume (ESV)

Question 9

what are the two forms of abnormal valve function ?

Answer 9

Stenosis - Vavle does not open enough - obstruction to blood flow, when valve is normally open

Regurgitation - Valve does not close all the way - back leakage when valve should be closed

Question 10

Explain Aortic Valve Stenosis

Answer 10

Causes:
• Degenerative (senile calcification/fibrosis)
• Congenital (bicuspid form of valve)
• Chronic rheumatic fever –inflammation- commissural
fusion

shear stress - Microangiopathic
haemolytic anaemia

less blood can get through valve

• increased LV pressure - LV Hypertrophy
• Left sided Heart Failure - Syncope (fainting) - Angina (lack of blood to cronary arteries)

Question 11

Explain Aortic Valve Regurgitation

Answer 11

causes:
• Aortic root dilation (leaflets pulled apart)
• Vlavular damage (endocarditis rheumatic
fever)
• Blood flows back into LV during diastole
• Increases stroke volume
• Systolic pressure increases
• Diastolic pressure decreases

• Bounding pulse (head bobbing, Quinke’s sign)
• LV hypertrophy

Question 12

Explain Mitral Valve Stenosis

Answer 12

Chordae tendineae & papillary muscle
normally prevent prolapse in systole
• Myxomatous degeneration can weaken
tissue leading to prolapse

• Other causes:
• Damage to papillary muscle after
heart attack
• Left sided heart failure leads to LV
dilation which can stretch valve
• Rheumatic fever can lead to leaflet
fibrosis which disrupts seal formation

• As some blood leaks back into LA, this
increases preload as more blood enters
LV in subsequent cycles…can cause LV
hypertrophy

Question 13

Explain Mitral Valve Regurgitation

Answer 13

Main cause = Rheumatic fever (99.9% cases)
• Commissural fusion of valve leaflets
• Harder for blood to flow LA to LV

Increased LA pressure -

LA Dilation - Atrial Fibrillation - Thrombus (clot) formation
- Oseophagus Compression - Dysphagia (hard to swallow)

• Pulmonary Odema, Dyspena, Pulmonary Hypertension (high Pressure) - Causes RV hypertrophy