Physiology and Pharmacology 18: (davies) Cardiac Cycle

Question 1

Summarise pathway / cycle of the cardiovascular system

Answer 1

Deoxygenated blood enters the right atrium from the body, fills the right ventricle and is pumped into pulmonary circulation (low pressure) -> sent to lungs via pulmonary artery where CO2 is removed and blood oxygenated

Oxygenated blood enters left atrium from lungs via pulmonary vein, fills the left ventricle and pumped into systemic circulation (high pressure)

returns deoxygynated from body and cycle repeats

Question 2

Purpose of valves in the heart?

Answer 2

Ensure blood flows the correct direction

Question 3

Cardiac cycle pressure graph

Answer 3

look at graphs

Question 4

What is cardiac output - equation? Typical resting CO?

Answer 4

Cardiac output (CO) is the volume of blood the heart pumps in a given time, normally expressed in litres/min

Cardiac output is given by the product of the heart rate (HR) and stroke volume (SV)

CO = HR x SV

Typical resting HR = 70beats.min^-1
Typical resting SV = ml

so typical CO at rest = 4900ml/min or ~ 5l per min

Question 5

What ensures output of left and right heart are equal?

Answer 5

Frank-starling mechanism

Question 6

What is the fick principle? equation?

Answer 6

Fundamental method used to calculate blood flow through organs, or substances exchanged by them

CO = Vo2 / (Cv - CA)

CA = conc. O2 before (artery) (ml/l)
CV = conc. O2 after (vein) (ml/l)
Vo2 = Oxygen uptake rate (ml/min)

Question 7

Describe the Frank-starling mechanism

Answer 7

Balances the output of the two ventricles over time
- contributes to increased CO in exercise + mediates postural hypotension

Increased ventricular filling (diastolic volume)

• > leads to increased ventricular pressure
• > leads to increased ventricular stretch
• > leads to increase in output -> + stroke volume

i.e increase in venous returns increases left ventricular end-diastolic pressure (LVEDP)

Question 8

What is the basic of the Frank-starling mechanism? Why does this occur?

Answer 8

Increase in force generated as there is an increase in sarcomere length -> higher force at higher % of optimal sarcomere length

normal length = 1.9micrometres
optimal length = 2.2micrometres

This is for 2 reasons

1) Below 2micrometres, actin filaments overlap and interfere with cross bridge formation
2) Calcium sensitivity -> stretch increases cross-bridges activated at a given calcium level i.e stretch increases Ca2+ sensitivity

Question 9

guytons cross plot

Answer 9

get ur head around it