The Heart as a Pump Flashcards
What is the average cardiac output in a healthy adult?
4.9L/min
Which system primarily modulates heart rate?
The autonomic nervous system
How does the sympathetic nervous system affect HR?
It increases HR
How does the parasympathetic nervous system affect HR?
It decreases HR
What are the two primary factors that influence stroke volume?
- Muscle fibre length
- Contractility
What determines the initial length of cardiac muscle fibres?
End diastolic volume
What influences contractility of the heart?
Calcium availability and sympathetic stimulation
What does the Frank-Starling law of the heart state?
As end diastolic volume increases stroke volume increases due to greater fibre stretch
What are three mechanisms that increase venous return?
- Skeletal muscle pump
- Respiratory pump
- Sympathetic vasoconstriction of veins
What determines end diastolic volume in the heart?
Venous return
What is the primary requirement for blood flow through vessels?
A pressure gradient
What is the relationship between flow and resistance?
Flow is inversely proportional to resistance
What does the Poiseuille’s law describe?
The relationship between resistance, viscosity, length and radius
Which variable has the greatest impact on resistance?
Radius of the vessel
What happens when the ventricle ejects blood into the aorta?
The aorta expands to accommodate the blood creating pressure
What maintains blood flow during ventricular diastole?
Elastic recoil of the arteries
What is pulse pressure?
The difference between systolic and diastolic pressure
How is mean arterial pressure calculated?
MAP=Diastolic pressure+1/3(pulse pressure)
Why is MAP not the simple average of systolic and diastolic pressures?
Because diastoles lasts longer than systole
What two main factors determine MAP?
- Cardiac output
- Total peripheral resistance
What happens to MAP if flow in exceeds flow out of the arteries?
It increases
What happens to MAP if flow out exceeds flow in of the arteries?
It decreases
