Cardiovascular system Flashcards
Describe the flow of blood in and out of the heart
- In through superior vena cava
- Right atrium
- Tricuspid valve
- Right ventricle
- Pulmonary valve
- Pulmonary arteries (to the lungs)
- Pulmonary veins (from the lungs)
- Left atrium
- Mitral valve
- Left ventricle
- Aortic valve
- Aorta (out to body)
What is the function of the vascular endothelium?
- Regulates vessel tone (by releasing vasoactive molecules)
- Regulates movement of fluid into tissue (permeability)
- Regulates leukocyte adhesion, platelet aggregation & tendency for thrombus (blood clot) formation (releasing molecules that regulate platelet activation
and coagulation)
What is the difference between cardiac action potentials and skeletal muscle action potentials?
Cardiac = myogenic (SA node generates its own impulses)
Skeletal= neurogenic (needs nerve impulse)
sino-atrial node= SA node
What does the AV node do?
atrioventricular node= AV node
Delays signal until atria are completly empty of blood
What is the path of electrical impulse through cardiac tissue?
SA -> AV -> Bundle of His -> Purkinje fibres
Stimulation of purkinje fibres does what?
Contract the lateral ventricular walls
This is the huge spike on an EKG (the QRS complex)
What is the resting membrane potential of a cardiomyocte?
-80 mV to -90 mV
What is the ionic mechanisms of generating an action potential in the heart?
Slow leak of Na into the cell causes slow depolarization towards threshold
Then when it reaches threshold Na channels open and HUGE depolarization
What happens after depolarization in a cardiomyocte?
Ca 2+ released from SR (80% of total)
Ca 2+ enters enters via voltage-operated calcium channels ( 20% of total)
This causes CONTRACTION
Some K leaks out of the cell bc Na came in
SR= sarcoplasmic reticulum in the cell
What is the ionic basis of repolarization in a cardiomyocte?
Is the heart contracted or relaxed and why?
- Na/K ATPase removes 3 Na from the cell and brings 2 K into the cell to restore gradient
- The heart is still contracted because of the high Ca2+, so its either returned to the SR or exits the cell through the Ca/Na exchanger
What is bradycardia/tachycardia and what HR would you typically see with it?
Bradycardia= slow HR ~ 60 bpm
Tachycardia= fast HR ~ 100 bpm
What are the stages of the cardiac cycle and what happens during them?
- Ventricular filling (tricuspid/mitral open, end of diastole)
- Atrial contraction (^^)
- Isovolumetric contraction (tricuspid/mitral close, systole)
- Ventricular ejection (pulmonary/aortic open, systole)
- Isovolumetric relaxation (early distole)
mitral valve closing causes first heart sound
Aortic valve closing causes second heart sounds
What is stroke volume?
Volume of blood pumped out by each ventricle in one contraction
SV= end-diastolic volume (full) - end-systolic volume (empty)
Approx 70 mL
What is cardiac output?
heart rate x stroke volume
~5L/min
What is ejection fraction?
% of the blood volume that is pumped out by the ventricle (~60%)
Determined by contractility, can increase to 80% during exercise, and decrease to 20% in heart failure
Which part of the heart contracts during systole?
The left ventricle contraction= systole
The left ventricle relazation= diastole
What is mean arterial blood pressure and how is it calculated?
Average arterial pressure through 1 cardiac cycle
MAP= DP + 1/3 (pulse pressure)
MAP= cardiac output x total peripheral resistance
Total peripheral resistance = artery/arteriole lumen diameter
What is Starling’s Law of the Heart?
Relationship btw stroke volume & end diastolic volume
Stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch, cardiomyocytes stretch more: induces greater contraction force = more forcefull systolic contraction
What is Laplaces law?
Wall tension (T) is ~ pressure x radius
Wall tension, T, is the force acting at all points in the vessel wall tending to pull it apart
Large diameter vessels: thick muscle walls to withstand pressure
Capillaries: small diameter, low pressure= thin walls
What is Ohm’s Law?
Flow (Q) is equal to the pressure gradient (ΔP) divided by resistance (R)
- Blood flows because of pressure differences
- Pressure differences arise because of cardiac output and vessel compliance.
What is Poiseuille’s Law?
R~ (n x L)/ r^4
so Flow rate ~ [(P1-P2) x r^4]/ (n x L)
R=resistance, n=viscosity, L=length, r=radius, P1-P2= pressure differenc
Why should you care?
- Small changes in artery /arteriole diameter exert large changes in tissue perfusion
- Total peripheral resistance increases when peripheral beds vasoconstrict
