Cardiovascular system

Question 1

Describe the flow of blood in and out of the heart

Answer 1

1. In through superior vena cava
2. Right atrium
3. Tricuspid valve
4. Right ventricle
5. Pulmonary valve
6. Pulmonary arteries (to the lungs)
7. Pulmonary veins (from the lungs)
8. Left atrium
9. Mitral valve
10. Left ventricle
11. Aortic valve
12. Aorta (out to body)

Question 2

What is the function of the vascular endothelium?

Answer 2

1. Regulates vessel tone (by releasing vasoactive molecules)
2. Regulates movement of fluid into tissue (permeability)
3. Regulates leukocyte adhesion, platelet aggregation & tendency for thrombus (blood clot) formation (releasing molecules that regulate platelet activation
   and coagulation)

Question 3

What is the difference between cardiac action potentials and skeletal muscle action potentials?

Answer 3

Cardiac = myogenic (SA node generates its own impulses)
Skeletal= neurogenic (needs nerve impulse)

sino-atrial node= SA node

Question 4

What does the AV node do?

atrioventricular node= AV node

Answer 4

Delays signal until atria are completly empty of blood

Question 5

What is the path of electrical impulse through cardiac tissue?

Answer 5

SA -> AV -> Bundle of His -> Purkinje fibres

Question 6

Stimulation of purkinje fibres does what?

Answer 6

Contract the lateral ventricular walls

This is the huge spike on an EKG (the QRS complex)

Question 7

What is the resting membrane potential of a cardiomyocte?

Answer 7

-80 mV to -90 mV

Question 8

What is the ionic mechanisms of generating an action potential in the heart?

Answer 8

Slow leak of Na into the cell causes slow depolarization towards threshold
Then when it reaches threshold Na channels open and HUGE depolarization

Question 9

What happens after depolarization in a cardiomyocte?

Answer 9

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

Question 10

What is the ionic basis of repolarization in a cardiomyocte?
Is the heart contracted or relaxed and why?

Answer 10

• 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

Question 11

What is bradycardia/tachycardia and what HR would you typically see with it?

Answer 11

Bradycardia= slow HR ~ 60 bpm
Tachycardia= fast HR ~ 100 bpm

Question 12

What are the stages of the cardiac cycle and what happens during them?

Answer 12

1. Ventricular filling (tricuspid/mitral open, end of diastole)
2. Atrial contraction (^^)
3. Isovolumetric contraction (tricuspid/mitral close, systole)
4. Ventricular ejection (pulmonary/aortic open, systole)
5. Isovolumetric relaxation (early distole)

mitral valve closing causes first heart sound
Aortic valve closing causes second heart sounds

Question 13

What is stroke volume?

Answer 13

Volume of blood pumped out by each ventricle in one contraction
SV= end-diastolic volume (full) - end-systolic volume (empty)
Approx 70 mL

Question 14

What is cardiac output?

Answer 14

heart rate x stroke volume
~5L/min

Question 15

What is ejection fraction?

Answer 15

% 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

Question 16

Which part of the heart contracts during systole?

Answer 16

The left ventricle contraction= systole
The left ventricle relazation= diastole

Question 17

What is mean arterial blood pressure and how is it calculated?

Answer 17

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

Question 18

What is Starling’s Law of the Heart?

Answer 18

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

Question 19

What is Laplaces law?

Answer 19

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

Question 20

What is Ohm’s Law?

Answer 20

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.

Question 21

What is Poiseuille’s Law?

Answer 21

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