lecture 8 - CVS 4: blood pressure Flashcards
MAP
mean arterial blood pressure
MAP = CO x TPR
TPR
total peripheral resistance
resistance to flow
• sum of individual resistance to flow
arterioles have the highest resistance so have the biggest influence on TPR
average CO
5 L/min at rest
25-30 L/min at exercise
average HR
72 beats/min
average SV
70ml
EDV - ESV
135 - 65 = 70
contractility
strength of contraction
effect of parasympathetic nerves (vagus) on contractility
release ACh
activates muscarinic ACh receptors
decreases HR
effect of sympathetic nerves on contractility
release NE
activates beta-adrenergic receptors
increases HR and contractility
chronotropic effects
those that change the HR
tachycardia
increase in number of APs
limit to how high you can increase the HR
RMP is less negative
bradycardia
decrease in number of APs
more negative RMP
what increases the number of APs?
adrenaline
2 mechanisms in the regulation of the force of contraction (SV)?
intrinsic - frank-starling
extrinsic
intrinsic mechanism in regulation of force of contraction - Frank-Starling mechanism
force of contraction is proportional to the initial muscle fibre length in diastole
• heart will pump volume of blood it receives
an increase in VR will increase EDV which stretches cardiac muscle
• extra stretching causes increase in force of next contraction
• will only increase by 50%
• overstitching too much damages tissue
basis for starlings law
increased stretch increases the sensitivity of the contractile proteins to Ca++
intracellular [Ca++] required to generate 50% max tension is lower when muscle fibre is stretched
optimises the actin-myosin interactions
importance of the starling effects
helps in matching output of right and left sides of the heart
enables heart to adapt its pumping capacity when either VR or MAP change
what happens if RV output was more than LV output?
more blood would be going to lungs than the body with every contraction
pulmonary blood volume would go up
would produce sever oedema in the lungs and you would drown
extrinsic mechanism in regulation of force of contraction
increase in sympathetic activity
• increases contractility of cardiac muscle
• increases SV
• smaller ESV at end of contraction
known as positive inotropic effect
what are catecholamines?
adrenaline and noradrenaline
how do catecholamines increase contractility?
- channels open for longer
- more Ca++ entry into cell
- more trigger Ca++ so more more Ca++ induced Ca++ release
- phosphorylation can affect respiratory proteins on the calcium pump
- cardiac cycle gets shorter and stronger - relaxation occurs quicker
what is VR maintained by?
- venous pressire
- venomotor tone - sympathetic
- valves
- respiration
- skeletal muscle contraction - acts as a pump
