lecture 8 - CVS 4: blood pressure

Question 1

MAP

Answer 1

mean arterial blood pressure

MAP = CO x TPR

Question 2

TPR

Answer 2

total peripheral resistance

resistance to flow
• sum of individual resistance to flow

arterioles have the highest resistance so have the biggest influence on TPR

Question 3

average CO

Answer 3

5 L/min at rest

25-30 L/min at exercise

Question 4

average HR

Answer 4

72 beats/min

Question 5

average SV

Answer 5

70ml

EDV - ESV
135 - 65 = 70

Question 6

contractility

Answer 6

strength of contraction

Question 7

effect of parasympathetic nerves (vagus) on contractility

Answer 7

release ACh

activates muscarinic ACh receptors

decreases HR

Question 8

effect of sympathetic nerves on contractility

Answer 8

release NE

activates beta-adrenergic receptors

increases HR and contractility

Question 9

chronotropic effects

Answer 9

those that change the HR

Question 10

tachycardia

Answer 10

increase in number of APs

limit to how high you can increase the HR

RMP is less negative

Question 11

bradycardia

Answer 11

decrease in number of APs

more negative RMP

Question 12

what increases the number of APs?

Answer 12

adrenaline

Question 13

2 mechanisms in the regulation of the force of contraction (SV)?

Answer 13

intrinsic - frank-starling

extrinsic

Question 14

intrinsic mechanism in regulation of force of contraction - Frank-Starling mechanism

Answer 14

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

Question 15

basis for starlings law

Answer 15

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

Question 16

importance of the starling effects

Answer 16

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

Question 17

what happens if RV output was more than LV output?

Answer 17

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

Question 18

extrinsic mechanism in regulation of force of contraction

Answer 18

increase in sympathetic activity
• increases contractility of cardiac muscle
• increases SV
• smaller ESV at end of contraction

known as positive inotropic effect

Question 19

what are catecholamines?

Answer 19

adrenaline and noradrenaline

Question 20

how do catecholamines increase contractility?

Answer 20

• 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

Question 21

what is VR maintained by?

Answer 21

• venous pressire
• venomotor tone - sympathetic
• valves
• respiration
• skeletal muscle contraction - acts as a pump