Cardiodynamics

Question 1

Define cardiodynamics

Answer 1

movements of blood + forces generated during cardiac contractions

Question 2

What is end diastolic volume (EDV)

Answer 2

volume of blood remaining in each ventricle at end of ventricular diastole

Question 3

what is end systolic volume (ESV)

Answer 3

volume of blood remaining in each ventricle at the end of ventricular systole (40% of EDV)

Question 4

what is the ejection fraction

Answer 4

the percentage of EDV represented by SV (60%) of EDV

Question 5

list the factors affecting CO

Answer 5

Factors affecting HR -
- autonomic intervention
- hormones

factors affecting sv -
- EDV
-ESV

Question 6

Describe the autonomic innervation of the heart

Answer 6

both SNS + PNS innervate SA, AV nodes + atrial/ventricular muscle cells

• SNS control greater in ventricles than PNS

Question 7

State where the cardiac centres are located + differentiate b/t them

Answer 7

found in medulla oblongata

cardioinhibitory centre = PNS, decreases HR

cardioaccelatory centre = SNS, increase HR

Question 8

What regulates cardiac centres

Answer 8

Reflex pathways eg. baroreceptors, chemoreceptors + CNS

Question 9

What NS is dominant in a healthy, resting heart

Answer 9

PNS

Question 10

How does the autonomic NS effect the SA node

Answer 10

by changing the rate of spontaneous depolarisation or duration of repolarisation
-> alters HR by changing time required for cells to reach threshold

Question 11

What occurs during PNS stimulation of the heart

Answer 11

ACh released, extending repolarisation therefore decreasing rate of spontaneous depolarisation

Question 12

What occurs during SNS stimulation of the heart

Answer 12

NE released, shortening repolarisation + accelerating rate of spontaneous depolarisation / increases HR

Question 13

List the hormones that increase HR and the locations they act in

Answer 13

• adrenaline, noradrenaline + thyroid hormones
• act on SA node + adrenaline/noradrenaline act on contractile cells too

Question 14

List the 3 factors affecting EDV

Answer 14

• filling time (duration of ventricular diastole)
• venous return
• preload

Question 15

Describe preload

Answer 15

Frank-Starling principle -
- degree of ventricular stretching -> greater EDV, greater preload
- affects ability of muscle cells to produce tension ‘more in = more out’

SV increases as EDV increases

has physical limits eg. connective tissue, pericardial sac

Question 16

List the 3 factors affecting ESV

Answer 16

• preload (inversely proportional)
• contractility
• afterload

Question 17

Describe contractility

Answer 17

• force produced by contraction at a given preload
  -> influenced by adrenaline/noradrenaline of PNS/SNS activity

Question 18

Describe afterload

Answer 18

tension the ventricle produces to open the semilunar valve + eject blood
-> increased by restricted arterial flow

Question 19

Define inotropic agent

Answer 19

any chemical that influences contractility of a muscle cell -> causes inotropic effect

if chemical increases force of contraction = positive inotropic agent eg. noradrenaline
-> SV can increase w/out same increase in EDV as ESV reduced