L6 control of HR

Question 1

what part of nervous system influences HR

Answer 1

-ANS so SNS and PNS

Question 2

does the cardiac cells need innervation to beat

Answer 2

no, the cells are myogenic so they depolarise and contract w/o nerves

Question 3

effect on HR if SNS activity is increases

Answer 3

HR increases

Question 4

effect on HR if PNS activity increases

Answer 4

HR decreases

Question 5

how to work out SV

Answer 5

EDV-ESV

Question 6

how to work out CO and how to change CO

Answer 6

CO=HR X SV(EDV-ESV)

-change HR/EDV/ESV

Question 7

what is EDV

Answer 7

• end diastolic vol
• it’s the vol of blood in ventricle at the end of diastole
• around 120 ml

Question 8

what leads to EDV

Answer 8

there’s central venous pressure (CVP) in the vena cava which then allows cardiac filling (venous return).

Question 9

factors determining venous return

Answer 9

1. skeletal muscle pump - respiratory pump
   - blood vol
   - venous tone
   - gravity

Question 10

how does an increase in EDV leads to an increase in SV

Answer 10

• if the heart contracts more due to increased length of ventricular fibres, the venous return increases so the EDV increases leading to an iincrease in SV

Question 11

how does ESV change to increase SV

Answer 11

-it decreases as the contractility increases

Question 12

how can the contractility be increased

Answer 12

by increased SNS activity or adrenaline acting on Beta receptors

Question 13

what is afterload

Answer 13

load or pressure where the heart must contract against to eject blood out

Question 14

examples of after load in the heart

Answer 14

• for left ventricle to eject blood out, after load is aortic pressure
• for right ventricle, it’s pulmonary pressure