L12 Control of Cardiac Output

Question 1

Define cardiac output

Answer 1

Volume of blood ejected by EACH ventricle per MINUTE

Question 2

Cardiac output formula

Answer 2

CO = HR x SV

Question 3

What is heart rate in terms of CO

Answer 3

Number of heart beats per minute

Question 4

Define stroke volume

Answer 4

Volume of blood ejected by each ventricle PER BEAT

Question 5

What factors can affect heart rate?

Answer 5

Autonomic Innervation
Hormones
Venous return

Question 6

How is HR lowered by cardiac reflex?

Answer 6

• Cardioinhibitory centre within the cardio regulatory centre is activated
• This is connected to Parasympathetic system
• Impulses sent along VAGUS nerve using ACETYLCHOLINE to
• SAN which lowers heart Rate

Question 7

How is HR increased?

Answer 7

Cardioaccelerator centre is activated in the cardio regulatory centre
- Which is connected to SNS
- Impulses are sent to SAN using noradrenaline
- SAN increases HR
- AT the same time SNS stimulates the adrenal medulla to release hormones which also increase heart rate

Question 8

What is TACHYCARDIA?

Answer 8

Pathologically HIGH HR

Question 9

What is BRADYCARDIA?

Answer 9

Pathologically low heart rate

Question 10

How does the PNS affect SAN?

Answer 10

• PSN releases Acetylcholine
• Acetylcholine activates many K+ channels
• More K+ move out of the cell
• SAN cells are hyperpolarised so it will take longer for them to be repolarized
• HR is slowed

Question 11

How does the SNS affect SAN?

Answer 11

SAN increases amount of Na+/Ca2+ entering SAN cells
Cells are continuously depolarized
More rapid depolarization
Increases heart rate

Question 12

SAN normally would lead heart to beat at 100 bpm, so why is heart rate 60ish?

Answer 12

• Vagal tone; background of parasympathetic activity
• No/little SNS activity so nothing accelerates heart rate

Question 13

What factors can affect Stroke volume?

Answer 13

EDV and ESV

Question 14

How can stroke volume be calculated?

Answer 14

EDV-ESV

Question 15

What happens if EDV increases to SV and CO?

Answer 15

They both increase

Question 16

What happens to CO and SV if ESV decreases?

Answer 16

Both increase

Question 17

What factors can affect EDV and ESV?

Answer 17

• preload
• contractility
• Afterload

Question 18

How does venous return affect heart rate when you are exercising?

Answer 18

• Exercising = more venous return
• detected by stretch receptor in atria
• heart rate is increased

Question 19

What is PRELOAD?

Answer 19

• The degree at which ventricular muscles are stretched at the end of diastole
• Or how air filled is the baloon

Question 20

What is contractility?

Answer 20

The force produced by ventricular muscles at a given preload
or force produced by elastic recoil of the baloon

Question 21

What is afterload?

Answer 21

The force the ventricle needs to overcome to open the
semilunar valve and eject blood
(CHUNDI on the baloon)

Question 22

What factors can affect PRELOAD?

Answer 22

• venous return
• available VENTRICULAR filling time

Question 23

What are the 3 factors affecting venous return and how do the affect it?

Answer 23

• posture = decreases venous r
• skeletal muscles = Increase venous return
• Respiratory system = inspiration expands chest size blood squeezed upwards

Question 24

What factors can affect contractility?

Answer 24

• Autonomic innervation
• hormones
  +ve inotrphic(SNS) effects and -ve inotrophic(PSN) effects

Question 25

What is AFTERLOAD affected by?

Answer 25

Vascular tone
Vasoncstriction increases afterload
Vasodilation reduces afterload