12 - Control of Cardiac Output

Question 1

Formula for CO?

Answer 1

CO = HR X SV

Question 2

What is Cardiac Output?

Answer 2

Volume of blood ejected by EACH ventricle per min

Question 3

What is Stroke Volume?

Answer 3

Volume of blood ejected by EACH ventricle per beat

Question 4

What is Vascular Tone?

Answer 4

Degree of vasoconstriction/dilation within the vascular network

Question 5

What is Preload?

Answer 5

Amount of stretch experienced by cardiac muscle cells prior to contraction (end of diastole)

Question 6

What is Afterload

Answer 6

The force the ventricle needs to overcome to open the semilunar valve and eject blood

Question 7

What is Contractility?

Answer 7

The force produced ventricular muscle cells during systole at a given preload

Question 8

What is end diastolic volume?

Answer 8

amount of blood in ventricle at the start of contraction (end of diastole)

Question 9

What is end systolic volume?

Answer 9

amount of blood in ventricle at end of systole (start of diastole)

Question 10

What factors affect CO?

Answer 10

HR & SV

Question 11

What factors affect HR?

Answer 11

Hormones & Autonomic innervation
Venous Return

Question 12

What factors affect autonomic innervation & what does it effect?

Answer 12

Affected by: Atrial Reflex (HR)
Effects: HR
Contractility (SV)

Question 13

What factors affect SV?

Answer 13

EDV & ESV

Question 14

How is SV calculated?

Answer 14

EDV - ESV

Question 15

What factors affect EDV?

Answer 15

Preload

Question 16

What factors affect ESV?

Answer 16

Preload
Contractility
Afterload

Question 17

What factors affect Preload?

Answer 17

Venous Return
Filling Time

Question 18

What is Venous Return?

Answer 18

Amount of blood flow back into the right atrium

Question 19

What factors affect Contractility?

Answer 19

Autonomic Innervation & Hormones
(Nervous system & Endocrine system)

Question 20

What factors affect Afterload?

Answer 20

Vascular Tone

Question 21

What is Vascular Tone?

Answer 21

Vascular Resistance

Question 22

What are Chronotropic effects?

Answer 22

Factors which affect HR
- Autonomic Innervation
- Hormones
- Venous Return

Question 23

What are Inotropic effects?

Answer 23

Factors which affect contraction of the cardiomyocytes & thus SV

Question 24

What happens when the cardiac output is too high?

Answer 24

• Sensors detect CO too high
• Cardioinhibitory centre stimulated
• Sends impulses along vagus nerve (ACh)(Parasympathetic NS activated)
• Impulses arrive at SAN -> pacemaker cells slow down HR

CO decreased

Question 25

What happens when the cardiac output is too low?

Answer 25

• Sensors detect more blood required by body
• Cardioacceleratory centre stimulated
• Sends impulses along symp NS via sympathetic ganglia (Noradrenaline) (Sympathetic NS activated)
• Impulses arrive at SAN -> pacemaker cells increase HR

CO increased

Question 26

What is Vagal Tone?

Answer 26

Background parasympathetic activity
(Increased Vagal Tone = Decreased HR)

Question 27

What is the Atrial Reflex?

Answer 27

Stretch receptors in right atrium -> detect when more blood returning to atrium -> send impulses to medulla -> activates Symp NS -> increase HR

Question 28

What is the Frank-Starling Law?

Answer 28

Force developed in a muscle fibre is dependent on the extent it’s stretched

Question 29

What factors affect Venous Return?

Answer 29

• Posture
• Skeletal Muscle Pump
• Respiratory Pump

Question 30

Effects of SNS on contractility?

Answer 30

Increases:
- Force of contraction
- Velocity of conduction (impulses from atria to ventricles)