Regulation of Cardiac Output:

Question 1

Cardiac output

Answer 1

• Cardiac output is the volume of blood pumped by each ventricle per minute
• Heart rate (bpm) x stroke volume (ml) = Cardiac output (CO)

Question 2

sympathetic activity of CO

Answer 2

– Heart rate is decreased by parasympathetic stimulation and increased by sympathetic stimulation
– Stroke volume is determined by sympathetic activity and by venous return

Question 3

autonomic nervous system

Answer 3

Sympathetic nervous system: ganglia are close to spinal column
Parasympathetic nervous system: ganglia are close to effector organ

Question 4

neurotransmitters

Answer 4

all Ach except postsymapthetic transmitter is noradrenaline

Question 5

sympathetic

Answer 5

Innervates SA and AV nodes, myocardium & conduction sys

Question 6

parasympathetic

Answer 6

Innervates

SA and AV nodes & atrial muscle

Question 7

Controlling Heart Rate (HR)

Answer 7

Heart rate is a balance between parasympathetic (inhibitory) and sympathetic (excitatory) control

Parasympathetic & Sympathetic innervation:
both have chronotropic effects (changing heart rate) and ionotropic effects (activating or deactivating voltage-gated ion channels)

Question 8

heart intrinsic rate

Answer 8

The heart has an intrinsic rate of 100-110 bpm, but at rest, HR is 60-80 bpm, suggesting that it is under constant inhibitory control, known as ‘vagal tone’

Question 9

Controlling heart rate: changing the pacemaker

- Parasympathetic:

Answer 9

Parasympathetic: Acetylcholine decreases slow inward Na+ and Ca2+
(slower depolarisation); increases K+ out in AP (more hyperpolarisation) = longer time to reach threshold

Question 10

Controlling heart rate: changing the pacemaker

- sympathetic

Answer 10

Sympathetic: Noradrenaline increases slow inward Na+ and Ca2+
(faster depolarisation); decreases K+ out in AP (less hyperpolarisation) = shorter time to reach threshold

Question 11

Controlling Stroke Volume (SV)

- directly

Answer 11

Sympathetic stimulation has two ways of influencing stroke volume:
1. Directly by excitatory innervation of the myocardium (atria & ventricles), increases strength of contraction, results in larger stroke volume = ‘extrinsic control’

• more stretch placed on heart > harder contraction
• no parasympathetic acitivity

Question 12

Controlling Stroke Volume (SV)

indirectly

Answer 12

2. Indirectly by stimulating the Adrenal Medulla to produce Adrenaline, acts on veins to cause venoconstriction
   • increases venous return (more blood returned to heart)
   • increases ventricular filling and leads to increased EDV
   • results in a larger stroke volume, through length–tension relationship called the ‘Frank–Starling law’
   = ‘intrinsic control’

Question 13

Together: Intrinsic + Extrinsic effects

Answer 13

even greater increase in SV

• Intrinsic effect shifts up curve through increased EDV
• Extrinsic effect shifts curve to the left through increased contractility