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HHP > Cardiac Output + Regulation Of Function > Flashcards

Cardiac Output + Regulation Of Function Flashcards

1
Q

How much blood does each ventricle pump per minute at rest

A

5 litres

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2
Q

What is cardiac output

A

Rate ventricle pumps blood (L/min)

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3
Q

What is heart rate

A

Number of contractions per minute

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4
Q

What is the equation for cardiac output

A

Cardiac output = heart rate x stroke volume

CO = HR X SV

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5
Q

What is stroke volume

A

Volume per contraction

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6
Q

What is extrinsic control

A
  • Regulation of heart by neutral input

- circulating hormones or any other factor from outside the heart (external factors)

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7
Q

What is intrinsic control

A

Regulation by factors originating in the heart

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8
Q

What system enables to body to switch between resting state and fight or flight

A

Central nervous system (CNS)

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9
Q

What are the components of the CNS

A

1) afferent (coming into CNS)
2) efferent (sent out of CNS)

  • remember bc E after A in alphabet
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10
Q

What controls muscles and other organs

A

signals sent through efferent branch of PERIPHERAL NERVOUS SYSTEM (PNS)

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11
Q

What are the 2 branches of the PNS

A

1) Autonomic

2) somatic (voluntary skeletal muscle control)

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12
Q

What are the 2 division of the autonomic branch of the PNS

A

1) sympathetic

2) parasympathetic (part of efferal branch)

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13
Q

What is parasympathetic nervous system

A
  • Rest state

- input through autonomic nervous system into different organs (esp the heart)

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14
Q

What is the sympathetic nervous system

A

Fight or flight response

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15
Q

What is the nerve supply to the parasympathetic nervous system

A

CRANIOSACRAL

  • 4 cranial nerves supply parasympathetic efferent output (III, VII, VIIII, X)
  • S2, S3, S4 from sacral levels of spinal cord
  • ganglia located in/near target viscera
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16
Q

What do neurones have entering / leaving the ganglia

A

Entering = pre-ganglionic neurone

Leaving = post ganglionic neurone

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17
Q

What is the structure of neurones in the parasympathetic division

A
  • Pre-ganglionic long

- Synapse with post-ganglionic neurones at ganglia

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18
Q

Which cranial nerve are most major parasympathetic nerves in and what do these supply

A

VAGUS NERVE (cranial nerve X)

  • vagal fibres to heart, lungs, upper GI tract
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19
Q

What is the nerve supply to the sympathetic nervous system

A

THORACOCOLUMBAR

  • nerves originate from thoracic + lumbar levels of spinal cord (T1-L3) = paraspinal ganglia
  • nerves come out of spinal cord in thoracic region and reach paraspinal sympathetic trunks
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20
Q

What is the structure of sympathetic neurones

A
  • Pre-ganglionic neurones short
  • reach para-spinal ganglia (found either side of spine)
  • from here post-ganglionic sympathetic neurones travel to the viscera they supply
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21
Q

How do the divisions of the autonomic nervous system innervate the heart

A
  • para = nerves that innervate heart travel by vagus nerve

- sympa = nerves supply heart from paraspinal ganglia

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22
Q

Where are the nuclei of para neurones

A
  • medulla oblongata

- brainstem

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23
Q

What part of the heart is innervated by para nerves

A

1) sino-atrial node

2) AV node

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24
Q

What is the neurotransmitter in the parasympathetic division

A

ACETYLCHOLINE

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25
Q

What part of the heart is innervated by sympathetic nerves

A

1) SA + AV node

2) ventricular myocardium (innervated by sympathetic neurones directly)

26
Q

What is the neurotransmitter in the sympathetic division

A

NORADRENALINE

27
Q

What influences changes in heart rate

A 
- Different neural inputs to SA + AV nodes
Also
- age
- fitness
- emotional state 
Etc
28
Q

What is the heart rate of a normal adult

What can heart range range from/to

What regulates this

A

70-90 BPM

  • 30-180BPM
  • extrinsic controls
29
Q

What is the role of pacemaker cells of the SA node (first branch) when sympathetic activity INCREASES

A

1) increase action potentials
2) increase heart rate
3) increase cardiac output

30
Q

What is the role of AV node and conduction system (2nd branch) when sympathetic activity INCREASES

A

1) increase speed of conduction
2) ventricular contraction sooner after atrial contraction
3) decreases duration of systole

31
Q

Given the action of the pacemaker cells of the SA node and of the AV node and conduction system

How does increased sympathetic activity support an increased heart rate

A

Decreasing systole

Allows for increased cardiac output so more cardiac contractions

32
Q

What happens when parasympathetic activity is increased compared to sympathetic

A

EXACT OPPOSITE of sympathetic

33
Q

So how does increase in parasympathetic activity support a decreased heart rate

A
  • Duration of systole increases

- so less cardiac output and less blood pumped per minute

34
Q

How do pacemaker cells of the SA node cause decrease in action potentials in the parasympathetic division

A
  • gradual slow depolarisation from pacemaker cells is prolonged
  • so less frequent action potentials
35
Q

How does cardiac output decrease

A
  • fewer BPM

- but stroke volume is always the same

36
Q

Explain the hormonal control of heart rate

A
  • adrenaline acts via the blood stream and is released from adrenal medulla
  • increased action potential firing of SA node so increases heart rate (similar to noradrenaline of sympathetic division)
37
Q

How does adrenaline increase velocity of action potentials

A

Sympathetic activity is coupled with adrenaline secretion

38
Q

What else increases force of myocardial contraction thus promote increase in heart rate

A

1) thyroid hormones
2) glucagon
3) insulin

39
Q

Why does stroke volume change

A
  • varies between individuals and from moment to moment
40
Q

What factors affect ventricular contractility (force of ventricular contraction)

A

1) sympathetic activity increases
2) ventricular contractility increases
3) cardiac output increases
- due to increase is Ca2+ permeability across the membrane

41
Q

What increases myocardial contractility

A

adrenaline

42
Q

What are changes in end diastolic volume controlled by and what does increasing it cause

A
  • intrinsic control

1) increase in EDV
2) increases force of ventricular contraction
3) increases stroke volume and cardiac output

43
Q

Define starlings law of the heart

A

‘When the rate at which blood flows into the heart from the veins (venous return) changes, the heart automatically adjusts its output to match the flow’

44
Q

What is visible on a graph of starlings law of the heart (for normal patient with contrast sympathetic output)

A

An increase in EDV causes stroke volume to increase

45
Q

How does an increase in EDV increase the force of contraction in myocardium

A
  • muscle fibres of myocardium stretch
  • increases affinity of troponin (contractile proteins expressed in cardiomyocytes) in muscle fibres for calcium
  • so increase in number of cross bridges activated in contractile machinery
  • in cardiac muscle optimum length of muscle for generating force is greater than the resting length so with increase in EDV muscle fibres are closer to optimum length for contraction
  • and are moved into region where they can contract with greater force
46
Q

So what happens to an (individual cardiomyocyte) cardiac muscle when it’s
A) at rest
B) physically stretched
in buffer suspensions

A

A) regularly contracting, looks clear

B) increased rate of contraction can see activity is happening inside it

47
Q

How does an increase in sympathetic activity (increase in contractility) influence starlings law

A
  • shifts curve upwards
  • so at any given EDV, SV is higher
  • due to increase in ventricular contractility
48
Q

How does starlings law work to regulate when sympathetic activity is increased

A
  • regulates heart size
  • by adjusting SV so CO matches venous return
  • blood going in matches blood going out so no backlog
49
Q

What determines EDV

A

Pressure of blood inside the heart before contraction

Tension on myocardium

50
Q

What determines preload

A

1) Filling time (dependent on heart rate, ie if higher = less filling time)
2) Atrial pressure (dependent on venous return, amount of blood flowing into atria determines its pressure and force of atrial contraction)

51
Q

What is afterload

A
  • the load/pressure placed on the myocardium by arterial pressure (the arteries) after contraction starts
  • when heart ejects blood
  • it contracts and pumps blood out
  • has to work against arterial pressure (pumping against this)
52
Q

So how does an increase in arterial pressure influence SV

A
  • DECREASES stroke volume
  • heart is working against higher pressure
  • so for given amount of force the blood pumped out is slightly less
53
Q

What determines afterload in the left ventricle

A

Pressure in the aorta that the heart is pumping against

54
Q

Describe the factors affecting stroke volume starting with central venous pressure

A

central venous pressure -> venous return -> atrial pressure -> ventricular end diastolic pressure (pre-load) -> EDV -> SV

55
Q

Describe the factors affecting stroke volume starting with atrial contraction

A

Atrial contraction -> atrial pressure -> ventricular end diastolic pressure (pre-load) -> EDV -> SV

56
Q

Describe the factors affecting stroke volume starting with filling time

A

Filling time -> ventricular end-diastolic pressure (preload) -> EDV -> SV

57
Q

Describe the factors affecting stroke volume starting with adrenaline and sympathetic nerves to the heart

A

adrenaline and sympathetic nerves to the heart -> ventricular contractility -> SV

58
Q

Describe the factors affecting stroke volume starting with afterload

A

Afterload -> SV

59
Q

So in extrinsic control what is the heart regulated by

A

1) para and sympa neurones

2) hormones

60
Q

In intrinsic control what is the heart regulated by

A

1) factors within heart

2) ie influence of EDV on SV -> basis of starlings law

61
Q

An increase in venous return causes an increase in…

A

1 - stroke volume

2 - cardiac output

HHP (10 decks)

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