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Human Physiology > Control of Blood Pressure > Flashcards

Control of Blood Pressure Flashcards

1
Q

How does cardiac excitation occur?

A

1% of Cardiac Cells in the Heart are Autorhythmic cells which are responsible for Pacemaker activity

99% Cardiac Cells are contractile

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2
Q

What is the SA Node?

A

Sinoatrial Node - specialised region in the right atrial wall near opening of vena cava

Cells in SA Node normally fire fastest to generate the heartbeat

-Does not have resting potential

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3
Q

How does the SA Node achieve the ability of not having a resting potential?

A
  • Slow depolarisation (Slow Na+ influx; Ca2+ influx; reduced K+ efflux)
  • ‘Rapid’ depolarisation (Ca2+ influx)
  • Repolarisation (K+ efflux)

Potential of the Node always chaning so no resting potential

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4
Q

How does the action potential of the ventricular cell occur?

A

No pacemaker potential (meaning cells remain essentially at rest (-90mV) until excited by electrical activity propagated from the pacemaker

  • Rapid depolarisation (Na+ influx)
  • Plateau Phase (Ca2+ influx)
  • Repolarisation (K+ efflux)
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5
Q

How does Cardiac Excitation occur?

A

-Needs to be efficient and co-ordinated

  • Action potentials generated at SA Node
  • Rapid excitation through both atria
  • excitation reaches AV Node where conduction is SLOW (allow atria to contract and empty blood into ventricles)
  • Excitation spreads rapidly down the bundle of His & Purkinje fibres to ensure almost simultaneou s activation of ventricular cells
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6
Q

What do the sections of an ECG represent?

A

P wave - Atrial depolarisation
Ventricular depolarisation (QRS) -this masks atrial repolarisation so no wave for atrial repolarisation
T Wave - Ventricular repolarisation

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7
Q

What occurs during Atrial Systole?

A

AV Valves open & atria empty blood into ventricles

- Atrial excitation and contraction should be complete before onset of ventricular contraction

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8
Q

What occurs during Ventricular systole?

A

Part 1:
- Ventricles contract; rise in pressure closes AV Valve
Part 2:
- Pressure in ventricle rises above aortic pressure therefore aortic valve opens & blood is ejected from heart

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9
Q

What occurs during ventricular diastole?

A

Part 1:
-pressure in ventricles falls below aortic pressure therefore aortic valve closes
Part 2:
-pressure in ventricles falls below atrial pressure therefore AV Valve opens and filling begins

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10
Q

What factors are stroke volume influenced by?

A

1) End Diastolic Volume (Preload)
2) Aortic Pressure (Afterload)
3) Contractility (increased by sympathetic nerve stimulation)

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11
Q

What is the equation for Cardiac Output?

A

Cardiac Output = Stroke Volume x Heart Rate

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12
Q

What are the values of Cardiac Output during rest and exercise?

A

At rest = 5L/min

During Exercise = 22L/min

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13
Q

What does cardiac output depend on?

A
  • Stroke Volume and the factors that affect it

- Heart Rate and the factors that affect that

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14
Q

What are the factors affecting heart rate?

A

Intrinsic rate: -Pacemaker (Sino-atrial node)
-Conduction (Atrio-ventricular node)

Influenced by:

  • Sympathetic nervous system - Noradrenaline acting on beta-adrenoceptors to cause an increase in heart rate
  • Parasympathetic nervous system - acetylcholine acting on muscarinic receptors to cause a decrease in heart rate
  • Hormones - adrenaline acting on beta-adrenoceptors to cause an increase in heart rate
  • Extra/intracellular ions - eg Potassium
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15
Q

What is the average systolic BP? What is it determined by?

A

120mmHg
determined by:
-Stroke volume (increased stroke volume, increased SBP)
-Aortic elasticity (decrease elasticity, increase SBP)

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16
Q

What is the average systolic BP? What is it determined by?

A

80mmHG
determined by:
-Peripheral resistance (increase TPR, decreased DBP)
-Aortic elasticity (decrease elasticity, decrease DBP)
-Heart rate (decrease HR, decrease DBP)

17
Q

What is the equation for Pulse Pressure?

A

Pulse Pressure = SBP - DBP = 40

18
Q

What is the equation for mean blood pressure?

A

Mean BP = DBP + 1/3 Pulse Pressure = approx 93mmHg

19
Q

How does heart rate affect Cardiac Output?

A

Sympathetic Nervous System leads to release of noradrenaline binding to beta1-adrenoceptors which leads to an INCREASE IN HEART RATE

Parasympathetic nervous system leads to a release of acetylcholine binding to muscarinic receptors which leads to a DECREASE IN HEART RATE

Increasing Heart Rate increases CO
Decreasing Heart Rate decreases CO

20
Q

How does Stroke Volume affect heart rate?

A

When a ventricular muscle is innervated by the autonomic NS through the sympathetic nervous system which causes the release of Noradrenaline that binds to beta1-adrenoceptors leading to an increase in contractility

Ultimately, sympathetic stimulation causes increase in HR, increase in StV and therefore an increase in CO

21
Q

What are the factors that affect peripheral resistance?

A

Changes in vessel radius have the greatest influence on resistance:

Vasoconstriction - decrease in diameter therefore increased resistance

Vasodilatation - increase in diameter therefore decreased resistance

22
Q

How are arterioles’ vessel diameter influenced?

A

Arterioles are innervated by sympathetic NS:

  • release of noradrenaline binding to ALHPA1-adrenoceptors causes vasoconstriction
  • release of noradrenaline binding to BETA2-adrenoceptors causes vasodilatation

Generally, sympathetic stimulation leads to vasoconstriction and increased TPR

23
Q

Why is control of arterial blood pressure important?

A

-Driving force for the provision of blood to tissues

Too Low -> inadequate supply of nutrients to tissues

Too High -> excessive strain on the heart and increased risk of vascular damage

24
Q

How is the control of arterial blood pressure achieved?

A

Effector mechanisms - autonomic nervous system
Pressure sensors - baroreceptors
Central Integration - CNS cardiovascular centres

25
Q

What are the pressure sensors? Where are they and what do they do?

A

Baroreceptors

  • Located in the walls of major arteries and the heart/pulmonary blood vessels
  • Sense changes in transmural pressure (stretch)
26
Q

How do Baroreceptors cause change of blood pressure?

A
  • Fall in Blood Pressure
  • Sensed by Baroreceptors
  • Afferent input to CNA cardiovascular centres
  • Information centrally integrated
  • Efferent output via autonomic nervous system
  • Increased sympathetic drive to heart and blood vessels
  • Increase in HR, Stv and TPR
  • Rise in Blood Pressure towards Normal
27
Q

How does Postural adaptation cause blood pressure change?

A
  • Moving from supine to upright posture causes pooling of blood in abdomen and limbs
  • Reduced venous return, therefore reduced cardiac output
  • Reduced arterial blood pressure
  • Baroreceptor-Mediated Reflex
  • Increased sympathetic output to heart and blood vessels
  • Increased HR, Stv and TPR
  • Rise in blood pressure towards normal
28
Q

How do you calculate mean arterial BP?

A

Mean arterial BP = cardiac output x total peripheral resistance

Human Physiology (29 decks)

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