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PHA112 > The Circulatory System 5 > Flashcards

The Circulatory System 5 Flashcards

1
Q

what is the efficiency + work of the heart as a pump measured as?

A

cardiac output

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2
Q

what is cardiac output?

A

vol of blood heart pumps out every min (ml/min or L/min)

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3
Q

what is cardiac output determined by?

A
  • stroke vol

- heart rate

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4
Q

formula to find CO?

A

CO = SV x HR

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5
Q

what is stroke volume?

A

vol of blood ejected by the left ventricle with each heart beat (ml/beat)

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6
Q

what are the determinants of heart rate?

A

ANS/autonomic tone on heart

  • inc in SNS/sympathetic tone INC heart rate
  • inc in PNS/parasympathetic tone DEC heart rate
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7
Q

what are the determinants of stroke volume?

A
  • preload
  • afterload
  • cardiac contractility
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8
Q

what is preload?

A

workload imposed on heart before contraction begins

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9
Q

what does preload =

A

end-diastolic vol / pressure

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10
Q

what is EDV/EDP?

A

vol of blood/pressure in ventricle prior to contraction (i.e at end of diastole)

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11
Q

what does EDV =

A

venous return (VR)

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12
Q

what is Frank-Starlings law of the heart?

A

SV = directly proportional to preload (or VR)

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13
Q

what does an inc in preload lead to?

A
  • inc in stretch of cardiac muscle fibres
  • inc in contraction
  • inc in SV
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14
Q

what is afterload?

A

pressure heart must generate/overcome in order to eject blood into aorta

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15
Q

what does afterload =

A

aortic pressure = systemic arterial BP

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16
Q

what is afterload determined by?

A

systemic/total peripheral resistance (TPR)

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17
Q

what is SV inversely proportional to?

A

afterload (or TPR)

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18
Q

what does an increase in afterload lead to?

A

decrease in SV

19
Q

what is contractility?

A

ability of heart to change its force of contraction without changing rest of muscle length

20
Q

what does contractility =

A

strength of contraction at any given EDV

21
Q

what does contractility depend on?

A

availability of intracellular ca2+ to participate in contractile process

22
Q

what is SV directly proportional to?

A

cardiac contractility

23
Q

what does an inc in [Ca2+]i lead to?

A
  • inc in actin-myosin crossbridge formation
  • inc in contractility
  • inc in SV
24
Q

what is cardiac contractility inc by?

A

SNS activation

- inc in SV

25
Q

control of cardiac output

A
  • inc in symp activity (+ epinephrine) inc heart rate and SV —> inc cardiac output (via EXTRINSIC control)
  • inc in end-diastolic vol inc SV —> inc CO (via INTRINSIC control)
  • inc in venous return —> inc SV —> CO (via INTRINSIC control)
26
Q

what is systolic BP?

A

force exerted by blood on arterial walls during systole

27
Q

what is diastolic BP?

A

force exerted by blood on arterial walls during diastole

28
Q

what is the mean arterial BP?

A

average pressure responsible for driving blood forward into tissues

29
Q

formula to find pulse pressure?

A

systolic BP - diastolic BP

30
Q

formula to find mean BP?

A

diastolic BP + (1/3 x pulse pressure)

31
Q

what is BP determined by?

A
  • cardiac output

- total peripheral resistance (TPR)

32
Q

formula to find BP?

A

CO x TPR

33
Q

what is TPR determined by?

A
  • sympathetic tone: vascular alpha 1 + beta 2 adrenoreceptors
  • circulating hormones - Ang II + catecholamines
  • local hormones - NO, ETs, PGs + adenosine
34
Q

cardiac output is determined by HR and SV.

give further examples within these 2 points

A

HR- autonomic tone, catecholamines

SV- cardiac contractility, venous return

35
Q

the mean BP is closely regulated + kept within narrow physiological range.

give the 2 reasons why?

A
  • must = high enough to ensure adequate perfusion of organs + tissues
  • must not be so high that places undue strain on heart + risks damaging blood vessels
36
Q

homeostatic control involved 2 mechanisms

give the 2 mechanisms?

A
  • short-term control mechanism: via baroreceptors

- long-term control mechanisms: via kidneys

37
Q

short term control adjustments

A
  • happens in seconds
  • involves alterations in CO + TPR
  • mediated via autonomic nervous system influences on heart, arterioles + veins
38
Q

long term control adjustments

A
  • needs minutes to days

- involves renal mechanisms of normal salt + water balance —> adjustments in total blood vol

39
Q

short term BP control mechanism (parasympathetic output)

A
  • inc in BP
  • inc in firing of baroreceptors in carotid arteries + aorta
  • sensory neurones
  • medulla oblongata
  • inc in parasympathetic output
  • more ACh on muscarinic receptor
  • SA node
  • dec heart rate
  • dec CO
  • dec BP
40
Q

short term BP control mechanism

sympathetic output

A
  • inc in BP
  • less NE released
  • alpha receptor —> arteriolar smooth muscle —> vasodilation
  • dec peripheral resistance
  • beta receptor —> ventricular myocardium —> dec force of contraction. —> dec CO
  • dec BP
41
Q

what kind of mechanism is the short control BP control mechanism?

A

negative feedback

42
Q

long term BP control mechanism

kidneys

A
  • dec in extracellular fluid
  • dec in arterial BP
  • renin released
  • convertes angiotensinogen to angiotensin I
  • angiotensin I converted into angiotensin II
  • goes to adrenal cortex + arterioles
  • adrenal cortex rel aldosterone —> Na+ reabsorption by kidney
  • —> inc in vascular vol
  • arterioles vasoconstrict
  • —> inc in arterial BP
43
Q

long term BP control mechanism

hypothalamic neuron

A
  • hypothalamic osmoreceptors stimulate hypothalamic neurons
  • inc thirst
  • —> water intake
  • —> inc in plasma bol and plasma osmolarity
  • —> relieves inc in osmolarity
  • —> relieves dec in ECF vol + arterial blood pressure
  • stimulates left atrial volume receptors
  • stim hypothalamic neurones
  • inc in vasopressin
  • —> water permeability of DCT and PCT
  • —> inc in water reabsorption
  • dec in urine output
  • inc in plasma vol
44
Q

integrated BP control mechanism

A
  • inc in blood vol
  • —> inc BP
  • triggers compensation by cardiovascular system (FAST**) + compensation by kidneys (SLOW*)
  • ** —> vasodilation + dec CO —> dec BP to normal
    • —> excretion of fluid in urine dec blood vol
  • —> dec BP

PHA112 (37 decks)

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