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Cardiovascular: physiology > special circulations > Flashcards

special circulations Flashcards

1
Q

where do the right and left coronary arteries arise from?

A

the base of the aorta

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2
Q

where does most coronary venous blood drain via?

A

the coronary sinus into the right atrium

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3
Q

Oxygen demand of cardiac muscle is ___ especially during ___. Coronary circulation requires ______

A

Oxygen demand of cardiac muscle is high especially during exercise

Coronary circulation requires special adaptations

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4
Q

what are three special adaptations of the coronary circulation?

A

High Capillary Density

High Basal Blood Flow

High Oxygen Extraction (~75% compared to 25% whole body average) under resting conditions

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5
Q

what does the high oxygen extraction of the coronary arteires under resting conditions mean when further O2 is required?

A

This means extra O2 (when required) cannot be supplied by increasing O2 extraction

Can only be supplied by increasing coronary blood flow

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6
Q

what is the only way of increased the supply of oxygen to the coronary circulation?

A

Can only be supplied by increasing coronary blood flow

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7
Q

what are the two types of mechanisms for coronary blood flow control?

A

intrinsic and extrinsic

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8
Q

what three intrinsic mechanisms are there to increase coronary blood flow?

A
  1. decrease Po2 causes vasodilatation of the coronary arterioles
  2. Metabolic hyperaemia matches flow to demand decreased PO2
  3. Adenosine (from ATP) is a potent vasodilator
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9
Q

what mechanisms are involved in the extrinsic control of coronary blood flow?

A
  • the coronary arterioles are supplied by sympathetic nerves (causing vasoconstriction)
  • also circulating adrenaline activates B2 adrenergic receptors found on cardiac smooth muscle arterioels causing vasodilatation
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10
Q

what intrinsic mechanism over-rides the sympathetic innervation to the coronary arterioles? and how is this done?

A

metabolic hyperaemia over-rides sympathetic as a result of increased hr and SV.

The effect of sympathetic innervation on the heart causes:

  • Decreased local PO2
  • Increased local PCO2
  • Increased local [H+] (decreased pH)
  • Increased extra-cellular [K+]
  • Increased osmolality of ECF
  • Adenosine release (from ATP)
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11
Q

so
So sympathetic stimulation of the heart results in coronary vasodilatation/constriction despite direct vasoconstrictor effect (functional sympatholysis)

A

vasodilatation

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12
Q

what are the receptors for sympathetic neurotransmitter signals in the coronry vascular SM? and what is the neurotransmitter?

A

noradrenaline acting on alpha 1

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13
Q

what does adrenaline act on in coronary SMc?

A

beta receptors

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14
Q

where are the adrenaline beta receptors found in the body?

A

in the skeletal and cardiac smooth muscle arterioles

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15
Q

where are the alpha adrenaline receptors found in the body? and what does this cause>

A

found in the gut, skin, and kidney arterioles and cause vasoconstriction

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16
Q

look at the table in khogali’s special circulations lecture

A

x

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17
Q

when does most of the left coronary artery filling occur?

A

during diastole when the subendocardial vessels from the left coronary artery are not compressed

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18
Q

what causes a short diastole period?

A

a very fast heart rate - so get reduced coronary flow

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19
Q

which main arteries supply the brain?

A

the internal carotids and the vertebral arteries

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20
Q

why does the brain need a secure supply of oxygen?

A

Grey matter VERY sensitive to hypoxia - consciousness lost after few seconds of ischaemia, irreversible cell damage within ~ 3 minutes

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21
Q

what forms the basilar arteries?

A

two vertebral arteries and the carotid arteries

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22
Q

what do the basilar arteries do to improve circulation?

A

they anastamose to form the circle of Willis

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23
Q

the circle of willis gives rise to?

A

major cerebral arteries

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24
Q

what does anastamoses ensure?q

A

Cerebral perfusion should be maintained even if one carotid artery gets obstructed.

25
Q

what could happen if a smaller branch in the cerebral circulation is occluded?

A

obstruction of a smaller branch of a main artery would deprive a region of the brain of its blood supply

26
Q

what are the two types of stroke?

A

haemorrhagic and ischamic

27
Q

what happens in a haemorrhaguc stroke?

A

blood leaks out of artery wall which is damaged

28
Q

what happens in ischaemic stroke?

A

blood clot forms on atheroma on artery wall or comes from another part of the body and gets stuck

29
Q

what is the main special adaptation of the cerebral circulation to ensure secure blood flow?

A

autoregulation

30
Q

whihc two mechanisms that are noramlly important in maintaining blood pressure have little effect on the brain?

A

Direct sympathetic stimulation has very little effect in overall cerebral blood flow

Participation of the brain in baroreceptor reflexes is negligible,

31
Q

what happens in the cerebral circulation in response to a rise in MABP?

A

resistance vessels automatically constrict to limit blood flow

32
Q

what happens in the cerebral circulation in response to a fall in MABP?

A

resistance vessels automatically dilate to maintain blood flow

33
Q

what are the limits for autoregulation of cerebral blood flow?

A

Autoregulation fails if MABP falls below ~ 60mmHg (cerebral blood flow falls) or rise above ~ 160mmHg (cerebral blood flow rises)

34
Q

what does a MABP below 50 mmHg result in?

A

confusion, fainting, and brain damage if not quickly corrected

35
Q

what is the effect of increased PCO2 on cerebral circulation?

A

↓ Pco2 causes vasoconstriction, this is why hyperventilation could lead to fainting.

36
Q

what is regional hyperaemia in the brain?

A

Blood flow increases to active parts of the brain (regional hyperaemia). Mechanism unknown. May be due to rise in [K+]O as a result of K+ efflux from repetitively active neurones?

37
Q

what is the normal intracranial pressure?

A

8 - 13 mmHg

38
Q

how is the cerebral perfusion pressure calculated?

A

MAP- ICP

39
Q

what does increased ICP (due to head injury or brain tumour) do to CPP?

A

decreases CPP and cerebral blood flow

40
Q

what pathological processes can lead to failure of autoregulation of cerebral blood flow

A

Some conditions which increase ICP

41
Q

what is responsible for the blood brain barrier

A

cerebral capillaries have very tight intercellular junctions - THE BLOOD BRAIN BARRIER

42
Q

which two molecules are cerebral capillaries highly permeable to ?

A

oxygen and CO2

43
Q

how does glucose cross the BBB?

A

by facilitated diffusion using specific carrier molecules

Brain has obligatory requirement for glucose

44
Q

what is the BBB exceptionally impermeable to?

A

hydrophilic substances such as ions, catecholamines, proteins

45
Q

what is the protective function of the BBB by not letting hydrophilic substances contact neurones?

A

This helps protect brain neurones from fluctuating levels of ions etc in blood

46
Q

what is the normal range of pulmonary artery BP

A

20 - 25/ 6-12 mmHg

47
Q

the absorptive forces in the pulmonary arteries exceed the filtration forces because of the low pressure. What does this healp to protect against

A

pulmonary oedema

48
Q

what is the effect of hypoxia on the systemic arterioles

A

the arterioles dilate

49
Q

what is the effect of hypoxia on the pulmonary arterioles?

A

they vasoconstrict

50
Q

why do the pulmonary arterioles vasoconstrict during hypoxic conditions?

A

to help divert blood away from poorly ventilated areas of the lung.

51
Q

the resistance of skeltal muscle vascular bed has a large impact on….

A

blood pressure

52
Q

why is the resting blood flow low in skeletal muscle

A

because of the sympathetic vasoconstrictor tone

53
Q

what overcomes the sympathetic vasoconstrictor tone during exercise?

A

metabolic hyperaemia

54
Q

what does circulating adrenaline do to skeletal vascular smooth muscle?

A

causes vasodilatation through beta 2 adrenergic receptors

55
Q

what effect does adsrenaline have on the heart rate?

A

activates B1 adrenergic receptors in nodal and cyocyte cells in the heart causing increase in HR

56
Q

what does the skeletal muscle pump prevent?

A

hypotension and fainting as it aids venous return

57
Q

what causes varicose veins?

A

Blood pools in lower limb veins if venous valves become incompetent

58
Q

why do varicose veins not usually lead to a reduction of CO?

A

because things happen over time and through hormones and things - the CO is compensated for

Cardiovascular: physiology (11 decks)

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