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Cardiovascular > Physiology 9 > Flashcards

Physiology 9 Flashcards

1
Q

Where does coronary venous blood drain?

A

Drains via coronary sinus into the right atrium

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2
Q

When is oxygen demand of heart muscle increased?

A

During exercise etc

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3
Q

What is coronary heart disease?

A

Area of cardiac muscle deprived of blood supply due to blockage of coronary vessels

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4
Q

Special adaptations of coronary circulation? (3)

A
  • High Capillary Density (to meet O2 demand)
  • High Basal Blood Flow
  • High Oxygen Extraction (~75% compared to 25% whole body average) under resting conditions - means extra O2 cannot be supplied by increasing O2 extraction
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5
Q

Since extra O2 cannot be supplied by increasing O2 extraction in coronary circulation, how is O2 increased? What is this controlled by?

A
  • Increasing coronary blood flow

* Coronary blood flow controlled by intrinsic & extrinsic mechanisms

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6
Q

Intrinsic mechanisms controlling coronary blood flow? What is this process known as? Example of metabolite?

A
  • Decrease in PO2 causes vasodilation of coronary arterioles
  • Metabolic hyperaemia - matches flow to demand
  • Adenosine - potent vasodilator
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7
Q

What would cause a decrease in PO2 of cardiac muscle?

A

Muscle consuming more O2

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8
Q

Extrinsic mechanism of controlling coronary blood flow? What is the effect of this? Why? What is this called?

A
  • Coronary arterioles supplied by sympathetic vasoconstrictor nerves
  • Sympathetic stimulation of heart results in coronary vasodilation despite direct vasoconstrictor effect
  • Because over-ridden by metabolic hyperaemia as a result of increased HR and SV
  • FUNCTIONAL SYMPATHOLYSIS
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9
Q

What effect does adrenaline acting on B2 adrenoceptors have?

A

Vasodilation of coronary arteries

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10
Q

What are other examples of metabolites other than adenosine? (3) What is there effect?

A
  • K+, PCO2, H+

* Vasodilation

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11
Q

Describe coronary blood flow in LEFT coronary artery during systole? Diastole? What happens if diastole shortens i.e. in tachycardia? What are the symptoms of this?

A
  • Becomes almost 0 during systole due to constriction of coronary arteries
  • Most left coronary blood flow occurs during diastole
  • If diastole shortens, shortens period of coronary flow to left ventricle
  • Ischaemic-like chest pain
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12
Q

Describe coronary blood flow in RIGHT coronary artery during systole?

A

Right ventricular pressure not as high as LV pressure so coronary arteries will not be squeezed as tightly and coronary blood flow will be present furing both systole and diastole

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13
Q

When does peak left coronary flow occur? What does shortening diastole due to a very fast HR result in?

A
  • Peak left coronary flow occurs during diastole

* Shortening diastole results in decrease in coronary flow

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14
Q

When does most myocardial perfusion occur?

A

Diastole - when the subendocardial vessels from the left coronary artery are not compressed

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15
Q

What arteries supply the brain? (2) Why is the Circle of Willis an important feature of the brain?

A
  • Internal carotids and vertebral arteries
  • Grey matter VERY sensitive to hypoxia - consciousness lost after few seconds of ischaemia, irreversible cell damage within ~ 3 minutes
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16
Q

What are special adaptations of cerebral circulation? (2)

A
  • Circle of Willis

* Autoregulation of cerebral blood flow

17
Q

What arteries compose the Circle of Willis? What arise from circle of willis? What is advantageous about circle of Willis? Disadvantageous?

A
  • Basilar (formed from 2 vertebral arteries) and carotid arteries anastomose to form circle of willis
  • Major cerebral arteries
  • Cerebral perfusion maintained even if one carotid artery gets obstructed
  • Obstruction of a smaller branch of a main artery would deprive a region of the brain of its blood supply
18
Q

Stroke caused by? Main types of stroke? (2)

A
  • Stroke caused by interruption of blood supply to region of brain
  • Haemorrhagic stroke
  • Ischaemic stroke e.g. blood clot
19
Q

What is the purpose of autoregulaton of cerebral blood flow? Range? Explain effect? (2)

A
  • Prevents changes in cerebral blood flow if mean arterial blood pressure changes within a range
  • 60 - 160 mmHg
  • If MAP drops, resistance vessels dilate to maintain blood flow
  • If MAP rises, resistance vessels constrict to limit blood flow
20
Q

Does brain participate in baroreceptor reflex? Why?

A
  • No

* Do not want fluctuation in cerebral blood flow with every change in MAP

21
Q

Does sympathetic stimulation have an effect on cerebral blood flow? Rank methods of cerebral blood control in order of most effect to least effect (3)

A
  • Very little effect
  • Hypercapnia (most effect)
  • Autoregulation
  • Sympathetic nerve stimulation (least effect)
22
Q

When does autoregulation fail? (2) What happens if MAP drops below 50 mmHg? (3)

A
  • If MABP falls below 60 mmHg (cerebral blood flow falls)
  • If MAPBP rises above 160 mmHg (cerebral blood flow rises)
  • MABP below 50 mmHg results in confusion, fainting and brain damage
23
Q

What is other important regulation of cerebral blood flow other than autoregulation and sympathetic innervation? (2)

A
  • PCO2

* Regional hyperaemia

24
Q

What is the effect of PCO2 in regulation of cerebral blood flow? (2)
What common reaction does this explain?

A
  • Increased PCO2 causes cerebral vasodilation
  • Decreased PCO2 causes cerebral vasoconstriction
  • This explains why hyperventilation can lead to fainting
25
Q

What is regional hyperaemia? Mechanism?

A
  • Increase in blood flow to active parts of the brain

* Unknown - could be rise in [K+] as a result of K+ efflux from active neurones??

26
Q

What does the skull contain? (3) What is normal intracranial pressure (ICP)?

A
  • Brain (80%), blood (12%) and cerebrospinal fluid (CSF - 8%)
  • Normal ICP = 8 - 13 mmHg
27
Q

Equation for cerebral perfusion pressure (CPP)? What does increased ICP result in? What causes raised ICP? What can this lead to?

A
  • CPP = MAP - ICP
  • Increasing ICP decreases CCP and so cerebral blood flow
  • Head injury, brain tumour
  • Can lead to failure of autoregulation of cerebral blood flow
28
Q

What is blood brain barrier? What can cross blood brain barrier? What about glucose?

A
  • Very tight intracellular junctions in cerebral capillaries
  • O2 and CO2
  • Glucose crosses BBB by facilitated diffusion using specific carrier molecules
29
Q

What is BBB impermeable to? Why?

A
  • Hydrophilic substances like ions, catecholamines, proteins etc
  • Protects brain neurones from fluctuating levels of ions etc in blood
30
Q

What percentage of CO does pulmonary circulation recieve? How are metabolic needs of airways met?

A
  • Entire CO from right ventricle

* Metabolic needs of airways met by systemic bronchial circulation

31
Q

What is the value of pulmonary resistance? What is pulmonary blood pressure?

A
  • Pulmonary resistance only 10% of that of systemic circulation
  • Pulmonary artery BP = 20-25/6-12 mmHg
32
Q

Special adaptations of pulmonary circulation? What is the purpose of this?? (2)

A
  • Pulmonary capillary pressure low (8-11 mmHg) compared to systemic pressure (17-25 mmHg)
  • Absorptive forces exceed filtration forces
  • Hypoxia causes vasoconstriction of pulmonary arterioles - COMPLETE OPPOSITE effect of hypoxia on systemic arterioles

WHY???

  • Absorptive forces - protects against pulmonary oedema
  • Vasoconstriction to hypoxia - to divert blood from poorly ventilated areas of the lung
33
Q

What mass of body is skeletal muscle? How does skeletal muscle affect blood pressure? Why is resting blood flow low?

A
  • 40%
  • Resistance of skeletal muscle vascular bed has large impact on BP
  • Low because of sympathetic vasoconstrictor tone
34
Q

Why is resting blood flow in skeletal muscle increased during exercise?

A

Metabolic hyperaemia overcomes sympathetic vasoconstrictor activity

35
Q

What is the skeletal muscle pump? What allows blood to move towards the heart? What are the benefits of the skeletal muscle pump?

A
  • Large veins in limbs lie between skeletal muscles and contraction aids venous return
  • One-way venous valves allow blood to move towards the heart
  • Skeletal muscle pump reduces postural hypotension and fainting
36
Q

What happens if venous valves become incompetent?

A

Blood pools in lower limbs causing varicose veins

37
Q

Do varicose veins reduce CO? Why?

A
  • No

* It is a chronic process so there is a compensatory increase in blood volume e.g. RAAS

Cardiovascular (28 decks)

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