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1020: Physiology FM1020 (E) > P: Regional circulations > Flashcards

P: Regional circulations Flashcards

1
Q

What increases O2 delivery to myocardial cell?

A

Increasing coronary blood flow –> supply is flow limited

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2
Q

Increase in cardiac activity triggers a corresponding increase in ___

A

coronary blood flow

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3
Q
  • Driving force is provided by ____.
  • Rate of blood flow determined by ____.
A
  • aortic pressure
  • constriction/dilation of resistance vessels
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4
Q

____ regulation is the primary controller of resistance of coronary vessels

A

Metabolic

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5
Q
  • Inadequate ____ blood flow, decreased ____ and/or ____ metabolic activity will trigger active hyperemia.
  • ____ and ____ are mediators of active hyperemia
  • Reduction in [ATP]i results in opening of ____ channels and a ___ –> relaxation of coronary SM
A
  • coronary, arterial O2 content, increased
  • Adenosine and nitric oxide (NO)
  • K ATP channels, hyperpolarisation
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6
Q

What are the direct effects of stimulation of autonomic nerves on coronary blood flow?

A
  • Direct effects on blood vessels themselves
  • Activation of sympathetic nerves: triggers vasoconstriction via alpha-adrenergic receptors on coronary VSM, other coronary vessels express beta-adrenergic receptors (dilation)
  • Vagal nerve stimulation slightly dilates coronary resistance vessels
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7
Q

What are the indirect effects of stimulation of autonomic nerves on coronary blood flow?

A
  • Indirect effects result from changes in coronary blood flow caused by changes in the activity of cardiac muscle
  • SN activity increases contractility and tachycardia of cardiac muscle –> indirect vasodilation in coronary circulation (increased cardiac activity –> metabolic vasodilatory metabolites –> increase coronary blood flow)
  • Vagal activity –> indirect vasoconstriction
  • Illustrates primacy of metabolic regulation in coronary circulation
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8
Q

Extravascular compression: contraction of LV slows, halts and temporarily reverses ____.

A

left arterial blood flow

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9
Q

Blood flow of skeletal muscle is regulated by a combination of ___ and ___ factors.
- At rest: ___
- Exercise: ___

A

Combination of neural and intrinsic factors.
- At rest: neural regulation
- Exercise: local factors

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10
Q

Resting skeletal muscle: tonic SN activity maintains a degree of ___. Constant ___ release and binding to ____ receptors of VSM in skeletal muscle blood vessels.

A
  • vasoconstriction
  • noradrenaline
  • alpha1 adrenergic
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11
Q
  • Noradrenaline binds ___ and ___ receptors, little affinity for ___ receptors
  • Noradrenaline exclusively triggers ____
A
  • alpha and beta1 adrenergic, beta2
  • vasoconstriction
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12
Q
  • SN activity to skeletal muscle is modulated by ___
  • Resistance in skeletal muscle blood vessels contributes a large part of ___
A
  • baroreceptor reflex
  • total peripheral resistance
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13
Q
  • Carotid artery occlusion reduces ____ –> increased ___ activity immediately reduces muscle blood flow + ___ in MAP
  • Release of carotid artery increases ____ –> vasodilation caused by reduced ___ activity greatly increases muscle blood flow + ___ in MAP
A
  • baroreceptor firing, SN, increase
  • baroreceptor firing, SN, reduction
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14
Q

What are the vasodilatory metabolites that rapidly increase blood flow in active muscle?

A
  • Adenosine
  • K+
  • CO2
  • lactic acid
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15
Q

Unopposed increased ____ in inactive muscles diverts blood flow to ___ muscles

A

vasoconstriction, active

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16
Q
  • Beginning of exercise, adrenaline (released from ___) has higher affinity for ___ and ___ receptors –> low concentrations of circulating adrenaline preferentially bind ___ receptors —> triggers ___ and ___ blood flow to skeletal muscle
  • High concentration of adrenaline: ____ receptors effects predominate –> triggers ____
A
  • adrenal medulla, Beta1 and Beta2, Beta2, vasodilation, increased
  • alpha1 adrenergic, vasoconstriction
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17
Q

ACh can trigger ___ release from endothelial cells (potent ___): ACh activates ___

A

NO, vasodilator, endothelial nitric oxide synthase (eNOS)

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18
Q

Early stages of exercise:
1. ACh spillover from NMJ may diffuse to local blood vessels, promoting ____ production –> VSM ___ and further ____
2. Metabolites in actively contracting muscle induce ___ in microcirculation promoting a ____ with upstream feed arteries –> resultant increase in blood flow elevates ____, release of ____ and further ____

A
  1. endothelial nitric oxide (NO), relaxation, vasodilation
  2. dilation, pressure gradient (ΔP), sheer stress, endothelial-derived NO, vasodilation
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19
Q

During exercise:
- Overall increase in ____ activity, but vasoconstrictor activity in contracting muscles is ___ –> functional ____ (increase activity of a tissue blocks SN activity in the active tissue). ___ may inhibit noradrenaline release from varicosities and also directly opposes ____ of VSM
- Skeletal muscle fibres also contain ____ and contraction increases ____ release –> promote vasodilation locally

A
  • sympathetic, blunted, sympatholysis, NO, alpha2-mediated constriction
  • neuronal NOS (nNOS) , NO
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20
Q

What is the technique for measuring limb blood flow called? Explain how it works.

A
  • Venous Occlusion Plethysmography (VOP)
  • Venous return from forearm is briefly interrupted by inflating a cuff placed around the upper arm
  • Hand circulation = completely occluded with a wrist cuff inflated to > systolic pressure
  • Arterial inflow is unaltered –> linear increase in forearm volume overtime (changes in arm circumference + forearm volume measured by a stain-gauge plethysmograph)
  • VOP provides a measure of arterial blood flow to that part of the forearm enclosed by 2 cuffs
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21
Q

What’s the main purpose of skin circulation?

A

Regulation of body temperature

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22
Q

What regulates cutaneous circulation and what do vessels express?

A

SN activity –> vessels express mostly alpha1 adrenergic receptors (AV anastomoses contract when SN are stimulated, no intrinsic regulation)

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23
Q

What is blushing/blanching caused by?

A

Blushing: inhibition of SN –> vasodilation of arterioles and AV anastomoses –> increased blood flow to skin in face
Blanching: activation of SN –> vasoconstriction –> decreased blood flow to skin in face

24
Q

What happens to skin colour following deflation of cuff on arm?

A
  • Inflation occludes inflow of blood into limb
  • Deflation –> increased blood flow caused by vasodilatory metabolites –> skin becomes red below point of occlusion (reactive hyperaemia = increased blood flow following ischaemia)
25
Q

Explain what happens when a region of the body is exposed to cold initially + after sustained exposure and why

A

Initially:
- Temperature receptors signal to temperature regulating centre of hypothalamus –> stimulates SN activity of skin –> vasoconstriction of resistance/capacitance vessels at that region (local axon reflex) and at other extremities
- Diverts blood from skin at extremities preventing it from being cooled by external cold

Sustained exposure to cold:
- Localized cold vasodilation
- Warm blood flows in skin –> colour becomes flushed (reddening of cheeks)

If coldness persists further: vasoconstriction and vasodilation alternate (local axon reflexes)

26
Q

Explain what happens when a region of the body is exposed to heat and why

A
  • Heat receptors trigger hypothalamus to inhibit SN activity
  • Vasodilation at affected region (local axon reflexes) and at other regions of the body
  • Increases flow of warm blood to sub-epidermal circulation –> cooled by proximity to external environment and by perspiration
27
Q

What stimulates sweat production during exercise/in response to heat?

A
  • Cholinergic sympathetic nerves innervate sweat glands (parasympathetic nerves don’t innervate cutaneous blood vessels)
28
Q

Sweat production causes an increases in ____, a potent vasodilator

A

Bradykinin

29
Q

Bradykinin stimulates formation of ___ –> promotes vasodilation

A

Nitric oxide (NO)

30
Q

Exercise causes an overall increase in ____:
1. Initial ____, diversion of blood to ____
2. ___ nerves then promote perspiration/vasodilation as a mechanism to ____

A

sympathetic outflow:
1. vasoconstriction, active muscles
2. Cholinergic sympathetic , lose heat

31
Q

Local axon reflexes:
- Sensory nerves activated by ___ and ___ receptors can release neurotransmitters locally
- These act to promote local ___ (skin ___), localised ___ production and pain

A
  • Pain and temperature
  • pain and heat
  • vasodilation (skin reddening), sweat
32
Q

Close proximity of major arteries and veins allows ____; cooled venous blood returning from hand is warmed by arterial blood

A

countercurrent heat exchange

33
Q

Explain blood supply to brain

A
  • Internal carotid and vertebral arteries deliver blood (via basilar artery) to circle of Willis which loops around the brainstem
  • Redundancy in blood: if blockage of a section of the circle –> blood flow from other vessels preserve cerebral perfusion
34
Q

What’s the equation of central perfusion pressure (CPP)? What does elevated intracranial pressure (ICP) cause?

A
  • CPP = MAP - ICP
  • Normally, ICP > CCP
  • Elevated ICP (>20 mmHg) reduces CPP –> compression of venous vessels + reduction of blood flow
35
Q

What is the driving force for brain perfusion?

A

MAP

36
Q

Cerebral circulation exhibits autoregulation (myogenic) between ___ and ___ mmHg

A

60 and 160

37
Q

What happens to cerebral circulation below 60 mmHg and above 160 mmHg?

A
  • Below 60 mmHg: fainting (syncope) as CPP falls and blood flow is reduced
  • Above 160 mmHg: damage to blood-brain barrier –> cerebral oedema
38
Q

___ factors are paramount in regulating cerebral blood flow

A

Local

39
Q

Why does maximum SN activity only increase cerebral resistance by ~20%?

A
  • Metabolic regulation exerts functional sympatholysis (opposition to the stimulation of the SN system)
  • Baroreceptor reflex has little effect on cerebral blood flow
40
Q

____, ____ and K+ regulate blood flow by ____

A

Vasodilatory metabolites, adenosine, active hyperemia

41
Q

What is the most important vasodilatory factor in cerebral blood flow?

A
  • Increased production of CO2 by neuronal cells –> increases blood flow
  • CO2 diffuses across blood-brain barrier –> reduces pH of cerebrospinal fluid (CSF) –> vasodilation of cerebral arterioles
  • Reduction in CPP also reduces washout of CO2 from brain
42
Q
  • Increased PCO2 (hypercapnia) triggers ___
  • Decreased PCO2 (hyocapnia) triggers ___
A
  • vasodilation
  • vasoconstriction
43
Q

Explain effect of reduction in O2 on cerebral blood flow

A
  • Initial reduction = not a big effect on haemoglobin oxygen saturation
  • PO2 < 50 mmHg = strong vasodilation to maintain O2 supply to brain (rapid activation of SN)
44
Q

Explain Cushing reflex

A
  • CPP = MAP - ICP
  • ICP > MAP –> severe cerebral ischaemia
  • Increase in ICP –> shift in brain tissue within skull (herniation)
  • Cushing reflex activates SN system –> peripheral vasoconstriction + increase in CO –> increases MAP –> stimulates baroreceptors in carotid bodies –> slows HR drastically (bradycardia)
45
Q

What is Cushing’s triad?

A

Hypertension + bradycardia + irregular respirations

46
Q

In vili there is ___ of O2 directly from arterioles to venules

A

Countercurrent exchange

47
Q

What can low intestinal blood flow cause?

A
  • Blood shunted directly from arterioles to venules at base of microvilli
  • Reduces O2 supply to mucosal cells at the tip
  • Can result in necrosis of villi –> intestinal bleeding
48
Q

Explain regulation of intestinal blood flow

A
  • SN and intrinsic mechanisms
  • Activation of SN –> vasoconstriction of mesenteric arterioles and capacitance vessels via alpha adrenergic receptors –> reduces blood flow to GI tract (especially to villi)
  • Occurs especially during exercise (blood diverted to active muscles and heartt)
49
Q

What are the factors that trigger vasodilation upon ingestion?

A
  • Functional hyperaemia –> increase in blood flow
  • Digestive hormones (gastrin) = vasodilatory properties
  • Absorption of biomolecules in GI increases metabolic activity of tissue –> adenosine levels increase (vasodilatory properties)
  • Breakdown of glucose and fatty acids causes vasodilation
  • NO is produced locally to enhance vasodilation
  • Parasympathetic nerves only innervate intestinal smooth muscle and glands to increase motility and secretions (may indirectly increase blood flow by stimulating metabolic activity + by producing bradykinin and NO)
50
Q
  • GIT-derived nutrients in portal vein pass from capillaries into liver cells for ___ or reentry into general circulation
  • Liver also acts to clear the blood of ___ and ___
  • ___ in hepatic artery is required for this metabolic activity
  • Another important function of the liver is ____ of blood
A
  • Processing/storage
  • Drugs and toxins
  • O2
  • reservoir
51
Q

What allows rapid exchange in hepatic circulation?

A

Leaky capillaries

52
Q
  • Capillaries very ___, lymph fluid has [protein] of 6 g/dl –> oncotic pressure of plasma is ___ in liver
  • Hydrostatic pressure in sinusoidal capillaries profoundly affects ___, ____ and ____
  • Therefore, ___ is tightly controlled and rates of blood flow in portal venules and in hepatic arterioles are reciprocally regulated
A
  • Porous, low
  • Filtration, lymph production and substance exchange
  • Hepatic pressure
53
Q

Explain ascites process

A
  • Heart failure –> increase in central venous pressure (right atrial pressure) –> increases in hepatic venous and hepatic sinusoidal pressures –> increased hydrostatic pressure and hepatic oedema –> accumulation of fluid in abdominal cavity (ascites)
  • Also occurs as a consequence of liver cirrhosis which causes portal hypertension
54
Q

Cerebral vasoconstriction caused by hyperventilation (decrease in ___) results in ___

A

PCO2, dizziness

55
Q
  • Another important function of the liver is as a ___
  • SNS-induced ___ of capacitance venules in the liver can rapidly return half of liver blood to ___ and back into ___ —> occurs during ___ or ___
A
  • reservoir of blood
  • constriction, the heart, arterial circulation, exercise, sever blood loos

1020: Physiology FM1020 (E) (12 decks)

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