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Physiology > Regulation of Regional Circulation (B2: W3) > Flashcards

Regulation of Regional Circulation (B2: W3) Flashcards

1
Q

Despite their relatively small mass, a large portion of cardiac output goes to which two ogans?

A

Liver and Kidneys

Busy eliminating the waste that is coming from different tissues

Receive about 50% of total cariac output

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2
Q

Relative to their mass, which two organs are the most perfused?

A

Heart and Kidneys

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3
Q

Which organ has a high O2 consumption relative to the amount of cardiac ouptut it receives?

A

The heart

Receives less than 5% of cardiac ouput, but accounts for more than 10% of total O2 consumption

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4
Q

For which organs is autoregulation of blood flow most important?

A

Heart, brain, and kidneys

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5
Q

What are examples of situations in which we experience active hyperemia (increased blood flow duirng increased metabolic activity)?

A
  • During exercise
  • While thinking/reasoning/brainstorming - more blood flow goes to the brain
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6
Q

What is an example of a situation in which we experience reactive hyperemia (blood flow after occlusion is released)?

A

Weight lifting - muscles occlude blood vessels

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7
Q

What is the main response of the vascular system when sympathetic ANS activity is increased?

A

Vasoconstriction

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8
Q

Upon sympathetic stimulation, where does the vascular resistance increase the most?

A

Skin, muscle, and kidney

  • Slight increase in the brain
  • Vasodilation in the heart
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9
Q

What is the role of natriuretic peptides?

A

To control blood volume

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10
Q

Which vasoactive substances affect coronary circuation?

A

Adenosine and Potassium (K+)

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11
Q

What is the most important local vasodilator for cerebral circulation?

A

CO2

Cerebral circulation is controlled almost enteriely by local metabolic factors - sympathetic nerves play a minor role

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12
Q

What are the specialized functions of the brain?

A
  • Requires uninterrupted blood supply
  • Increase local perfusion to local activity
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13
Q

What are the functional adaptations of the brain?

A
  • High basal flow
  • Protects its own supply
  • Autoregulation
  • Sensitivity to CO2 and hypoxia
  • Local metabolic hyperemia (active hyperemia)
  • Blood brain barrier
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14
Q

How long can the brain last without continous blood flow?

A
  • Seconds of deprivation causes loss of consciousness
  • 4-5 minutes causes irreversible brain damage

Total blood flow to the brain fluctuates less than that of any other organ

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15
Q

The brain does not depend solely on the carotid arteries for flow. What are the structural adaptations for receiving constant blood flow?

A
  • Circle of Willis
  • Hight capillary density
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16
Q

What are the special challenges of the brian in terms of circulation?

A
  • Effects of gravity (postural hypotension)
  • Occupies a “rigid box”
    • Not much room for expansion
    • Affects circulation
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17
Q

What is hypercapnia, and does it affect autoregulation of blood flow to the brain?

A

Incrased concentration of carbon dioxide in the brain

  • Overrides autoregulation and causes vasodilation
  • Blood flow will increase
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18
Q

How could hyperventilation cause syncope?

A
  • During hyperventilation, CO2 decreases
  • Cerebral circulation decreases
  • Syncope can occur
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19
Q

What determines the distribution of blood flow in the brain?

A

Blood flow is costant

The pattern of blood flow changes in characteristic ways with certain forms of cerebral activity

Different activities can redistribute blood flow

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20
Q

What are the 3 factors that provide intrinsic control of cerebral blood flow?

A
  • Metabolic - increased activity increases flow
  • Autoregulatory
  • Chemical - increased CO2 increases flow
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21
Q

What is the cushing reflex and what occurs as a result?

A
  • A high intracranial pressure (300+mmHg) produces the Cushing reaction
    • Cardiovascular centers are stimulated
    • Both sympathetic and parasympathetic input to the cardiovasuclar system increase
  • Causes compression of the blood vessels
  • Blood flow decreases
  • Ischemia results
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22
Q

What compensatory mechanisms does the body use to try to fix the effects of the Cushing reflex?

A
  • Stimulates vasomotor center
  • Peripheral vasoconstriction
    • Sends more blood to the brain
  • Increased systemic arterial pressure
  • Restoration of cerebral blood flow
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23
Q

What is a potential problem that could result from the peripheral vasoconstriction involved in correcting the Cushing reflex?

A

High systemic pressure can lead to high pulmonary arterial pressure, leading to edema in the lung

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24
Q

Why does increased cranial pressure lead to bradycardia?

A

Due to compression-induced activation of the cardioinhbtory center

  • High blood pressure results in slow heart rate
  • Patient has edema in the brain cavity
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25
Q

What are the specialized functions of the heart?

A
  • Works 24 h/d
  • Demands high energy an O2 to perform all this work
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26
Q

What are the functional adaptations of the heart to meet these demands?

A
  • Coronary flow is regulated in large part through changes in coronary vascular resistance
  • Weak neural control (a1 vasoconstriction, ß2 vasodilation)
  • Metabolic intrinsic factors are most important (direct correlation between blood flow and work of the heart = active hyperemia)
  • Coronary reserve - room for increased blood flow
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27
Q

What are the most important local metabolites in the coronary circulation?

A
  • Hypoxia
  • Adneosine
  • Acidosis
  • Hyperkalemia (K)
  • Nitric Oxide
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28
Q

What are the structural adaptations of the heart that lead to high perfusion?

A
  • Every muscle fiber has at least one supplying capillary
  • Maximum diffusion distance about 10 µm
    • Good because muscle cells are long
    • Not sufficient for large hearts
29
Q

What is the disadvantage of coronary arteries as end arteries?

A

Sudden occlusion of one artery will cause ischemia or infarction

30
Q

What is there danger to the heart’s blood supply with cardiac hypertrophy?

A

The diameter of fibers increases, but many not be accompanied by increased vascularization

Enlarged hearts are more vulnerable to circulatory insufficiency

31
Q

What are the special challenges of the heart?

A
  • Reactive hyperemia - during diastole occurs with each beat, as coronary arteries are compressed during systole
  • Supply: demand imbalance during tachycardia
  • Coronary reserve and coronary steal - during exercise in disease states
32
Q

What is an example of reactive hyperemia in regular heart function?

A
  • Systole causes a high subendocardial pressure, occluding arteries and stopping flow
  • There is a spike in blood flow at the beginning of diastole
33
Q

Which area of the heart is most susceptible to ischemic injury?

A

Endocardium, where compression is the greatest

34
Q

What happens to coronary flow during tachycardia?

A

Coronary flow decreases

  • More frequent coronary compression
  • Shortened diastole
  • Not enough time for cornary arteries to fill
  • Increased oxygen demand
  • Risk of supply/demand imbalance
35
Q

What are the most important vasodilators for cornoary circulation?

A
  • Adenosine
  • Lactate
  • K
  • NO

Coronary circulation is controlled almost entirely by intrinsic factors

36
Q

What is the relationship between gender and coronary artery disease?

A

Over 75, the death rate CAD is equal for men and women

At younger ages, even below 50, women die more from MI than men

37
Q

What is generally the cause of ischemic heart disease in women and men?

A
  • Women tend to have major arteries that are clear of plaque, but the smaller coronary blood vessels cease to constrict and dilate properly
  • Men more often suffer from plaque buildup in the large arteries around the heart
38
Q

What are other names for coronary microvascular disease (MVD) that is more typical in women?

A
  • Cardiac syndrome X
  • Non-obstructive cornoary heart disease
  • Microvascular angina
  • Microvascular ischemia

Microvessels are affected, not the major ones

39
Q

What is the male pattern of heart disease?

A

Obstructive CAD is more prevalent in men

Females can still get it, but it is not as common

40
Q

What is the argument of exercise in patients with coronary MVD?

A

Exercise is helpful in treatment of these patients because it developes new capillaries

41
Q

What are the specialized functions of the skeletal muscle?

A
  • Contributes to maintenance of BP (significant amount of vascular tone at rest)
  • Oxygent/substrate delivered to exercising muscle
    • Blood flow can increase up to 20 fold in exercising muscle
42
Q

What are the two types/fibers of skeletal muscle?

A
  • Slow twitch - Red (type I)
    • High capillary density
    • High mitochondrial content
    • High myoglobin
    • Muscles with almost constant metabolic demands
  • Fast twitch - White (type II)
    • Sprinters
43
Q

Why does vasoconstriction dominate at rest?

A

Due to persistent sympathetic activation

Resting tone

44
Q

What are the two mechanisms for increasing blood flow during exercise?

A

Vasodilation increases by:

  1. Metabolic vasodilation and capillary recruitment
  2. The skeletal muscle pump
45
Q

During exercise, vasoconstrictor sympathetic nerve activity generally increases, even to exercising skeletal muscle.

How then can the increased oxygnen and nutritional demands of the exercising muscle be met?

A

Local metabolic vasodilation

Caused by ischemic metabolites: K, O2, adenosine, hyperosmolarity

46
Q

What ratio of capillaries is closed at rest, and how are more recruited during exercise?

A
  • At rest, 2/3 of capillaries are not open
  • Local factors are released during exercise, and more are recruited

Capillary recruitment shortens the distance for nutrients to travel and improves energy delivery and waste removal

47
Q

What is the influence of the skeletal muscle pump on circulation during exercise?

A
  • Rhythmic muscle contraction during exercise expels the venous bloo from the capacitance vessels back to the heart
  • This emptying of musscle veins lowers intramuscular venous pressure, and helps drive arterial blood into skeletal muscle
48
Q

What are the special challenges of the skeletal muscle during exercise in regards to blood flow

A
  • Increased metabolic deman increases mean blood flow - active hyperemia
  • Contraction of the skeletal muscle transiently inhbits its blood flow by mechanically compressing the blood vessels inside the muscle - reactive hyperemia
49
Q

What causes edema in exercising muscle?

A

Intravascular pressures are increased in exercising muscle, leading to increased capillary filtration

50
Q

What are the primary vasodilator substances in skeletal muscle?

A
  • Lactate
  • Adenosine
  • K
51
Q

When is sympathetic innervation dominant and when are local metabolic factors dominant in the control of skeletal muscle circulation?

A
  • Sympathetic nervous system is the primary regulator of blood flow at rest
  • Local metabolic mechanisms are dominant during exercise, when O2 demand is high
52
Q

What are the specialized functions of the skin?

A
  • Regulation of internal temperature (especially during exercise)
  • Protection/response to injury
53
Q

What is the control mechanism for cutaneous blood flow?

A

Extrinsic control, exclusively

Sympathetic fibers are linked to temperature

54
Q

Where are arteriovenous anastomoses located?

A

In apcial skin (plantar aspect of feet, palms, nose, lips)

55
Q

Where is blood flow mainly located on a cold day versus a hot day?

A

Cold day - mainly in the core

Hot day - increased flow to the skin so that heat can be lost

56
Q

What are the arteriovenousus anastomoses (AVAs) of the apical skin?

A

These small vessels bypass capillaries

  • Normally constricted by sympathetic activity
  • Dilate when core temperature rises - increase blood flow to skin
    • Dilation is due to removal of sympathetic tone
  • Don not participate in exchange
57
Q

What controls the arteriovenous anastomoses (AVAs)?

A

Hypothalamus

“Thermostat” in the body

58
Q

What are the structural adaptations of the skin for blood flow?

A
  • Extensive sympathetic innervation
  • Arteriovenous anastomoses
  • Large venous plexus (blood depot)
59
Q

When it is cold outside, is sympathetic tone to AVAs high or low?

A

High

Cold = vasoconstriction

60
Q

How is blood flow controlled in the apical skin?

A

AVAs (glomus bodies) are controlled by symapthetic activity

  • When it is cold - activity increases and vessels constrict
  • When activity is withdrawn, they relax and vasodilate
61
Q

How is blood flow controlled in nonapical skin?

A

Sympathetic activity

  • Normally symapthetic stimulation of the blood vessels causes vasoconstriction
  • Sympathetic stimulation of the sweat glands releases bradykinin, which causes vasodilation in nonapical skin
62
Q

If sympathetic activity constricts AVAs when it is cold, why do we have red noses when we go skiing?

A

Paradoxical cold vasodilation

  • Thought to be due to paralysis of sympathetic neurotransmission
  • Prevents skin damage during prolonged cold exposure
    • Still receiving oxygnen and nutrients
63
Q

How does temperature influence sympathetic activity?

A

Abient temperature evokes a weak spinal reflex

Anterior hypothalamus senses core temperature an controls brainstem neurons, which govern sympathetic neural dischange to skin

64
Q

What is the mechansim for increasing blood flow to the skin as the core temperature rises?

A
  • Withdrawal of sympatheic tone (in apical/acral skin)
  • Vasodilation due to bradykinin release from sweat gands
65
Q

What happens during hemorrhagic shock?

A
  • Severe hypotension
  • Skin vasoconstriction
    • Supports blood pressure
    • About 1 L of blood can be stored in the skin
    • Warm blanket rescue results in rapid death
  • Cold and pale appearance
66
Q

What happens to circulation to the skin during strenuous exercise in hot weather?

A
  • Mandates increased blood flow to working muscle and increased core temperature
  • Decreases peripheral resistance
  • Decreases plasma volume due to transcapillary filtraton (relative volume depletion)
  • Capacity of heart to maintain cardiac output may be exceeded, leading to hypotension and collapse
  • Heat stress, exhaustion, stroke
67
Q

What happens tp cutaneous flow upon mechanical damage, thermal injury, bug bites, etc?

A

Vasodilation (caused by histamine)

  • Swelling
  • Redness
  • Edema

(Triple response)

68
Q

What pathway is involved in the cutaneous flare response?

A

Axon reflex - driect reflex from skin to blood vessels

  • Cause for local vasodilation
    • Neurovascular response conducted through the C nociceptive nerve tibers
    • Releases vasodilators: substance P, bradykinin, ATP, and calcitonin gene related peptive (CGRP)
69
Q

How does diabetic neuropathey lead to microcirculatory problems?

A

By damaging the axon reflex

Physiology (29 decks)

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