Regulation of Regional Circulation (B2: W3) Flashcards Preview

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Flashcards in Regulation of Regional Circulation (B2: W3) Deck (69)

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

Liver and Kidneys

Busy eliminating the waste that is coming from different tissues

Receive about 50% of total cariac output


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

Heart and Kidneys


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

The heart

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


For which organs is autoregulation of blood flow most important?

Heart, brain, and kidneys


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

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


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

Weight lifting - muscles occlude blood vessels


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



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

Skin, muscle, and kidney

  • Slight increase in the brain
  • Vasodilation in the heart


What is the role of natriuretic peptides?

To control blood volume


Which vasoactive substances affect coronary circuation?

Adenosine and Potassium (K+)


What is the most important local vasodilator for cerebral circulation?


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


What are the specialized functions of the brain?

  • Requires uninterrupted blood supply
  • Increase local perfusion to local activity


What are the functional adaptations of the brain?

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


How long can the brain last without continous blood flow?

  • 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


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

  • Circle of Willis
  • Hight capillary density


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

  • Effects of gravity (postural hypotension)
  • Occupies a "rigid box"
    • Not much room for expansion
    • Affects circulation


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

Incrased concentration of carbon dioxide in the brain

  • Overrides autoregulation and causes vasodilation
  • Blood flow will increase


How could hyperventilation cause syncope?

  • During hyperventilation, CO2 decreases
  • Cerebral circulation decreases
  • Syncope can occur


What determines the distribution of blood flow in the brain?

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


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

  • Metabolic - increased activity increases flow
  • Autoregulatory
  • Chemical - increased CO2 increases flow


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

  • 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


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

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


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

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


Why does increased cranial pressure lead to bradycardia?

Due to compression-induced activation of the cardioinhbtory center

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


What are the specialized functions of the heart?

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


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

  • 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


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

  • Hypoxia
  • Adneosine
  • Acidosis
  • Hyperkalemia (K)
  • Nitric Oxide


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

  • 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


What is the disadvantage of coronary arteries as end arteries?

Sudden occlusion of one artery will cause ischemia or infarction


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

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

Enlarged hearts are more vulnerable to circulatory insufficiency


What are the special challenges of the heart?

  • 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


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

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


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

Endocardium, where compression is the greatest


What happens to coronary flow during tachycardia?

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


What are the most important vasodilators for cornoary circulation?

  • Adenosine
  • Lactate 
  • K
  • NO

Coronary circulation is controlled almost entirely by intrinsic factors


What is the relationship between gender and coronary artery disease?


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


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

  • 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


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

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

Microvessels are affected, not the major ones


What is the male pattern of heart disease?

Obstructive CAD is more prevalent in men

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


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

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


What are the specialized functions of the skeletal muscle?

  • 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


What are the two types/fibers of skeletal muscle?

  • 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


Why does vasoconstriction dominate at rest?

Due to persistent sympathetic activation

Resting tone


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

Vasodilation increases by:

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


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?

Local metabolic vasodilation

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


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

  • 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


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

  • 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


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

  • 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


What causes edema in exercising muscle?

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


What are the primary vasodilator substances in skeletal muscle?

  • Lactate
  • Adenosine
  • K


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

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


What are the specialized functions of the skin?

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


What is the control mechanism for cutaneous blood flow?

Extrinsic control, exclusively

Sympathetic fibers are linked to temperature


Where are arteriovenous anastomoses located?

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


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

Cold day - mainly in the core

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


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

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


What controls the arteriovenous anastomoses (AVAs)?


"Thermostat" in the body


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

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


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


Cold = vasoconstriction


How is blood flow controlled in the apical skin?

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


How is blood flow controlled in nonapical skin?

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


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

Paradoxical cold vasodilation

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


How does temperature influence sympathetic activity?

Abient temperature evokes a weak spinal reflex

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


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

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


What happens during hemorrhagic shock?

  • 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


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

  • 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


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

Vasodilation (caused by histamine)

  • Swelling
  • Redness
  • Edema

(Triple response)


What pathway is involved in the cutaneous flare response?

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)


How does diabetic neuropathey lead to microcirculatory problems?

By damaging the axon reflex