Special circulations Flashcards
What are the 2 circulations of the lungs?
Pulmonary circulation (gas exchange,low resistance/pressure)
Bronchial: lung’s metabolic need
What are 2 factors that promote an efficient gas exchange?
Large SA (high density of capillaries), short diffusion distance
What is the optimal V/Q ratio?
0.8:1
What causes hypoxic pulmonary vasoconstriction and how does it ensure optimal VQ?
Small pulmonary arteries constrict with low O2 - (reduces K+ channels/sensitive to low O2) -> vasoconstriction -> more bloodflow to better ventilated alveoli
What is chronic hypoxic vasoconstriction, what can it lead to and when can it occur?
Chronic increase in vascular resistance -> hypertension -> RHF
*lung disease or high altitudes
Why does gravity have such a big effect on the vessels of the lungs?
Less muscular
What are the 3 main layers of vessels in the lungs going from superior-inferior
Apex: collapse during diastole
Mid heart: continually open
Base: gravity pushes blood, vessels distended
What happens to the pulmonary vessels during exercise?
CO must match pulmonary circulation
Increased CO -> increases pulmonary pressure -> opens capillaries at lung’s apex
How low can capillary transit time drop to without compromising gas exchange?
0.3 seconds
What is the normal pressure in pulmonary circulation, and what are the 2 main competing forces?
9-12 mmHg
Plasma oncotic and interstitial oncotic
What happens to the pulmonary vessels when there’s increased pressure on L side of heart
Increases hydrostatic pressure
hydrostatic + interstitial oncotic»_space; plasma oncotic
-> pulmonary edema
What drug and non-drug help could you recommend to treat symptoms in a patient with pulmonary edema?
Sleep upright, less fluid in the apex
Diuretics
How does cerebral circulation meet the high O2 demand
- High capillary density: large SA, reduced diffusion distance.
- High basal flow rate
- High O2 extraction
If the brain loses perfusion, how long will it take to become unconscious and have irreversible neurone damage?
Unconscious: 10 seconds
Irreversible damage: 4 minutes
How is the brain ensure its blood supply structurally and functionally?
Structurally: anastomoses
Functionally:
Brain stem - (+) sympathetic -> increases resistance to other pathways and HR
Myogenic autoregulation: intrinsic mechanism in vascular sm muscle to constrict when BP drops
What is the vascular response to hypercapnia and hypocapnia?
Hyper: vasodilation
Hypo: vasoconstriction
What can panic hyperventilation lead to, how should it be managed?
Hypocapnia and cerebral vasoconstriction -> dizziness, fainting
*breathe into bag to increase CO2
What is Cushing’s reflex and what is it indicative of? How does this result in the triad?
Increased ICP (i.e space-occupying lesion)
Low bloodflow -> brainstem -> sympathetic: (+) HR and BP
Baroreceptors (vagus) -> slow HR
Cushing’s Triad: Bradycardia, high BP and irregular ventilation (due to stimulatory and inhibitory effects of hypoxia and baroreceptors)
Name 2 molecules that can and can’t diffuse across the BBB
Can: lipid-soluble; O2, CO2
Can’t: lipid insoluble; K+ and catecholamines
How do metabolically active areas of the brain ensure their own perfusion?
Release metabolic vasodilators: H+, K+ adenosine, CO2.
Name 3 factors that assist coronary arteries in maintaining perfusion to the myocardiumWhy still then are the coronary arteries prone to atheromas?
High capillary density, small diffusion resistance, coronary endothelia secrete NO
But LACK collateral circulation: narrowed coronary artery (atherosclerosis, vasoconstriction due to stress or cold, obstruction) can quickly lead to angina and MI
Generally, what determines how much perfusion skeletal muscle receives?
Capillary density depends on muscle type
Skeletal muscle has high vascular tone; easier vasodilation)
How does skeletal muscle circulation change from being at rest to exercising?
Rest: 1/2 capillaries open and, increases during exercise
What is the main role of cutaneous circulation?
Temperature regulation
*skin is main dissipating surface
