Special circulations

Question 1

What are the 2 circulations of the lungs?

Answer 1

Pulmonary circulation (gas exchange,low resistance/pressure)

Bronchial: lung’s metabolic need

Question 2

What are 2 factors that promote an efficient gas exchange?

Answer 2

Large SA (high density of capillaries), short diffusion distance

Question 3

What is the optimal V/Q ratio?

Answer 3

0.8:1

Question 4

What causes hypoxic pulmonary vasoconstriction and how does it ensure optimal VQ?

Answer 4

Small pulmonary arteries constrict with low O2 - (reduces K+ channels/sensitive to low O2) -> vasoconstriction -> more bloodflow to better ventilated alveoli

Question 5

What is chronic hypoxic vasoconstriction, what can it lead to and when can it occur?

Answer 5

Chronic increase in vascular resistance -> hypertension -> RHF

*lung disease or high altitudes

Question 6

Why does gravity have such a big effect on the vessels of the lungs?

Answer 6

Less muscular

Question 7

What are the 3 main layers of vessels in the lungs going from superior-inferior

Answer 7

Apex: collapse during diastole

Mid heart: continually open

Base: gravity pushes blood, vessels distended

Question 8

What happens to the pulmonary vessels during exercise?

Answer 8

CO must match pulmonary circulation

Increased CO -> increases pulmonary pressure -> opens capillaries at lung’s apex

Question 9

How low can capillary transit time drop to without compromising gas exchange?

Answer 9

0.3 seconds

Question 10

What is the normal pressure in pulmonary circulation, and what are the 2 main competing forces?

Answer 10

9-12 mmHg

Plasma oncotic and interstitial oncotic

Question 11

What happens to the pulmonary vessels when there’s increased pressure on L side of heart

Answer 11

Increases hydrostatic pressure

hydrostatic + interstitial oncotic&raquo_space; plasma oncotic
-> pulmonary edema

Question 12

What drug and non-drug help could you recommend to treat symptoms in a patient with pulmonary edema?

Answer 12

Sleep upright, less fluid in the apex

Diuretics

Question 13

How does cerebral circulation meet the high O2 demand

Answer 13

1. High capillary density: large SA, reduced diffusion distance.
2. High basal flow rate
3. High O2 extraction

Question 14

If the brain loses perfusion, how long will it take to become unconscious and have irreversible neurone damage?

Answer 14

Unconscious: 10 seconds

Irreversible damage: 4 minutes

Question 15

How is the brain ensure its blood supply structurally and functionally?

Answer 15

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

Question 16

What is the vascular response to hypercapnia and hypocapnia?

Answer 16

Hyper: vasodilation

Hypo: vasoconstriction

Question 17

What can panic hyperventilation lead to, how should it be managed?

Answer 17

Hypocapnia and cerebral vasoconstriction -> dizziness, fainting

*breathe into bag to increase CO2

Question 18

What is Cushing’s reflex and what is it indicative of? How does this result in the triad?

Answer 18

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)

Question 19

Name 2 molecules that can and can’t diffuse across the BBB

Answer 19

Can: lipid-soluble; O2, CO2

Can’t: lipid insoluble; K+ and catecholamines

Question 20

How do metabolically active areas of the brain ensure their own perfusion?

Answer 20

Release metabolic vasodilators: H+, K+ adenosine, CO2.

Question 21

Name 3 factors that assist coronary arteries in maintaining perfusion to the myocardiumWhy still then are the coronary arteries prone to atheromas?

Answer 21

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

Question 22

Generally, what determines how much perfusion skeletal muscle receives?

Answer 22

Capillary density depends on muscle type

Skeletal muscle has high vascular tone; easier vasodilation)

Question 23

How does skeletal muscle circulation change from being at rest to exercising?

Answer 23

Rest: 1/2 capillaries open and, increases during exercise

Question 24

What is the main role of cutaneous circulation?

Answer 24

Temperature regulation

*skin is main dissipating surface

Question 25

What specialized feature does the apical (acral) skin have in regulating heat loss? How are they regulated?

Answer 25

Arteriovenous anastomoses (AVAs) under sympathetic control:
I.e core temp raises - symp tone to AVAs decreases: vasodilation and more heat loss