Session 8- Special Circulations

Question 1

what blood supply is there to the lungs

Answer 1

bronchial circulation
-part of systemic circulation for metabolic needs

pulmonary circulation

• blood supply to alveolar
• required for gas exchange

Question 2

what is cardiac output at rest

Answer 2

5 litres per min

Question 3

what is the maximum cardiac output

Answer 3

20 -25 litres/min

Question 4

what conditions does pulmonary circulation work at

Answer 4

low pressure and low resistance

pulmonary artery

• 15-30 mmHg systolic
• 4-12 mmHg diastolic

Question 5

how is the low resistance in pulmonary circulation achieved

Answer 5

short wide vessels
lots of capillaries
arterioles have relatively little smooth muscle

Question 6

what adaptations promote efficient gas exchange

Answer 6

very high density of capillaries in alveolar wall
short diffusion distance
large surface area and short diffusion distance produce high 02 and CO2 transport capacity

Question 7

what is (V/Q ratio)

Answer 7

ventilation - perfusion

for efficient oxygenation- they need to match ventilation of alveoli with perfusion of alveoli

Question 8

what is optimal v/q ratio

Answer 8

0.8

maintaining this means diverting blood from alveoli which aren’t well ventilated- hypoxic pulmonary vasoconstriction

Question 9

what ensures optimal ventilation/ perfusion ratio

Answer 9

hypoxic pulmonary vasoconstriction

this is because in hypoxia partial pressure of oxygen drops, vascular smooth muscle contracts, this ensures perfusion matches ventilation as blood supply drops.

poorly ventilated alveoli are less well perfused
optimises gas exchange

Question 10

how can chronuc hypoxic vasoconstriction cause right ventricular failure

Answer 10

chronic increase in vascular resistance- chronic pulmonary hypertension

high afterload on right ventricle- can lead to right ventricular heart failure

Question 11

what is orthostasis

Answer 11

normal physiological response of the sympathetic system to counteract a fall in blood pressure when a person is laying down and assumes the upright position

Question 12

how does orthostasis affect hydrostatic pressure in the lungs

Answer 12

in the upright position there is greater hydrostatic pressure on vessels in the lower part of the lungs

Question 13

how does exercise affect pulmonary blood flow

Answer 13

• increased cardiac output
• small increase in pulmonary arterial pressure
• open apical capillaries
• increased o2 uptake by lungs
• capillary transit time reduced

Question 14

what prevents lung lymph

Answer 14

low capillary pressur e

oncotic pressure of tissue fluid in lungs > than in periphery
capillary hydrostatic pressure in lung < systemic capillaries
plasma oncotic pressure is the same

Question 15

what causes pulmonary oedema

Answer 15

a rise in capillary pressure

• if left atrial pressure rises to 20-25 mmHg
• mitrial valve stenosis
• left ventricular failure

Question 16

how does the cerebral circulation meet the high demand for o2

Answer 16

high capillary density
high basal flow rate
- x10 average for whole body
high o2 extraction
-35% above average

Question 17

what are the effects of ischaemia of the brain

Answer 17

loss of consciousness after a few seconds of cerebral ischaemia
begin to get irreversible damage to neurones in 4 minutes

Question 18

how is secure blood supply ensured to the brain structurally

Answer 18

anastomoses between basilar and internal carotid arteries

Question 19

how is secure blood supply ensured to the brain functionally

Answer 19

myogenic autoregulation maintains perfusion during hypotension- cerebral arteries dilate whke the rest of the body vasocontricts in hypotension

metabolic autoregulation- if there is high metabolic activity therefore high c02 then the cerebral arteries vasodilate to allow more blood flow

Question 20

what is myogenic autoregulation

Answer 20

increase in BP- vasoconstriction

decrease in BP- vasodilation

Question 21

metabolic regulation of cerbreal blood supply

Answer 21

cerebral vessels very sensitive to changes in arterial Pco2

if neurones are very active you get more co2 so vasodilataion occurs to meet metabolic demands vice versa

Question 22

hypercapnia

Answer 22

increase in pco2 -

Question 23

hypocapnia

Answer 23

decrease in pCo2

Question 24

what are the effects of hyper ventilation

Answer 24

hypocapnia

cerebral vasoconstriction leading to dizziness or fainting

Question 25

what is cushings reflex

Answer 25

increases in intracranial pressure impair cerebral blood flow
-cerebral tumour or haemorrhage

impaired blood flow to vasomotor control regions of the brainstem increase sympathetic vasomotor activity

• increases arterial BP
• Helps maintain cerebral blood flow
• increased BP causes relex bradycardia
• bradycardia and acute hypertension- hallmark of space occupying lesion

Question 26

what ensures good coronary circulation

Answer 26

high capillary density facilitates efficient o2 delivery
diffusion distance <9 micro metres
continuous production of NO by coronary endothelium maintains a high basal flow

Question 27

what agents act as vasodilators

Answer 27

increase in potassium
increase in osmolarity
adenosine
increase in pH 
adrenaline

Question 28

what are arterovenous ansastomoses

Answer 28

speacilised structures in apical skin

in cold temp they decrease blood supply to apical skin

reduced vasomotor drive to AVA’s allows them to dilate- diverts blood to veins near surface

Question 29

what is raynauds

Answer 29

excessive vasoconstriction in response to cold

affects hands and feet