Session 8- Special Circulations Flashcards
what blood supply is there to the lungs
bronchial circulation
-part of systemic circulation for metabolic needs
pulmonary circulation
- blood supply to alveolar
- required for gas exchange
what is cardiac output at rest
5 litres per min
what is the maximum cardiac output
20 -25 litres/min
what conditions does pulmonary circulation work at
low pressure and low resistance
pulmonary artery
- 15-30 mmHg systolic
- 4-12 mmHg diastolic
how is the low resistance in pulmonary circulation achieved
short wide vessels
lots of capillaries
arterioles have relatively little smooth muscle
what adaptations promote efficient gas exchange
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
what is (V/Q ratio)
ventilation - perfusion
for efficient oxygenation- they need to match ventilation of alveoli with perfusion of alveoli
what is optimal v/q ratio
0.8
maintaining this means diverting blood from alveoli which aren’t well ventilated- hypoxic pulmonary vasoconstriction
what ensures optimal ventilation/ perfusion ratio
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
how can chronuc hypoxic vasoconstriction cause right ventricular failure
chronic increase in vascular resistance- chronic pulmonary hypertension
high afterload on right ventricle- can lead to right ventricular heart failure
what is orthostasis
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
how does orthostasis affect hydrostatic pressure in the lungs
in the upright position there is greater hydrostatic pressure on vessels in the lower part of the lungs
how does exercise affect pulmonary blood flow
- increased cardiac output
- small increase in pulmonary arterial pressure
- open apical capillaries
- increased o2 uptake by lungs
- capillary transit time reduced
what prevents lung lymph
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
what causes pulmonary oedema
a rise in capillary pressure
- if left atrial pressure rises to 20-25 mmHg
- mitrial valve stenosis
- left ventricular failure
how does the cerebral circulation meet the high demand for o2
high capillary density high basal flow rate - x10 average for whole body high o2 extraction -35% above average
what are the effects of ischaemia of the brain
loss of consciousness after a few seconds of cerebral ischaemia
begin to get irreversible damage to neurones in 4 minutes
how is secure blood supply ensured to the brain structurally
anastomoses between basilar and internal carotid arteries
how is secure blood supply ensured to the brain functionally
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
what is myogenic autoregulation
increase in BP- vasoconstriction
decrease in BP- vasodilation
metabolic regulation of cerbreal blood supply
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
hypercapnia
increase in pco2 -
hypocapnia
decrease in pCo2
what are the effects of hyper ventilation
hypocapnia
cerebral vasoconstriction leading to dizziness or fainting
what is cushings reflex
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
what ensures good coronary circulation
high capillary density facilitates efficient o2 delivery
diffusion distance <9 micro metres
continuous production of NO by coronary endothelium maintains a high basal flow
what agents act as vasodilators
increase in potassium increase in osmolarity adenosine increase in pH adrenaline
what are arterovenous ansastomoses
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
what is raynauds
excessive vasoconstriction in response to cold
affects hands and feet
