special circulations Flashcards
special circulations
2 blood supplies to lungs
- bronchial circulation
provide 02 to areas of lungs that cant reach 02 (systemic)
- pulmonary circulation
blood supply to the alveoli
needed for gas exchange
pressure
- works with low pressure
blood flows form low - high pressure but pressure should never exceed right atrial pressure
systolic
diastolic
left side of heart
aorta has elastic recoil so can maintain pressure
features of pulmonary circulation
adaptions for gas exchange
- many alveoli
- short diffusion distance
- large surface area
ventilation perfusion ratio
V/Q ratio
- need to match ventilation with perfusion
- optimum = 0.8
- ventilation = diffusion of gases
- perfusion blood passing alveoli
if this ventilation/perfusion mismatch is occluded by thromus = VQ missmatch
hypoxic pulmonary circulation
- diverts blood away from poorly ventilated alveoli
- vasoconstriction of pulmonary vessels to move blood to better ventilated alveoli
- perfusion = ventiliation
- optimise gas exhange
BUT can cause hypertension of this is chronic
- opposite effect in systemic (hypoxic = vasodialation)
chronic hypoxia
cronic vasoconstriction
= increase resistance
=hypertension
=harder for right ventricle to pump blood out
= right ventricular heart failure
gravities influence on pulmonary vessels
capillaries at apex = pressure is lower
capillaries at level of the heart are patent
capillaries at base = increase in hydrostatic pressure
effect of exercise on pulmonary blood flow
- increase cardiac output
- increase in arterial pressure
- opens apical capillaries
- increase 02 uptake in lungs
- increase in blood flow = reduces capillary transit time
forming tissue fluid
- relies on starling forces
- hydrostatic pressure = push fluid out
- osmotic = fluid in
- pressure drops from artery to capillary
- increase venous pressure = increase capillary pressure
what leads to pulmonary odema
increase in venous/ arterial pressure = pressure in capillaries increase
why might pressure in capillaries increase
left atrial pressure rises to 20-25mmHg
- mitral valve stenosis (valve between left atria and ventricle = blood cant pass through = build up of pressure in atria = blood moves back to veins = increase in venous pressure)
- left ventricular failure = (volume at end of systole is greater = hard for blood to pass from left atria to ventricle = increase in atrial pressure = increase in venous pressure)
pulmonary odema
impares gas exchange
- odema more likley to be at the base of the lungs
- when patient lies down = even capillary pressure = more blood to heart
- treatment = diuretics
cerebral circulation
brain has high 02 demand = needs a strong supply of oxygen
how does cerebral circulation meet 02 demand
- high capillary density (large SA, reduced diffusion distance)
- high basal flow rate
- high 02 extraction
why is secure 02 important for brain
- neurones sensitive to hypoxia
- damage to neurones is irreversible
how is a secure blood supply to brain ensured
structurally
-anastomoses (connection) between basilar and internal carotid arteries
functionally
- myogenic autoregulation maintains perfusion during hypotension
- metabolic factors control blood flow
- brainstem regulates other circulations
myogenic autoregulation
maintains cerebral blood flow
metabolic regulation
cerebral vessels sensitive to P(co2)
- panic = hypocapnia + cerebral vasoconstriction = dizziness/fainting
what factors cause vasodialation in cerebral areas
high p(co2)
high K conc
high adenosine
low p(o2)
cushings reflex
in response to a space occuping region in the brain
- rigid cranium protects brain
- increases in intercranial pressure = impair cerebral blood flow
- impared blood flow increases sympathetic activity
- increase arterial BP = bradycardia (activating stretch receptors) and hypertension = red flag
coronary circulation
- must be able to deliver 02 at basal rate
- must meet increased demand
- coronary blood flow proportional to myocardial demand due to metabolic hyperaemia (vasodialation)
comparison between cardiac musccle and skeletal muscle circulation
