special circulations Flashcards
name the different special circulation
cerebral coronary skeletal cutaneous pulmonary
how are the lungs adapted for pulmonary circulation
low pressure and low resistance (short, wide vessels with little smooth muscle) . must accept all the blood from the entire systemic circulation from heart. this obviously increases during exercise so need some leeway which is why functions at much lower pressure than heart also doesnt need to travel as far so can be lower pressure.
also large SA and short diffusion distance for more effective gaseous exchange
pressure in pulmonary artery and right ventricle vs in aorta and left ventricle
pulmonary artery = 15-30/4-12
right ventricle = 15-30/0-8
aorta = 100-140/60-90 - elastic recoil helps to maintain pressure in aorta
left ventricle = 100-140/1-10
what is the vasodilation perfusion ratio (V/Q ratio)
efficient oxygenation requires matching ventilation and aveoli perfusion - means direct blood away from the badly ventilated alveoli
what is hypoxic pulmonary constriction and what is the problem with this
alveolar hypoxia= vasocontrisction of pulmonary vessels. so perfusion matches ventilation
BUT chronic hypoxia can occur due to high altitude/emphysema which leads to a chronic increase in vasocontriction = pulmonary hypertension. results in back pressure on right heart which can cause right sided ventricular heart failure
influence of gravity on the lungs
sitting up = less perfusion to apical vessels because blood has to travel up higher against gravity to these vessels. this means they vasocontrict and hydrostatic pressure is higher
what is the effect of exercise on lungs
increased CO = increased arterial pressure leading to apical vessels being opened because more oxygenated blood able to reach them and more oxygen being taken up by lungs. this does mean transit time increases (how long RBC in vessel) BUT doesnt make a difference because a v efficient process.
when/how is tissue fluid formed in pulmonary system
if hydrostatic pressure in pulmonary system increases due to mitral valve stenosis or left ventricular failure then hydrostatic pressure increases meaning less interstitial fluid is moved back into the vessels at the venous end. leads to oedema
consequences of pulmonary oedema
imparts gas exchange.
this is also affected by posture. the oedema will form at base of lung when sitting up due to gravity and form throughout when laying down = much worse and cause severe breathlessness.
how to treat pulmonary oedema
treat underlying cause and relieve symptoms wit diuretics
what is special about the cerebral circulation
brain has a v high o2 demand so it must be secure- this is because neurones are v sensitive to hypoxia and interruption to this blood supply can result in stroke/ death
how is cerebral demand met
high capillary density (large SA and short diffusion distance)
high basal flow rate
high o2 extraction
how is a secure blood supply ensured
anastomoses between basilar and internal carotid arteries- this means that if one of them is blocked then it can still be supplied by the other
myogenic auto regulation
metbabolic factors control blood flow
brain stem regulates other circulations
how does brain stem regulate other circulations (cushings reflex)
rigid cranium protects brain but doesn’t allow volume expansion
if volume does increase this would impair cerebral blood flow
impaired blood flow to vasomotor control reigns of the brainstem increase sympathetic vasomotor activity which increase arterial BP by vasoconstriction to peripheries meaning cerebral flow is helped to be maintained
how do metabolic factors control blood flow **
areas with increased neuronal activity have increased blood flow. this is because increase in Po2, K+, adenosine all result in vasodilation therefore increasing blood flow. decrease in Po2 decreases blood flow. so if have more metabolites result in more blood flow.
