Control of blood flow Flashcards
how does vasoconstriction occur
SNS post-gnaglionic neurones release NA pn arteriolar SMC to stimulate A1-AR to activate Gq causing contraction of vessel, which inc arteriolar wall stiffness, reduces radius of lumen
how to trigger medullary cardiovascular centre
activation of dorsolateral medulla (pressor region) is responsible for vasoconstriction, cardiac acceleration and enhanced myocardial contractility. Caudal and ventromedially to region is a depressor region, which aims to reduce BP through direct spinal inhibition and inhibits pressor region
how is venous return increased during exercise
sympathetic venoconstriction, skeletal muscle pump and respiratory muscle pump
difference between arteries and veins
arteries are stiff and resist expansion, so there is a large arterial vol, increase arterial pressure so increase blood flow to veins
veins are compliant and allow expansion, so inc venous vol so no change in BP so no inc in blood flow to heart, theerefore store blood
what is transmural pressure
pressure difference across hollow organs e.g. if the pressure acting on a vessel is high, it dec the radius of vessel so inc pressure of blood inside
what is skeletal muscle pump
muscle contraction causes compression of veins and inc blood pressure and therefore inc rate of venous return. The more activity, the more contractions so the greater venous return
Respiratory muscle pump
inspiration causes dec intrapleural pressure causing dialation of blood vessels, so blood is pulled from systemic circulation then during expiration there is an inc in intrapleural pressure so blood vessels are squashed so blood pushed to the heart
why is pumonary circulation low resistance
the circulation has to pass the entire CO at low pressure to prevent pulmonary oedema and limits afterload on R. Ventricle. This can be altered by lung volume
why is perfusion greater at base of lungs
BP is higher at the base than apex, as due to the weight and gravity greater blood flow at the base, so on expiration the alveoli don’t expand so vessels are not compressed so less vascular resistance. On expiration the oppisate happens, which causes increase vascular resistance. When there is higher ventilation rate vessels in the apex are recruited to compensate and ensure there is less resitance so blood can flow w/o changing BP
how is pulmonary blood flow inc without altering blood pressure
inc pulmonary artery pressure causes decreased vascular resistance by recruitment and distention of pulmonary vessels
what is functional hyperaemia
inc release of lactate, pCO2, low pH, adensoine and K+ causes arteriolar vasodialation, therefore inc blood floq to skeletal muscle
what is poiseulle’s law
resistance= (8 x fluid viscosity x vessel length)/ (n x r4)
