Vascular system and special circulations Flashcards
how do arteries carry blood?
at high pressure
why are arteries thick walled?
a thick smooth muscle layer will allow artery to withstand high systemic pressure
why do arteries contain elastin?
elastin for elasticity - must have elastic properly - ability to recoil
has elastin - allows vessel to expand temporarily to hold blood pumped out during systole and must rebound again in diastole
why do arteries contain collagen?
collagen for strength
what are arterioles?
smaller arteries
properties of arterioles?
high resistance
less compliant than larger arteries
control flow of blood into capillaries
what is blood flow controlled by?
controlled by local factors:
autoregulation and sympathetic vasoconstriction
describe properties of capillaries:
flattened endothelium - high permeability
allow gases, nutrients and electrolytes to be exchanged
large network
connects arterioles to venules
properties of veins?
low pressure flow so wall is thin
rich sympathetic innervation - so in sympathetic vasoconstriction - blood from veins supply a large portion of venous return
where do veins carry blood?
carry blood back to heart
circle of willis?
provides important redundancy
provides lots of different roots for blood into brain - so if one is blocked, no problem
brain has a high?
metabolic consumption
what is the myogenic theory?
increased BP –> stretch of vascular smooth muscle –> reflex vasoconstriction –> No increase in CBF
what is the metabolic theory?
increased BP –> increased CBF –> washes away local vasodilations metabolites such as CO2, NO, H+, K+, adenosine etc –> leads to vasoconstriction –> blood flow stabilisation –> cerebral vessels are especially sensitive to CO2
when there is light input via retina - what happens?
blood flow increase to visual cortex (increased metabolic activity - vasodilation)
potential mediators of CBF?
K+
Adenosine
Nitric oxide
how does K+ mediate cerebral blood flow?
increased extracellular potassium due to hypoxia cause vasodilation
how does adenosine mediate cbf?
released when there is increased activity and also during hypoxia
how does nitric oxide act as a mediator for CBF?
from vascular endothelium - vasodilation (release may be stimulated by low pH or hypoxia)
cushing’s reflex caused by?
by intracranial hypertension
what happens during the cushing’s reflex?
brain is enclosed in a rigid structure - a rise in ICP will compress vessels
leads to CNS ischaemia
systemic vasoconstriction occurs - BP is elevated because of total peripheral resistance (TPR) but HR is low (no effect on actual rate of firing of the heart)
increased BP leads to increased perfusion - CBF is maintained
vicious cycle as the pressure keeps on increasing
basically, cushing’s reflex is…
where the patient has high BP with low HR
where can the heart get energy from?
from a variety sources: glucose, fatty acid, amino acid and ketones
describe the innervation of coronary vessels:
they have sympathetic innervation - alpha-1 and beta-1 adrenoreceptors
noradrenalin released when in sympathetic mode typically causes vessel dilation at capillary level and vasoconstriction in large vessels
extrinsic factors influencing the splanchnic circulation:
general hemodynamic conditions of the cv system
autonomic nervous system
circulating neurohumoral agents
intrinsic factors influencing the splanchnic circulation:
special properties of the vasculature
local metabolites
intrinsic innervation
paracrine substances
local hormones
what does the existence of a multiplicity of regulatory mechanisms provide?
it provides overlapping controls and restricts radical changes in tissue perfusion
short/fast splanchnic circulation regulation in fight/flight?
marked vasoconstriction of splanchnic arteries - divert blood to skeletal muscle and cardiac muscle
prolonged splanchnic circulation regulation?
e.g. shock/haemorrhage
prolonged vasoconstriction - hypoxic damage
GIT - damages microvilli - bacteria liberated
Liver - necrosis of hepatocytes - liver failure
Kindye - reduced GFR - necrossi of nephrons - renal failure
