Circulatory system and blood pressure Flashcards
components of the circulatory system
arteries: high pressure conduits
arterioles: control volume of blood entering capillaries
capillaries: site of fluid exchange
venules: collect blood from capillaries and interstitial fluid
veins: reservoir of blood
lymphatics: return excess fluid back to circulation from interstitium
layers of blood vessels
tunica externa (adventitia)
tunica media
tunica intima
layers of cells lining the GIT and respiratory tract to blood barrier
simple squamous epithelial cells
simple cuboidal epithelium cells (basement membrane)
simple squamous endothelial cells (blood vessels)
what cells secrete the basement of capillaries
simple squamous endothelial cells
where are continuous capillaries
where you don’t want strong contact between blood and tissue
where the blood can harm the tissue
e.g. blood brain barrier
what allows larger molecules to cross the endothelium of continuous capillary
pinocytotic vesicles
where are fenestrated capillaries
where perfusion is high but proteins need to remain in the blood
e.g. kidneys
where are sinusoid capillaries
where proteins are allowed to cross the membrane easily
e.g. liver
(have large fenestrations and discontinuous basement membrane)
what is the maximum length of capillaries
1 mm
formula for flow through capillaries (Q dot)
Q dot = arterial pressure - venous pressure / resistance
= pressure dif / resistance
(Ohm’s law)
Poiseuille - Hagen Formula for resistance
R = 8ηL / pi r^4
L = length
η = viscosity
r = radius (most important)
what is hydrostatic pressure in the veins dependant on
what is hydrostatic pressure in the arteries dependant on
veins: volume only because there is no resistance
when pressure is low, volume is low
arteries: volume and resistance
main site of resistance
what regulates them
arterioles
ANS, paracrine regulation, hormones
sympathetic tone of arterioles
at rest all arterioles are under sympathetic signal to maintain a degree of resistance and pressure
allows the ability to reduce resistance and increase flow to certain organs if needed
how do anaesthetics cause CV hypotension
affect sympathetic signalling to the vessels and reduce tone
pressure and volume in arteries and veins
arteries: high pressure, low volume
veins: low pressure, high volume
effect of contraction of veins vs arterioles
veins: reduces capacitance, resistance is low so does not change peripheral resistance, can increase CO
arteries: increases peripheral resistance, volume is small so does not change capacitance
what determine colloid osmotic pressure
how does it relate to hydrostatic pressure
determined by plasma proteins
when lower than hydrostatic pressure fluid exits capillary
when higher fluid re-enters
when equal there is no not movement
lymphatic circulation
3L/day
drains excess fluid absorbed into tissues from capillaries
can be blocked by cancer, infection leading to edema
important causes of edema
increased venous pressure (right side heart failure)
decreased oncotic pressure (liver or kidney failure)
decreased lymphatic flow
increased capillary permeability (inflammation)
why does BP drop when you stand
gravity pulls blood to legs due to compliance of veins
decreased venous return to heart
decreased SV
decreased arterial pressure
where are arterial baroreceptors
how do they detect pressure change
aortic arch and carotid arteries
stretch receptors in the walls of the arteries
short term regulation of BP
reduction in parasympathetic inhibition of SA node
sympathetic action
occurs in seconds but short lasting
long term regulation of BP
volume regulation by the kidneys modulating fluid absorption
active hyperaemia
metabolic mediators
increased metabolic rate increased blood flow to an organ by spontaneous dilation of the arteries that supply it
reduced oxygen
greater CO2, acidity, adenosine and K+
pulmonary exception to metabolic mediators of vasoconstrictors
O2 is a vasodilator and CO2 is a vasoconstrictor in lungs
opposite in tissues
allows blood flow to well ventilated areas
pulmonary circulation
lower pressure: 22/8 mmHg
CO of left and right heart are on average the same
blood flow through skeletal muscle
low at rest
increases due to metabolic change, keeps flow localised to active muscles
reduced during contraction due to compression of the vessels
coronary blood flow
reduced during systole but less than skeletal muscle as vessels are more on the surface of the muscle
greater during diastole
5% of CO
controlled by active hyperaemia
little response to sympathetic nerves or circulating hormones
cerebral blood flow
autoregulation by metabolites
almost constant from 60 mmHg to 160 mmHg
below - ischemia
above - cerebral edema
increases when you think
skin blood flow
heat exhaustion/stroke
receives more blood flow than needed for metabolism - transports heat and cools blood
depends on temperature
during exercise in heat skin blood flow is as high a muscle blood flow
heat exhaustion - CO increased to skin and CVS is unable to supply skin, muscle, and heart
