Circulatory system and blood pressure

Question 1

components of the circulatory system

Answer 1

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

Question 2

layers of blood vessels

Answer 2

tunica externa (adventitia)
tunica media
tunica intima

Question 3

layers of cells lining the GIT and respiratory tract to blood barrier

Answer 3

simple squamous epithelial cells
simple cuboidal epithelium cells (basement membrane)
simple squamous endothelial cells (blood vessels)

Question 4

what cells secrete the basement of capillaries

Answer 4

simple squamous endothelial cells

Question 5

where are continuous capillaries

Answer 5

where you don’t want strong contact between blood and tissue
where the blood can harm the tissue
e.g. blood brain barrier

Question 6

what allows larger molecules to cross the endothelium of continuous capillary

Answer 6

pinocytotic vesicles

Question 7

where are fenestrated capillaries

Answer 7

where perfusion is high but proteins need to remain in the blood
e.g. kidneys

Question 8

where are sinusoid capillaries

Answer 8

where proteins are allowed to cross the membrane easily
e.g. liver
(have large fenestrations and discontinuous basement membrane)

Question 9

what is the maximum length of capillaries

Answer 9

1 mm

Question 10

formula for flow through capillaries (Q dot)

Answer 10

Q dot = arterial pressure - venous pressure / resistance
= pressure dif / resistance
(Ohm’s law)

Question 11

Poiseuille - Hagen Formula for resistance

Answer 11

R = 8ηL / pi r^4

L = length
η = viscosity
r = radius (most important)

Question 12

what is hydrostatic pressure in the veins dependant on
what is hydrostatic pressure in the arteries dependant on

Answer 12

veins: volume only because there is no resistance
when pressure is low, volume is low

arteries: volume and resistance

Question 13

main site of resistance
what regulates them

Answer 13

arterioles

ANS, paracrine regulation, hormones

Question 14

sympathetic tone of arterioles

Answer 14

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

Question 15

how do anaesthetics cause CV hypotension

Answer 15

affect sympathetic signalling to the vessels and reduce tone

Question 16

pressure and volume in arteries and veins

Answer 16

arteries: high pressure, low volume
veins: low pressure, high volume

Question 17

effect of contraction of veins vs arterioles

Answer 17

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

Question 18

what determine colloid osmotic pressure
how does it relate to hydrostatic pressure

Answer 18

determined by plasma proteins

when lower than hydrostatic pressure fluid exits capillary
when higher fluid re-enters
when equal there is no not movement

Question 19

lymphatic circulation

Answer 19

3L/day
drains excess fluid absorbed into tissues from capillaries
can be blocked by cancer, infection leading to edema

Question 20

important causes of edema

Answer 20

increased venous pressure (right side heart failure)
decreased oncotic pressure (liver or kidney failure)
decreased lymphatic flow
increased capillary permeability (inflammation)

Question 21

why does BP drop when you stand

Answer 21

gravity pulls blood to legs due to compliance of veins
decreased venous return to heart
decreased SV
decreased arterial pressure

Question 22

where are arterial baroreceptors
how do they detect pressure change

Answer 22

aortic arch and carotid arteries
stretch receptors in the walls of the arteries

Question 23

short term regulation of BP

Answer 23

reduction in parasympathetic inhibition of SA node
sympathetic action
occurs in seconds but short lasting

Question 24

long term regulation of BP

Answer 24

volume regulation by the kidneys modulating fluid absorption

Question 25

active hyperaemia
metabolic mediators

Answer 25

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+

Question 26

pulmonary exception to metabolic mediators of vasoconstrictors

Answer 26

O2 is a vasodilator and CO2 is a vasoconstrictor in lungs
opposite in tissues

allows blood flow to well ventilated areas

Question 27

pulmonary circulation

Answer 27

lower pressure: 22/8 mmHg
CO of left and right heart are on average the same

Question 28

blood flow through skeletal muscle

Answer 28

low at rest
increases due to metabolic change, keeps flow localised to active muscles
reduced during contraction due to compression of the vessels

Question 29

coronary blood flow

Answer 29

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

Question 30

cerebral blood flow

Answer 30

autoregulation by metabolites
almost constant from 60 mmHg to 160 mmHg
below - ischemia
above - cerebral edema
increases when you think

Question 31

skin blood flow
heat exhaustion/stroke

Answer 31

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