Blood Flow and Pressure

Question 1

blood flow definition and equation

Answer 1

volume of blood that passes by a given point in a given unit of time
flow = ∆pressure/ resistance

Question 2

what and why is the pressure difference between different venous systems

Answer 2

pressure highest in left ventricle, aorta and large arteries during systole lowest in right atrium
difference in pressure is important for maintaining blood flow
most blood is in veins during circulation

Question 3

why is venous pressure low

Answer 3

the vessels are able to expand and compress in reaction to changes in blood flow

Question 4

equation linking resistance, radius, length and viscosity of vessel

Answer 4

Resistance = 8lengthviscosity/pi*radius^4

Question 5

explain laminar flow

Answer 5

blood travelling close to the vessel wall travels slower than blood in middle of vessel due to resistance at the edge of vessel. wider the vessel the less resistance and more conductance

Question 6

Explain turbulent blood flow

Answer 6

up to a certain point as pressure increases flow increases linerally (laminar flow). after this point the rate of increase slows this is turbulent flow.

Question 7

equation and meaning of reynold’s number (Re)

Answer 7

Re = vessel diameteraverage velocityblood density/blood viscosity
at Re>2000 vessel has turbulent flow
turbulent flow can increase risk of thrombosis

Question 8

what is blood pressure
what does its nomenclature mean
equation for mean arterial blood pressure

Answer 8

the force exerted against vessel walls by blood
top number = systolic pressure
bottom number = diastolic pressure
both measured in mmHg
mean arterial blood pressure = diastolic pressure + (1/3 * difference between systolic and diastolic)

Question 9

how does aorta maintain constant flow

Answer 9

aorta swells up and expands during ventricle systole to hold extra blood and during ventricle diastole the aorta contract to push out the extra blood to maintain a constant flow

Question 10

Equations relating blood pressure, cardiac ouput and heart rate

Answer 10

blood pressure = cardiac output* total preipheral resistance
cardiac output = heart rate* stroke volume
TPR = resistance of systemic blood vessels

Question 11

what happens when you stand up too quickly

Answer 11

significant amount of blood falls to your feet due to gravity resulting in decrease blood volume in upper body which can lead to further harmful effects

Question 12

what are and where are they baroreceptors

Answer 12

specialised nerve endings with high expression in walls of aortic arch and right atrium both located on the vagus nerve and where the carotid sinus splits into internal and external carotid arteries.

Question 13

what are mechanoreceptors

Answer 13

specialised sensory endings on the glossopharengeal nerves which detect stretching of the vessel wall to detect BP

Question 14

what is a baroreflex

Answer 14

blood pressure directly correlates to frequency that baroreceptors fire action potentials

Question 15

where do the impulses from baroreceptors go

Answer 15

go to various places in the brains then down the spinal chord to regulate vasoconstriction and to neurons of sympathetic nervous system to control kidneys and heart

Question 16

what will change of blood pressure do and why

Answer 16

decrease in BP increases renal sympathetic activity and increases heart rate as heart rate is related to cardiac ouput and affects cardiac pressure. same goes in reverse

Question 17

sympathetic and parasympathetic response

Answer 17

in low BP parasympathetic is inhibited in brainstem and sympathetic system fibres are activated in spinal chord this increases heart rate
arteries and arterioles vasoconstrict due to sympathetic by making adrenal medulla release adrenaline and noradrenaline as well as affecting smooth muscles to increase TPR which increases HR

Question 18

role of renal sympathetic nerves

Answer 18

in glomerulus specialised cells called juxtaglomerular surround afferent arteriole and distal convoluted tubule are able to produce and release hormone renin

Question 19

Renin-angiotensin-aldesterone system (RAAS)

Answer 19

macula densa cells sense low sodium or blood levels and cause juxtaglomerular cells to secrete renin
renin then binds to its active site, angiotensinogen which is continuously produced by the liver
this forms angiotensin 1 which is converted to its active form angiotensin 2 by ACE
angiotensin 2 has many function including promoting release of adesterone from adrenal gland

Question 20

how does angiotensin 2 increase blood pressure

Answer 20

vascular walls have angiotensin 1 receptors and when angiotensin 2 binds to it, it vasoconstricts the vessel to increase TPR and blood pressure

Question 21

how does angiotensin 2 increase thirst

Answer 21

it binds to angiotensin 1 recptors in the hypothalamus and vasopressin is secreted which acts as a neurotransmitter to increase thirst
this leads to increased blood and stoke volume

Question 22

how and where does aldesterone maintain blood volume

Answer 22

works on collecting duct and distal convoluted tubules
it increases expression of epithelial Na+ channels which causes the influx of Na+ ions out of filtered fluid and into the cell
this creates an electochemical gradient and with anti-diuretic hormone increasing aqauporin expression this means more water can be absorbed to control blood content

Question 23

how does Na+ reabsorption relate to cardiac output to affect blood pressure

Answer 23

aldesterone increases end diastolic volume which increases stroke volume then…
CO = HRSV so cardiac ouput increases and…
BP = COTRP so blood pressure increases

Question 24

local regulation of blood pressure and flow

Answer 24

blood passing through vessels causes stress on walls which causes influx of Ca2+ into endothelial cells
this results in nitrous oxide diffusing into neighbouring smoot muscle cells
this activates K+ channels leading to K+ efflux and hyperpolarisation of cell membrane
it also closes Ca2+ channels which stops Ca2+ influx which vasodilates blood vessels which reduces blood pressure

Question 25

treatment of hypertension

Answer 25

renin inhibitors, ACE inhibitors, angiotensin 2 receptor antagonists and mineralocorticoid receptor antagonists
side effect may include hyperkalaemia

Question 26

treatment of hypertension in black patients

Answer 26

black patients are more sensitive to salt and so is a more likely cause of hypertension
black people also have lower levels of renin so renin antagnoists (and further antagnoists for its products) will be less affective