microcirculation Flashcards
what does each individual organ have
it’s own microcirculation
which branches off the main artery an rejoins to main vein
what does the 1st order arteriole do
lots of smooth muscle
deliver blood to capillaries (where exchange takes place) across organ/tissue
goes to venule > drains to main vein
what is the overall aim of the cardiovascular system
to get adequate blood flow through the capillaries
what is blood flow rate
volume of blood passing through a vessel per unit time
what is Darcy’s law
fluid circuit
change in pressure gradient = flow rate x resistance
Q = pressure gradient / resistance
equation for pressure gradient (change in P)
pressure gradient = pressure A - pressure B
what is flow rate directly proportional to
pressure gradient
what is flow rate inversely proportional to
resistance
what is the definition of resistance
hindrance to blood flow due to friction between moving fluid and stationary vascular walls
what is the equation for resistance
R = 8Ln/pi r^4
vessel length = L
vessel radius = r halving the radius decreases the flow 16 times
blood viscosity = n
only the radius really changes minute to minute - the rest are fairly constant
what happens to pressure gradient and flow rate when increased BP
pressure gradient goes up
flow rate goes up
what happens to resistance and flow rate with arteriolar vasoconstriction
resistance goes up
flow rate goes down
what is mean arterial pressure (number)
93 mmHg
pressure in arteries same amount around the body
what is blood flow of an organ is dependent on
pressure gradient
using pressure B as the pressure leaving the organ (venule)
if flow rate cannot be the same for each organ - what does this indicate about the resistance for each organ
considering pressure entering and leaving are the same for each organ - the resistance must change significantly
without this pressure difference, blood would not reach capillary beds
what does vasoconstriction do to radius, resistance and flow rate
radius decreases
resistance increases
flow rate decreases
(contraction)
what does vasodilation do to radius, resistance and flow rate
increase radius
decrease resistance
increase flow rate
(relaxation)
what does vascular tone mean
partial constriction of arteriolar smooth muscle
this way you can either constrict further or dilate (if completely dilated then you can only constrict) -
in a state of partial constriction you can both dilate and constrict to increase or decrease blood flow
what are 2 reasons why radii of arterioles are adjusted independently
1) to match blood flow to the metabolic needs of specific tissues (depending on bodys momentary needs)
2) to help regulate systemic arterial blood pressure
describe ACTIVE HYPERAEMIA
regulated by intrinsic controls and is independent of nervous or endocrine stimulation
ACTIVE HYPERAEMIA
1) tissue is doing more
2) using more oxygen
3) generates metabolites (influences and is detected by arterioles)
4) arterioles dilate
describe MYOGENIC AUTOREGULATION
MYOGENIC AUTOREGULATION
1) damage to tissue
2) leakage of fluid
3) ice pack/decreased blood temp
4) vasoconstriction - diverting blood away from cold area to preserve body temp
increased stretch (distension) due to high BP > myogenic autoregulation
use exercise as an example to describe matching blood flow to meet demands
perfusion pressure - pressure through tissue bed
1) start exercise
2) pressure increases (good in some tissue but in most = not)
3) increased pressure leads to increased flow to that tissue
4) immediate increase in flow stretches arterioles
5) the arterioles respond to physical stretch
6) cause local constriction called AUTOREGULATION to bring the pressure/flow down
equation for blood pressure
cardiac output (Q) = blood pressure (MAP) / total peripheral resistance (TPR) so blood pressure (MAP) = cardiac output (Q) x total peripheral resistance (TPR)
definition of cardiac output
amount of blood flowing through system
definition for total peripheral resistance
total resistance in every arteriole in the body
equation to calculate MAP
SBP + 2(DBP) all / 3
equation for cardiac output
cardiac output = SV x HR
equation for stroke volume
SV = end diastolic - end systolic
how do arterioles regulate systemic arterial blood pressure
regulated by extrinsic controls which travel via nerves or blood and are usually centrally coordinated
- neural
- hormonal
describe neural methods for arterioles to help regulate systemic arterial blood pressure
cardiovascular control centre in the medulla
can cause vasoconstriction
eg lost a lot of blood > need to get blood pressure back up > force multiple tissue beds to constrict at the same time > increased TPR > increased BP
describe hormonal methods for arterioles to help regulate systemic arterial blood pressure
brain can send signals to endocrine tissues/glands - to release vasoconstrictors
vasopressin/ADH
angiotensin 2
adrenaline/noradrenaline
what is the purpose for capillaries and what are it’s measurements
the delivery of metabolic substrates to the cells of the organism (ultimate function of the cardiovascular system)
7 micrometres in diameter
1 micrometre in cell width
why is the highly branched structure of capillaries important
it is close to tissues/organs
ideally suited to enhance diffusion - Fick’s Law
minimise diffusion distance
maximise the SA and time for diffusion
do highly metabolically active tissues have more dense or less densely capillary networks
more dense!
density of capillaries in skeletal muscle
100 cm2/g
density of capillaries in myocardium/brain
500 cm2/g
density of capillaries in lung
3500 cm2/g
you want capillaries to be as close to air for diffusion
what can some tissues do to direct blood away from less important tissues
they can constrict to try and direct blood away from less important tissues to areas that need more eg gut constriction
what are the 3 types of capillary structure
continuous
fenestrated
discontinuous
what structure do most capillaries have
continuous structure - things that are really small - can get through H2O filled gap junctions eg sodium ions or water
bigger molecules have to diffuse or be moved by transporters eg glucose
other structures = fenestrated = bigger gaps > allow glucose to pass through and other bigger molecules
discontinuous structure = huge gaps > eg liver > drugs can pass through to liver and get metabolised by liver
also seen in bone marrow and spleen > for WBC to move in and out of cell
what is the blood brain barrier
capillary structure but no H2O gap junctions
IMPENETRABLE CAPILLARY STRUCTURE
anything remotely water soluble needs transporter
TIGHTER CONTROL
what is bulk flow
a volume of protein free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed
pressure forcing blood through capillaries (with water filled gap junctions) > fluid is forced out of these junctions and enters tissue
what pressure draws fluid back in
oncotic pressure draws fluid back in
what does osmotic force do
draws fluid back in
what kind of a force is hydrostatic force
it is a pushing force
what kind of a force is oncotic force
a pulling force
what is Starling’s hypothesis
needs to be balanced else you’ll be decreasing blood volume
describe the forces and therefore net movement of fluid through the journey of a capillary
hydrostatic pressure at the start of arteriole is high and drops as it moves down but fluid is still being forced out
oncotic pressure is constant
net pressure - due to high hydrostatic pressure at the start = massive net loss of fluid > as hydrostatic pressure drops then oncotic pressure is dominant and fluid moves back in
what is ultrafiltration
if pressure inside the capillary is greater than in the IF then ultrafiltration occurs
what is reabsorption
if inward driving pressures are greater than outward pressure across the capillary then reabsorption occurs
is ultrafiltration more effective than reabsorption
yesssssss
net loss of fluid into tissues from the blood
what is the role of lymphatic system
needs to bring the loss of fluid back otherwise blood volume will keep decreasing
describe the lymphatic system
wherever there is a capillary there is a lymphatic capillary too
fluid loss forced out of the blood drains into lymphatic > drains back to major lymphatics and returns to blood
what do lymph nodes/glands do
respond to bacteria/virus in the fluid that is returning to blood and triggers immune response (eg lymphocytes)
is there a pump to induce flow of lymphatics
no
requires skeletal muscle forcing lymphatics back up the leg
requires negative pressure in the lungs to draw fluid up
where is drainage
right lymphatic duct and thoracic duct and right and left subclavian beins
how many L per day are returned
3
what happens if the rate of production is greater than the rate of drainage
oedema ensures
what happens if there is parasitic blockage of lymph nodes
elephantiasis
