CVS Unit 1 L5
What is the diameter of capillaries?
3 um
What is the Starling equation?
Jv = Kf [(Pc-Pi)- (Pi_c - Pi_i)]
When is lymphatic drainage is impaired when
LN are surgically removed or irradiated in malignancy; in filiariasis = parasitic infection of LN; lack of muscular activity
What are some lipid soluble substances?
O2 and Co2
What force opposes filtration (hydrostatic)?
Pi, interstitial hydrostatic pressure;close to zero or slightly negative
What force opposes filtration (oncotic pressure)?
Pi_c; effective osmotic pressure of capillary blood due to plasma protein
What force favors filtration (oncotic)
Pi_i; interstitial fluid protein conc determines it;
What is net fluid movement into the capillary called?
absorption
What is the main source of osmotic pressure>
albumin
What determines Pc?
arterial and veous pressures (becuase capillaries are intersposed)
Is the value for Pc closer to arterial or venous pressure?
arterial;
What cuases increase in Pc?
arteriolar dilation, venous constriction, increased venous pressure, heart failure, ECF vol. expansion
Where is Pc the highest in the capillary?
arteriolar end
What vessels are part of microcirculation?
arterioles, metarterioles, capillaries, postcapillaru venules, venules
What is the purpose of clefts/pores?
between endothelial cells, allows passage of water-soluble substances; small fraction of surface area
Where are tight clefts foun? where are wide clefts found?
brain in blood brain v. liver and intestine
What is Pc
capillary hydrostatic pressure, favoring filtration out of capillary
What can increase Kf? what will happen?
cappilary injury (e.g. toxins, burns); increase premeability to water and loss of protein from capillary
What capillaries have the lowest Kf and therefore lowest magnitude of fluid movement ?
cerebral capillaries
What controls microvascular flow?
contraction and dilation of terminal arterioles to control microvascular flow
What promotes lymph flow back to the thoracic duct?
contraction of the smooth muscle in the lymph vessles and compression of lymph vessels by the activity of surrounding skeletal muscle
What affects blood flow to the capillaries/ determining TPR?
degree of constriction/relaxtion of arterioles
describe variance in Kf.
differnt for tissue types: e.g. fenestrated
What is an increase in interstitial fluid volume
edema
What is net fluid movement out of the capillary called?
filtration
What direction does microcirculation?
from arteriole to venule
What is microcirculation?
functions of smallest blood vessels, capillaries and neightboring lymphatic lvessel
What does the Starlin principle state?
gfluid movement (Jv) across a capillary wall is determined by net pressure across a walll
What capillaries have the highest Kf and therefore magnitude of fluid movement ?
glomerular capillaries
Decribe the area and velocity of capillaries?
highest cross sectional area, slowest velocity
What determines magnitude of fluid movemnet?
hydraulic conductance, Kf of capillary wall
What drives osmosis, the most importnat mechanisms for fludi transfer across capillary wall?
hydrostatic and osmotic pressures = Starling forces
Wheere are lymphatic capillaries?
in the intersitital fluid, close to vascular capillariess
What processes cause edema?
increaed filttration or when lymphatic drainage is impaired
___- in protein concetration cause ____ in Pi_c and ____ in filtration.
increase; increase; decrease
What mechanisms increase filtration?
increased Pc, decreased Pi_c, increased Kf due to drestruction of capillary wall
Where do lymphatic capillaries merge into?
larger lymphatic vessels, into thoroacic duct into large veins
Are capillaries open or closed at rest?
osciallate between open and closed, with precapillary sphicters closing capillary to stop flow
How do large water soluble substances cross?
pinocytosis
Describe osmotic pressure.
pulling force on water due to presence of solutes
Describe hydrostatic pressure.
pushing force on water due to more fluid in one region than another
What is the lymphatic system responsible for?
returning interstitial fluid and proteins to the vascular compartment
What are precapillary sphincters
rings of smooth muscle cells that determine blood flow to the capillaary bed; not innervated
How do lipid soluble substances andsmall water soluble substance s pass through capillary endothelial cells?
simple diffusion v. water filled slefts
What is the composition of capillaries?
single layer of endothelial cells surrounded by a basement membrane (collagen)
Why is delivery of blood to and from the capillaries important?
site of exchange of nutrients and waste products in the tissue AND site of fluid exchange between vascular and interstitial compartment
Why is Pi_i low?
there is little loss of protein from capillaries
Why do lymphatic capillaries possess one way flap valves?
to permit interstitial fluid and protein to enter but not leave the capillaries
What affects Pc more? What is the exception?
venous pressure; glomerular capillaries, as Pc declines along the length of the capillary becuase of filtration of fluid
When does edema form?
volume of interstitial fluid from filtration exceeds ability of lyphatics to return it to the circulation
What are some small water soluble substances?
water, glucose, amino acids
What does smooth muscle wall enable lympathic vessels to do?
which has intrinsic contractile ability