Peripheral Vasculature Flashcards
What are the 4 things that transcapillary solute diffusion depends on?
the concentration difference
surface area for exchange
diffusion distance
permeability of capillary wall to the substance
Why is the capillary system to efficient at diffusion?
It maximizes area available for exchange while minimizing distance to diffuse.
What are the two general ways things can diffuse across a capillary?
- lipid soluble substances can just diffuse through the membrane
- Charged substances use pores (is the organ in question allows)
Note that molecules larger than 40 angstroms just can’t cross capillaries because the pores aren’t big enough
Net fluid OUT of the capillary is called what>
Net fluid INTO the capillary is what?
out = filtration
in - reabsorption
What determines the direction fluid will move - in or out of the capillary?
the balance between hydrostatic pressure and oncotic pressure
What is hydrostatic pressure and what is ocncotic pressure?
hydrostatic = the pressure of blood forcing fluid OUT
oncotic - attraction of water into the lumen due to higher protein concentrations in the lumen
What is the starling hypothesis for the direction of fluid flow?
net filtration rate is equal to a constant K times (hydrostatic pressure in the cap - hydrostatic pressure in the interstitial fluid) - (oncotic pressure in the capillary - oncotic pressure in the fluid)
A positive value from that equation will give you what? filtration or reabsorbtion?
positive value - filtration (moving out of the capillary)
negative value - reabsorption (moving into the capillary)
What are the hydrostatic and oncotic pressures of the interstitial fluid?
usually 0
Where in the vascular system does filtration occur?
arteriole end of the capillary
Where in the vascular system does reabsorption occur?
the venule end of the capillary
Why does fluid leak out of the capillaries in injured tissue?
injured tissue releases histamine, which makes capillaries leaky. This means proteins from inside the vessel will leak into the interstitial fluid so you decrease the oncotic pressure pushing fluid in and the hydrostatic pressure stays. this means you get a net movement of fluid out of the capillaries and edema
What other body system is responsible for keeping the interstitial protein concentration low and removing excess capillary filtrate?
the lymphatic tissue
If vessels are in series, how do we calculated the total resistance across them?
You sum their total resistances.
For vessels in series, what vessel will have the highest impact on pressure and flow?
whichever vessel has the highest resistance
For vessels in parallel, what is the primary determinant for resistance?
it’s not the diameter of individual capillaries, but rather the TOTAL cross-sectional area of ALL capillaries in the parallel. So the more cpaillaries there are, the higher the cross sectional area, the lower the resistance (think of it as more route options and therefore less resistance)
How do we calculate the total resistance in a parallel network then?
we sum the inverse of the resistances, which is equal to the inverse of the total resistance
If all the resistances are equal in a series, what can we do to find the total resistance?
just divide that resistance by the number of vessles in parallel
Because the total cross-sectional area of vessels changes througout the body, what must also change to maintain flow rate?
flow velocity
What are the two types of flow that can occur within a vessel?
laminar (smooth, streamline, low-friction)
turbulent (disorder, mixing, high friction)
Where in the vessel is blood flowing the fastest?
in the center - no friction
What sort of reservoir does the peripheral venous system serve as?
a volume reservoir
What’s the “secondary” volume reservoir?
central venous system of great veins of the thorax and the right atrium
What happens to stroke volume when peripheral veins constrict?
peripheral blood is displaced and enters the central venous system, increasing central venous volume, pressure, cardiac filling and augments stroke volume
What happens to blood pressure as you go down the ranks of vasculature from arteries to veins?
blood pressure decreases
What is central venous pressure?
about 0 mmHg - the filling pressure for return to the right side of the heart
What set of vasculature has the highest resistance to flow?
arterioles
If individual organs have blood flowin gin series and blood flows between organs in parallel, how do you determine total peripheral resistance?
You add the sum of resistance within individual organs to find that’s organ’s resistance
then you add the inverse of all the organ resistances to find the TPR
How is the elastic nature of veins describe?
compliancy - the change in volume over the change in pressure….
even small changes in pressure can cause a large amount of blood to shift into/out of the peripheral venous pool
How are the arteries capable to converting the pulsatile flow from the heart into a steady laminar flow through the vascular bed?
THey store pressure energy in the walls during expansion so that they can continue pumping blood continuously via elastic recoil even when the heart isn’t pumping.
Describe how you can take a blood pressure in terms of blood flow types?
- you collapse the artery with a cuff
- as you let pressure out, you’ll reach a point where blood can just barely start going through - since the radius is too small it will be turbulent flow whch you can hear - this is systole
- you keep letting air out until the flow can convert back to laminar - this is diastole
what is the mean arterial pressure?
the average effective pressure that drives the blood through the systemic organs.
What is the equation for meal arterial rpessure - both of them?
Pa = CO a TPR Pa = Pd + 1/3(Ps - Pd)
What factors determina arterial pulse pressure?
it’s equal equal to systolic pressure minus diastolic pressure
so it’s determined by stroke volume and compliance (increases with stroke volume and decreases with compliance)
What happens to arterial pulse pressure as one ages?
- increase arterial volume
- increased arterial stiffness and decreased compliance
- thus, increased arterial pulse pressure and increased mean arterial pressure
done
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