Flashcards in Peripheral Vascular system Deck (31):
What are some factors that affects diffusion?
1. conc. diff
2. Surface area for exchange
3. distance of diffusion
4. perm of capillary wall to substance
What some other factor besides diffusion that affects fluid movement?
Hydrostatic pressure- fluid pushed
Osmotic pressure - water attracted
What is starling hypothesis?
Describes the relationship between opposing hydrostatic and oncotic forces on net bulk flow
- either filtration or resorption
Net flow= K[(Pc-Pi)-(Pie(c)-Pie(i))]
What is Pc?
Hydrostatic pressure of intracapillary fluid
Whta is pie(c)?
Oncotic pressure of intracapillary fluid
What are Pi and Pie(i)?
Same quantities for interstitial fluid
What is K?
Constant expressing how readily fluid can move across capillaries
What is filtration and what is its starling flow?
Net movement of solutes and fluid out into the interstitial fluid
- Positive net pressure gradient
What is reabsorption and what is its starling flow?
Net movement of solutes and fluid into the capillary from IF
- Negative net pressure gradient
Where does filtration and reabsorption happen?
Venule- oncotic pressure usually doesn't change
What is an exception to the oncotic pressure rule? How does it work?
Release of histamine
-Increase cap perm and protein leak into IF (lowers oncotic pressure)
What is the role of the lymphatic system?
Keeping IF protein conc. low
- Very porous
- Collects particles and moves to LN where particles are removed and fluid is returned to venous system
What is the resistance across vessels in series?
Total resistance is sum of individual resistances
- pressure with highest R will have greatest impact of pressure and flow
How does one compare vessels in parallel?
Resistance of vessels in parallel is not determined by diameter by total cross sectional area of all capillaries
If all the same Rp=Rx/n
What is the relationship between flow and flow rate?
Since vessels have diff total cross sectional area and thus diff resistance something must change to keep flow (Liters/Min) the same
- Flow velocity changes (mm/sec)
What the purpose of the peripheral venous system?
Serve as a reservoir (60%) blood here
- secondary is central venous system
What consists of the central venous system?
Great veins of thorax and right atrium
When peripheral veins constrict what happens?
Blood is displaced and enters central system
- raises venous volume, pressure and cardiac filling
- thus more in and more out (starling)
Where does blood pressure decrease the most?
Pulsatile nature disappears across arterioles
about 25 mmHg in Caps
What is the pressure in the central venous system?
What compensates for increased resistance in arterioles? Why?
Pressure drop Q= ^P/R
- flow must remain the same
- arterioles have increase resistance and to keep flow the same pressure drop must do so to compensate
What determines the resistance of organs?
Typically arterioles since greatest resistance
- lumen diameter is regulated to adjust resistance
What is total peripheral resistance?
Overall resistance to flow through the entire systemic circulation
- organs are in parallel
What are 2 ways to decrease resistance TPR?
1. Add another organ system
2. Decrease resistance in any organ
What is compliancy?
How much pressure in response to volume change
- Large shifts in blood into/out of PVS has only small changes in pressure
What counters blood pooling?
Active venous constriction
What is the purpose of the elastic properties of arteries?
1. Convert pulsatile flow coming from heart into smooth steady flow before entering vascular bed]
2. Store pressure energy during expansion to push blood through the periphery
What is mean arterial pressure?
Average effect pressure that drives the blood through the systemic organs
how does one calculate the arterial pulse pressure?
Systolic minus diastolic
What determines arterial pulse pressure?
Stroke volume and Compliance