Nordgren- The Peripheral Vasculature Flashcards
What is the purpose of the CV system?
To maintain INTERSTITIAL FLUID homeostais.
What is the Fisk principle?
Determines how substances are transported via blood bewteen the capillary bed in one location to another.
Where does passive diffusion often occur?
capillaries
What does diffusion depend on?
- concentration difference
- SA for exchange
- Diffusion distance
- permeability of capillary wall to the substance
Why are capillaries so efficient?
They maximize the area available for exchange while minimizing the distance to diffuse
The number of pores in the capillary depends on….
tissue location
ex. brain capillaries have FEW bores (tight)
What won’t cross a capillary wall?
Anything larger than 40 A (albumin)
Will a lipid soluble substance cross a membrane easily?
YES
b/c the membrane is only one cell thick
Net fluid OUT of a capillary =
filtration
Net fluid INTO a capillary=
resorption
Fluid flows in response to what two variables?
- Hydrostatic p (P)
2. oncotic pressure (pi)
What is hydrostatic pressure?
pressure of blood forcing fluid OUT of capillary
What is oncotic pressure?
osmotic attraction of water IN to regions of higher protein conentration
What is starling hypothesis?
Describes the relationship between opposing hydrostatic and oncotic forces on the net movment of transcapillary fluid (filtration or reabsorption)
What is the formula for the net filtration rate?
Net filtration rate = k (constant) {(hydrostatic pressure of intracapillary fluid- quantity of interstitial fluid)- (oncotic P of intracapillary fluid- quantity of intersitital fluid)}
What is filtration?
the net movement of solutes and fluid OUT of hte capillary and into the interstitial fluid
A POSITIVE pressure gradient is indicative of…
filtration
A NEGATIVE net pressure gradient is indicate of …
reabsorption
Why are the hydrostatic and oncotic pressures usually 0?
oncotic b/c very few proteins in IF
What occurs at the arteriole ned of a capillary?
filtration
What occurs at the venule end of a capillary?
reabsortpion
What does the release of histamine do?
INCREASES the capillary permeability to hte extent that proteins leak into the IF and LOWERS the oncotic pressure.
*exception to the oncotic P rule
What is the lymphatic system important?
keeps the interstitial protein concentration LOW and removes excess capillary filtrate from the tissues.
Why are lymphatic capillaries very porous?
Collect large particles and move them to lymph nodes then return fluid to the peripheral venous blood entering the right heart.
If vessels are in a row they are in…
series
What is flow equal to?
Q = change in pressure/ resistance
What is the total resistance equal to?
The SUM of all the individual resistances
What vessel has the greatest impact on flow?
the vessel w/ the highest resistance
What is the primary determinant for resistance of vessels in parallel?
not the diameter of an individual capillary, but the total cross sectional area of ALL capillaries
What is resistance equal to for vessels in parallel?
R= 8Ln/πr4
The overall effective resistance of any parallel network will always be _____ than that of any elements of that network.
LESS
If flow must remain the same throughout the peripheral system, and the total cross-sectional area of vessels changes thorughout hte body, what must change to maintain the flow rate?
flow velocity
What is laminar flow?
orderly, streamlined, low friction
What is turbulent flow?
disordered, mixing, hgh friction
What is friction?
shear stress, the force inside the wall of the vessels that wants to drag the inside surface along with the blood flow
What serves as a volume reservoir in the CVS?
The peripheral venous system
What is a secondary reservoir in the CVS?
Central venous system (great veins of the thorax and the RA)
What happens when peripheral veins constrict?
Blood is displaced and enters the central venous system–> increases central venous volume, pressure, cardiac filling–> augments stroke volume (Starling!)
What happens when blood pressure decreases across the vasculature?
- The pulsatile nature of blood pressure disappears across the arterioles
- Central venous pressure is about 0 mm HG
What present a large resistance to flow?
arterioles
What happens as resistance increases in arterioles?
The flow velocity is still high and bp must decrease to maintain flow rate
What determines overall organ resistance?
Resistance in the arterioles
What regulates resistance in the arterioles?
Adjustments in the diameter of the lumen
What happens when arterioles are OPEN?
- low reservoir
- high flow velocity
- high downstream volume
What happens when arterioles are CLOSED?
- High reservoir
- low flow velocity
- low downstream volume
What is TPR?
Overall resistanct to flow thorugh the ENTIRE systemic circulation
What will adding an organ to a system in parallel do to the TPR?
DECREASE the TPR
What will decreasing the resistance in any organ do to the TPR?
DECREASE the TPR
What describes the elastic properties of veins?
Compliancy (C)
What is compliancy related to?
- How much volume changes in response to a change in pressure
C= change in V/ change in P
- Volume reservoir
When do arteries act as a blood reservoir?
On a beat to beat basis.
- They convert the pulsatile flow coming out of the heart into a steady flow of blood through the vascular bed.
- Store pressure energy in walls during expansion–> pressure resrvoir
What drives blood through peripheral vascular system during systole?
Arteries recoiling to shorter lengths and give up stored potential energy
When measuring arterial pressure which sounds is systolic and which sound is diastolic?
first- systolic
last- diastolic
What is MAP?
The average effective pressure that drives blood through the systemic organs
Pa= COxTPR
What causes changes in MAP?
Changes in either CO or TPR
What’s another way to calculate MAP?
PA= PD + 1/3 (Ps-Pd)
What is arterial pulse pressure?
Psystolic- P diastlic
What determines arterial pulse pressure?
Pp= SV/Ca
Stroke volume and arterial compliance
Greater compliance leads to ______ pulse pressure.
SMaller
The larger the volume ejected the ________the pulse pressure.
larger
What causes changes in arterial compliance?
aging!
increased arterial volume, arterial stiffness, arterial pulse pressure, MAP
