What is the basic function of the circulatory system?
Support cell metabolism by:
-delivering O2 and nutrients to cells
-removing CO2 and wastes from cells
By what mechanism are nutrients delivered by the circulatory system?
Over what distances is diffusion timely? Why?
Timely only over tiny distances (over large distances, diffusion is too slow to keep up w/ cells' metabolic rates)
How is diffusion maximized?
-Larger surface area
-Minimal distance and membrane thickness
-Large concentration gradient
What is Fick's Law of Diffusion?
Qx = rate of diffusion of X
D = diffusion coefficient
As = surface area for exchange
Δ[X] = concentration gradient
ΔL = diffusion distance
What drives transcapillary solute movement?
How do capillaries affect Fick's Law of Diffusion?
-Increases surface area for exchange
-Minimizes diffusion distance
How are capillaries made to maximize diffusion?
-Thin membrane wall
-Large number throughout body
How are CSA and speed of flow in the CV system related?
-large CSA = slower flow
-small CSA = rapid flow
Why is it important for CSA and speed of flow in the CV system to have an inverse relationship?
Large CSA --> velocity slows --> allows more time for nutrient exchange
What is the basic function of the heart?
Develops the pressure gradient that creates flow of blood w/in the circulatory system
Over what distances is convection (bulk flow) timely?
Timely over large distances
Why is bulk flow (convection) important?
-Maintains the driving force for diffusion, so nutrients are coming in at a rate proportional to their leaving
-Shortens time b/t capillary beds --> speeds up diffusion
Bulk flow of blood around the circulatory system
How could one increase the delivery rate of a substance?
-Increase blood flow rate
-Increase concentration of substance in blood
Equation for delivery rate
X = Q[X]
X = rate of delivery of x (mass/time)
Q = blood flow rate (volume/time)
[X] = concentration of X in blood (mass/volume)
What is the Fick Principle?
- Xtc = transcapillary efflux of X
- Q = blood flow rate
- [X]a = concentration of X in arterial blood
- [X]v = concentration of X in venous blood
What is the equation for convective flow?
What are the 2 ways to alter how quickly blood flows to an organ?
-Change the pressure difference across its vascular bed
-Change its vascular resistance
What are the resistance vessels controlling the radius?
What does arterial dilation promote?
Filtration (fluid exit across the capillaries)
-Less of the oncoming pressure from heart is resisted out --> capillaries leak a lot
What does arterial constriction promote?
Reabsorption (fluid movement back into the capillaries)
-Arterioles resist out most of the pressure, so the actual pressure entering the capillaries is much lower --> capillaries leak less
What drives transcapillary fluid movement?
What governs fluid movement into and out of the circulation?
4 starling forces (pressures) in the blood and tissue compartments
What are the 4 starling forces?
Which starling forces push fluid into circulation? Out of circulation?
What occurs on the arterial end of a capillary?
What occurs on the venous end of a capillary?
Transcapillary solute movement vs. transcapillary fluid movement
-Solute: has to do w/ rate of diffusion of solute/gas from the capillary to the cell
-Fluid: has to do w/ volume distribution b/t plasma in capillaries and interstitial space