Exam 3 Kirk L4: Microcirculation Flashcards
What are the precapillary resistance vessels?
Exchange vessels?
Post-capillary resistance vessels?
Precapillary resistance vessels: arterioles, metarterioles (bypass the capillary system) and pre-capillary sphincter
Exchange vessels: capillaries
Post capillary resistance vessels (much lower resistance, like 4:1) are the venules
Describe Capillary Flow:
___ velocity
Intermittent
Direction
Uniform?
___ pressure
Capillary Flow:
Low velocity
Intermittent (pulsitility from arteries to push it through)
Direction (pressure gradients)
NOT uniform
low pressure (pressure is really low but it is still critical for function)
Explain fick’s law of diffusion modified for capillaries
J = -PS (Co-Ci)
P stands for permeability
S stands for Surface Area
Water salt, O2, and urea diffuse rapidly and move almost unrestrictred, therefore the amount delivered to tissues is dependent on ______
With larger molecules, the limiting factor is ____
(What do you have to do if you want to increase O2 to a tissue)
Water, salt, o2, urea are “FLOW limited”
This means that the amount of o2 you’re delivering is dependent on the amount of flow because they are delivered so effeciently (if you want to increase O2 to a tissue you have to increase blood flow to that tissue)
With larger molecules, their ability to diffuse is the limiting factor
Factors governing Trans-capillary fluid exchange:
1.
2.
3.
4.
Factors governing transcapillary fliud exchange: it is the oncotic and hydrostatic pressures inside and outside of the capillaries SO
1. oncotic pressure of plasma
- hydrostatic pressure in capillaries
- Tissue oncotic pressure
- Interstitial hydrostatic pressure
What does the starling hypothesis say:
Flow of fluids between capillary walls depends on….
Starling Hypothesis:
flow of fluid across capillary walls depends on the balance between the osmotic forces and hydrostatic forces across the walls
Explain the change in hydrostatic AND oncotic pressure from the arterial side of the capillaries to the venous side.
So, the oncotic pressure throughout the capillaries does not change much at all, and stays at 25 mmHg.
The hydrostatic pressure however, goes from 32mmHg in the capillary side to 15mmHg at the venous side. This is important because at the arteriole side you get 7 mmHg pushing water OUT of the capillaries for filtration, and by the time you reach the venous side, you get net 10mmHg into capillaries for absorption.
Where in the body is the hydrostatic pressure in the capillaries the highest?
Where in the body is the hydrostatic pressure in the capallaries the lowest?
The kidneys want to be constantly filtering out blood, so they have really high hydrostatic pressures at 60mmHg.
The hydrostatic pressure in the capillary bed in the lungs is only 25mmHg, because you want to keep the lugns very dry and don’t want to push too much fluid out of the lungs.
Define pinocytosis
Where does it happen
How much does it contribute to overall transport
Pinocytosis is vesicle transport of larger lipid inolsuble molecules across endothelial cells
Varies amoung tissue (lots in muscle, very little in brain)
Responsible for little overall transport
Arterial pressure exerts a ____ effect on capillary hydrostatic pressure because of _________
Venous pressure exerts a relatively _____ effect on capillary hydrostatic pressure because of ______
Arterial pressure exerts SMALL effect on capillary hydrostatic pressure becaue of the significant precapillary resistance.
Venous pressure exerts relatively LARGE effect on capillary hydrostatic pressure because of little post capillary resistance.
An increase in _____ will exert a greater increase in capillary hydrostatic pressure than an increase in ____
An increase in VENOUS PRESSURE will exert a greater increase in capillary hydrostatic pressure than an increase in arterial pressure.
This is due to backing up effect
What causes an increase in venous pressure?
LVHF causes an increase in venous pressure
(pressure backs up into left atrium, into the pulmonary veins, edema)
Does arterial pulmonary hypertension cause PE?
Arterial pulmonary hypertension does NOT cause pulmonary edema becaue the pulmary arteries are before the lungs
What is the total osmotic pressure of plasma?
What mainly contributes to that total osmotic pressure>
Total osmotic pressure of plasma is 6000 mmHg.
This is due to the salts that exist in plasma
These salts RAPIDLY diffuse (almost immediately), once in the capillaries so those salts don’t affect oncotic pressure as much
The key factor that holds fluid within the capillaries is _______.
Key factor that holds fluid within the capillaries is oncotic pressure
This is primarily caused by the protein albumin which stays in the blood and does not diffuse out