5 - Microcirculation Flashcards
What is being referred to by “exchange vessels” and “resistance vessels”?
Exchange vessels - capillaries
Resistance vessels - arterioles
Capillaries will be able to do its function of exchange due to (3)
- Physical structure
- Large number of capillaries
- Surface Area
The “stopcocks” because they control the blood flow through the particular capillary that each one guards?
Precapillary sphincters
Role of arterioles
Important in changing blood pressure occurring throughout the vascular system
Pressure drop so capillaries will not burst
Precapillary Sphincters when tissue metab increases
When tissue metab increases, the local metabolic changes -> relaxation of precap sphincters -> increasing the number of open capillaries
When there is an inc in metab activity, tissues will be using a lot of O2 that’s why PO2 dec, PCO2 inc, pH dec bc of this you have:
>Relaxation of precap sphincters = allowing more blood to enter capillaries
>Number of open cap inc
When metabolic changes/tissue activity is dec, precap sphincters contracting -> constriction -> less blood flow towards capillaries
Transport mechanisms
- Diffusion
- For transporting gases like O2 and CO2 and other lipid soluble substances (e.g. steroid hormones) - Bulk flow
- small molecules, electrolytes, water
- due to presence of intercellular/slit-like gaps/clefts - Vesicles
- how macromolecules are transported -e.g. proteins - Actin Transport
DIFFUSION >effect of: 1. Concentration gradient 2. SA for exchange 3. Diffusion distance 4. Permeability of capillary wall to the diffusing substance
- Directly proportional
- Directly
- Inversely
- Directly
Components of microcirculation
Arterioles Capillaries Venules Metarteriole（thoroughfare channel） Precapillary sphincters
Precapillary sphincters
>Yes or no?
1. Innervated
2. Have a high degree of myogenic tone
3. Sensitive to local metabolic changes (PO2, PCO2, pH)
4. Referred to as stopcocks. Explain your answer.
- NOT innervated
- Yes
- Yes
- Yes. Only way to control blood flow to the particular capillary that they are guarding
Importance of extensive capillary branching in diffusion
Good so if ever specific tissues need more blood supply, they have a higher number of capillaries
How exchangeable proteins are transported
Vesicular transport
What happens when you have an increase in metabolic activity?
If you have inc in metab activity = less O2, inc in CO2…
First there’s relaxation of precap sphincters and arteriolar vasodilation
Relaxation of PCS -> inc open capillaries -> SA for exchange higher, diffusion distance will be smaller
Through arteriolar vasodilation -> delivery of O2 will be more efficient -> conc grad of O2 and CO2 across cap wall will be greater
And those in the red box will be favoring exchange of matls bet blood and tissues
Starling forces
- Capillary hydrostatic pressure (Pc)
- Pressure when your blood reaches capillaries
- Favors filtration - Osmotic force due to plasma protein concentration (pi c)
- aka Oncotic pressure due to plasma proteins)
- Due to presence of plasma proteins within your blood
- Pushes fluid in - Interstitial fluid hydrostatic pressure (P IF)
- Osmotic force due to interstitial protein concentration
Significance: Net Filtration Pressure -Net difference between the forces that favor filtration versus forces that inhibit filtration
= Pc + pi IF - P IF - pi c
Which of the following mechanisms is most important quantitatively for the exchange of electrolytes across capillaries? A. Bulk flow B. Diffusion C. Osmosis D. Vesicular Transport
A
Which of the following can increase the rate of oxygen diffusion from blood to tissue?
A. Arteriolar vasodilation
B. Decreased arteriolar PO2
C. Increased tissue PO2
D. Decreased number of flowing capillaries
A
***B & C: affecting conc gradient; D. Affected: SA (dec)
