Microcirculation Flashcards
The primary function of the circulatory system is __
- to transport and distribute essential substances
- to remove metabolic byproducts
What is microcirculation?
The circulation of blood through the smallest vessels of the body (arterioles, capillaries and venules)
What. is the pressure of small arteries? Why?
Small arteries: have higher pressures than 120 and that’s because the wall rigidity is changing and increasing in the small arteries.
What is the diameter of arterioles?
Below 300µm
Do arterioles contain smooth muscle cells?
Yes, they contain a large amount of smooth muscles
How can myogenic tone be expressed in arterioles?
They are single unit smooth muscle with a pacemaker activity.
-> There is always a contraction from these muscles providing a myogenic tone.
-> There is also a sympathetic innervation providing a sympathetic tone.
-> Both tones together are called the resting tone.
-> The sympathetic tone and myogenic tones can be different in different organs.
Make a Table with mean pressure, flow and resistance of vessel
The pressure decreases throughout the vessels reaching about __ in the venous system
zero
How to calculate the resistance?
by getting pressure difference over the flow.
What are the resistance vessels
Arterioles that have the highest resistance (this was for systemic circulation)
Compare the resistance in pulmonary and systemic circulations
The resistance in the pulmonary circulation is 1/10 of the resistance in the systemic circulation due to the large compliance.
Why do we consider arterioles as resistance vessels?
This is because if we take the reciprocal of the resistance the arterioles will have a higher resistance
In systemic circulation, calculate the mean arterial pressure?
= CO X TPR
In systemic circulation, is the Cardiac Output constant?
The cardiac output systematically will be constant as the heart is independently regulated.
What happen to the TPR If constriction of arterioles occurs ?
the TPR will increase
-> that will cause an increase in the mean arterial pressure
-> So constriction of arterioles can regulate the arterial pressure.
In a local level, will the resistance affect arterial pressure?
Np, because it’s a small part of the entire circulation
The constriction of arterioles will ____ (increase/decrease) the resistance and since the P is constant the flow (Q) will decrease.
increase
What are the 6 components of the microcirculation?
- terminal arterioles
- Metarterioles
- Precapillary sphincter
- True capillaries
- Postcapillary venule
- AV-shunt
Characteristics of terminal arterioles (diameter, feature, inneravation)
1) 10 - 30 µm
2) continuous smooth muscle layer
3) innervated sympathetically
Characteristics of metarterioles (diameter, feature, inneravation)
- Smaller than terminal arterioles
- discontinuous smooth muscle layer
- Not innervated => but locally regulated
Characteristics of precapillary sphincters
- Contain 1 - 2 smooth muscle cells
- Not innervated => but locally regulated
Characteristics of true capillaries
- Diamater -> 5 - 7 µm
- Inner surface -> 5000 - 7000 m2
- surrounded by endothelial cells
- contain pores which are filled with H2O
- Basal membrane -> filtration
What is so special about AV shunt (a component of microcirculation)
in the skin there is an exception which is the existence of an AV shunt and its important for thermoregulation.
What are the 4 different types of capillaries?
- Continuous
- Fenestrated
- Discontinuous
- Tight
Describe continuous capillaries
- Most common; found in the skeletal muscle, skin, lungs, etc..
- Wall thickness: 100 - 200 µm
- very small pore size: 5 - 7 µm
- Their endothelial cells contain a lot pinocytotic vesicles that form pinocytotic channels.
=> The pores and the channels will together form the water filled compartment and provide the high permeability of the capillary.
Why does continuous capillary have high permeability
The pores and the channels will together form the water filled compartment and provide the high permeability of the capillary.
Describe fenestrated capillaries
- Decreased wall thickness
- Increased pore size
- Found in the GI tract kidney and the exocrine gland as they can provide a higher transport rate
Describe discontinuous capillaries
- Small wall thickness
- Large pore size
- The pores are so huge that cells can penetrate
- Can be found in the bone marrow spleen liver where the huge cell transport through the capillaries.
Describe tight capillaries
- Tight junctions
- No pores found
- Transcellular trasport regulated
- Basis for blood-brain barrier
What are the 3 transport processes that can be found in capillaries?
diffusion, pinocytosis, hydrodynamic water exchange.
Hydrodynamic water exchange only exists only in capillaries.
-> T/F?
True
How does diffusion occur in capillaries
- Based on Fick’s law
- Allow lipid soluble molecules
- Allow water soluble molecules
- Small molecules
How can pinocytosis occur in capillaries?
large molecules that cannot diffuse through capillaries (>60kdalton) can be transported through pinocytosis. There are pinocytotic vesicles in the endothelial cells allowing macromolecules (ex: lipoproteins) to cross the capillary wall.
How does hydrodynamic water exchange (filtration and absorption of water) occur?
fluid moves due to forces and permeability available in the capillaries.
-> Increase in this transport might cause oedema.
What is Filtration?
when water moves from capillaries to interstitium and reabsorption is when water moves from interstium to capillaries.
What are Starling forces?
- Hydrostatic pressure in the capillaries
- Hydrostatic pressure of interstitum
- Colloid osmotic pressure in the interstitum
- Colloid osmotic pressure in the capillaries
Positive Oncotic pressure in the capillaries and positive hydrostatic pressure in the interstium cause___
absorption
Positive oncotic pressure in the interstium and positive hydrostatic pressure in the capillaries causes ____.
filtration
What is the effective filtration pressure (P effective)?
: filtration values of pressure will be positive and absorption values will be negative.
What is the value of sigma if there is complete impermeability?
1
What is the value of sigma in case of continuous capillary?
In case of continuous capillary the value of sigma will be between 0.75 and 0.95 changing the p
effective.
What is Hydrostatic Capillary pressure?
the blood pressure generated by the heart.
-> Its around 30-35 at the beginning of the arteries and in the venous end its 10-15.
What is Hydrostatic interstium pressure?
A value found in a huge range from -6(in the skin) to 25(in the kidney).
-> Inflammation can cause a huge increase in that value.
How is Oncotic pressure calculated?
Oncotic pressure can be both calculated from the Hoff’s law based on the protein concentration in blood plasma and interstium.
what is the oncotic pressure value in the capillaries and interstium?
In the capillaries its about 25 mmgh and in the interstium its about 5 mmgh.
what is the oncotic pressure value in the capillaries and interstium?
In the capillaries its about 25 mmgh and in the interstium its about 5 mmgh.
