Microcirculation and Lymphatics Flashcards
What are the pre capillary resistance vessels?
Arterioles
Metarterioles (precapillary sphincters)
What are the post capillary resistance vessels?
Venules
Where is most of the resistance in the microcirculation?
In the pre capillary vessels
What is the structure of the metarterioles and how does this contribute to the resistance?
The metarterioles are vessels that link the arterioles and the venules and they have discontinuous smooth muscles that form pre capillary sphincters along the length of the metarterioles that can reduce or shut off blood flow.
What is the velocity of capillary blood flow?
Low velocity
What is the direction of capillary blood flow?
High to low pressure from the arterioles to the venules
How would you describe the flow of blood in capillaries?
Not uniform and intermittent. It is not continuous.
What is the Rouleaux Formation?
RBCs touch and stack in the tight vessel of the capillaries because they must squeeze through.
Is there more pre or post capillary resistance? How much more?
Precapillary. There is about a 4:1 ratio of pre to post capillary resistance.
What is the importance of the Rouleaux Formation in capillaries?
It allows the membranes of the RBCs and the capillaries to be in close contact and allows for good gas exchange.
What is transcapillary fluid exchange?
It is the movement of fluid or the exchange of nutrients in and out of the capillary.
What is the plasma oncotic pressure?
Osmotic pressure exerted by contents of the plasma, mainly proteins.
What is the capillary hydrostatic pressure?
Mean capillary blood pressure
What is the tissue oncotic pressure?
Osmotic pressure of the substances in the interstitial area, like proteins. It is the counterpart of the plasma osmotic pressure.
What is the interstitial hydrostatic pressure?
Hydrostatic pressure caused from the volume of fluid in the interstitial area
How is transcapillary exchange controlled in terms of the oncotic and hydrostatic pressure?
The capillary hydrostatic pressure will overcome the interstitial hydrostatic pressure and will cause a net movement of fluid from the capillary. However the oncotic pressure will hold fluid in the capillaries due to the proteins present.
What is the main protein determining the plasma oncotic pressure?
Albumin
How does albumin increase the oncotic pressure to retain fluid in the capillaries?
Albumin interacts with Cl- and leads to the retention of more Na in the capillaries, which exerts an oncotic pressure to uptake fluid from the interstitial area.
How does RV failure affect TCF exchange?
RV failure will lead to increased blood in the vena cava which will go to the liver and can cause cirrhosis and portal hypertension.
How does LV failure affect TCF exchange?
LV failure will cause backups in the pulmonary vein, which can lead to filtration and cause a pulmonary edema due to the high venous pressure.
Which system has a larger effect on the hydrostatic pressure?
Venous system
How does liver disease affect TCF?
It can cause a loss of the protein albumin, which will lead to fluid loss in the capillaries and result in fluid accumulation in the interstitial space.
What is the pre capillary resistance?
It determines the arterial blood flow into the capillary
What is the post capillary resistance?
It determines the flow of blood into the veins from the capillary
Why does the venous system have a larger effect on the hydrostatic pressure?
The venous system has less post capillary pressure so the hydrostatic pressure is nearly entirely determined by the post capillary pressure
If the pre and post capillary pressure both increase, what happens to the hydrostatic pressure?
Increases the capillary hydrostatic pressure
If the pre and post capillary pressure both decrease, what happens to the hydrostatic pressure?
Decreases the capillary hydrostatic pressure
What do prostacyclins result in?
Vasodilation via cAMP
What do Endothelium-Derived Relaxing Factor (EDRF) result in?
Vasodilation via NO
What does nitric oxide result in?
Vasodilation via cGMP
What does endothelin result in?
Vasoconstriction via IP3
What does metabolites like K+/H+/CO2/adenosine cause?
Vasodilation
Describe the structure of the lymphatics.
- Unidirectional blood flow as they have valves
- Non fenestrated endothelium and no smooth muscle
- Large vessels return fluid to the subclavian vein
What is an edema? What symptoms do they show?
It is excess fluid in the interstitial space. They show as swelling of the ankles and ascites.
What can cause edemas?
- Reduction in albumin concentration
- Increase in hydrostatic pressure of the capillaries
- Increased capillary permeability
- Lymphatic obstruction
