Microcirculation and Capillary Function Flashcards
What does microcirculation include?
The terminal arterioles, capillaries, and post - capillary venules
What is the function of microcirculation?
Transfer of gases, water, nutrients and other substances between blood and tissues
How does microcirculation work involving temperature control?
To promote heat loss: decrease in sympathetic drive to AVA’s causes vasodilation, blood shunted to dermal venous plexus raising cutaneous flow and promoting heat loss
To conserve heat:
increase sympathetic drive, AVA’s constrict, less heat loss
AVA’s = arteriovenous anastomoses
What does the density of the microcirculation depend on?
The supply of blood to each tissue (terminal arterioles). The tone of this is controlled by local factors
What do capillaries and post - capillaries have to make them constrict?
What do these capillaries act as? What type of epithelium do they have?
They have pericytes because they do not have any smooth muscle
They acts as exchange vessels. They have continuous epithelium.
What is the role of the lymphatic capillaries and where do they drain to?
The role is to absorb fluid and protein and return this back to the blood through the venous circulation.
What is the process of vasomotion?
What is transit time?
- terminal arterioles constrict and relax periodically
- how long blood takes to flow through the capillaries (decrease in arteriolar tone causes transit time to fall (during exercise)
What is the arrangement of smooth muscle and epithelium cells around a blood vessel?
Smooth muscle is wrapped around the vessel and epithelium cells.
What affect does nitric oxide have on the blood vessels?
Nitric oxide
What are the 3 types of capillary walls?
Continuous - cells are very packed together, continuous have 1-3 endothelial cells in each layer and surrounded by a basement membrane.
They are exchange vessels.
It is permeable to some substances but not others.
Efficient exchange due to short trans-capillary diffusion distance.
Fenestrated - Endothelium perforated by small fenestrae bridged by a fenestrae diaphragm.
Discontinuous - Endothelial gaps >100nm wise basal lamina is also interrupted
Where are the 3 types of continuous, fenestrated, discontinous found?
Continuous - lung, skeletal muscle, myocardium, skin, connective tissue, fat
Fenestrated - kidneys, intestinal mucosa, joints
Discontinuous - bone marrow, spleen and liver
What ways can substances permeate the capillary wall?
Transcellular
Intercellular
Fenestrated
Movement of solutes across exchange vessel walls:
- Gases
- Small solutes
- Water
- Proteins
Gases: can move across the plasma membrane - very fast, diffusion
Small solutes: e.g. salts, glucose, amino acids: move via intercellular junctions or fenestrae
Water: about 90% via intercellular junctions, about 10% via water channels in the plasmalemma
Proteins: mainly vesicular transport, endothelial channels transiently formed by vesicular fusion - very slow, convection
What substance is most permeable to the capilarries?
What is this compared against?
Oxygen (3000)
Water (1)
What net volume leave the microcirculation in litres and returned to the bloodstream via the lymphatic system?
8 litres