36 - Physiology of microcirculation. Functional organization of the microcirculatory unit. Organ related specific of the capillaries. Control of the microcirculation

sections

microcirculation

functional organisation of microcirculatory units

organ related to specification of capillaries

control of microcirculation

microcirculation

flow of blood within the smallest vessels. These vessels are embedded in the organ tissues. The microcirculation is made of the arterioles, capillaries, and venules, terminal lymphatic cells.

functional organisation of microcirculatory units

1. Arterioles- branch off arteries

   • innervated by the sympathetic adrenergic fibers and they are highly responsible for the sympathetic vasoconstriction

   • The rhythmical contraction and the relaxation of the arterioles occurs, spontaneously via spontaneous vasomotor.

2. capillaries one cell thick for diffusion

   • There are 3 main structural classifications: fenestrated, discontinuous and continuous

   • The capillaries are known for their high surface area and high permeability, to fluid and macromolecules

   • primary site of the exchange for fluid, electrolytes gases and macromolecules.

3. venules

   • The sympathetic innervation of the large venules alters the venular tone, which regulates the hydrostatic pressure.

4. Terminal lymphatic vessels

   • The spontaneous and stretch activated vasomotion acts as a “pump” to the lymph.

   • The sympathetic nerves cause contraction.

   • have one-way valves direct lymph from the tissue and back to the systemic regulation via the thoracic duct and subclavian veins.

types of capillaries and their specific organs

1. Continuous- e.g. muscle, skin and lung and CNS --- uninterrupted lining, for the small ions (water, ions) to pass through

2. Fenestrated e.g. exocrine glands and intestinal mucosa --- small pores (fenestrae) in walls so more permeable and allow small proteins to diffuse.

3. Discontinuous/sinusoidal e.g. in the liver, spleen and bone marrow. large gaps between endothelial cells and a discontinuous basement membrane, allowing even blood cells and large proteins to pass through.

control of microcirculation

• neural control - SNS releases norepinephrine which binds to alpha receptors causing vasoconstriction

• Hormones - angiotensin ii and vasopressin cause vasoconstriction and atrial natriuretic peptide promote vasodilation

• accumulation of CO2, H, adenosine and low O2 cause vasodilation to increase perfusion