Cardiac - Microcirculation Flashcards
What pathways can blood take through the microcirculation?
Arterioles - capillaries - venules
Arterioles - Metaarterioles - Capillaries - Venules
Arterioles - Metaarterioles - Venules
What is the structure of capillaries?
They contain no connective tissue or smooth muscle
They consist of a thin tube of endothelial cells with their wall eing only one cell thick
What type of innervation do the arterioles, metaarterioles, precapillary sphincter, and venules all receive?
Sympathetic
Do the capillaries receive sympathetic innervation?
No
Where is capillary density generally high?
Metabolically active tissue (heart)
Where is capillary density usually low?
Tissues with low metablic activity
What is blood flow like in capillaries?
Turbulent
How does blood flow through the capillaries?
RBCs tendn to flow in a single fle formation and are usually folded to fit through the capillary lumen.
Blouses of plasma turbulently flow between RBCs
Why is the turbulent mixing of flow as plasma moves through capillaries important?
It helps expose all the pladma to the endothelial surface/exchange area
How is flow in the microcirculation regulated and controlled?
By active modulatin of anatomical components
Balance between constrictor influences and metabolic vasodilators
Vessel radius has a major influence on flow
What are the major mechanisms that modify vessel radius?
Metabolic activity
Activity of autonomic nerves
Ciculating vasoactive agents (NE, Angiotensin II, etc.)
Endothelium derived vasoconstrictors and dilators
What is the primary regulators of capillary flow? Why?
Precapillary vessels because they have the most vascular smooth muscle
What regulates capillary flow?
Vascular smooth muscle and sympathetic innervation in the arterioles, metarterioles,or precapillary sphincters and their exposure to tissue metabolites
Vascular smooth muscles in enules effect vascular capacitance more and has little effect on vascuale flow
Arterioles are most sensitive to..
neural stimuli
Precapillary sphincters are most sensitive to…
Tissue metabolites (H+, CO2, adenosine, etc.)
Under normal circumstancs, the degree of vasoconstriction in the microcirculatory vasculature is determined by…
The algebraic sum of the effects of constrictor neural stimuli and vasodilatory metabolites
Increasing the neural activity in sympathetic efferents results in…
constriction
Dilation of vasomotor tone occurs by…
passievly reducing sympathetic efferent activity
What mediates active vasodilation?
Sympathetic Cholinergic fibers
What effect does increased metabolic activity have on precapillary vessels and over all capillary perfusion?
There is an increase in the number of precapillary vessels that are open, resulting n increased capillary perfusion
By products of metabolism are all local….
Vasodilators
Oxygen, BP, circulating catecholamines, and sympathetic nerves are all vaso…
vasoconstrictor stimuli
What are the types of exchange vessels?
Capillaries
Portions of terminal arterioles
Venules not encircled with smooth muscle