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57 Cards in this Set
- Front
- Back
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ACUTE control of local and humoral control of tissue blood flow occurs within what time frame
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seconds to minutes
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ACUTE control of local and humoral control of tissue blood flow occurs via what mechanisms
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local and neurohormonal
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LONG-TERM control of local and humoral control of tissue blood flow occurs within what time frame
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over days to months
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LONG-TERM control of local and humoral control of tissue and blood flow is due to what
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change in size or number of blood vessels
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baseline tone is acheived how
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by partial constriction of the resistance vessels which allows both vasodilation and further vasoconstriction
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the walls of resistance vessels are composed of what
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primarily of smooth muscle
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variation of smooth muscle contraction allows for what to occur
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*preferential distribution of blood flow throughout the body
*control of arterial & venous tone *total peripheral resistance |
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muscle can increase how much from resting to active state
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20 fold
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smooth muscle contraction develops slowly or rapidly
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very slowly
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smooth muscle contraction develops low or high forces
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high
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smooth muscle maintains contraction for how long
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long periods
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what are the mechanisms for contraction of smooth muscle
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*electromechanical coupling
*pharmacmechanical coupling |
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what is occuring with electromechanical coupling
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increased myoplasmic Ca+ via voltage gated Ca channels when an AP arrives
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what is pharmacomehanical coupling
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*occurs via receptor mediated Ca channels
*occurs in the ABSENCE of electrical excitation |
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what is the primary mechanism for smooth muscle contraction
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pharmacomechanical coupling
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what are the theories of local blood flow regulation
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1-vasodilator theory
2-oxygen lack theory |
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what is the vasodilator theory
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vasodilator substances produced and released d/t and increase in metabolism or a decrease in supply of o2 or other nutrients
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what are the proposed vasodilator substances r/t to the vasodilator theory
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*adenosine
*CO2 *histamine *K+ or H+ ions *nitric oxide *prostaglandins **combo of these** |
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what does the oxygen lack theory state
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*in the absence of adequate o2 (or some other nutrient) the smooth muscle is not able to maintain contraction
*when it relaxes the blood vessel dilates allow more blood & o2 to be provided |
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what would occur with too much blood flow or hyperoxygenation
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it would allow for increased contraction of smooth muscle thereby decreasing blood vessel diameter & returning blood flow to acceptable level
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what is reactive hyperemia
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*following occulusion of blood supply to tissue upon release of the occlusion the blood flow may increase to several times the baseline
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with reactive hyperemia what is the duration
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it is related to duration of occlusion
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what is active hyperemia
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increased blood flow in highly active tissue
(e.g. exercising skeletal muscle) |
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what is autoregulation
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maintenance of or rapid return to approximately normal blood flow following abrupt changes in arterial pressure
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what are the proposed mechanisms for autoregulation
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1-metabolic theory
2-myogenic theory |
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what is metabolic theory
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*similar to o2 lack theory of local blood flow regulation
*excess o2 or other nutrient causes increased smooth muscle contraction w/ subsequent decrease in blood flow |
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what is myogenic theory
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increase or decrease in pressure initially increases or decreases flow, but the change in transmural pressure initiates contraction or relaxation of vascular smooth muscle
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with myogenic theory what allows rapid Ca+ entry resulting in contraction
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stretch induced vascular depolarization
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myogenic theory of autoregulation is independent of what factors
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*neurohumoral influences
*intact endothelium |
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what is the myogenic theory of autoregulation overriden by
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metabolic needs of the tissue
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locally mediated vasodilation affects only what vessels
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the small arteries and arterioles
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locally mediated vasodilation does NOT affect what vessels
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larger upstream arteries
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what occurs when vasodilation occurs downstream
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*it increases flow through the larger arteries upstream
*this increased flow places a shear stress on the vascular endothelium upstream which releases EDRF (primarily NO) w/ subsequent vasodilation of these vessels |
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what is baseline tone of blood vessels INDEPENDENT of
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nervous system input
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baseline vascular tone is possibly d/t what factors
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*myogenic activity in response to stretch imposed by the blood pressure
*high o2 content of arterial blood *presence of Ca+ *some unknown plasma factor |
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regarding neurohormonal control how are substances produced and released
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both centrally and locally
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vasoconstrictors include what substances
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*norepi
*epi *angiotension II *vasopressin (ADH) *endothelin |
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where is norepi released from
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sympathetic nerve endings and the adrenal medulla
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where is epi released from
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the adrenal medulla
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what does angiotension II cause to occur
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widespread constriction of small arterioles resulting in increased peripheral resistance
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vasopressin (ADH) is released from where
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the posterior pituitary
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vasopressin (ADH) has what function
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functions to increase tubular reabsorption of water
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endothelin is released from where
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damaged endothelial cells
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what does endothelin cause to occur
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local vasoconstriction and reduced bleeding
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vasodilators include what substances
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*bradykinin
*histamine |
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what is enzyme kallikrein
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it is activated by many factors and acts on alpha-2 globulin to release kallidin which is converted to bradykinin
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what does bradykinin do
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produces arteriolar dilation and increased capillary permeability
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which substance is an importat factor in capillary leakage in inflammation and in regulation of skin blood flow
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bradykinin
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what does histamine do
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causes arteriolar dilation and increases capillary permeability following release from inflammed or damaged tissues
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what are other factors that cause vasodilation
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*increased K
*increased Mg *increased H *acetate *citrate *increased CO2 (cerebral) |
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what are other factors that cause vasoconstriction
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*increased Ca
*decreased H *increased CO2 (systemically via SNS) |
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long term regulation of blood flow regulates blood flow fairly well b/t what blood pressures
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50-250 mmHg
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long term blood pressure control occurs in what time frame
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over days to months
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long term regulation of blood flow is primarily acheived how
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through change in vascularity of tissues
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angiogenesis is stimulated by what factors
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*inadeqate o2
*lack of other necessary nutrients |
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what are the mediators of angiogenesis
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(multiple substances id'd which stimulate vascular growth)
*vascular endothelial growth factor (VGEF) *fibroblast growth factor *angiogenin |
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what is stimulation of angiogensis dependent on
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MAXIMUM need rather than average need
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