control of blood flow Flashcards
Acute (metabolic control)
response in seconds. finite response. Controlled mainly vasodilation / vasoconstriction of
arterioles, metarterioles, precapillary sphincters
Long-term
sow response – takes days / weeks
More permanent changes in metabolism; oxygen content; input
pressure
Almost infinite response
Controlled by increasing / decreasing physical size and
number of blood vessels within tissue
8 fold increase in metabolism results in
four fold increase in BF
Acute Control – Response to Decrease in oxygen
results in an increase in blood flow through the tissue. Increased flow almost makes up for decreased oxygen carrying capacity
causes of decraesed arterial oxygen saturation
High altitude Pneumonia Carbon monoxide poisoning Cyanide poisonin
Precapillary Sphincters
Open and close multiple times each minute
As duration of open phase increases, flow through the tissue increases
Duration of open phase inversely proportional to oxygen content and
directly proportional to concentration of metabolic waste
Theories for Acute Regulation
Oxygen (nutrient) lack theory
Oxygen & other nutrients needed for smooth muscle
contraction
Nutrients not available – muscle relaxes producing dilation
As metabolism increases local decrease in oxygen content
results in vasodilation
Theories for Acute Regulation Vasodialator theory
As metabolism increases production / concentration of
metabolic waste increases
Metabolic waste interacts with smooth muscle resulting in dilation
both Oxygen (nutrient) lack theory and Vasodialator theory
affect tone of smooth muscle mainly in metarterioles
and precapillary sphincters with some affect on arterioles
Overall tone of arterioles depends
on tone of autonomic nervous system
vasodilator factor release proportional to
tissue metabolism
on tone of autonomic nervous system
overall concentration of vasodilator factors. Factors cause direct dilation of metarterioles & precapillary sphincters.
Adenosine
vasodilator Released from tissue in response to decreased oxygen
concentration
Released by cardiac cells when coronary blood flow
inadequate, oxygen concentration has decreased, & stores of
ATP has decreased.
Carbon dioxide
potent vasodilator especially in the brain
Adenosine phosphate compounds
Result of increased ATP degradation. vasoldilator
histamine
potent vasodilator released from mast cells & basophils
Hydrogen ions
vasodilator Released from tissue in form of lactic acid in response to decreased oxygen concentration
potassium
vasodilator
Active Hyperemia
Response to increased metabolic demand with a tissue
Example
Increased metabolic activity of skeletal muscle