Lecture 12: Control of blood flow Flashcards
Acute control of blood flow
Rapid changes in local vasodilation/vasoconstriction
Occurs in seconds/minutes
Theories include vasodilator theory and oxygent lack theory
Long term control of blood flow
Increase in sizes/numbers of vessels
Occurs over days, weeks or months
Vasodilator theory
Increased metabolism causes decreased oxygen availability, which causes formation of vasodilators
Vasodilators include
Adenosine Carbon dioxide Adenosine phosphate compounds Histamine Potassium/hydrogen ions
Oxygen lack theory
Decreased oxygen causes blood vessel relaxation causes vasodilation
Vasomotion is
Cyclical opening and closing of precapillary sphincters
Number of precapillary sphincters open at any given time is roughly proportional to nutritional requirements of tissues
Autoregulation
In any tissue, rapid increase in arterial pressure leads to increased blood flow
Within minutes, blood flow returns to normal even with elevated pressure
Theories to explain autoregulation
Metabolic theory
Myogenic theory
Metabolic theory
Increase in blood flow–>too much oxygen/nutrients–> washes out vasodilators
Myogenic theory
Stretching of vessels–> reactive vasculature constriction
Blood flow control mechanism in kidneys
Tubuloglomerular feedback- involves the macula densa/juxtaglomerular apparatus
Have you looked at endothelial derived mechanism for blood flow control
OK maybe do that
Humoral circulation control- Vasoconstriction
Norepinephrine
Epinephrine
Angiotensin II (Normally acts to increase total
Vasopressin (aka: ADH- very powerful vasoconstrictor)
Humoral circulation control- Vasodilation
Bradykinins (also increases capillary permeability)
Histamine
Adrenal medulla secretes
Epinephrine and norepinephrine
Sympathetic system innervates
All vessels except capillaries
Primarily results in vasoconstriction
Vasoconstrictor area in brain
Anterolateral portions of upper medulla
Transmits continuous signals to blood vessels
Continuous firing results in sympathetic vasoconstrictor tone
Partial state of contraction of blood vessels= vasomotor tone
Vasodilator area in brain
Bilateral in the anterolateral portions of lower medulla
Inhibits activity in vasoconstrictor area
Sensory area in brain
Bilateral in tractus solitarius in posterolateral portion of medulla
Recieves signals via Vagus nerves (CN X) and glossopharyngeal nerves (CN IX)
Controlled by higher nervous centers
Reticular substance (RAS)
Hypothalamus
Cerebral cortex
Baroreceptors function/location
Inhibit vasoconstrictor center
Stimulate vasodilator center
Located in carotid and aortic sinus
Carotid sinuses baroreceptors are stimulated by pressure
Greater than 60mm Hg
Aortic sinus baroreceptors are stimulated by pressure
Greater than 80mm Hg
Signals from baroreceptors do what
Inhibit vasoconstrictor center
Excite vasodilator center
Signals cause either increase or decrease in arterial pressure
Primary function is to reduce the minute by minute variation in arterial pressure