Regulation of Blood Flow Flashcards
What is the equation for Ohm’s Law?
Q= deltaP/R
What is the equation for arterial pressure?
deltaP= CO X TPR
How does the body change the perfusion pressure?
altering the resistance (does not make sense to change the perfusion pressure)
What law do we use to account for turbulent flow?
Poiseuille’s Law
What is Poiseuille’s Law?
Q= pi(radius)^4delatP / 8 * viscosity * tube length
A higher Reynold’s number means what about turbulence?
the higher Reynold’s number, the more turbulent the flow (high resistance, reduced flow)
Name the 3 determinants of rapid vascular resistance regulation?
1) Regulation by local factors (active and reactive hyperemia)
2) Regulation by SNS
3) Regulation by humoral (circulating factors)
Name the 3 determinants of slow vascular resistance regulation?
1) Decrease in vessel lumen size (hypertrophy)
2) Change in vessel number (vascularity)
What is active hyperemia?
when blood flow goes up in organs with increased function (ex. like during exercise)
what causes decreased blood flow to organs that are not needed for exercise during exercise?
increased sympathetic activity (attempts to decrease demand on the heart)
What is reactive hyperemia?
increase in blood flow above resting level that follows reduction of blood flow to a specific tissue (blood flow is inversely related to oxygen tension)
The magnitude and duration of hyperemia is related to what factor?
the length of reduction of blood flow (ischemia)
What is the basic mechanism of hyperemia?
vasodilation in response to decrease in tissue oxygen in order to increase blood flow to oxygen starved tissues
How does low oxygen stimulate vasodilation?
1) Low oxygen decreases SM cell metabolism which will decrease SM force generation (may lead to vascular relaxation)
2) Small arteries MAY have an oxygen-sensing capacity that leads to vascular relaxation
What are the important vasodilator metabolites?
ATP, ADP, AMP, CO2, Lactic Acid, K+
Why do vasodilator metabolites accumulate in active hyperemia?
they are generated at a higher rate than can be efficiently removed
Why do vasodilator metabolites accumulate in reactive hyperemia?
the metabolites are not removed properly due to the ischemia
What is autoregulation?
the capacity of blood vessels to oppose changes in blood flow that are imposed by changed blood pressure
Describe metabolic control of autoregulation?
increased pressure leads to increased flow to tissue that flushes out metabolites and leads to high oxygen levels which stimulates vasoconstriction that decreases flow
Describe myogenic control of autoregulation?
Increased pressure leads to increased flow that stretches vessel and activates calcium stretch channels. This results in an increased forceful vasoconstriction which decreases flow.
What blood vessels ARE NOT innervated?
capillaries
What areas have dense innervation by the ANS?
cutaneous
renal
splanchnic
skeletal muscle
What areas have sparse innervation by the ANS?
cerebral
coronary
What does epinephrine react with at low concentrations?
beta receptors
What does epinephrine react with at higher concentrations?
alpha receptors (especially alpha 1)
Name the 2 circulating vasoconstrictors? How do these work?
angiotensin II
vasopressin
Both of these work to decrease urine output in the kidneys AND are direct vasoconstrictors
Name the circulating vasodilators?
bradykinin, histamine (also increases vascular permeability), prostaglandins
What is the role of atrial natriuretic peptide?
directs kidneys to increase urine output
What is the role of nitric oxide?
released with increased extracellular ATP and shear stress–decrease intracellular calcium and induce vasodilation in LARGE vessels upstream of hyperemic tissues
What is rarefaction?
decrease int he number of blood vessels in tissue
What may induce antiogenesis?
ischemia
What are the angiogenic factors?
FGF, VEGF, angiogenin
What is hypertrophic vascular remodeling?
reduction in the size of the vascular lumen
What are the most important factors regulating coronary blood flow?
metabolic end products
altered oxygen levels
What chemical is thought to contribute to aroudn 25% of exercise-induced vasodilation?
norepinephrine
During what part of the cardiac cycle does the left side of the heart have the lowest blood flow? Why?
systole
Mechanical compression of arteries during systole increases left coronary artery resistance during systole
What allows the left side of the heart to get back blood after each ischemic episode with contraction?
reactive hyperemia during diastole occurs (pressure must be low during this time in order for the heart to be adequately perfused)
What controls skeletal muscle vessels at rest?
SNS
What controls skeletal muscles during exercise?
local control (NO, prostaglandins, potassium, etc.)
Why does reactive hyperemia occur in skeletal muscles during exercise?
because each mechanical compression of arteries stops blood from flowing to the tissue (brief ischemia)
Why does active hyperemia occur in skeletal muscles during exercise?
because they are increasing their function
What is the major control of cerebral circulation?
local control (CO2, ADENOSINE, NO, prostaglandins)
What type of hyperemia occurs upon neuronal stimulation?
active hyperemia
What occurs in splanchnic blood vessels at the start of a meal?
vasoconstriction
What occurs in splanchnic blood vessels due to the SNS as we eat?
active hyperemia increases vasodilation (decreases resistance)
What controls vessels in the skin?
almost entirely controlled by the SNS
The hypothalamus controls activity of what structures in the skin?
arteriovenous anastomoses
What occurs when the skin is heated?
decreased sympathetic activity to anastomoses which leads to vasodilation and increased blood flow to skin to encourage evaporation of heat
What happens when the skin is cooled?
hypothalamus senses this and causes vasoconstriction of arteriovenous anastomoses leading to decreased blood flow to skin to prevent heat loss
