Lecture 12 Flashcards
Acute Blood Flow Control
Causes rapid changes in local vasodilation/vasoconstriction
Occurs in seconds to minutes
Long-Term Blood Flow Control
Results in a increase in sizes/numbers of vessels
Occurs over a period of days, weeks, or months
Vasodilator Theory
As metabolism increases, oxygen availability decreases; this results in the formation of vasodilators (adenosine, CO2, histamine, K+, H+, adenosine phosphate compunds)
Oxygen (Nutrient) Lack Theory
As the concentration of oxygen decreases, blood vessels relax, which leads to vasodilation
Vasomotion
Cyclical opening and closing of precapillary sphincters; # of precapillary sphincters open at any given time is roughly proportional to nutritional requirements of tissues; assumption is that smooth muscles require oxygen to remain contracted
Reactive Hyperemia
Tissue blood flow is blocked from seconds to hours or more; when unblocked, blood flow increases 4-7 times normal
Active Hyperemia
When any tissue becomes active, rate of blood flow increases
Autoregulation
Rapid increase in arterial pressure leads to increased blood flow; within minutes, blood flow returns to normal even with elevated pressure
Metabolic Theory
Increase in blood flow leads to too much oxygen or nutrients, which washes out vasodilators
Myogenic Theory
Stretching of blood vessels leads to reactive vasculature constriction
Kidney Blood Flow Control Mechanism
Tubuloglomerular feedback; involves the macula densa/juxtaglomerular appartus
Brain Blood Flow Control Mechanism
Concentration of CO2 and/or H+ increases, which leads to cerebral vessel dilation, which washes out excess CO2 and/or H+
Skin Blood Flow Regulation
Blood flow linked to body temperature and controlled by sympathetic nerves via CNS; 3mL/min/100g of tissue in COLD weather; 7-8 mL/min for entire body in HOT weather
Vasoconstrictors under Humoral Circulation Control
Norepinephrine, epinephrine, angiotensin II (normally acts to increase total peripheral resistance), vasopressin (very powerful vasoconstrictor; major function is to control body fluid volume), catecholamines, endothelin
Vasodilators under Humoral Circulation Control
Bradykinins (causes both vasodilation and increased capillary permeability), histamine (powerful vasodilator derived from mast cells and basophils), prostaglandins, nitric oxide
Sympathetic System (What vessels it innervates and its function)
Innervates all vessels except capillaries and primarily results in vasoconstriction
What secretes epinephrine and norepinephrine?
Adrenal medulla
Vasoconstriction Area
Anterolateral portions of upper medulla; transmits continuous signals to blood vessels; continual firing results in sympathetic vasoconstrictor tone; partial state of contraction of blood vessels = vasomotor tone
Vasodilator Area
Bilateral in the anterolateral portions of lower medulla; inhibits activity in vasoconstrictor area
Sensory Area
Bilateral in tractus solitarius in posterolateral portion of medulla; receives signals via: Vagus Nerves (CN X) Glossopharyngeal Nerves (CN IX)
Neural Rapid Control of Arterial Pressure
Simultaneous Changes: Constriction of most systemic arteries, constriction of veins, and increased heart rate
Rapid response, increased blood pressure during exercise (accompanied by vasodilation), and alarm reaction (fight or flight)
Baroreceptors
Located in carotid sinuses and aortic sinus; stimulated by low arterial pressures; controlled by reticular substance (RAS), hypothalamus, and cerebral cortex
At what pressure is carotid sinus baroreceptors stimulated?
> 60 mm Hg
At what pressure is aortic sinus baroreceptors stimulated?
> 80 mm 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
Chemoreceptors
Located in carotid bodies in bifurcation of the common carotids and in aortic bodies; chemosensitive cells sensitive to lack of oxygen, carbon dioxide excess, and H+ excess; signals pass through Herring’s nerves and vagus nerves and play a more important role in respiratory control
Atrial Reflexes
Low pressure receptors are located in the atria and pulmonary arteries and play an important role in minimizing arterial pressure changes in response to changes in blood volume
Increase in Atrial Stretch results in:
Reflex dilation of kidney afferent arterioles (increases kidney fluid loss, decreases blood volume), increase in heart rate (via CN X to medulla), signals to hypothalamus (to decrease ADH), atrial natriuretic peptide, which goes to the kidneys to increase glomerular flow rate and decrease Na+ reabsorption
How is arterial pressure calculated?
Cardiac output X total peripheral resistance
