Traffic - week 10 Flashcards
exchanges between blood and tissue cells takes place in the
the interstitial fluid
all organs receive fresh blood (need)
amount to each organ adjusted based on need
the blood is constantly “reconditioned” so (shower)
its constant
1. it increases cardiac output (digestive system, kidneys)
organization “vascular tree” (aacvv)
aacvv
- arteries
- arterioles
- capillaries
- venules
- veins
flow rate (volume of blood passing through a particular segment of vascular tree per unit time)
- directly proportional to pressure gradient
- inversely proportional (one value decreases another) to resistance (delay to flow from friction)
a. vessel radius - smaller vessels ➝ more resistance
b. viscosity of blood - thicker blood ➝ more resistance
c. length of vessel - longer vessel ➝ more resistance
Arteries are..
fast transport, large
act as a pressure reservoir (arteries)
- walls contain endothelial lining surrounded by smooth muscle and connective tissue fibers (collagen and elastin), which allow walls to stretch to contain pumped blood
- when the heart is relaxing the arteries recoil and keep the blood flowing
fluctuates
arterial pressure
blood pressure is the force exerted by blood on vessel walls
a. depends on blood volume and expansion of vessel
b. systolic pressure is the maximum pressure during systole (should be <120 mmHg)
c. diastolic pressure is the pressure during diastole (should be <80 mmHg)
mean arterial pressure is
the main driving force for blood flow to tissues. MAP = diastolic pressure + 1/3 pulse pressure
Arterioles
major resistance vessels (small radii) - radii adjusted by smooth muscle
- vasoconstriction and vasodilation (narrowing and enlarging)
- normally partially constricted (vascular tone) a. myogenic activity
b. sympathetic innervation
local control of arteriolar radius matches blood flow to…
tissue needs
metabolic factors causing vasodilation (in arterioles)
(1) decreased O2
(2) increased CO2
(3) increased acid (from CO2 and lactic acid)
(4) increased K+ (APs outpacing Na+-K+ pump in brain or skeletal muscle)
(5) increased osmolarity (more solutes formed during times of elevated metabolism)
(6) release of adenosine (in cardiac muscle)
(7) release of prostaglandins (not well understood)
local metabolic factors that cause vasodilation probably act by causing (epiq)
release of chemical mediators from endothelial cells (called vasoactive mediators), e.g. (1) endothelial-derived relaxing factor (EDRF), also known as nitric oxide (NO) inhibits Ca2+ influx in smooth muscle – vasodilator
(2) endothelin – vasoconstrictor
physical influences on vasodilation (runner - mye)
application of heat (vasodilation) or cold (vasoconstriction)
b. myogenic (muscle) responses to stretch (vasoactive substances probably contribute)
(1) tone increases in response to increased stretch (resists stretch) - important to keep flow to tissues constant as MAP changes (pressure auto regulation)
(2) tone decreases in response to decreased stretch - important in restoring flow to previously deprived tissue (reactive hyperemia)
extrinsic control of arteriolar radius helps..
regulate arterial BP
(extrinsic control of bp) sympathetic activity produces
generalized vasoconstriction, increasing resistance and BP (don’t vasoconstrict brain) MAP = CO x total peripheral resistance
a. NE at α receptors causes vasoconstriction
b. E at β2 receptors causes vasodilation (heart, skeletal muscles)
other hormones - extrinsic control of arteries (constrict angie)
a. vasopressin-important in fluid balance, vasoconstrictor
b. angiotensin II-important in fluid balance, vasoconstrictor
local control mechanisms can override
vasodilation
Capillaries are responsible for exchanges between
plasma and interstitial fluid (solute exchange mainly by diffusion)
capillaries have (window tree)
thin, high, slow, lipids, water soluble, transport, leakiness
thin-walled, narrow vessels
- highly branched
- blood flows slowly through individual vessels
- lipid soluble substances pass through cells (O2, CO2)
- water soluble substances pass through pores (ions, glucose, amino acids)
- some vesicular transport (hormones)
- degree of “leakiness” may change due to actin-myosin in capillary cells
precapillary sphincters
rings of smooth muscle can block flow through capillaries in less active tissues
a. sensitive to local metabolic changes
fluid shifts and bulk flow (only 2 fluids)
important in distribution of fluids between plasma and interstitial fluid
fluid(not proteins) pushed out through (art pressure cooker)
pores at arteriolar end (ultrafiltration)
(1) capillary blood pressure (pushes fluid out) exceeds plasma-colloid
osmotic pressure (oncotic pressure - force drawing water toward plasma proteins)
b. fluid reabsorbed at venule end
(1) capillary BP lower than plasma-colloid
osmotic pressure (pulling fluid in)
ultra filtration occurs in.. (open)
open capillaries, reabsorption in closed capillaries
fluid shifts occur as needed - capillaries (closet)
a. loss of blood, shifts to plasma
b. excess fluid in blood, shifts to interstitial fluid
c. keeps plasma volume relatively constant (temporary)