Chapter 14 - Blood vessels, flow, and pressure Flashcards
what determines flow rate
it’s directly proportional to the difference between the pressure at the two ends of the pipe and inversely proportional to the resistance of the pipe
what is bulk flow
flow due to pressure gradient
how does heart move blood
it creates a pressure gradient for bulk flow of blood. a gradient must exist throughout the circulatory system to maintain blood flow
does flow rate depend on absolute pressure
no it depends only on the pressure gradient
what is delta P for systemic circuit
pressure in aorta minus pressure in vena cava just before it empties into right atrium
what is the pressure in the aorta
mean arterial pressure (MAP) = 88mm Hg
what is pressure in vena cava
cenral venous pressure (CVP = 0 mm Hg
what does MAP provide
it is the overall driving force that pushes blood through systemic circuit
how dose pressure gradient in pulmonary circuit compare to systemic circuit
there is a smaller pressure gradient in pulmonary than systemic
what is delta P for pulmonary circuit
pressure in pulmonary arteries minus pressure in pulmonary veins = 15 mm HG
what is pulmonary arterial pressure
15 mm HG
what is pulmonary venous pressure
0mm HG
how does the amount of flow through pulmonary and systemic circuits compare
they are equal. While systemic pressure gradient is much higher the resistance in the pulmonary circuit is much less so it balances out
name 3 factors affecting resistance
radius of vessel (arterioles [and small arteries] can greatly change radius). Length of vessel (stays the same in a person). and viscosity of fluid (blood viscosity depends on the amount of RBCs and proteins - usually constant).
what is the equation for flow
(delta P)(pi)(r^4)/(8)(viscosity)(L)
what is vasoconstriction
decreased radius of arterioles and small arteries. leads to increased resistance
what is vasodilation
increased radius in arterioles and small arteries. leads to decreased resistance
what is total peripheral resistance (TPR)
combined resistance of all blood vessels within the systemic circuit
how does the equation for flow = delta P/R apply to systemic circulation
flow = cardiac output (CO). Delta P = mean arterial pressure (MAP). R = total peripheral resistance (TPR). CO = MAP/TPR
compare arteries and veins
arteries carry blood away from heart while veins return blood to the heart
describe walls of blood vessels
3 layers found in all vessels except capillaries. endothelium lines all blood vessels. smooth muscle layer (also containing elastin and collagen fibers). and connective tissue layer. Capillaries have only endothelium
what is compliance
a measure of the relationship between the pressure and volume changes in a blood vessel.
what is compliance like in arteries
low compliance. Small increase in blood volume causes a large increase in pressure (or a large increase in pressure causes only small degree of expansion of blood vessel wall)
describe blood pressure in the aorta
fluctuates with cardiac cycle. systolic blood pressure = maximum pressure due to ejection of blood into aorta. diastolic blood pressure = minimum pressure (not zero due to elastic recoil)
what does pressure in cuff higher than systolic cause
a fully compressed brachial artery so there are no sounds
what is the pressure at first sound
the systolic blood pressure
what is pressure when sound disappears
diastolic blood pressure
how is measure BP shown
SP/DP
what is pulse pressure
SP - DP ex. 110-70 = 40 mm Hg
how do you calculate MAP from measured BP
SP + (2xDP)/3 ex. (110 + 140)/3 = 88.3 mm Hg
describe arterioles
part of microcirculation. they connect arteries to capillaries. regulate blood flow into capillary b4ds. arterioles are resistance vessels. they can greatly change their diameter through vasoconstriction or vasodilation; arterioles are the best site to regulate resistance
what percentage of TPR is caused by arterioles
more than 60% of TPR is attributable to arterioles
where and how much is the largest pressure drop in vasculature
it is along the arterioles and it is 90 mm Hg to 40 mm Hg
what two things to arteriolar resistance regulate
blood flow into individual capillary beds and MAP
what does radius of arterioles depend on
contraction state of smooth muscle in arteriole wall
what is arteriolar tone
continuously contracted at mid-level. contraction level (radius) is independent of extrinsic influences
how is local blood flow regulated
local blood flow in individual organs/capillary beds is regulated through intrinsic (local) mechanisms
how is systemic arterial pressure (MAP) regulated
it is regulated through extrinsic mechanisms (neural, hormonal)
describe intrinsic control of blood flow to organs
regulation of blood flow to organs is based on need. regulated by varying resistance. vasulcar resistance is regulated through changes in radius of arterioles. local factors regulate radius, thereby regulating blood flow
describe intrinsic control of blood flow to organs based on metabolic activity
changes associated with increased metabolic activity generally cause vasodilation. (carbon dioxide, potassium, hydrogen ions). Changes associated with decreased metabolic activity generally cause vasoconsriction (oxygen)
describe active hypermia
increased blood flow in response to metabolic activity. Steady state: O2 is delivered as fast as it’s consumed, CO2 is removed as fast as it is produced. Increased metabolic rate: O2 is consumed faster than it’s delivered, CO2 is produced faster than its removed.
what is response to low O2 and high CO2
vasodilation and increase in blood flow thus more O2 delivered and more CO2 removed
describe reactive hypermia
increased blood flow in response to a previous reduction in blood flow. Blockage of blood flow to tissues: metabolites increase and oxygen decreases, vasodilation, increased blood flow due to low resistance. When blockage is released: blood flow remains elevated until metabolites are removed, oxygen is delivered, normal concentration restored
what is a myogenic response
change in vascular resistance in response to stretch of blood vessels in absence of external factors
what is the purpose of myogenic autoregulation of blood flow
keep blood flow constant (autoregulation)
describe myogenic autoregulation of blood flow
increased perfusion pressure increases blood flow and pressure in arterioles. increased pressure in arteriole stretches arteriole wall.stretch of vascular smooth muscle induces conraction of vascular smooth muscle (inherent property of smooth muscle). vasoconstriction decreases blood flow
describe regulation of blood flow during exercise
CO increases during exercise. distribution of blood does not increase proportionally: dilation of vessels to skeletal muscle and heart increases blood flow to muscles. constriction of vessels to GI tract and kidneys decreases blood flow to these organs. So disproportionate flow diverts blood flow to muscles
describe sympathetic control of arteriolar radius
sympathetic innervation of smooth muscle of arterioles. smooth muscle of most arterioles (not those in brain) has alpha adrenergic receptors. norepinephrine binds to alpha adrenergic receptors. produces vasoconstriction. increases TPR, increases MAP
what is distribution of adrenergic receptors in skeletal and cardiac muscle
predominately beta 2 receptors. epinephrine causes vasoconstriction at alpha receptors and vasodilation at beta 2 receptors. epinephrine has greater affinity for beta 2 receptors and binds beta 2 in lower concentrations
describe effects of epinephrine on arteriole radius at higher concentrations
binds both alpha and beta 2. this causes vasodilation in cardiac and skeletal vascular beds due to beta 2 receptors and promotes blood flow to these tissues. vasoconstriction due to alpha receptors at most vascular beds. this maintains/increases TPR, and an increase in MAP maintains systemic blood pressure
describe hormonal control of arteriole radius and MAP
epinephrine: released from adrenal medula. Vasopressin (ADH): secreted by posterior petuitary, increases water reabsorption by kidneys, vasoconstriction. Angiotensin II: vasoconstriction increases TPR.
what is the equation for MAP
CO x TPR
what is the equation for CO
HR x SV
what is the total equation for MAP
MAP = HR x SV x TPR
what happens if MAP is less than normal
hypotension leading to inadequate blood flow to tissues
what happens if MAP is greater than normal
hypertension leading to damaging of heart and blood vessels
how is MAP regulated
through control of heart (CO) and arterioles and veins (TPR) due to both neural control and hormonal control
describe short term regulation of MAP
seconds to minutes. regulates CO and TPR, involves heart and blood vessels, primarily neural control.
describe long term regulation of MAP
hours to days. regulates blood volume. involves the kidneys. primarily hormonal control
describe neural control of MAP
negative feedback loops: detector = baroreceptors. integration center = cardiovascular centers of brainstem. controllers = autonomic nervous system. effectors = heart and blood vessels
describe baroreceptors
pressure receptors. mechanoreceptors sensitive to stretch. nerve ending of visceral afferent neurons. high pressure baroreceptors - arterial and are located in aortic arch and in the carotid sinuses. they respond to stretching due to pressure changes in arteries
what is the integration center for blood pressure regulation
medulla oblongota of brainstem
describe inputs and outputs of cardiovascular control center
input comes from: arterial baroreceptors, low-pressure baroreceptors, chemoreceptors, proprioceptors, and higher brain centers. Output goes to sympathetic nervous system and parasympathetic nervous system
describe paraympathetic input into cardiovascular effectors
SA node (decreases HR), and AV node (decreases conduction velocity)
describe sympathetic input into cardiovascular effectors
SA node (increases HR). AV node (increases conduction velocity). ventricular myocardium (increases contractility). arterioles (vasoconstriction increases resistance). Veins (vasoconstriction increases venomotor tone, lower compliance)
what is baroreceptor reflex
fast neural mechanism to mediate short-term regulation of MAP
what are detectors, afferents, integration center, efferents, and effectors of negative feedback loop to maintain blood pressure at normal level
detectors = baroreceptors. afferents = visceral afferents. integration center = cardiovascular control center. efferents = autonomic nervous system. effectors = heart, arterioles, and veins
describe epinephrine control of MAP
released by adrenal medulla in response to sympathetic activity. increases MAP. acts on smooth muscle of arterioles (increases TPR). acts on smooth muscle of veins (increases venomotor tone). acts on heart (increases HR and SV)
where are low pressure baroreceptors located
located at strategic low-pressure sites: walls of large systemic veins, walls of atria, and pulmonary veins.
what do low pressure baroreceptors detect
changes in blood volume. decrease in blood volume activates receptors which trigger responses that act in parallel with the baroreceptor reflex
where is thermoregulation mediated
through the hypothalamus (the bodies thermostat)
what does an increase in core body temp stimulate
decrease in sympathetic activity to skin vasculature. vasodilation in skin blood vessels. increase in heart radiation to environment.
which takes presedence during vigorous exercise: thermoregulation or baroreceptor reflex
thermoregulation
describe baroreceptor reflex contribution to restoring near normal MAP during hemorrhage
Hemorrhage leads to decrease in blood volume - lower CO - decrease in MAP. triggers baroreceptor reflex. increases sympathetic activity. increases peripheral resistance and decreased blood flow in extremities, skin, skeletal muscles, and abdominal viscera. blood diverted to brain and heart (at expense of all else). MAP is restore and maintained at near normal levels
describe capillary anatomy
10-40 billion per body. 5-10 micro meter in diameter. allows blood cells to pass in single file. Walls are single cell layer of endothelium. have greatest total cross-sectional area. have slowest velocity of blood flow which enhances exchange
describe continuous capillaries
found in most organs. have narrow clefts between endothelial cells. allow passage for small water-soluble molecules between cells (exception is brain capillaries)
describe fenestrated capillaries
found in intestines, kidneys, choroid plexuses, and glands. have pores (60-80 nm) that run through endothelial cells. allow more flow of solutes (including small proteins) through
describe discontinuous (sinusoid) capillaries
found in liver spleen and bone marrow. have large gaps between the cells. allow for passage of whole cells
describe metarterioles
structurally between capillaries and smallest arterioles.. directly connect arterioles to venules bypassing capillaries. have smooth muscle at strategic locations: contract and relax in response to local factors.
what does metarteriole contraction cause
increased blood flow through capillary bed
what does metarteriole relaxation cause
decreased blood flow through capillary bed
how does lipophilic diffusion in capillaries work
diffusion across the membrane
how does hydrophilic diffusion in capillaries work
diffusion through clefts/gaps between the cells (paracellular route)
what is transcytosis
endocytosis on luminal side, exocytosis into intersitium on the other side for large macromolecules
are capillaries permeable to water
yes all capillaries, including in the brain are freely permeable to water
describe mediated transport in brain
in brain capillaries tight junctions do not allow solutes to pass between cells (blood-brain barrier)
how does water move in capillaries
through paracellular route between the cells and through water channels in the cells
what is filtration in capillaries
movement out of capillary into interstitial space
what is absorption in capillaries
movement into capillary from interstitial space
what is hydrostatic pressure
force generate by fluid itself (due to blood pressure inside capillary, gravity, fluid outside capillary)
what is osmotic pressure
force exerted on water by non-permeating solutes: large plasma proteins (albumin, globulins, fibrinogen) and proteins in interstitial fluid
what is capillary hydrostatic pressure at arteriole end and venous end
arteriole end = 38 mm Hg. and venous end = 16 mm Hg
what is interstitial hydrostatic pressure
low and constant 0-1 mm Hg
what is capillary and interstitial fluid osmotic pressure
capillary osmotic pressure = 25 mm Hg, constant. interstitial fluid osmotic pressure = 0-1 mm Hg, constant
describe venules
smaller than arterioles. connect capillaries to veins. little smooth muscle in walls. some exchange of material between blood and interstitial fluid
describe veins
large diameter, thinner walls. valves allow unidirectional blood flow: present in peripheral veins (upper and lower limbs). absent in central veins (veins in thorax and abdomen)
describe compliance in veins
high compliance vessels: expand with little change in pressure. function as volume reservoir for blood. 60% of total blood volume in systemic veins at rest
name 4 factors than influence venous pressure and venous return
skeletal muscle pump. respiratory pump. venomotor tone. blood volume.
describe skeletal muscle pump
one-way valves in peripheral veins. when skeletal muscle contracts: squeezes on veins, increasing pressure. blood moves toward heart. blood cannot move backward due to valves. when skeletal muscle relaxes: blood flows into veins between muscles
describe respiratory pump
inspiration: decreases pressure in thoracic cavity. increases pressure in abdominal cavity. pressure on veins in abdominal cavity creates pressure gradient favoring blood movement toward thoracic cavity. increases central venous pressure. increases venous return
describe venomotor tone
it is smooth muscle tension in veins. an increase in venomotor tone: contraction of smooth muscle in the wall of a vein. smooth muscle in walls of veins is innervated by sympathetic nervous system. norepinephrine acting at alpha adrenergic receptors causes venous constriction. increases central venous pressure. decreases venous compliance. increases venous return
describe blood volume as influencer of venous pressure and venous return
increased blood volume leads to increased venous pressure. decreases blood volume leads to decreased venous pressure
describe the lymphatic system
system of vessels that collects and returns excess filtrate to circulation. lymphatic capillaries collect interstitial fluid from loose CT. lymph travels in lymphatic vessels of increasing size. lymphatic vessels resemble veins (much thinner and with more valves). lymphatic vessels go through one or more lymph nodes (full of immune cells). lymphatic vessels merge to form larger trunks, which merge to form two ducts that deliver lymph to the great veins at base of neck (brachiocephalic veins). lymph flows from tissues toward heart (one-way system)
