venules - similarities and differences
similar: thin endothelium, little connective tissue
different: convergent pattern of flow. smooth muscle found in larger venules
venules > veins > vena cavae > right atrium
veins compared to arteries
more numerous and larger than arteries.
veins = volume reservoir because they hold > half of blood within circulatory system
thinner walls, more elastic and expandable than arteries
close to surface of the body - you see it through skin! tourniquette stops blood flow and you see bulge before nurse draws out blood!
development of new blood vessels; required for tumour growth; controlled by angiogenic and antiangiogenic cytokines.
cytokines which encourage angiogenesis
"mitogens"; normally produced by smooth muscle cells or pericytes
1) vascular endothelial growth factor (VEGF)
2) fibroblast growth factor (FGF)
cytokines that inhibit angiogenesis
angiostatin and endostatin; treatment for cancer by starving tumours of blood/O2
coronary heart disease aka "coronary artery disease"
blood flow to myocardium is decreased due to fatty deposits narrowing lumen of the coronary arteries; spontaneous development of new collateral circulation to the heart to replace occluded arteries solves the problem
following the ventricular relaxation and aortic valve closure, what is the driving pressure to deliver blood?
elastic recoil of the arteries! allows blood to be propelled further into the systemic circulation - smaller arteries and arterioles
flow is proprotional/ inversely proportional to
proportional to pressure gradient; inverse proportional to resistance of vessels to flow
blood pressure highest in _____ lowest in _____
highest in arteries, lowest in veins;
pressure decreases because energy is lost to resistance from vessels to blood flow and between blood cells
the highest pressure in the systemic circulation; due to pressure from the ventricles.
120 mmHg (ventricular systole)
80 mmHg (ventricular diastole)
diastolic pressure in the arteries during ventricular diastole remains
relatively high! due to elasticity of the arteries (capture and stores energy), even when the ventricles' pressure reduces to 0 during relaxation
pressure wave from the ventricular pushing the blood into the aorta; pulse is after ventricular contraction, but wave travels 10x faster than the actual blood flow. pulse dissapears as it gets to capillaries
strength of the pressure wave;
systolic pressure - diastolic pressure
in the aorta, pulse pressure = 120 - 80 = 40mmHg
valves in the veins; no valves are found in the _____
due to decr in pressure wave, internal one-way valves are required to prevent backward flow when travelling uphill against gravity. no vaves in the vena cava
venous blood flow is continuous rather than pulsatile. venous return is aided by skeletal muscle pump, respiratory pump
would you expect to find valves in the veins leading from brain to heart?
pulse at the carotid and left wrist were checked at the same time, occur simulatneously?
NO. carotid before wrist, because carotid artery is closer to the heart
who's got the higher pulse pressure? 90/60 or 130/95?
130/95 has pulse pressur eof 35mmHg
ventricular blood presure is hard to measure
use arterial pressure instead; (aterial blood pressure or simply called blood pressure)
mean arterial pressure (MAP)
represent driving pressure;
diastolic pressure + 1/3 pulse pressure
ie for person with 120/80, MAP = 80+1/3(40) = 93 mmHg
pressure, flow, resistance
pressure gradient drives flow
flow is opposed by resistance
resistance factors: L, d of vessel, viscosity of fluid
flow (mL/min); velocity (cm/min)
velocity is primarily determined by cross-sectional area
why is MAP closer to diastolic pressure?
because diastole lasts twice as long as systole
low arterial blood pressure; driving force is too low, cannot overcome gravity; dizziness from low O2 levels
elevated arterial blood pressure;
can cause hemorrhage - rupture of blood vessel walls (ie cerebral hemorrhage if in brain -- leading to stroke, loss of neurological function); if rupture of major artery, blood pressure falls below minimum
if heart rate increases what happens to contribution of systolic pressure to arterial pressure? MAP?
blood spends less time the ventricles, therefore increases contribution of systolic pressure to mean arterial pressure. MAP increases too.
112/68. what is the pulse pressure and MAP?
pulse pressure is 112-68=44 mmHg and MAP=68+1/3(44)=82.7 mmHg
used to estimate arterial BP in the radial artery of the arm based on Korotkoff sound; consist of inflatable cuff and pressure gauge;
cuff exerts a pressure higher than systolic pressure driving arterial blood. when cuff pressure exceeds arterial pressure, flow into lower arm stops.
Korotkoff sound is heard through stethoscope as pressure is slowly released, limited flow is permitted: blood squeezes through still compressed artery.
Korotkoff lasts from 120 mmHg down to 80 mmHg. when cuff pressure no longer compress the radial artery, no thump.
Interpretation of Korotkoff sound
when first hear -- systolic pressure
when stop hearing -- diastolic pressure
avg BP value vs abnormal
~120/80; should actually remain below this value; hypertension (abnormal) if systolic rise about 140 mmHg or diastolic is about 90 mmHg
what determines MAP?
simply blood flow in vs out of the arteries.
MAP proportional to CO and R (arterioles)
flow into the aorta is equal to CO of ventricle;
flow out depends on peripheral resistance (resistance to flow from arterioles)
MAP is therefore proportional to
CO X R(arterioles)
why are people with high BP at greater risk for having hemorrhage (bleeding) stroke?
higher pressure stress the walls of the blood vessels, causing weaker areas of vessels to rupture, blood then leaks out. in the brain it is called cerebral hemorrhage -- leads to stroke: insufficient O2 levels to the brain, brain ceases to function
most cases of hypertension are due to _______
changes in blood volume affects BP
volume of blood in body remain relatively constant, but if blood volume increases/decreases, BP will increase/decrease. body is like a baloon filled with water
changes to blood volume
1) injestion of fluids/food (homeostatic compensations) --kidney compensates for increased volume by excreting exess water in the urine.
2) compensation for fluid loss: integration of both kidneys and cardiovascular system.
- drinking, or intraveous infusions
- kidney cannot restore, it can only try to conserve blood, prevent further decrease
- vasoconstriction and incr sympathetic stimulation as cardiovascular compensation -- limited effectiveness
distribution of absolute volume of blood in the cardiovascular system (arterial/venous sides)
important in arterial blood pressure;
arteries= 11% of total blood volume; veins = 60% (blood reservoir - can direct blood to arterial side if needed).
if arterial blood pressure decreases, increased sympathetic activity constricts the veins, decrease their capacity and redistribute blood to arterial side of cirulation.
arterial blood pressure affected by
CO -- effectivness of the pump; stroke volume x heart rate
blood volume (fluid intake vs loss (kidney regulation)
distribution of absolute blood volume (diameter of the veins)
severe circulatory failure; low CO, falling peripheral blood pressure -- tissue perfusion cannot keep up with tissue oxygen demand, so damage to tissues from inadequate oxygen supply, and buildup of metabolic wastes result. must be managed by administration of oxygen, fluids, norepinephrine (stimulate vasoconstriction and CO)
cardiogenic shock: fail to maintain normal CO
hypovolemic shock: decreased circulating blood volume
septic shock: bacterial toxins
anaphylactic shock: massive immune reactions
resistance - primary factor
radius of arterioles; resistance is variable due to smooth muscle in arteriolar walls which can constrict/dilate the vessel;
arterioles responsible for 60% of resistance to blood flow
arteriole resistance is influenced by
1) local control of arteriolar resistance
2) sympathetic reflexes
local control of arteriolar resistance
match tissue blood flow to metabolic needs of the tissue. takes precedence over CNS reflex control in cardiac and skeletal muscles
mediated by CNS to maintain MAP and govern blood distribution for homeostatic needs ie temp regulation
salt and water regulation by kidneys - act either directly on arterioles or by altering autonomic reflex control
vascular smooth muscle automatically adjust own contraction and blood flow; in response in higher pressure, constriction of vessel to reduce blood flow
in absense of autoregulation, increase blood pressure cause increased blood flow through arteriole. but smooth muscle fibers (arteriole wall) stretch because of increased blood pressure. arteriole constricts, this increases the resistance from the arteriole, decrease blood flow through vessel.
cellular level: mechanically gated Ca2+ channels open when vascular smooth muscle cells are stretched. Ca2+ enters and binds calmodulin, activates MLCK which increase myosin ATPase activity, increased crossbridge activity, result: contraction!
local regulation accomplished through __________
paracrines ie O2, CO2, NO; they are secreted by endothelium or by cells that blood is being supplied to
local regulation of arteriolar resistance
a way that tissues regulate own blood supply
metabolic activity of cells change...
levels of paracrines change as cell become more/less metabolically active. ie aerobic metabolism increases CO2 and decreases O2. both factors dilate arterioles.
an increase in blood flow in response to increase in metabolic activity (increased O2 demand, and accumulation of CO2)
if blood vessle is occluded what happens?
accumulation of paracrines in ISF; local hypoxia (low oxygen) leads to secretion of vasodilator NO by endothelial cells
increase in tissue blood flow in response to period of low blood perfusion
NO best known for
male erection reflex; treats erectile dysfunction by prolonging NO activity; also important in pre-eclampsia (elevated blood pressure during pregnancy) and hypertensions
vasodilator paracrine; released in response to myocardial hypoxia (low cardiac tissue O2 in the heart because supply < consumption); effect: dilation of coronary arteries to bring additional flow to heart
paracrines-- not all involved in metabolism
kinins, histamines, serotonin
kinins and histamines
vasodilators in response to inflammation
vasoconstiction, released by activated platelets during damage of blood vessels to reduce blood loss. serotonin agonist (mimic serotonin) stimulate serotonin receptors and cause vasoconstriction to treat migranes (cerebral vasodilation)
atrial natriuretic peptides and angiotensin II (ANG II)
significant vasoactive properties; kidney excretion of ion + water
most systemic arterioles are innervated by sympathetic neurons, exception: __________
erection reflex of penis and clitoris are due to parasympathetic innervation due to release of paracrine vasodilator NO - vasodilation!
myogenic tone of arterioles are due to ________
tonic release of norepinephrine from sympathetic neuron: NE binds alpha receptors on vascular smooth muscle to cause tonic level vasoconstriction. Incr NE = arterioles constrict, Decr NE = dilate
alpha receptors also bind ________ with _______ affinity, but will _______ vasoconstriction
epinephrine (adrenal medulla), binds alpha receptors with lower affinity than NE, will increase vasoconstriction
beta-2 receptors are found in __________ and they respond to/ bind ___________ to cause __________
vascular smooth muscle of heart, liver, skeletal muscle arterioles. binds epinephrine to cause vasodilation
fight or flight! we want more blood flow! epinephrine or NE?
epinephrine release; binds beta-2 receptors; vasodilation of blood vessels; enhanced blood flow to heart, skeletal muscles, liver.
alpha receptors of arteriolar vessels respond to NE -- vasoconstrict; incr resistance/divert blood from nonessential organs (GI) to skeletal muscles, liver, heart.
Swollen, distended, and knotted veins which usually occur in the lower leg(s). The result from a stagnated or sluggish flow of blood in combination with defective valves and weakened walls of the veins
the ratio of the volume occupied by packed red blood cells to the volume of the whole blood as measured by a hematocrit
Hormone secreted by the posterior lobe of the pituitary gland; stimulates the kidneys to reabsorb water. Also called antidiuretic hormone or ADH.`
chemical released in response to falling blood pressure that causes vasoconstriction and release of aldosterone
a spontaneous loss of consciousness caused by insufficient blood to the brain; triggers baroreceptor reflex
condition in which fatty deposits called plaque build up on the inner walls of the arteries
High blood pressure occurring as a sequel to a pre-existing disease or injury
kidney disease, vasoconstriction of
peripheral vessels and Na+ retention.
adrenal medullary tumour secrete excessive catecholamines; high CO and periph vasoconstriction
defect in cardiovascular control center or in baroreceptor/osmotic receptors; strong stimulation of the sympathetic nervous system
treatment of hypertension
Ca2+ channel blockers; diuretics; beta-binding drugs; ACE inhibitors and angiotensin receptor blockers
the product of the metabolism of a substance such as a drug, any substance involved in metabolism (either as a product of metabolism or as necessary for metabolism)