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Blood Vessels
chapter 20-saladin
87
Anatomy
Graduate
11/07/2009

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Term
Tunica interna (intima)
Definition
smooth inner layer repels blood cells and platelets
simple squamous and basement membrane (layer of fibrous tissue)
Term
Tunica media
Definition
middle layer
thickest; smooth muscle, collagen, some elastic
smooth muscle for vasomotion
Term
Tunica externa (tunica adventitia)
Definition
outer layer
loose connective tissue with vasa vasorum
Term
Conducting (elastic) arteries
Definition
pulmonary, aorta and common carotid
expand during systole, recoil during diastole; lessens fluctuations in BP
tunica media: perforated sheets of elastic tissue
Term
Distributing (muscular) arteries
Definition
distributes blood to specific organs; femoral and splenic
smooth muscle layers constitute 3/4 of wall thickness
Term
Resistance (small) arteries
Definition
arterioles control amount of blood to various organs
Term
Metarterioles
Definition
short vessels connect arterioles to capillaries
muscle cells form a precapillary sphincter about entrance to capillary
Term
Venules
Definition
postcapillary venules more porous than capillaries
Term
Medium veins ~ 10 mm D
Definition
low pressure (~ 10 mmHg)
thin elastic walls have high capacitance
valves aid upward blood flow
Term
Venous sinuses
Definition
very thin walls, large lumen
no smooth muscle
Term
Large veins- D >10 mm
Definition
Venae cavae, pulmonary veins
Term
Carotid sinuses
Definition
baroceptors
wall of internal carotid artery
monitors BP – signals brainstem
-HR dec and vessel dilation detection
Term
Carotid bodies
Definition
chemoceptors
oval bodies near carotids
monitor blood chemistry
-adjust respiration to stabilize pH, -CO2, and O2
Term
Aortic bodies
Definition
chemoceptors
walls of aorta
aorta also contains baroceptors
Term
Precapillary sphincters
Definition
control bed perfusion
~25% of the capillaries are open at a given time
~90% closed in resting skeletal muscle
Term
Continuous Capillaries
Definition
most tissues
endothelial cells with tight junctions and intercellular clefts (passage of solutes)
Term
Fenestrated Capillaries
Definition
kidneys, small intestine
organs that require rapid absorption or filtration
filtration ‘pores’ thin glycoprotein layer; allows passage of small molecules
Term
Sinusoids Capillaries
Definition
liver, bone marrow, spleen
irregular blood-filled spaces; large fenestrations, allow proteins and blood cells to enter
Term
Simple Circulation pathway
Definition
heart --> arteries --> arterioles -->capillaries --> venules -->veins
Term
Portal Circulatory system
Definition
blood flows through two consecutive capillary networks before returning to heart
Term
Anastomoses
Definition
is a network of streams that both branch out and reconnect, such as blood vessels or leaf veins.
Term
Arteriovenous shunt
Definition
artery flows directly into vein
Term
Venous anastomosis
Definition
most common, blockage less serious
alternate drainage of organs
Term
Arterial anastomosis
Definition
collateral circulation (coronary)
Term
Blood Flow
Definition
amount of blood flowing through a tissue in a given time (ml/min)
Term
Perfusion
Definition
rate of blood flow per given mass of tissue (ml/min/g)
Term
Hemodynamics
Definition
blood flow dependent on pressure and resistance
flow is proportional to the change in pressure dived by resistance of flow
Term
Pulse pressure
Definition
systolic - diastolic
important measure of stress exerted on small arteries
Term
Mean arterial pressure (MAP)
Definition
measurements taken at intervals of cardiac cycle, best estimate: diastolic pressure + (1/3 of pulse pressure)
varies with gravity: standing; 62 - head, 180 - ankle
Term
Hypertension
Definition
chronic (rest) BP > 140/90
Higher in males
weakens small arteries (aneurysm)
exacerbates athersclerosis
Term
Hypotension
Definition
chronic low resting BP
caused by blood loss, dehydration, anemia
Term
Treatment of Hypertension
Definition
Diuretics (thiazides)
a1 blockers (b blockers)
ACE inhibitors
Angiotensin II antagonists
Ca2+ channel blockers
Term
Angiotensin System
Definition
Angiotensinogen-->Angiotensin I
-->Angiotensin II(potent vasoconstrictor)
Term
Renin
Definition
kidney enzyme that converts angiotensinogen to angiotensin 1
-enzyme released when BP is low
Term
angiotensin-converting enzyme
Definition
ACE
converts angiotensin 1 --> angiotensin 2
ACE inhibitors block this conversion to lower BP
Term
Angiotensin 2 Antagonists
Definition
Losartan, Valsartan
competes at glomerous of kindey
no constriction of arterioles
Term
Blood viscosity
Definition
regulated by RBC’s and albumin
dec viscosity with anemia, hypoproteinemia
inc viscosity with polycythemia , dehydration
Term
Vessel length
Definition
pressure and flow dec with distance (friction)
Term
Vessel radius
Definition
very powerful influence over flow
most adjustable variable, controls resistance quickly
Term
vasomotion
Definition
change in vessel radius
(vasoconstriction, vasodilation)
Term
laminar flow
Definition
flows in layers, faster in center
Term
Blood flow and Radius of Vessel
Definition
blood flow (F) proportional to the fourth power of radius (r)
arterioles can constrict to 1/3 of fully relaxed radius
3X inc in radius results in 81X inc in flow
Term
From aorta to capillaries
Definition
flow dec for 3 reasons
greater distance, more friction and dec flow
smaller radii of arterioles and capillaries
farther from heart, greater total cross sectional area
Term
From capillaries to vena cava
Definition
flow inc again
large amount of blood forced into smaller channels
never regains velocity of large arteries
Term
Metabolic autoregulation
Definition
local control
decreased perfusion causes waste accumulation = vasodilation
Term
Vasoactive chemicals
Definition
histamine, bradykinin
Term
Reactive hyperemia
Definition
blood supply cut off then restored
Term
Angiogenesis
Definition
growth of new vessels
controlled by growth factors and inhibitors
Term
Neural Control: Baroreflex
Definition
aortic arch
aortic sinuses (behind aortic valve cusps)
carotid sinus (base of each internal carotid artery)
right atrium
detect changes
Term
Autonomic negative feedback response
to Baroreceptors
Definition
inc BP causes rate of signals to rise, inhibits vasomotor center, dec sympathetic tone, vasodilation causes BP dec

dec BP causes rate of signals to drop, excites vasomotor center, inc sympathetic tone, vasoconstriction and BP inc
Term
Orthostatic Hypotension
Definition
sudden loss of input from baroceptors
sudden standing from rest pools blood in lower limbs
dec BP causes fainting
Term
Autonomic response to changes in blood chemistry
Definition
pH, O2, CO2
primary role: adjust respiration
secondary role: vasomotion
Term
Medullary ischemic reflex
Definition
inadequate perfusion of brainstem
inc cardiac output and causes widespread vasoconstriction
inc BP
Term
Vasomotor center of medulla
Definition
sympathetic control stimulates most vessels to constrict (dilates vessels in skeletal and cardiac muscle)
baroreflexes
chemoreflexes
medullary ischemic reflex
(all autonomic reflexes)
Term
Aldosterone
Definition
promotes Na+ and water retention by kidneys
increases blood volume and pressure
Term
Atrial natriuretic factor
Definition
(ANP) (inc urinary sodium excretion)
general vasodilator
Inhibits renin and aldosterone secretion
elevated in congestive heart failure (BNP assay kits)
nesiritide (Natrecor®) recombinant human BNP
Term
ADH
Definition
antidiruetic hormone
pathologically high concentrations, vasoconstriction
(water retention)
Term
Epinephrine and NE
Definition
most blood vessels
binds to alpha-adrenergic receptors, vasoconstriction
skeletal and cardiac muscle blood vessels
binds to beta-adrenergic receptors, vasodilation
Term
Localized vasoconstriction
Definition
pressure downstream drops, pressure upstream rises
Term
Arterioles
Definition
most control over peripheral resistance
located on proximal side of capillary beds
most numerous
more muscular by diameter
Term
Capillary Exchange - Diffusion
Definition
Lipid soluble substances
steroid hormones, O2 and CO2 diffuse easily
Term
Capillary Exchange - Transcytosis
Definition
Pinocytosis - transport vesicles across cell - exocytosis
Important for fatty acids albumin and large peptides - hormones
Term
Filtration and Reabsorption
Definition
blood (hydrostatic) vs colloid osmotic pressure (COP)
filtration on aterial end
absorption on venous
Term
blood (hydrostatic) pressure
Definition
drives fluid out of capillary
high on arterial end of capillary, low on venous end
Term
colloid osmotic pressure (COP)
Definition
draws fluid into capillary
results from plasma proteins (albumin)- more in blood
oncotic pressure = net COP (blood COP - tissue COP)
Term
Causes of Edema
Definition
inc cap filrtaion
poor venous return
kidney failure
inc histadine
dec capilarry reabsorption
obstructed lymphatic drainage
Term
Tissue necrosis
Definition
edema
oxygen delivery and waste removal impaired
Term
Pulmonary edema
Definition
result =suffocation
Term
Cerebral edema
Definition
result=headaches, nausea, seizures and coma
Term
Circulatory shock Results
Definition
excess fluid in tissue spaces causes low blood volume and low BP
Term
Mechanisms of Venous Return
Definition
Gravity drains blood from head and neck
Skeletal muscle pump in the limbs
Pressure gradient
Thoracic pump
Cardiac suction of expanding atrial space
Term
Thoracic pump
Definition
inhalation - thoracic cavity expands (pressure dec) abdominal pressure inc, forcing blood upward
Term
Circulatory Shock
Definition
Any state where Cardiac output insufficient to meet metabolic needs
Term
cardiogenic shock
Definition
- inadequate pumping of heart (MI)
Term
hypovolemic shock
Definition
low venous return shock
most common
loss of blood volume: trauma, burns, dehydration
Term
obstructed venous return shock
Definition
tumor or aneurysm
Term
venous pooling (vascular) shock
Definition
low venous return
long periods of standing, sitting or widespread vasodilation
neurogenic shock - loss of vasomotor tone, vasodilation
causes from emotional shock to brainstem injury
Term
Septic shock
Definition
bacterial toxins trigger vasodilation and inc capillary permeability
Term
Anaphylactic shock
Definition
severe immune reaction to antigen, histamine release, generalized vasodilation, inc capillary permeability
Term
Compensated shock
Definition
dec BP triggers baroreflex and production of angiotensin II, both stimulate vasoconstriction
Term
Decompensated shock
Definition
positive feedback loops
slow circulation -> disseminated intravascular coagulation -> slow circulation
Term
ischemia and acidosis of brainstem -> dec vasomotor tone, vasodilation -> dec CO -> ischemia and acidosis of brainstem
Definition
Term
cerebral arteries
Definition
dilate as BP dec, constrict as BP rises
main chemical stimulus: pH
hypercapnia (CO2 inc) in brain, pH dec, triggers vasodilation
hypocapnia, inc pH, vasoconstriction
Term
transient ischemic attacks
Definition
TIA
dizziness, loss of vision, weakness, paralysis, headache or aphasia; lasts from a moment to a few hours, often early warning of impending stroke
Term
cerebral vascular accident
Definition
stroke
CVA
brain infarction caused by ischemia
atherosclerosis, thrombosis, ruptured aneurysm
effects range from unnoticeable to fatal
blindness, paralysis, loss of sensation, loss of speech common
Term
Special Circulatory Routes - Skeletal Muscle
Definition
During exercise
arterioles dilate in response to epinephrine and sympathetic nerves
precapillary sphincters dilate due to lactic acid, CO2
blood flow can increase 20 fold
Muscular contraction impedes flow
isometric contraction causes fatigue faster than isotonic
Term
Special Circulatory Routes - Lungs
Definition
Low pulmonary blood pressure
flow slower, more time for gas exchange
capillary fluid absorption
pulmonary arteries constrict, redirects flow to better ventilated region
during hypoxia
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