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Terms in this set (78)
What are the three layers (tunics) of the arteries and veins?
tunica interna, tunica media, and tunica externa
central blood-containing space surrounded by tunics
what are capillaries composed of?
endothelial cells with sparse basal lamina
what is the difference between thicknesses of tunica media in arteries and veins?
tunica media much thicker in arteries than in veins
what are varicose veins?
tunica interna (tunica intima)
endothelial cell layer that lines the lumen of all vessels
smooth muscle and elastic fiber layer, regulated by sympathetic nervous system
-controls vasoconstriction/vasodilation of vessels
tunica externa (tunica adventitia)
collagen fiber covering that protects and reinforces vessels
elastic conducting arteries
-large diameter thick-walled arteries near the heart (the aorta and its major branches)
-large lumen= low resistance flow of blood
-withstand and smooth out large blood pressure fluctuations
-allows blood to flow fairly continuously
muscular (distributing) arteries/arterioles
muscular arteries- distal to elastic arteries
-have thick tunica media with more smooth muscle and less elastic tissue
-active in vasoconstriction
control flow into capillary beds via vasodilation and vasoconstriction
the smallest blood vessels
-walls consisting only of a thin tunica internal, one cell thick (endothelial cells)
-allow only a single RBC to pass at a time
endothelial cells joined by tight junctions, making them least porous (in brain)
more leaky, found where absorption or filtration occurs (small intestines, endocrine glands, and kidneys)
very leaky and allow large molecules such as proteins and even some blood cells to pass through (liver, bone marrow, lymph tissue)
a micorcirculation of interwoven networks of capillaries consisting of vascular shunts, true capillaries, pre capillary sphincters
blood flow regulated by vasomotor nerves and local chemical conditions, so blood can either flow through the capillary bed or bypass it (vascular shunt)
vascular shunts (metarteriole)
channel that connects an arteriole directly with a venule
branch off the met arteriole and return to the venule at the distal end of the bed
cuff of smooth muscle that surrounds the arteriole end of each true capillary
regulates blood flow into the capillary
formed when capillary beds unite
smallest venules, composed of endothelium
veins are formed when
what are the tunics of veins like
have all three
thin tunica media and thicker tunica externa
what do veins act as
capacitance vessels (blood reservoirs) that contain 60-65% of the total blood volume
what is pressure of veins and thickness of walls of veins like compared to arteries
veins have lower blood pressure and thinner walls
what do veins in limbs have to prevent back flow of blood?
Blood flow (Q)=
volume of blood flowing through a vessel, an organ, or the entire circulation in a given time period
what are the units of blood flow and what other measure is it equal to
equals the cardiac output (CO) for the entire vascular system
is the blood flow (Q) steady throughout the body?
varies widely through individual organs (and even at each capillary bed), according to needs of the tissue
Blood Pressure (BP)
force per unit area exerted on the wall of a blood vessel by the blood
what units is BP measured in and what is it measured in reference to
millimeters of mercury (mm Hg)
measured in reference to systemic arterial BP in large arteries near the heart
Resistance (R) and what else is it referred to as
force opposing blood flow
what is resistance (R) also referred to as?
What are the three important sources of resistance
blood viscosity (thicker, more viscous fluid= more resistant)
total blood vessel length
blood vessel diameter (radius)-what we try to change when we want to fix probs
what is blood flow directly proportional to and inversely proportional to
directly proportional to the hydrostatic pressure differential
inversely proportional to resistance to flow
What is the formula for blood flow (Q)
Pi= inflow pressure (arterial)
Po=outflow pressure (venous)
what is resistance directly proportional and inversely proportional
directly: viscosity of fluid, length of "tube"
inversely: fourth power of the radius of the "tube"
What is the formula for Resistance (R)
What is the equation for Poiseuille's Law for flow?
when does Poiseuille's Law for flow hold true and when does it break down?
holds true for laminar flow
breaks down for turbulent flow
-resistance to flow is much higher for turbulent flow than laminar flow, if everything else remains constant)
fatty plaque deposits in arteries
what is the overall systemic blood pressure
the pumping action of the heart generates blood flow through the vessels along a pressure gradient, always moving from higher to lower pressure areas
Where is systemic blood pressure highest and how does it change
highest in aorta
declines throughout length of pathway
only ~2mm Hg in right atrium
Where does the steepest change in blood pressure occur?
pressure exerted on arterial walls during ventricular contraction
lowest level of arterial pressure during a ventricular cycle
the difference between systolic and diastolic pressures
Mean arterial pressure (MAP)
MAP= diastolic pressure + 1/3 pulse pressure
capillary blood pressure
-ranges from 20 to 40 mm Hg
-low capillary pressure is desirable because high BP would rupture fragile, thin-walled capillaries
-low pressure is sufficient to force filtrate out into interstitial space and distribute nutrients, gases, and hormones between blood and tissues
Venous blood pressure
-relatively steady and doesn't change much during the cardiac cycle
-pressure gradient in venous system is only about 20 mm Hg
difference between blood flowing out of cut vein or cut artery
cut vein has even blood flow, lacerated artery flows in spurts
pressure changes created in the chest cavity during breathing "suck" blood toward the heart
contraction of skeletal muscles "milk" blood toward the heart, in conjunction with the valves that prevent back flow during venous return
sympathetic NS maintains venous smooth muscle contraction
What does maintaining normal blood pressure require?
-cooperation of the heart, blood vessels, and kidneys
-supervision by brain and a variety of hormones
What are the three main factors influencing blood pressure are
1. cardiac output (CO): SV x HR
2. peripheral resistance (PR): blood vessel radius
3. Blood volume
what does blood pressure =
CO x PR
cardiac output times peripheral resistance
how is acute blood pressure controlled
-mediated by the nervous system and blood-borne chemical effects on CO and PR
-counteract moment-to-moment fluctuations in blood pressure by altering peripheral resistance
Who is chronic blood pressure controlled
-involves the kidneys
-regulate blood volume by altering water and salt excretion in the urine (and thirst)
cardiac output and acute control of blood pressure
stimulus: decreased blood pressure
result: increased CO by increasing both SV and HR
mechanism: activation of medullary cardiac center
What are neural controls of peripheral resistance?
alter blood distribution to respond to specific demands
maintain MAP by altering blood vessel diameter
Neural controls operate via reflex arcs involving what kind of receptors for input, what center for processing, and what effectors for output?
input: baroreceptors (pressure receptors)
chemoreceptors (chemical receptors)
processing: vasomotor center of the medulla
output: vasomotor fibers affecting the tone of vascular smooth muscle (primarily arterioles)
vasomotor center plus the cardiac centers that integrate blood pressure control by altering cardiac output and blood vessel diameter
baroreceptor-mediated vasomotor control of blood pressure
what happens if high pressure is detected and what happens if low pressure is detected?
high pressure detected: activation of cardio-inhibitory center
-decreased HR (CO)
low pressure detected: activation of cardio-accelatory center
-increased HR (CO)
what is blood pressure also acutely regulated by?
chemoreceptor reflexes sensitive to oxygen and carbon dioxide
What do chemoreceptors in the carotid and aortic bodies respond to do?
-raise blood pressure with decreased arterial O2
-raise blood pressure with increased arterial C02
Are chemoreceptors or baroreceptors more important most of the time in control of blood pressure?
-baroreceptors more important unless the O2 or CO2 levels are very different from normal
What hormones increase blood pressure by causing vasoconstriction?
-adrenal medulla hormones: norepinephrine and epinephrine
-antidiuretic hormone (ADH; also called vasopressin)-causes intense vasoconstriction in cases of extremely low BP
-angiotensin II-kidney release of renin generates angiotensin II, which causes intense vasoconstriction
What hormones/chemicals cause vasodilation?
-atrial natriuretic peptide (ANP)-causes blood volume and pressure to decline
-nitric oxide (NO)- has brief but potent vasodilator effects (usually a local effect)
-inflammatory chemicals- histamine, prostacyclin, and kinins are potent vasodilators
-alcohol- causes BP to drop by inhibiting ADH release
long-term mechanisms controlling BP chronically by altering blood volume
-increasing BP stimulates the kidneys to eliminate salt and water, thus decreasing blood volume and reducing BP
-decreasing BP stimulates the kidneys to retain salt and water, thus increasing blood volume and raising BP
How is systemic arterial BP measured directly?
the ausculatory method
What is the ausculatory method?
-a sphygmomanometer is placed on the arm superior to the elbow
-pressure is increased in the cuff until it is greater than systolic pressure in the brachial artery
-pressure is released slowly and the examiner listens with a stethoscope downstream from the cuff
-the first sound heard is recorded as the systolic pressure
-the pressure when sound disappears is recorded as the diastolic pressure
low BP in which systolic pressure is 100 mm Hg or below
what is orthostatic hypotension?
temporary low BP and dizziness when suddenly rising from a sitting or reclining position
What is acute hypotension?
important sign of circulatory shock (threats to patients undergoing surgery and those in intensive care units)
condition of sustained elevated arterial pressure of 140/90 or higher
-transient elevations are normal and can be caused by fever, physical exertion, and emotional upset
-chronic elevation is major cause of heart failure, vascular disease, renal failure, and stroke
primary (essential) hypertension
no clearly defined cause for the increased blood pressure
-the most common form seen clinically
-many known risk factors for primary hypertension, including high fat diet, obesity, age, race, heredity, stress, and smoking
due to identifiable disorders, including excessive renin secretion, arteriosclerosis, and endocrine disorders
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