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Force exerted by blood
Pressure
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Flow =
Pressure gradient / resistance (Chg P/R)
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Compare flow, pressure gradient, and resistance of systemic system vs pulmonary system (which is greater)
- Flow: equal
- Pressure gradient: systemic greater
- Resistance: systemic greater
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What 3 factors affect vessel resistance?
Radius of vessel, length of vessel, viscosity of fluid
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Which has greater resistance? Short or long vessels? Thicker or thinner vessels? Thick or thin blood viscosity?
- Longer vessels
- Thinner vessels
- Thick viscosity
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What affects blood viscosity?
Amt of red blood cells & proteins in blood
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Combined resistance of all blood vessels within the systemic circuit
Total peripheral resistance (TPR)
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What are the effects of vasodilation and vasoconstriction on TPR and flow?
- Vasodilation --> decrease resistance --> increase flow
- Vasoconstriction --> increase resistance --> decrease flow
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Cardiac Output =
MAP / TPR
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What type of cells line inner layer of all blood vessels?
Endothelial cells
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What kind of muscle is in the walls of some blood vessels? What are the other 2 types of tissues in bv walls?
- Smooth muscle
- Fibrous connective tissue (collagen)
- Elastic connective tissue (elastin)
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Arteries or veins thicker walls?
Arteries
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What makes blood vessels walls more stiff?
Fibrous connective tissue (collagen)
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What type of vessels have largest diameter and which have thickest walls?
- Largest diameter: veins
- Thickest walls: arteries
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Is the resistance in arteries high or low? How compliant are arteries? Does blood pressure change much
in the arteries?
- high; low compliance;
- yes; small increase in blood volume causes lrg increase in pressure
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Which blood vessels contain smooth
muscle?
Arterioles
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Which vessels have largest change (drop) in pressure?
Arterioles
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Which vessels have greatest resistance to blood flow
arterioles
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Vessels which contain rings of smooth muscle to regulate radius (resistance)
arterioles
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What component of the arterial wall allows them to act as pressure reservoir?
aortic valve
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Is resistance in the arterioles a major component of TPR? Does the blood pressure change appreciably when blood flows through the arterioles?
- yes, 60% of total TPR
- yes, largest pressure drop in the vasculature
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What are the functions of radius changes of the
arterioles affect resistance? (vasoconstriction & vasodilation)
- Controls flow to individual capillary beds so can regulated flow to organs based on need
- Regulats mean arterial pressure which maintains homeostasis
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How do changes in metabolic activity affect arteriole radius?
- Increased metabolism --> vasodilation
- Decreased metabolism --> vasoconstriction
- If nutrients aren't needed, vasoconstriction so flow is redistributed to where it's needed
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Blood flow increases during exercise. Does it increase to all organs evenly? Do all organs see an increase?
No; increase in cardiac output causes flow to skeletal muscles & less flow to organs
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How does the sympathetic nervous
system control arteriole radius? What does sympathetic activity cause? How does this change TPR? MAP?
Smmoth muscle of arterioles are innervated; these nerves get stimulated by sympathetic nervous system, causing vasoconstriction --> increased TPR --> increased MAP
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Which hormones affect arteriole radius? What do they cause?
- Epinephrine
- Vasopressin (ADH): minimizes water loss
- Angiotensin II: this & ADH cause vasoconstriction which increases TPR
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Does blood flow quickly through capillaries?
What purpose does this speed of flow serve?
flow is slow w/one cell layer thick walls, which increases xchg of nutrients, gases, & gets rid of wastes
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How do most substances move from in a capillary to out of a capillary? How to proteins move?
- diffusion
- transcytosis (in cell one side, out the other side)
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Rings of smooth muscle that surround capillaries on the arteriole end & contract and relax in response to local factors only; when contract, cause capillary constriction, decreasing flow
Precapillary Sphincters
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Directly connect arterioles to venules but are larger than capillaries
Metarterioles
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Connects capillaries to veins and are smaller than arterioles
Venules
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Do venules contribute much to control of TPR?
No b/c very little smooth muscle in walls, so lil control of pressure
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Do veins have thick walls? Do they have any smooth muscle?
No, but do have some smooth muscle in walls, so some control of radius
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What do valves of veins do & which ones have them?
Peripheral veins have valves for flow in one direction; but not in central veines
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What blood vessel type contains the most blood?
Veins
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Are veins compliant?
yes, expand w/little chg in pressure
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What 4 factors influence how much blood is returned to the heart?
- Skeletal muscle pump
- Respiratory pump
- Blood volume
- Venomotor tone
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How does the skeletal muscle pump work?
Via one-way valves in peripheral veins
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How does the respiratory pump work?
Pressure on veins in abdominal cavity during inspiration pushes blood to return to the heart (also decreased pressure in the thoracic cavity)
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How do increases & decreases in blood volume affect venous return?
- Increased blood volume --> increased venous pressure
- Decreased bv --> dec venous pressure
- Long-term reuglation of bp is through regulation of blood volume
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Smooth muscle tension in the veins
Venomotor tone
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What causes an increase in venomotor tone?
Sympathetic nervous system & norepinephrine stimulates contraction of smooth muscle, constricting veins
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An increase in venomotor tone causes ___ (inc or dec) in venous return
increase
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What is a MAP less than normal called? Higher than normal?
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Driving force for blood flow which is critical for normal functioning
MAP (Mean Arterial Pressure)
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How is MAP regulated in the short term? Long term?
(regulates ____, involves ____, primarily via ___)
- Short: regulates CO & TPR, involves heart & vessels, primarily via neural control
- Long: regulates BV, involves kidneys, primarily via hormonal control
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What do baroreceptors sense? Where
are they located? How does their firing rate (rate of action potentials) relate to blood pressure?
- Pressure changes
- Aortic arch & carotid sinuses
- Increased firing rate causes increased bp
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What is the baroreceptor reflex?
What does it do? What kind of feedback loop is it?
- provides a negative feedback loop in which an elevated blood pressure reflexively causes heart rate to decrease therefore causing blood pressure to decrease;
- quickly compensates for chgs in bp & long term, regulates through renal regulation of BV via renin-angiotensin-aldosterone system
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How does the body respond to hemorrhage (large blood loss)?
Decreases SV, CO, & MAP (HR, TPR don't chg) and decreases flow to GI tract & sends to brain instead
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What are chemoreceptor reflexes?
What is their primary function?
Respond to increase in CO2 in blood & regulate CO2 levels
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Epinephrine, vasopressin (ADH), and angiotensin II are all ____ and they increase ___ and ____
- vasoconstrictures
- TPR, MAP
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