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Force exerted by blood
Pressure gradient / resistance (Chg P/R)
Compare flow, pressure gradient, and resistance of systemic system vs pulmonary system (which is greater)
- Flow: equal
- Pressure gradient: systemic greater
- Resistance: systemic greater
What 3 factors affect vessel resistance?
Radius of vessel, length of vessel, viscosity of fluid
Which has greater resistance? Short or long vessels? Thicker or thinner vessels? Thick or thin blood viscosity?
- Longer vessels
- Thinner vessels
- Thick viscosity
What affects blood viscosity?
Amt of red blood cells & proteins in blood
Combined resistance of all blood vessels within the systemic circuit
Total peripheral resistance (TPR)
What are the effects of vasodilation and vasoconstriction on TPR and flow?
- Vasodilation --> decrease resistance --> increase flow
- Vasoconstriction --> increase resistance --> decrease flow
Cardiac Output =
MAP / TPR
What type of cells line inner layer of all blood vessels?
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)
Arteries or veins thicker walls?
What makes blood vessels walls more stiff?
Fibrous connective tissue (collagen)
What type of vessels have largest diameter and which have thickest walls?
- Largest diameter: veins
- Thickest walls: arteries
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
Which blood vessels contain smooth
Which vessels have largest change (drop) in pressure?
Which vessels have greatest resistance to blood flow
Vessels which contain rings of smooth muscle to regulate radius (resistance)
What component of the arterial wall allows them to act as pressure reservoir?
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
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
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
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
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
Which hormones affect arteriole radius? What do they cause?
- Vasopressin (ADH): minimizes water loss
- Angiotensin II: this & ADH cause vasoconstriction which increases TPR
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
How do most substances move from in a capillary to out of a capillary? How to proteins move?
- transcytosis (in cell one side, out the other side)
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
Directly connect arterioles to venules but are larger than capillaries
Connects capillaries to veins and are smaller than arterioles
Do venules contribute much to control of TPR?
No b/c very little smooth muscle in walls, so lil control of pressure
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
What do valves of veins do & which ones have them?
Peripheral veins have valves for flow in one direction; but not in central veines
What blood vessel type contains the most blood?
Are veins compliant?
yes, expand w/little chg in pressure
What 4 factors influence how much blood is returned to the heart?
- Skeletal muscle pump
- Respiratory pump
- Blood volume
- Venomotor tone
How does the skeletal muscle pump work?
Via one-way valves in peripheral veins
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)
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
Smooth muscle tension in the veins
What causes an increase in venomotor tone?
Sympathetic nervous system & norepinephrine stimulates contraction of smooth muscle, constricting veins
An increase in venomotor tone causes ___ (inc or dec) in venous return
What is a MAP less than normal called? Higher than normal?
Driving force for blood flow which is critical for normal functioning
MAP (Mean Arterial Pressure)
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
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
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
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
What are chemoreceptor reflexes?
What is their primary function?
Respond to increase in CO2 in blood & regulate CO2 levels
Epinephrine, vasopressin (ADH), and angiotensin II are all ____ and they increase ___ and ____
- TPR, MAP