Circulation 6 Flashcards
regulation of blood flow
- arterioles control blood distribution
how do arterioles control blood distribution (2)
- due to parallel arrangement, arterioles can alter blood flow to various organs
- changes in resistance using vasoconstriction and vasodilation alter flow
control of vasoconstriction and vasodilation (3)
- autoregulation
- intrinsic factors
- extrinsic factors
control of vasoconstriction and vasodilation: autoregulation
- direct response of the arteriole smooth muscle
control of vasoconstriction and vasodilation: intrinsic factors
- metabolic state of tissues/oxygen demand
control of vasoconstriction and vasodilation: extrinsic factors
- nervous and endocrine system
under resting conditions, which organs receive larger majorities of blood flow (4)
- brain
- liver and digestive tract
- kidneys
- skeletal muscle
under resting conditions, which organs receive smaller amounts of blood flow (3)
- heart
- skin
- bone
distribution of blood to tissues: increased flow
- relaxation of pre-capillary sphincters allow for blood to flow to the capillary beds
distribution of blood to tissues: decreased flow
- contraction of pre-capillary sphincters reduces blood flow to the capillary bed and blood is diverted elsewhere
myogenic autoregulation of flow (2)
- some smooth muscle cells in arterioles are sensitive to stretch
- smooth muscles cells ‘automatically’ contract when blood pressure increases
myogenic autoregulation of flow: feedback loop type
- negative feedback loop
what is the purpose of the myogenic autoregulation of flow
- to prevent excessive flow of blood into tissue
metabolic activity of tissues on flow (3)
- smooth muscle cells in arterioles sensitive to conditions of extracellular fluid
- levels of metabolites alter vasoconstriction/vasodilation
- blood flow matched to metabolic requirements
extracellular fluid (2)
- plasma of the blood
- interstitial fluid
metabolic activity of tissues on flow: feedback loop type
- negative feedback loop
increased metabolic rate in tissues: pathway step (5)
- increased tissue metabolic rate results in low O2 and high CO2 and waster
- arteriolar smooth muscle detect conditions and vasodilate
- vessel resistance is lowered, increasing blood flow
- O2 delivery, CO2 and waste removal increase
- tissue O2 increase and tissue waster and CO2 decrease, creating the negative feedback loop
neural and endocrine control of flow (4)
- norepinephrine
- decreased sympathetic tone
- vasopressin (ADH)
- angiotensin II
- atrial natriuretic peptide (ANP)
neural and endocrine control of flow: norepinephrine (2)
- from sympathetic neurons
- causes vasoconstriction
neural and endocrine control of flow: decreased sympathetic tone
- causes vasodilation
neural and endocrine control of flow: vasopressin (ADH) (2)
- from posterior pituitary
- causes generalized vasoconstriction
neural and endocrine control of flow: angiotensin II (2)
- produced in response to decreased blood pressure
- causes generalized vasoconstriction
neural and endocrine control of flow: atrial natriuretic peptide (ANP) (2)
- produced in response to increased blood pressure
- promotes generalized vasodilation
vertebrate circulatory system: blood pressure changes (3)
- blood pressure in left ventricle changes dramatically with systole and diastole
- pressure decreases as blood moves from left ventricle to arteries, arterioles, capillaries, venules, and veins
- pressure and pulse/degree of pressure oscillation decrease in arterioles after leaving the ventricle
why does the degree of oscillation/pulse decrease in the arterioles
- higher resistance in the arterioles
vertebrate circulatory system: average blood velocity changes (3)
- highest in arteries
- lowest in capillaries
- intermediate in veins
vertebrate circulatory system: total cross-sectional area (2)
- lowest in the arteries and veins
- highest in the capillaries
why are pressure fluctuations in the arteries smaller than those in the left ventricle (3)
- aorta acts as a pressure reservoir, dampening pressure fluctuations
- due to elasticity of vessel wall
- important for protection of downstream vessels from intense fluctuations and to even out blood flow
how does the vessel wall act during systole and diastole (2)
- expands during systole
- elastic recoil during diastole
vein structure (2)
- thin, compliant walls
- less constrictive due to lower muscle volume, making it more compliant to stretching
vein functions (2)
- volume reservoir
- small increases in blood pressure lead to large changes in volume of the veins
how much blood is held in the veins of mammals
- more than 60% of the blood
veins: control (2)
- vein volume and return is controlled by sympathetic nerves
- venomotor tone ensures pressure is sufficient to fill heart
why can it be difficult to move blood in veins back to the heart
- it is under low pressure
how do vertebrates move blood back to the heart (2)
- two pumps assist in moving blood back to heart
- valves in veins assure unidirection flow
moving blood back to the heart: pumps (2)
- skeletal muscle
- respiratory pumps
moving blood back to the heart: skeletal muscle pump
- contraction (shortening and thickening) of muscles squeeze the veins
moving blood back to the heart: respiratory pumps
- pressure changes in thoracic cavity during ventilation
what is the primary driving force for blood flow through organs
- blood pressure/mean arterial pressure
mean arterial pressure
MAP = CO x TPR
CO
- cardiac output
TPR
- total peripheral resistance
regulation of blood pressue
- body varies cardiac output and total peripheral resistance to main near constant MAP
how does the number of RBCs affect MAP (3)
- affects blood viscosity
- blood velocity affects TPR
- TPR affects MAP
how does vasopressin and angiotensin II affect MAP: non-kidneys (3)
- hormones affect arteriolar tone
- arteriolar tone affects TPR
- TPR affects MAP
how does vasopressin and angiotensin II affect MAP: kidneys (5)
- hormones affect kidney salt + water balance
- balance between interstitial fluid and blood is altered, changing the blood volume
- blood volume affects venous return and EDV
- EDV affects SV, which affects CO
- CO affects MAP
how does the sympathetic nervous system/epinephrine affect MAP: TPR side (3)
- it affects arteriolar tone
- tone affects TPR
- TPR affects MAP
how does the sympathetic nervous system/epinephrine affect MAP: CO side (3)
- it increases HR and SV
- increased HR and SV result in increased CO
- increased CO causes increased MAP
how do metabolites and paracrines affect MAP (3)
- affect arteriolar tone
- tone affects TPR
- TPR affects MAP
how does the parasympathetic nervous system affect MAP (3)
- decreases HR
- decreased HR causes decreased CO
- decreased CO causes decreased MAP
how does increased blood volume affect MAP (4)
- increases venous return and EDV
- increases SV
- increases CO
- increases MAP
how does increased respiratory and skeletal muscle pumps affect MAP (4)
- increases venous return and EDV
- increased SV
- increases CO
- increases MAP
baroreceptors (2)
- stretch-sensitive mechanoreceptors in the walls of major blood vessels
- present in carotid arteries and aorta
baroreceptor function
- send nerve signals to medulla oblongata, the cardiovascular control center
baroreceptor reflex (2)
- regulates MAP
- negative feedback system
baroceptor reflex: how does baroceptor firing affect norepinephrine release
- increased MAP causes in increased baroceptor firing
- stimulated afferent neurons and the cardiovascular control center (medulla)
- decreased sympathetic output results in decreased norepinephrine release
baroreceptor reflex: how does decreased NE from baroreceptor firing affect MAP (4)
- arteriolar smooth muscle undergoes vasodilation to decrease peripheral resistance -> decreased MAP
- ventricular myocardium decreases force of contraction to decrease cardiac output -> decreased MAP
- SA node decreases heart rate to decrease cardiac output -> decreased MAP
- creates negative feedback loop
how do kidneys help maintain blood volume (3)
- increases in blood volume lead to increase in blood pressure
- kidneys excrete or retain water to adjust blood volume and pressure
- form a negative feedback loop to regulate pressure
kidney feedback loop: steps (6)
- high arterial pressure
- kidneys excrete Na+ and H2O to reduce plasma volume
- blood volume and venous pressure decrease, decreasing EDV
- cardiac muscles contractility decreases (Frank-Starling effect)
- stroke volume decreases
- cardiac output decreases, decreasing arterial pressure
