-
arteriole function:
- will capillary bed receive blood (carry blood to tissue)
- determines MAP by effect on TPR
-
Arteriole Myogenic tone
spontaneous contraction of smooth muscle in tunica muscle.
- contract smooth muscle more-->VASOCONSTRICTION
- relax of smooth muscle-->VASODILATION
-
smaller the radius....
- GREATER the friction
- BIG increase in flow
- Friction-main factor in resistance (R)
-
RESISTANCE...
- R-inverseley proportional to radius (exponential) R=1/r4
- -SMALL Decrease radius=BIG increase in resistance=BIG decreased flow=BIG increase pressure
- -SMALL Increase radius=BIG decrease in resistance=BIG increase in flow=SMALL decrease in pressure
-
Regulation of Arterioles
- -local control
- -neural (reflex) contol
- -Hormonal Control
-
Intrinsic regulation of arterials
- -local control, no nerves, no hormones
- -Active Hyperemia: blood flow adjusted to meet tissue needs
- -arterioles radius will increase if it needs more O2 from release of chemical signals
-
Stimulus of Intrinsic local control of Arteriolar radius
- -decreased O2
- -increased CO2
- -increased H+
- -decreased pH
- -metabolites (K+), increase osmolarity
- DO NOT REGULATE MAP
-
How does Intrinsic (local) control of arteriolar radius respond?
increase Radius of arterioles, metarterioles and pre-capillary sphincters
*make sure tissues get blood/O2 they need
-
function of beta-2 receptors...
EPI- beta2- relax and opens smooth muscle
-
Flow Autoregulation..
- local/intrinsic control of arteriolar radius
- -decreased BP in organ-->arteriolar DILATION restores blood flow
-
flow autoregulation is mediated by
- several...
- decreased O2
- increased metabolites
-
extrinsic control (reflex-NEAURAL/HORMONAL-control of arteriolar radius
- *IMPORTANT IN MAP REGULATION*
- -SYMP STIMULIS-release of NE, bind to alpha-receptors -->mass vasoconstriction of arterioles-->increased TPR-->increased MAP
- -Sympathetic stimulus: adrenal medulla release EPI-->alpha-adrenergic receptors AND BETA2 RECEPTORS-->
- EPI will cause vasodilation (in arterioles, most skeletal muscles, heart, lungs brain)
-mass vasoconstriction-->inc. TPR-->inc MAP
-parasympathetic stim-less important
-
Angiotensin II
strong vasoconstrictor
-
Local controls are NOT important in.....
MAP regulation
-
NEURAL controls are important in....
regulation of MAP
-
During fight or flight, which control is more important? Why?
NEURAL controls will override local to make sure we stay alive
-
capillaries function:
- -transport via difussion, (between blood and interstitial fluid)
- -lipid-soluble, ion polar molecules-
- endothelial cell membrane
- -glucose: carrier mediated diffusion
- -RBC squeeze through in single file, so volume decreases and more time for exchange
*not leaky, carrier-mediated diffusion plays larger roles
-
structre of capillaries
ONE THIN capillary wall (tunica intima) and basement membrane
-
Capillary beds
- formed by capillarys
- metarteriole: connects arteriole with venule, true capillarys branch off metarteriole-
-
precapillary sphincter
ultime control if blood enters capillary/tissue
regulated by local/neural control
-
Capillary BP at entrance
35-40 mmHg
-
capillary BP at end
15-20 mmHg
-
Velocity of Capillary blood
- SLOW compared to rest of vascular system (due to so many capillaries), slows down rate of flow
- -slow rate of travel allows for COMPLETE EXCHANGE
-
filtration
fluid moving out of the capillary/blood
-
reabsorption
back to the blood (into capillary)
-
2 primary forces govern fluid movement in and out of capillary
- hydrostatis pressure (capillary BP) force driving fluid out. (filtration) *plasma protein can not diffuse*
- Colloid osmotic pressure of blood-caused by (reabsorbsorption)
- -caused by impenetrable non-plasma
- penetrating proteins
- filtration varies over time (beg-high, end-decrease)
- absorption (remains constant due to colloid osmotic presure
-
beginning/end of capillary (BP, OP, NPO)
- Beginning:
- Hydrostatic BP-INCREASE
- colloid OP- DECREASE
- Net filtration pressure (BP-CoP=NFP) MORE filtration
- End:
- BP: lower
- CoP: remains the same (BUT HIGHER THAN BP NOW)
- NFP= negative (reabsorption)
-
beginning of capillary (BP, OP, NPO)
-
Net filtration pressure equation
NFP= BP-CoP
ex: BP-32 (-) CoP-22 (=) NFP-10
-
NFP is 0 when...
- midway through capillary where both are balance
- -BP pushing out- 22mmHg
- -CoP reabsorbing- 22mmHg
-
NEGATIVE NFP at end of capillary bed means...
did not reabsorb all fluid we filtered out earlier
-filtered out 10 mmHg, only gained 70% back.... (bc NFP=-7)
-
Lympatic system
-excess fluid from capillary bed is absorbed by lympathic system
- 1-way vessels drain into systemic venous circulation-thus regaining loss fluid and levels staying equal
- (Lympatic veins-->lymphatic trunks-->lymphatic ducts-->subclavian veins to superior vena cava)
-
lymph appearance
- resembles plasma without the protein
- looks more like interstitial fluid
-
Venous system
- always return blood to heart
- systemic vein: leaves capillary bed with 15mmHg, pressure drops, but it must suffice to get blood ALL the way back to right heart
-
veins structure
- -large diameters
- -small resistance to flow
- -valves (prevent backflow) *esp important in lower limbs*
- -large lumens
- -high compliance can be DECREASED to stiffen wall
-
Vericose veins
- weak/loss elasticity in venous walls
- -veins widen and stretch
- -valves don't close (leading to back flow)
-
function of veins
- low pressure conduit back to heart
- pressure reservoir (high compliance-easy to stretch walls)
-
Vessels with high compliance can....
elastic arteries/veins: tolerate large increase of volume with little increase of pressure
-
AT REST 60% of blood volume is in...
veins
-
venous pressure determines...
VENOUS RETURN (impacting stroke volume and CO)
-
Factors increasing venous return:
- -skeletal muscle pump
- -respitory pump,
- -decrease compliance
- -stiffening wall
- -increase venous pressure
-
skeletal muscle pump
- -compression of veins by skeletal muscle contraction--raises venous pressure; valves prevent back flow
- -blood forced towards heart
-
respiratory pump
HEART AND THORACIC CAVITY (negative) gLESS THAN ATMOSPHERIC PRESSURE
--inhalation drops atmospheric pressure and explands lungs and cardiac channel (exercise effect)
-
ONE input determining EDV
venous return
-
pulmonary circulation
- low pressure system:
- capillaries-->O2 blood venules-->4 pulmonary veins
-
pulmonary-right heart PRESSURE
25/1
-
pulmonary-artery PRESSURE
25/8
-
pulmonary-MPAP PRESSURE
diastolic 8 + 1/3 (17) = 14 mmHg
-
Sources of resistance (opposition of flow): (pericarditis)
- increased viscosity
- blood vessel length
- decrease radius
-
compare r to R
VERY small changed in r --> BIG changes in R
-
most important factor of resistance
FRICTION
-
LaPlaces law:
T (tension/force) ALPHA R (radius) * P (pressure in vessels)
the tension/force stretching vessel is PROPORTIONAL to vessel diameter (or radius) * blood pressure
*=multiply
- LESS tension on walls of SMALL vessels
- more tension of walls of LARGE vessels (this is why aneurisms tend to occur in large vessels)
-
compliance equation
C= increase in V/increase in P
-
relate compliance, volume and pressure
HIGH compliance can accomodate LARGE increase increase in volume with SMALL increase in pressure
(and vise versa)
low compliance (stiff vessels)-->small increase in volume--> large increase in pressure
-
blood enters/leaves capillaries at what volume? what is the volume when blood enters veins
- enter: appx 93 mmHg (MAP)
- exit: appx 20 mmHg
- enter veins: 10 mmHg
-
Hormonal control in MAP regulation
- EXTRINSIC
- EPI: vasoconstrictor, a1-adrenergic receptors
- vasodilator, vessels with B2-adrenergic
- receptors
- Angiotension II: strong vasoconstrictor, part of RAAS (renin-angitotensin-aldosterone system)
-
arteriol pressure during DIASTOLE
80
-
ventricular pressure during DIASTOLE
0
-
Elastic arteries:
- CONDUCTIVE ARTERY: get blood to tissue without losing too much energy.
- 2.5-1.5 cm in diameter (aorta/pulm trunk)
- high compliance, easy to stretch
-
Muscular Arteries
- DISTRIBUTE ARTERIES
- 1cm-3mm in diameter
- more smooth muscle
- dilate/constrict lumen
- large lumem
-
Lumen's role in muscular arteries
small resistance to flow of blood. energy used for blood flow to small arteries
-
laminar sound
smooth flow (quiet)
-
Turbulent flow
blocking off, allows hearing
-
failure of lympatic system leads to
EDEMA: unable to p/u extra fluid
- failure due to:
- Filariasis (tropical parasite)
- chemotherapy
- surgery
- radiation
-
Function of veins
- low resistance flow back to RIGHT heart
- blood reservoir (due to high compliance of venous walls, veins can accomodate large volumes of blood with relatively little increase in pressure)
- venous pressure determines venous return
-
blood reservoir
high compliance of venous walls, veins can accomodate large volumes of blood with relatively little increase in pressure
-
Major determinant in CO
venous return
-
determinants in venous return
- total blood vol-->pressure-->VR
- compliance-->(normally high) can be stiffened
- sympathetic stim-->increase stiffness-->dec. compliance-->VP
- valves
- large lumen
- skeletal muscle pumps
- respiratory muscle pumps
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