# vasculature

## Terms

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what are two considerations in hemodynamics?
-reltnshp btwn pressure and flow

-reltnshp btwn resistnc and flow
how does flow change with pressure gradient change?
flow increases as change in P increases assuming resistance is the same throughout.
how does resistance cause flow to change?
as R increases, F decreases.
what 3 things determine resistance?
-viscosity
-length of tube
how do we physiologically change resistance?
what does increasing radius do to resistance and flow?
decreases resistance and increases flow.
what is viscosity defined as?
measure of resistance between molecules of a fluid - could increase by incr. RBCs
how does changing length alter resistance?
make tube longer increases resistance.
numerically how is resistance related to radius?
1
R = -----
r^4
What is Poiseuille's Law?
what is the equation for resistance?
8vl
R = ---
pi r^4
using the R equation what does Flow = ?
P pi r^4
F = --------
8vl
What are the 2 main functions of arteries?
1. To act as low resistance pathway to bloodflow.
2. To convert distcontinuous output to continuous blood flow.
what are the terms for the high and low ends of blood pressure?
HIGH = systole
LOW = diastole
how is bp reported?
Systole/diastole.
what is pulse pressure?
the difference between systolic and diastolic blood pressure. Felt as a pressure point when the aortic valve slams shut after systole.
what is MAP?
Mean arterial pressure.
MAP = DP + DP + SP / 3
what determines mean artial pressure?
blood volume in the arteries.
what are the 2 determinants of arterial blood volume?
1. Cardiac output
2. Total peripheral resistance to bloodflow.
what happens to the arterial blood volume if you increase total periph. resistance?
it increases. think about it; blood is in the arteries, resistance is in front of it; more will be in arteries.
what type of vessel provides th most resistance in the periphery?
arterioles
what is the fundamental equation for MAP?
MAP = CO X TPR
MAP
therefore, CO = -----
TPR
what is arterial compliance, and why is it important?
compliance = stretchiness of arteries.
The stretchier they are, the more volume can hold.
if the arteries are noncompliant, how does this affect blood pressure?
-why?
systolic increases and diastolic decreases.
ummmm
based on compliance, how does kinetic energy convert to potential?
During systole, KE is converted to PE as artery walls stretch.
During diastole, PE of stretched walls converts to KE as it drives blood out of arteries.
what does compliance really determine?
peripheral pressure.
as stroke volume increases what happens to periph. pressure?
it increases.
Does compliance have any affect on mean arterial pressure?
no - only on peripheral pressure.
what are resistance vessels?
arterioles
why are arterioles resistance vessels (2 reasons)?
1. beause most resistance is here.
2. because they can be changed.
why can we change artos?
because they have lots of smooth muscle. when smooth muscle contracts, it changes the radius of the tube.
what 2 changes occur when we constrict artos?
1. Global resistance increases
2. Cardiac output distribution changes - local changes.
what are 5 methods of changing resistance in arterioles?
1. sympathetic vasoconstrictor nerves
2. other nerves
3. hormones
4. local control
5. endothelial factors.
how do sympathetic nerves alter arteriole resistance?
-Release norepinephrine.
-Norepi binds alpha-adrenergic receptors on arterioles.
-artos constrict and TPR and MAP both increase.
how do arterioles vasodilate in opposition to sympathetic nerves causing constriction?
just decrease sympathetic output - here is no parasympathetic equivalent, no dual-innervation.
What other nerves control arterioles?
non-adrenergic, non-cholinergic autonomic nerves release NO and cause vasodilation
what types of arterioles recieve NO vasodilation commonly?
-genitalia
-GI tract
what three hormones alter resistance in arterioles?
-epinephrine
-angiotensin II
-Vasopressin
what 2 ways can epinephrine alter arterioles?
-If binds alpha receptor, vasoconstriction of SKIN vessels

-If binds beta receptor, causes dilation of vessels supplying skeletal muscle.
what do Angiotensin II and Vasopressin do to arterioles?
cause increase in blood volume by inducing vasoconstriction.
what are 2 ways of locally controlling arteriole resistance?
1. Active hyperemia
2. Flow autoregulation
What is active hyperemia?
blood flow adjustment to meet metabolic needs of tissue
how does active hyperemia control arteriole resistance?
arteriole smooth muscles sense changes in interstitial fluid and vasodilate/relax
what interstit. fluid changes occur in active hyperemia?
Decreased O2, pH
What is flow autoregulation?
a change in flow to an organ causing a change in resistance to compensate and keep flow nearly the same.
what is an example of flow autoregulation?
Kidneys - dilate when blood pressure is increased so that resistance is decr and same amt of blood will flow through.
what interstit. fluid changes occur when flow is decreased?
same as in active hyperemia -
Decreased O2, pH
how does flow autoreg cause
-Dilation
-Constriction
Dilation - sense changes in interstit. fluid

Constrict - sense Stretch
what's an example of flow autoreg to cause constriction?
1. Incr b. pressure
2. smooth muscle in vessels senses stretching.
3. Ca2+ channels open and cause stronger contractions
How do endothelial cells control arteriole resistance?
Secrete paracrine agents - diffuse to adjacent vascular smooth muscle, induce vasodil or constriction
what are 2 factors produced by endothelial cells?
-Nitric oxide
-Endothelin-1
what does nitric oxide do?

-Endothelin-1?
Vasodilates

Vasoconstricts
What 6 things cause arteriole vasoconstriction?
Sympath. vasoconst. nerves
Epineph on alpha receptors
Angiotensin II/Vasopressin
Vessel stretch
Endothelin-1
what are the units for flow and pressure gradient?
Flow = vol/time

Pressure = mm of Hg
what two factors are secreted by endothelial cells?
-nitric oxide
-endothelin 1
what is the effect of
-NO
-endothelin 1
no is a vasodilator

endothelin-1 is a constrictor
what type of vessel is a capillary?
EXCHANGE vessel
what are some characteristics of capillaries?
-tiny cells, about 1mm long and 5 microns in diameter.
-most cells w/in .1 mm of a capillary.
-composed of only ENDOTHELIAL cells
what is resistance in capillaries like?
fairly high, but all-together the capillaries have low R
what is the PURPOSE of capillaries?
to exchange blood nutrients and wastes
what are the 2 ways nutrient exchange takes place across capillaries?
1. diffusion
2. filtration
what exchanges across capillaries by diffusion?
CO2, O2, wastes, and nutrients.
how does water go through capillaries?

how does fat?
by pores.

fat crosses the lipid membrane.
what is filtration by capillaries for?
maintaining the distribution of extracellular fluid between plasma and interstitial fluid.
What is interstitial fluid really?
ultrafiltrate of plasma, without the plasma proteins.
What is Starling's Hypothesis?
-direction/magnitude of fluid movement across capillary walls is determined by Hydrostatic + Osmotic pressure.
What favors fluid movemnt from
-vessel->interstitial space?

-interstit. space -> vessels?
Increasing intracapillary hydrostatic pressure.

Increasing osmotic pressure.
how do you increase osmotic pressure in a capillary?
increase osmotically active particles (plasma proteins) inside it.
What direction is fluid move in
-filtration?
-absorption?
Filtration = movement of fluid out of capillaries.

Absorption = movemnt of fluid into capillaries from tissue.
what four pressures make up net filtration pressure?
-Capillary blood pressure
-Capillary osmotic pressure
-Tissue hydrostatic pressure
-Tissue osmotic pressure.
what does capillary hydrostatic pressure increase do to filt/absorp?
Filtration will increase, absorption will decrease.
what does capillary osmotic pressure increase do to filt and absorption?
Filtration will decrase
ABsorption will incrase
what is another name for capillary osmotic pressure?

what mostly causes this pressure?
colloid osmotic pressure.

-plasma proteins.
What is affect on filt/absoptn when tissue hdrostatic pressure increases?
filtration decreases, absorption increases.
what is affect on filt/absoptn when tissue osmotic pressure increases?
filtration increases, absorption decreases.
What causes filtration?
Filtration is caused by Hydrostatic capillary pressure and tissue osmotic pressure.
What causes absorption?
Absorpn is caused by capillary osmotic prssure and tissue hydrostatic pressure.
What is net filtration pressure?
(Causes of filtration) minus (Causes of absorption)
what four things can disturb hydrostatic-oncotic balance?
1. Arteriole costriction
2. Arteriole dilation
3. Low plasma proteins
4. Lymphatic damage
What effect does arteriole constriction have on:
-MAP and capillary pressure?
-Filtration?
-Absorption?
-Blood volume?
-Increases MAP
-Decreases Capillary pressure
-Decreases filtration
-Increases absorption
-Increases blood volume
How does arteriole dilation effect filtration/absorption?
-Increases capillary pressure
-Increases filtration
-Decreases absorption
-Decreases blood volume
-Decreased MAP
If plasma proteins are low how is NFP affected?
Lower capillary osmotic pressure and higher NFP.
What do we see in starving children with lower plasma protein?
Pitting edema - fluid in the interstitial space due to increased NFP
what 4 things cause decreased plasma proteins?
-chronic liver disease
-protein defic. diet
-kidney disease
-severe burns
how does lymphatic damage affect NFP?
-Normally lymphatics take up proteins and fluid leaked from capillaries and return to CVS.
-If defic, stay in ISF and swell
How does wearing an elastic cuff alter NFP?
Increases tissue hydrostatic pressure, increases absorption and decreases filtration.
what are veins?
the psgway from tissues to the heart.
what is the function of veins
to act as a reservoir - most - 2/3 of the blood at any given time is in the veins.
How do you increase Arterial blood?
By CONSTRICTING THE VEINS.
Why does vein constriction increase arterial blood?
because it increases venous return to the heart, which increases EDV, thus increasing stroke volume and arterial volume.
what is the difference between constricting arterioles versus veins?
Arteriolar constriction will cause big increase in resistance, less in blood vol.
Veinous constrictn will cause little affect on R, but big increase in blood volume.
what are 4 ways you can control venous return?
1. Sympathetic vasoconstrictor nerves to those veins.
2. Changes in blood volume
3. Skeletal muscle pumps
4. Respiratory movements
How do symp vasoconst. nerves control veinous return?
By releasing norepinephrine, which acts on smooth muscle to contract and constrict veins.
How does blood volume alter venous return?
If increased, it will cause more blood to go to heart, and thus increase EDV.
How does skeletal muscle alter venous return?
Long veins have valves; normally muscle movement pushes on the veins and blood moves toward heart.
How does respiratory movement alter venous blood return?
When inspire, venous return increases because diaphragm presses on veins.
Expiring decreases venous return.
What is the function of the lymphatics?
To return excess fluid and plasma to the CVS and dump it back into veins.
Why is MAP regulation important?
because it is the driving force for blood circulation through the body.
What happens if MAP is
-too low
-too high

High = heart overworked, damaaged arterial walls.
How is MAP regulated?
-Baroreceptors
-Hormones
-Capillary fluid shift
-Longterm regulation
What regulates MAP in the
-longterm?
-short-term?
longterm is done by kidneys.

shorterm is done by baroreceptors - elicitis an immediate change if necessary.
For example, what would baroreceptors respond to?
If you stand and your blood pressure decreases, these would immediately respond.
What are the Sensors in baroreceptor control?
Baroreceptors in the
-carotid artery
-aortic arch.
how do baroreceptors work?
when bp increases, vessel walls stretch; generates an action potential and signal is sent.
What is the integrating center in barorecp. control?
the Medulla of the brain.
What are the 3 effectors in barorecp. regulation?
1. Mean Arterial Pressure MAP
2. the HEART
3. vasculature
what 3 things about the heart can the brain change to alter MAP?
-Cardiac Output
-Nervous Control
-Hormone control
How does the brain alter cardiac output in the heart?
by altering
-Stroke volume
-Heart rate

b/c CO = SVxHR
what 3 types of nerves are changed to alter the heart to regulate MAP?
1. Cardiac Parasymp nerves
2. Cardiac Sympathetic nerves
3. Sympathetic vasoconstrictor nerves to the veins.
What is the effect of stimul:
-Cardiac Parasymp nerves
-Cardiac Sympathetic nerves
-Sympathetic vasoconstrictor nerves to the veins
Parasymp = decrease heartrate
Symp = increase heartrate
Symp vasoconsrictors constrict veins, to increase EDV and SV.
Specifically how do cardiac nerves alter heartrate?
Parasymp decrease slope of pacemaker potential.
Sympathetic increase slope.
How do hormones control the heart?
Epinephrine stimulates the SA node and ventricles to increase heart rate. Increases SV.
what two vasculature components does the medulla control to alter MAP?
-Arterioles
-Veins
wHAT IS THE AFFECT ON Mean arterial pressure when the medulla acts on arterioles to constrict?
Their vasoconstriction increases total peripheral resistance. This decreases venous return and SV.
Why does the medulla's control of veins alter MAP?
If veins constrict, it increases venous return to the heart, increasing EDV and Stroke volume.

Increasd SV alters cardiac output, which directly affects MAP.
If blood pressure decreases, what is response of
-Sympathetic nerves
-Parasympath nerves
Symp will stimulate constriction to increase bp

Parasymps will decrease.
Other than changing CO, TPR, and heartrate, how does the medulla control MAP?
-Capillary fluid shift
what is capillary fluid shift?
Negative feedback response to decreased MAP.
-arterioles constrict, causing capillary press to decrease, and NFP decreases.
-Absorption increases and causes increase in Blood vol.
What does increased RBC production do?
increases blood viscosity, increasing total peripheral resistance to blood flow.
what is primary polycythemia?
increased blood production due to tumor cells
what is secondary polycythemia?
increased RBC production in response to altitude, or a non-bmarrow problem.
what is erythropoeisis in response to hypoxia an example of?
negative feedback.

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