DSA: Circulation and Hemodynamics Flashcards
What are considered our pressure reservoirs?
Arteries: contain a stressed volume of blood,
Meaning that it increases venous compliance, which increases pressure in the arteries.
Blood is driven arterioles via elastic recoild
What are our resistance vessels?
What does resistance allow?
Arterioles.
When blood enters the arterioles and leaves, there is a huge drop in pressure. Thus, we can tell they create a lot of resistance.
Resistance allows the arterioles to direct blood to certain parts of the body.
How do we alter resistance of the arterioles?
Sympathetic NS: Alpha-1 (vasoconstrict) or beta-2 receptors (vasodilate)
Parasympathetic: release of NO through ACh binding to mAChR
What is our site of nutrient exchange?
Capillaries
Are all capillaries perfused with blood?
No.
Remember, arterioles alter their resistance via the sympathetic NS to direct blood to tissue in metabolic need of it.
What part of our circulation contains the most blood?
Vein.
Has about 65% of unstressed volume of blood.
What innervates the veins?
Sympathetic NS
Alpha1 adrenergic receptors; constrict the veins.
Velocity of blood (v) equation
v= Q/A
Q–> flow of blood (mL/s)
A–> cross sectional area (cm2)
Velocity is higher in what part of the circulatory system?
Velocity is higher in the arteries and veins, compared to the capillaries.
Blood flow through a vessel is determined by what?
Blood flow through a vessel is determined by the
1. Pressure difference between the inlet and outlet
2. Resistance of flow
How do we calculate flow of blood (Q)?
Q= change in pressure/ resistance
Major mechanism to change flow
changing the resistance.
Resistance to blood flow eqn
Poiseuille’s law/equation
R = (8 η l) / (π r4 )
Does resistance increase linearly by changing the radius?
Secondary effects?
No.
reducing the radius by ½. Will cause the resistance to increase by a 16 fold.
—> Alter flow (Q)
-
What is the difference between series resistance and parallel resistances?
Series resistance–> total resistance is the sum of individual resistances
Parallel resistances–> total resistance is less than any of the individual resistances.
Laminar flow is a streamlines blood flow. Velocity is greatest and lowest where?
(A PARABOLA)
Greatest–> center
Least–> towards the vessel walls.
When laminar flow is disrupted–>
turbulent flow, requiring more pressure to drive flow= more NRG
Can be heard as bruits.
Reynold’s Number is used to predict what?
whether flow will be turbulent or laminar.
<2k = laminar flow
Reynolds Number eqn
NR = (ρ d v) / η
p=density of blood
d=diameter of the BV
v= velocity of the blood flow
n= viscosity of blood flow
Difference in pressure of vessel 2 is 2x greater than vessel 1. What will the flow be?
Flow is vessel 2 is 2x greater.
Q: What happens to the velocity when a vessel is partially occluded by a thrombus?
Blood velocity will increase.
Shear
occurs when the velocity of blood is not the same along the vessel wall as it is in the center.
If all adjacent layers traveled at the same velocity, shear would be 0.
Shear is greatest along the vessel wall; lowest at the center.
Compliance of blood vessels is what?
What does low compliance mean?
can increase volume without a big increase in pressure
Low compliance–> stiff walls.
What do we do if we want blood to go back to the heart?
Increase compliance, making the walls stiffer.
Occurs by sympathetic stimulation of alpha-receptors. Increases venous return and SV.
Compliance is the greatest in _____.
VEIN
Decrease in compliance–>
venoconstriction: blood is redistributed from unstressed volumeà stressed.
Describe the pressure throughout the CV system?
Pressure–> greatest in the aorta and larger arteries
- Fall in the small arteries
- Decreases in arterioles, where the largest drop of pressure occurs d/t high resistance to flow
-Our BP oscillates between high levels with___________ (_____) when the ventricles contract and low levels with ______________ (_____) when they relax.
BP oscillates between high levels with systolic arterial pressure (SBP) when the ventricles contract and low levels with diastolic arterial pressure (DBP) when they relax.
What is pulse pressure?
Pulse pressure
is the pressure of the volume blood ejected from the L ventricle in 1 beat.
SBP-DBP
What is stroke volume?
The volume of blood ejected from the LV in 1 beat
MAP eqn
MAP= 2/3 DBP + 1/3 SBP
DBP + 1/3 pulse pressure
MAP is determined by:
Altered by:
MAP is determined by compliance and lung volume.
Altered by:
- arteriosclerosis: decrease diameter and compliance of vessels: increase SBP, pulse pressure, without a large influence on DBP;
- aortic stenosis; aortic valve narrows, SBP, pulse pressure and MAP decreases
Venous Pressures in the Systemic Circulations –
much lower than on arterial side, < 10 mm Hg and progressively decrease to near zero at the vena cava and right atrium.
Pressures also differ between body positions and in body locations
Reclining?
Standing?
When reclining, arterial pressure is fairly consistent between the head and feet; however, when standing arterial pressure is lower ( 180 mm Hg) at the feet.
Venous pressures will parallel the arterial pressures; however, with much lower values
Microcirculation–> ?
Describe it.
circulation in the capillaries, which branch from metaarterioles
simple diffusion, lipid soluble (o2 and co2) can be exchanged via pressure gradient and SA of capillaries, water soluble things do not, osmosis occurs via starting forces,
proteins do not cross
Fluid exchange occurs via Starling forces.
What are the starling forces?
- Capillary Hydrostatic pressure (Pc)- favors filtration
- Interstitial Hydrostatic pressure (Pi) – opposes filtration (normally 0 or slightly -)
- Capillary Oncotic pressure (πc) – oppose filtation
- Capillary Interstitial pressure (πi) – favors filtration (usually low due to low amount of proteins found in interstitium)
lymphatic capillaries return_________to the blood. How?
interstitial fluid
1. Increase Pc
2. Decrease in capillary oncotic pressure
—–can increase lymph flow into blood—-
3. Increased Kf d/t inflammation
Blood flow can be changed by local mechanisms (intrinsic) or neural/hormonal (extrinsic) control. What are the local mechanisms?
- Autoregulation
- Active hypernemia
- Reative hypernemia
Autoregulation–>______________________
- Explanation: _______________
Autoregulation–> maintain a constant BF as arterial pressure changes
- Explanation: myogenic hypothesis.
Active hyperemia–>
Explanation:
Active hyperemia–> Blood flow to an organ increases as metabolic activity increases
Explanation: metabolic hypothesis
Reactive hyperemia–> __________
- Reactive hyperemia–> blood flow increases when there is a period of decreased BF. Ex. BF after a stroke
if the vascular smooth muscle is stretched, what happens? What explains this?
It will contract, explained by autoregulation. This is due to the myogenic hypothesis.
Neural/hormonal (extrinsic)
- Sympathetic NS is the most important. PNS has very little influence over vasculature.
- HA and bradykinin–> vasodilator–> increased hydrostatic pressure and filtration, causing edema.
- 5HTà vasoconstrictorà released d/t damage.
- E-series prostacyclin and prostaglandins–> dilation
- F-series prostaglandin and thromboxane A2–> constriction
- Angiotensin II and vasopressin are constrictors that increase TPR.
- NOà vasodilator of smooth muscle
In coronary, cerebral, pulmonary, and renal circulation- local metabolic control is most important while…?
sympathetic control is least important
In skin and skeletal muscle (at rest) circulation, local metabolic control is least important while?
sympathetic control is most important using Alpha 1 adrenergic receptors for vasoconstriction and B2 for vasodialation
Preload
amount of blood in the ventricles at the end of diastole (once the ventricles are relaxed)
Afterload
pressure the heart must overcome to eject blood during systole.
SV is dependent on
Preload, contractility, afterload
CO= HR * SV
How do HR and SV work together?
HR and SV (volume of blood pumped from our L ventricle) will compensate for one another.
- HR increases, SV decreases= tachycardia
- SV decreases, HR increases= bradycardia
