3.3 Circulation Flashcards
Hemodynamics
Circulation of blood in the vasculature
What matters in maintaining blood flow?
Hydrostatic pressure and Mean arterial pressure
Hydrostatic pressure
Fluid physics, you need a driving force causing liquid blood to flow through the vascular tubing in all the tissues
Mean Arterial Pressure
“Average blood pressure”
Essential to maintaining adequate volume of blood circulation and perfusion of all tissues
MAP =
[(2 x diastolic) + systolic] / 3
Normal MAP
80-90 mm Hg
Why is normal MAP closer to diastolic?
Because we spend so much more time in diastole
MAP =
CO x SVR
Systemic Vascular Resistance
Pressure component of MAP that is dependent on the vasculature
(controlled through vasoconstriction and vasodilation)
SVR increases / decreases depending on..
1) Volume of entire vasculature
2) Blood Viscosity
Volume is a function of
- Total length of vascular system
- Diameter of vessels in the system
Larger diameter of vessels would lead to…
Lower resistance, lower back pressure
Blood viscosity
Thickness of the blood
What are vasculature lined with? (inside)
Endothelium comprised of endothelial cells
Elastic arteries
Largest arteries, lots of elastic tissue
What do elastic arteries do?
- Stretch during ventricular systole
- Recoil during diastole
What underlie the blood pressure measurement?
Stretch and recoil of elastic arteries
How does elasticity relate to high blood pressure in diabetics?
Too much sugar in blood hardens elastic arteries, blood going through never gets “tamped down” by elasticity of arteries
Muscular arteries
Medium sized arteries that branch from aorta, more smooth muscle than elastic tissue
Arterioles
Small arteries with vascular smooth muscle, involuntary yet highly regulatable
What do resistance vessels do?
They play a key role in rapidly changing SVR to respond to local tissue metabolic demands and the autonomic nervous system
What must larger arteries and arterioles do?
Reduce pulses of pressure and fast moving blood before entering capillaries
How does blood enter capillaries?
Smooth, laminar (even, no systole or diastole) flow
Capillaries
Single endothelial layer thick
Site of “capillary exchange” by diffusion (and pinocytosis)
Blood moves slowest in capillaries due to..
1) Arterioles
2) Massive “total cross sectional area’
Veins
- Lowest pressure
- One way valves
- Walls contain minimal vascular smooth muscle (but can still constrict
- Highly compliant
Compliance
“Stretchiness” in the walls of vessels.. small change in pressure leads to large change in volume
At rest, where is a majority (64%) of our blood?
Systemic veins and venues!
3 ways to mobilize the blood out of storage (veins) during exercise
1) Venoconstriction
2) Muscle activity
3) Valves
Venoconstriction (during exercise)
Sympathetic tone –> Contraction of smooth muscle surrounding veins –> decreases venous increases return of blood to the heart
What does an increase in return of blood to the heart cause and what is it due to?
Increases CO
Frank-Starling Law
Two components of muscle capacity in venous return
a) Contraction and movement of skeletal muscles
b) Respiratory pump
How do valves in the vein help during exercise?
Allow for no back flow of blood
Capillary exchange
How molecules move from blood to interstitial fluid and ultimately into cells
Primary and secondary routes of capillary exchange
Diffusion
Pinocytosis
Filtration
Water and some solutes from blood to interstitial space
Reabsorption
Water and some solutes from interstitial space back into blood
Forces driving filtration and reabsorption
1) Hydrostatic pressure
2) Osmosis
What is the hydrostatic pressure in capillary coming in and going out?
35 mm Hg
16 mm Hg
What is the hydrostatic pressure in the interstitial fluid?
ZERO
Osmosis can also be called…
Osmotic pressure of Colloidal osmotic pressure
What exerts vital osmotic pressure to counteract hydrostatic pressure?
Plasma proteins (liver albumin)
Does the interstitial space have a high or low osmolarity?
Very low, drives the liquid back into the “salty” blood
What is the net filtration when combining filtration and reabsorption?
14 + (-5) = 9mmHg net filtration OUT
What does the blood hydrostatic pressure do going through a capillary?
Plummets
What does the blood colloidal osmotic pressure do going through a capillary?
Holds steady at 26 mmHg between beginning and end of capillary
Interstitial COP is..
At a constant 5 mmHg
What happens to the extra “net filtrate”?
Picked up and moved by the lymphatic system and eventually returned to circulatory system
Lymphatic capillaries
Origin of lymph, low protein liquid filtrate that leaves blood capillaries and becomes interstitial fluid
Key features of lymphatic capillaries
“One-way door”
Anchoring filaments that are responsive to interstitial fluid accumulation
