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Cardiovascular Pressures & Fluid Balance
Terms in this set (45)
What are the Learning Objectives for this lecture?
1) Describe the parts of the cardiovascular system and the normal distribution of hydrostatic pressure therein.
2) Explain the relationship between pressure, flow and resistance of blood vessels.
3) Describe the role of arterioles and capillaries.
4) Describe the major fluid compartments of the body.
5) Define osmosis. Explain where it is important within the body.
6) Describe the factors controlling capillary filtration.
7) Describe the effects of fluid imbalance on cardiac output.
Edema is an example of what phenomenon?
Edema: an example of abnormal cardiovascular pressures and fluid balance
What are 3 problematic conditions that Edema affects?
1) Obstruction of venous flow
2) Critical diseases
What are the critical diseases that Edema causes?
1) heart disease (congestive heart failure)
2) Severe liver disease (cirrhosis)
3) kidney nephrotic syndrome
What do blood vessels do?
transport fluid and regulate flow. they can blow out, get clogged, and get damaged though.
What does the heart do?
It is an incredibly tough organ (pump) that produces pressure gradients in the body
What is the plasma in the blood?
the aqueous fluid
What is contained in the Vena Cava, veins, and venules?
a volume reservoir 2/3 of all blood in the vessels resides here. It helps determine Cardiac Output (CO)
What does Cardiac Output equal?
CO = SV x HR
What can and cannot pass through capillaries?
- All ions and gases can pass through the capillaries
- Not all proteins can pass through, this phenomenon results in the dev't of oncotic pressure gradients
What is aortic stenosis?
Constriction of the aortic which increases the afterload pressure on the L ventricle and thus heart as a whole
What does arterial constriction depend upon?
Constriction depends upon function of the arteries
What is Systole?
Systole: the time period during which the heart is contracting, stress on muscle, highest pressure
What is Diastole?
Diastole: heart is in a relaxed state as blood leaves, aortic valve shuts, low pressure
What is true of blood flow in the circulatory system?
Blood moves down its pressure gradient which is good because the capillaries don't blow out
Describe the resistance of blood flow through the lungs
The resistance of blood flow through the lungs is very low so only a low pressure is needed to push it through (about 25mmHg)
-even though this is a low pressure, the heart is very sensitive
Give the landmark pressure gradients across the circulatory system
Entering R atrium - 2mmHg
Leaving R Ventricle - 25 mmHg
Entering L atrium - 2 mmHg
Leaving L Ventricle - 120/80 mmHg
Entering capillaries - 30 mmHg
Leaving capillaries - 10 mmHg
Give the equation for flow
Flow = (Pi - Po)/R = ∆P/R
Give the equation for change in pressure
∆P = Flow X Resistance
Note: all of the organs are in parallel with regards to blood pressure directed to them
Give the equation for vessel resistance
Resistance = (8 x Length x Viscosity) / (p x radius^4)
What 2 things should you know about vessel resistance and radius?
1) The length of these tubes are vascular elements that don't change
2) Time is a constant but radius can change & that is the process by which the body changes blood flow
Describe the muscles that surround the arterioles
The muscle cells wrap around and can react appropriately. This action even includes blocking off blood flow
What is the main take-away when considering the differences between arterioles and capillaries?
Each capillary bed is different and contains structures in different places. Includes:
Luminal glycocalyx, Erythrocyte, tight junctions, endothelial cell nucleus, Pinocytotic vesicles, fenestrations, mitochrondrion, and junctions between endothelial cells
Describe water movement in the Body Compartments of a 70 kg healthy person
- Edema (swelling) is an abnormal accumulation of fluid in a body compartment
- Water moves by bulk flow and osmosis
Give the approximate fluid volumes in the different body compartments
- Most of the fluid foes to the interstitial spaces (~12L)
- Blood Plasma (~3L)
- Intracellular compartment (~30L)
What is osmosis?
Osmosis is the molecular flow of water down its concentration gradient
What is concentration of pure water?
The concentration of pure water is 1000 gms/L / 18 gms/mole or 55.55 moles/L.
In a solution with solutes the water is less concentrated than pure water so what would happen if you throw salt in pure water?
Since the pure water is less concentrated, more water will flow into this concentrated area of salt from surrounding areas of pure water
What does it mean when water travels down its concentration gradient?
If water will always diffuse from a region of low solute concentration into a region of high solute concentration
What are the basic things to know about osmotic pressure?
Higher levels of salt = high pressure
Lower levels of salt = low pressure
What does NaCl balance across cell membranes?
NaCl balances K+ and proteins and other cellular osmolytes
What balances osmotic pressure caused by serum proteins across capillary walls?
Hydrostatic blood pressure balances this oncotic pressure (osmotic pressure caused by blood serum proteins such as blood albumin)
Typically, where is osmotic equilibrium achieved in the circulatory system?
Between the interstitial and vascular tissues
What is Starling's Equation for Capillary Filtration?
Filtration = K*[( Pc - Pi ) - ( pc - pi )]
( Pc - Pi ) = hydrostatic pressure gradient
( piC - piI ) = oncotic pressure gradient
K = ultrafiltration coefficient
What does K increase with?
K (the ultrafiltration coefficient) increases with capillary wall area and permeability
Normal Capillary Filtration and Reabsorption
- Pressure across capillary wall changes with filtration and reabsorption
- Reabsorption from the interstitum space which helps in emergencies
What is the relationship between the net hydrostatic pressure between capillary and interstitial space
Net hydrostatic pressure across capillary wall = Pcapillary - Pinterstitial
Describe how High Venous Pressure Increases Filtration
The hydrostatic pressure is always higher than the oncotic pressure. Ergo, high venous pressure gives us filtration because it increases the interstitial volume and makes us swell up (edema)
Describe how Low Capillary Oncotic Pressure Increases Filtration
In liver cirrhosis there is less blood albumin circulating in the blood, low blood concentration, and drops oncotic pressure, more filtration, and causes swelling (edema)
What is the baroreceptor reflex?
Responds through medullary complex and is a very temporary fix for total peripheral resistance. It resets itself after a few days.
Describe basic fluid balance relationship between filtration and edema
- Arterial pressure drops when CO is down fluid volume increases in the venous side casing filtration and edema
- Faulty hearts can cause increases in venous pressure
- You get filtration and edema with high venous output
What role does BP play in fluid balance?
- If BP increases it increases in urinary output because you want BP back to a normal value
- If you decrease CO, you decrease BP
- BP has a striking effect on CO
What happens when we increase venous pressure?
we typically have filtration of blood across capillaries going into the interstitum followed by edema
Describe where the blood volume resides
About 2/3 of the blood volume is in the venous compartment (60%)
When comparing the of stiffness in arterial and venous compartments, what happens with an increase in blood volume?
When blood volume increases venous pressure increases much less than in the arterial compartment.
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