Body Fluids and Electrolytes Flashcards
CO
CO = SV x HR
MAP
Mean Arteriole Pressure
Equation for flow through a tube
Flow = delta P/ resistance (analogous to Ohm’s law)
How does the above equation derive in terms of the body
CO = P (arteries) - P (right atrium)/ Total peripheral resistance (TPR)
What determines TPR
The pressure is systemic arteries
Equation for MAP
MAP = CO x TPR (since P of right atrium is essentially zero)
Concentration of normal body fluids
290 to 300 mOsm
What is the concentration of Na, K, Ca and proteins in Plasma, ISF and ICF. What is their total concentrations in all the 3 compartments
Na: high in plasma, high in ISF, low in ICF K: low in plasma, low in ISF, low in ICF Ca: high in plasma, high in ISF, low in ICF Proteins: high in plasma, low in ISF, high in ICF Total concentrations is the same in all of the 3 compartments
What saline solution is used for IV fluids
0.9% saline
Using the Vant Hoff equation, what is the hydrostatic pressure required for each 1 mOsm osmotic pressure
20 mmHg per 1 mOsm of osmotic pressure
What is he trying to explain here.
3 important points to discuss here.
Know the concept og hydrostatic pressure and oncotic pressure.
When blood goes into the arterioles, hydrostatic pressure is more than the oncotic pressure resulting in filteration of the plasma into the tissues. However towards the venules the oncotic pressure is more than the hydrostatic pressure which results in reabsorption of the fluid into the venules.
It is important to know that there is a fine balance between filteration and reabsorption. However the balance is slightly in favor of filteration. This causes excess of fluid to go to the tissues which is taken up by the lymphatics
What example did he give us when the balance between filteration and reabsorption is disturbed
He talked about situations where there can be more protiens in the interstitial fluid which can cause the oncotic pressure to decreasem resulting in less reabsoption which eventually causes edema to develop. Once example that he mentioned was in case of allergy attack when granules are released by mast cells in response to allergens which can contribute to systemic or localized edema
What is the significance of Na-K pump
The concentration of proteins in the cytosol is higher than the intersitital fluid, causing water to continuously enter the cells. Na-K pump is then used to kick water out by expelling Na ions and decreasing the plasma concentration and also by the fact that water tends to follow the Na ion.
What is osmolality and tonicity
Osmolality: this property is determined by the concentration of both permeable and impermeable solutes in the cells
Tonicity: this is determined by the impermeable solutes in the cell
Na ions can cross the cell membrane but then why do we consider it essentially impermeable
Any Na that moves in is going to be expelled by the Na-K pump
Osmolality may not predict if a cell will change its volume when put in that solution. Why is that?
Cell volume may increase, decrease or may not change when placed in a solution with the same osmolality or osmotic pressure.
Assumption: Conctration of solute doesnt chnage when it or the water moves into the cell
Osmolality of the solution cannot predict tonicity as tonicity is only dependent on impermeable solutes. The next 3 slides demonstrate this concept in detail
290 mOsm urea concentration
This is the same concentration as plasma. However in this case the solute is urea which is permeable. So it enters the cell, the contration inside the urea increases causing the net flow of water into the cell. The cell will eventually burst
580 mOsm urea
Urea, again is a permeable solute. Initially the cell shrinks since water moves out of the cell faster than the urea can come in. Then the water starts to enter the cell and the cell bursts.
290 mOsm of urea and 290 mOsm of NaCl
NaCl is essentially an impermeable solute. So in this hypertonic solution the cell will initally shrink as water moves out of the cell fast than the urea can move in. Then the urea will move into the cell, bringing water along with it. The cell will eventually resume its normal volume.
So when we need to figure out the tonicity remember to ignore the permeable solute and only look at the osmolality of the impermeable solutes.
What are the take away points from this slide
- Solution containing only permeable solute will always be hypotonic
- Solution with osmalality of less than 290 mOsm due to impermeable will always be hypotonic
- Vice versa
