Lect 5: Renal Intro Flashcards
Kidneys function to regulate things:
Help maintain homeostasis by maintaining the EC fluid volume (BP), osmolarity (solute conc inside and outside the cell) and ion composition (Na, K, H, HCO3) which keeps up the blood pressure and blood flow. It also clears toxins drugs and metabolic end products. It has an endocrine function with erythropoietin (RBC production), active Vit D and renin: (Clearance=volume of solute removed).
Clearance
volume of plasma cleared of a solute per unit time
What are the major compartments of body fluids? 60-40-20 Rule
60% of body weight is Total Body Water
for a 70kg patient, IL=1 kg
so a person who weighs 70kg would have 42L of TBW
How is TBW in terms of body weight distributed? Intracellularly
40% of body weight is inside the cell= 28L
How is TBW distributed? Extracellularly
20% of body weight is outside the cell=14L
How can ECF be further subdivided?
intravascular and extravascular
Intravascular fluid accounts for what percentage of
7% (blood volume); it includes plasma, RBC, WBC and platelets
Extravascular fluid or intersitial fluid accounts for how much percentage of body weight?
15%
Whereas the solute composition of the ICF and ECF is different, the solute conc or osmolarity of the ICF and ECF
is essentially the same (-300mOsm/L)
Na/K ATPase is in every cell to
maintain the gradient
Body Fluid Balance
The kidneys compensate for the effects of variable consumption of solutes and water by increasing or decreasing the excretion of solutes and water into the urine
Hydrostatic pressure is greater within the capillary
It pushes fluid out of the capillary into the interstitial fluid
Oncotic pressure is the pressure within capillaries that is due to
the presence of proteins; it pulls fluid into the capillary
As the fluid advances from the arterial to the venous end, Hydrostatic pressure is being decreased (by filtration of intravascular fluid at the arteriole) and
bc the protein doesn’t move out of the fluid you are concentrating protein because you are losing fluid; you are losing plasma volume
Result is an decrease in hydrostatic pressure and an
increase in oncotic pressure so that now the driving force is in the direction of REABSORPTION of fluid on the venous end.
Net filtration or reabsorption will occur along the length of the capillary depending on the forces favoring either. On the arterial side you will have NET filtration of intravascular fluid (PH> PO) while on the venous side you have net reabsorption of extravascular fluid (PH
NOTE: it is the filtration of fluid from the intravascular to the extravascular that causes the decrease in intravascular oncotic pressure. This effect reverses the balancing of driving forces favoring reabsorption over filtration at the venous end of the capillary