Lect 5: Renal Intro Flashcards Preview

Unit 7 - Repro & Renal Physiology > Lect 5: Renal Intro > Flashcards

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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).



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?



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



excess accumulation of fluid in the interstitial (or extravascular) space coming from the intravascular space.



CHF raises capillary hydrostatic pressure on venous end, decr driving force to pull fluid into the capillary


Nephotic syndrome & liver dz

Nephrotic syndrome: you are leaking protein into your urine. This decreases plasma protein conc and capillary oncotic pressure: too little protein in urine, decr oncotic pressure so plasma cannot hold its pressure decreasing oncotic pressure. Hepatic dysfunction reduced synthesis of proteins that make up oncotic pressure.

o Together they change the starling forces in the capillaries causing 1. an isotonic retention of sodium in the extravascular space and in water 2.decreased circulating volume which decreases the renal perfusion pressure activating the renin-angiotensin-aldosterone system, further increasing sodium retention, maintaining the edema


Barrier now is cell membrane

o Net movement of water is driven by osmotic pressure differences across cell membrane. There is no hydrostatic pressure bc the membrane isn’t stiff enough, only gradient is the gradient of water is good enough

water conc is inversely proportional to solute conc. o Rule of water movement across barriers separating compartments is: passive transport of water follows active or passive transport of solutes. WATER FOLLOWS SOLUTE bc solute con changes osmolarity and water will flow in this direction to level this out


Perturbations to body fluids: Isosmotic Fluid Expansion
What happens to the ICF and ECF volume when you give and IV isosmotic fluid infusion (normal saline)

the ECF volume increases.
No change in the ICF volume (bc no gradient was created)

Neither the gradient nor the osmolarity of this volume changed; basically you have diluted the blood


Isosmotic Volume Contraction/ Loss

as occurs with diarrhea; we are losing volume of the ECF without changing the ICF.
No affect on the ICF volume or osmoloarity


Hyperosmotic Volume Contraction:

profuse sweating or water deprivation - loss of water in excess of solute from the ECF

==>you will increase the osmolarity and decrease the volume of ECF

so water moves from ICF to ECF so there is a compensatory decrease in ICF volume and an increase in osmolarity as well.

Basically both ICF and ECF volume decrease and both ICF and ECF osmolarity will increase


Hyperosmotic Volume Expansion

high NaCl intake without fluids (gain of solute in excess of water

==>increase ECF osmolarity

water will move from ICF to ECF, decreasing ICF volume and increasing ICF osmolarity

==>increase in ECF volume


What happens to the ICF conc of Na and Cl?

It remains unchanged due to the Na-K pump activity (Na extrusion) balancing Na entry.

(The high Na is initially buffered by increased cellular uptake of the excess Na consumed. However, this does not increase ICF sodium conc because of an increase in Na/K ATPase activity extruding Na out of the cell).


Hypoosmotic Volume Expansion as occurs with

Syndrome of Inapproriate Antidiuretic Hormone (SIADH)

decrease in ECF osmolarity so water moves from ECF to ICF

increase ICF volume and decrease ICF ismolarity

decrease in ECF volume

when plasma osmolarity goes up, ADH goes up; ADH acts on the collecting duct of the kidney--increase water reabsorption<--you have too much darn ADH activity so you keep retaining water and increasing your ECF volume


What happens with hypoosmotic volume expansion?

excess water reabsorption from the collecting ducts into the ECF putting it back into plasma causes
==>increased ECF volume and decreased ECF osmolarity

water moves from ECF to ICF increasing ICF volume and decreasing ICF osmolarity (diluting it)


Hypoosmotic Volume Contraction

Adrenal aldosterone insufficiency and decreased renal NaCl reabsorption (loss of solute in excess of water)

-you lose Na in your urine



stimulates Na reabsorption.

If you keep losing Na in your urine, you would deplete the plasma ECF osmolarity which increases the water conc. So this situation is high water, low salt. So water will move from out to in

Increasing ICF volume and decreasing ICF osmolarity

at the same time you would be decreasing ECF volume


Cell Volume Regulation

How does the cell respond to the perturbations