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
Edema
excess accumulation of fluid in the interstitial (or extravascular) space coming from the intravascular space.
CHF
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
Aldosterone
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
What does the cell do in response to an increase in ECF osmolarity?
the cell shrinks
it activates solute uptake mechanisms to increase ICF omolarity, driving water into cells to restore volume to normal (Regulatory Volume Increase, RVI)
What does the cell do in response to a decrease in ECF osmolarity?
the cell swells
-it activates solute efflux mechanisms to decrease ICF osmolarity driving water out of the cell to restore volume to normal (Regulatory Volume Decrease)
What are the basic renal processes INSIDE the kidney?
Filtration, Reabsorption, Secretion, Synthesis as it relates to solutes metabolized, Excretion
Filtration
the anatomical separation of an ultrafuiltrate from the blood. The ultrafiltration of blood through the glomerular capillaries excluding cells and large proteins from the filtrate. NOT urine
Reabsorption
The directional movement of solutes and water from the lumen of the kidney to the peritubular surface (blood side)
Secretion
the directional movement of solutes (NOT WATER) fron the peritubular side (blood side) of the kidney tubule to the lumenal side
Synthesis
metabolism within kidney cells degrading and creating organic solutes or hormones appearing in the blood or in the urine.
Excretion
the final result of the above processes. The amount of solute and water eliminated in the urine.
excretion is not a renal process;
Excretion is
the volume of the urine times the solute conc of the urine
Excretion equals
filtration plus secretion MINUS reabsorption
this is the Renal Handling of solutes and water; occurs at the levl of the nephron
To achieve its homeostatic functions, the kidneys separate the plasma from the blood (filtration) to form a tubular ultrafiltrate which changes in volume and solute composition as it passes down the nephron by reabsorption of water.
The nephron is an “assembly line” of cell-specific, solute reabsorptve and secretory processs, beginning with the proximal tubule and ending at the collecting duct. The final product at the end of the assembly line is urine, which is excreted. Urine is formed, collectively from 1 million nephrons in each kidney
Assembly line
afferent arteriole enters glomerulus where filtration occurs. Then there is tubular secretion followed by tubular reabsorption into the efferent arteriole. Result is urinary excretion
