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4. Kidney and Clearance Products


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List the 6 functions of the kidneys:
1. Urine formation
2. Fluid/electrolyte balance
3. Acid-base balance
4. Waste excretion
5. Hormone function
6. Protein conservation
What 3 processes occur to allow urine formation?
What 3 waste products are removed by the kidneys?
1. Urea
2. Creatinine
3. Uric acid
What 3 hormones are regulated by the kidneys?
1. Vitamin D - active form is produced
2. Renin - produced
3. Erythropoeitin
How much blood supplies the kidneys?
what %body wt are the kidneys?
-25% of cardiac output
What transport occurs in the proximal convoluted tubule?
1. Active transport of Glucose, amino acids, Na, K.
2. Water follows
3. Passive reabsorption of negative ions
What transport occurs in the loop of Henle?
Active transport of Cl-
What transport occurs in the distal convoluted tubule?
Active transport of Na, K, H.
What controls Na/K/H2O transport in the distal tubule?
What is the tonicity of filtrate as it leaves the distal tubule?
Isotonic to hypotonic
What happens to the filtrate tonicity when it enters the collecting duct?
Becomes hypertonic - H2O gets reabsorbed so the ion concentration increases.
What allows the filtrate to become hypertonic in the collecting duct? What controls this?
-The reabsorption of Water from the filtrate.
-Controlled by ADH
What is the function of ADH?
Increased permeability of collecting duct to H2O
How does the kidney buffer body pH?
-Excretion of organic acids and H+
What exactly is Urea?
Major nitrogen waste product from protein breakdown
How is Urea formed?
-Liver deaminates a. acids
-Produces ammonia
-Intest bacteria degrade NH3
What is the name of the chemistry test for Urea?
BUN - blood urea nitrogen
How is Urea excreted?
1. Glomerulus filters it at a constant rate
2. 40% is reabsorbed passively
3. Final excretion amt depends on protein diet and metabolism.
How do these physiological factors affect the BUN?
-Liver disease
-High protein diet
-Kidney disease
Liver dis: decreased BUN
Hi-protein diet: increased BUN
Starvation: increased plasma urea
Dehydration: increased BUN
Kidney disease: increased BUN
what is azotemia?
Increased urea waste products in the serum
What are 6 pre-renal causes of azotemia?
-GI hemorrhage
-Increased protein
-Cortisol/mannitol treatment
What are 4 renal causes of azotemia?
1. Vascular - arteriosclerosis
2. Glomerular disease
3. Acute tubular necrosis
4. Pyelonephritis
What causes post-renal azotemia?
Obstruction of urine flow - through ureters, bladder or urethra.
List 4 causes of a decreased BUN:
1. Liver disease
2. Malnourishment
3. Decreased protein diet
4. Over-hydration
What is Creatinine formed from?
Muscle creatine and phosphocreatine
How closely does Urine creatinine measurement approximate the GFR?
Close, but it overestimates it b/c about 10% is excreted.
Does creatinine fluctuate much in normal individuals?
No; it is relatively constant b/c it's a muscle byproduct.
How much of the body creatinine is filtered by the glomerulus?
About 90%
How do the urine Creat and the BUN change with decreasing Renal function?
They both increase
what is the normal Creat ref range?
0.6-1.2 mg/dl
what is the normal BUN ref range?
7-18 mg/dl
how high do the creat and bun get in renal failure?
Creat = about 10 mg/dl
BUN = about 35-110 mg/dl
how high do the creat and bun get in uremic syndrome?
Creat = >8 mg/dl
BUN = >80 mg/dl
List 3 tests for glomerular function:
1. Creatinine clearance
2. Inulin clearance
3. Urea clearance
How is the Creatinine clearance calculated?
see flashcard.
How is inulin clearance different from creatinine?
Inulin is given exogenously.
Which clearance test more accurately parralels the GFR?
Urea clearance
List 4 tests for evaluating Tubular Function:
1. Phenolsulfonphthalein (PSP)
2. Specific gravity
3. Osmolality
4. Concentration tests
What is the principle of the PSP test?
-Dye is given exogenously, the secretion is measured to determine how well the tubules function.
What is the definition of urine specific gravity?
The weight of dissolved solutes in the urine compared to water.
What is a normal specific gravity?
Above 1.000 (sp gr of H2O) up to about 1.030
What is a dilute Sp gr?
What 3 methods are used for measuring specific gravity?
1. Densitometry
2. T-S meter (refractometer)
3. Dipstick
How is osmolality different from specific gravity?
It takes into account the number of molecules, not just the weight.
What is the normal serum osmolality?
285-300 mOsm/kg
What is the normal urine osmolality?
App. 600 mOsm/kg
What is the normal Urine:Serum osmolality ratio?
After 12 hrs of fluid restriction what is the Urine:serum osmol. ratio?
Increased; 3-4.7
How does Urine:serum osmolality ratio change with:
-Renal tubular deficiency?
-Diabetes insipidus?
Ren. tubular. def: decreased
Diabetes insipidus: 0.2-.7

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