Glomerular Filtration and Creatinine Clearance + Urinalysis

For urinalysis it will only be part of it (most relevant)

What are the function of the cells in juxtaglomerular apparatus

Macula densa → Control GFR by blood flow; Juxtaglomerular cell → Constrict/relax vessel; Lacis cell → Phagocyte

What are the functions of the kidney

Excretion, homeostasis (water, electrolyte, acid/base), endocrine, + urine formation

What are the 3 layers of glomerulus

Glomerulus, basement membrane and podocyte

What is filtrate

Fluid from blood that has NOT undergone reabsorption or secretion

What is the function of GBM (basement membrane)

Maintains the negative charge of the glomerulus

What factors determine the ability for substances to pass through the glomerulus

Size (small size pass through), electrical charge (positively charged), protein binding (prevents some substances from passing)

What is the relationship between filterability and molecular weight

Smaller MW = filterability closer to 1; filterability = 1 means it will pass the membrane easily

What causes a patient to have proteinuria or albuminuria

Podocyte fusion and collapse + loss of GBM function

If there is 180L of glomerular filtrate produced, how much ends up as urine

1-2L → Most of it is reabsorbed back into the body

Which blood components have a HIGHER concentration in BLOOD/FILTRATE than in urine

Na+, bicarbonate, glucose

Which blood components have a LOWER concentration in BLOOD/FILTRATE than in urine

K+, Cl-, Glucose (there is NO glucose in urine), urea, creatinine

What substances are metabolic waste products found in high amounts in urine

Urea (1820 mg/dL) and creatinine (196 mg/dL)

What is the normal urea: creatinine ratio

20:1

What is hydrostatic pressure

Force of fluid on wall of container; pushes water OUT of capillary

What is colloid osmotic pressure

Pressure created by PROTEINS (albumin); pulls water INTO capillary

How is net filtration pressure calculated

(GHP - GCOP) - (CHP - CCOP) → (50-30)-(10-0) Normal is 10 mmHg

Why is the CCOP value normally 0

Because there is NO protein to cause this pressure ; increases when there is albumin in capsular space

What is the effect of vasoconstriction of AA

Decrease RBF, GHP and GFR

What is the effect of vasodilation of AA

Increase RBF, GHP and GFR

What is the effect of vasoconstriction of EA

Blood backs up in glomerulus → GHP and GFR increase

What is the effect of vasodilation on EA

Increase RBF OUT of glomerulus → Decrease GHP and GFR

What is the process of myogenic mechanism

ABP ↑ → RBF and GFR ↑ → Stretch of wall ↑ → Ca channel open → Ca influx → Contraction of vascular smooth muscle → RBF and GFR ↓

What is tubuloglomeruglar mechanism

Low NaCl sensed by macula densa → Low NaCl = low GFR = low RBF → Macula densa release substance to cause dilation → GFR increase

What formula is used to calculate clearance

C = UV/P (where v = urine flow in mL/min)

The concentration of substance X in the plasma is 1 mg/dL. The urine is collected over a 24 hour period. The total volume of urine is 1.5 L and urinary concentration of substance X is 72 mg/dL. What is clearance of substance X?

C = UV/P → V = 1.5(1000)/(24×60) = 1.04 → 72×1.04/1 = 75 ml/min

What substance is used to measure RBF and RBF

PAH → Almost all of it is completely filtered and secreted (underestimate value)

What substance is used to measure GFR (most ideal)

Inulin (polymer of fructose) → Completely filtered by glomerulus → Inulin clearance = GFR

What substance is used to measure GFR (most commonly used)

Creatinine (endogenous) → Produced at constant rate, a little bit secreted → Ccr > GFR

What biomarkers measure glomerular function

Serum BUN, creatinine + BUN/creatinine ratio; GFR and eGFR

What measures tubular function

Specific gravity, osmolarity, urine concentration test, urine dilution test

What is forms BUN

Breakdown of amino acid (transamination) → Urea

What forms creatinine

Muscle breakdown

What should NOT be found in urine

Glucose, protein, blood, WBC, ketone, nitrite, bilirubin, urobilinogen, ascorbic acid

Positive nitrite indicates what

Gram negative bacterial infection