The Kidneys

Question 1

How many nephrons are in each kidney?

Answer 1

About 1 million

Question 2

What percentage of the total cardiac output do the kidneys receive?

Answer 2

About 22% (1,100 mL/min of whole blood or 650 mL/min of plasma)

Question 3

What is the filtration fraction of the kidneys?

Answer 3

About 125 mL/min

Question 4

What is the formula for the urinary excretion rate?

Answer 4

Filtration rate - reabsorption rate - secretion rate

Question 5

What is the formula for net filtration pressure (NFP)?

Answer 5

Forces favoring filtration - forces opposing filtration

Positive value: Filtration favored
Negative value: Reabsorption favored

Question 6

What is the formula for renal clearance?

Answer 6

Cs = (Us x V)/Ps

Cs = clearance of substance S
Ps = plasma concentration of substance
Us = urine concentration of substance
V = urine flow rate

Question 7

What is the formula for glomerular filtration rate?

Answer 7

GFR = Cinulin = (Uin x V)/Pin

Cinulin = clearance of inulin
Pin = plasma concentration of inulin
Uin = urine concentration of inulin
V = urine flow rate

Clearance of substance less than clearance of inulin, substance mostly reabsorbed
Clearance of substance more than clearance of inulin, substance mostly secreted in renal tubule

Question 8

What is the GFR for renal insufficiency?

Answer 8

20-30% of normal GFR (AKI)

Question 9

What is the GFR for renal failure?

Answer 9

10-25% normal GFR

Question 10

What is the GFR for end-stage renal disease?

Answer 10

< 10-15% of normal GFR

Question 11

Glomerular diseases

Answer 11

Minimal change disease
Focal segmental glomerulosclerosis
Membranous nephropathy
Diabetic nephropathy
Post-streptococcal glomerulonephritis
IgA nephropathy

Question 12

Tubular and interstitial diseases

Answer 12

Acute tubular injury/necrosis
Pyelonephritis

Question 13

Vascular diseases

Answer 13

Renal artery stenosis

Question 14

Cystic diseases of the kidneys

Answer 14

Autosomal dominant and recessive polycystic kidney disease

Question 15

Urinary tract obstruction

Answer 15

Urolithiasis/nephrolithiasis

Question 16

Malignant neoplasm of the kidney

Answer 16

Renal cell carcinoma

Question 17

Nephrotic renal diseases

Answer 17

Minimal change disease
Focal segmental glomerulosclerosis
Membranous nephropathy
Diabetic nephropathy

Question 18

Nephritic renal diseases

Answer 18

Post-streptococcal glomerulonephritis
IgA nephropathy

Question 19

Minimal change disease

Answer 19

Most commonly affects children
Normal glomeruli under light microscope
Effacement of podocyte food processes under electron microscope
Selective proteinuria
No hypertension
Preserved renal function
Treatment is corticosteroids

Question 20

Focal segmental glomerulosclerosis

Answer 20

Most commonly affects adults
All glomeruli have diffuse effacement of foot processes of podocytes
Some glomeruli hardened and stiff at only certain segments
Non-selective proteinuria
Hypertension and hematuria MAY BE PRESENT (NOT DOMINANT)
Poor response to corticosteroid therapy

Question 21

Membranous nephropathy

Answer 21

Most commonly affects elderly
Diffuse thickening of glomerular capillaries due to IgG (autoantibodies to podocyte foot processes) and C3 deposition (sub-epithelial, granular appearance)
Highest incidence of renal vein thrombosis, PE, and DVT

Question 22

Diabetic nephropathy

Answer 22

Glomerular and renal vascular lesions
Pyelonephritis
Earliest manifestation: Microalbuminuria (> 30 but < 300 mg/day)

Question 23

Post-streptoccocal glomerulonephritis

Answer 23

Most commonly affects individuals under 20, primarily children 1-4 weeks after strep infection
Body generates anti-streptolysin (IgG) that forms complexes with bacterial antigen
Complexes deposit in sup-epithelial surface (granular immunofluorescence) and activate complement via classical or alternative pathway
Hypocomplementemia (low C3, but normal C4)
Complement activation recruits neutrophils and macrophages that damage glomeruli and decrease GFR
Smoky brown urine, gross hematuria, hypertension, mild to moderate azotemia, some proteinuria

Question 24

IgA nephropathy

Answer 24

Most commonly affects children and young adults
Upon exposure to mucosal antigen that induces URI, body generates degalactosylated IgA
Body forms antibodies to this IgA and forms complexes that deposit in mesangium
Activation of complement via alternative pathway, trigger proliferation of mesangial cells that narrow glomerular lumens
Gross hematuria after URI