Nephrology
On this page 8 sections
One Liners
- Renal Amyloidosis = Biopsy shows Apple Green bifringence
Drugs In Renal Failure
Renal Flow Measurement Concepts
- Renal Plasma Flow (RPF): Best measured using PAH clearance because PAH is both filtered at the glomerulus and actively secreted by the proximal tubules, clearing almost entirely (~90%) from the renal plasma in a single pass.
- Glomerular Filtration Rate (GFR): Best measured using Inulin clearance (the gold standard) or estimated via Creatinine clearance in clinical practice.
- Renal Blood Flow Fraction: Renal blood flow accounts for approximately 1/4 to 1/5 (20–25%) of total cardiac output at rest, not 1/3.Nep
Asthenuria
(also known as isosthenuria or the inability to concentrate/dilute urine appropriately) refers to the excretion of urine with a low fixed specific gravity (dilute urine), regardless of fluid intake.
Mechanism: Antidiuretic Hormone (ADH / Vasopressin) acts on the collecting ducts to reabsorb water and concentrate the urine.
- A decrease in ADH (as seen in Diabetes Insipidus) prevents water reabsorption, leading to the excretion of large volumes of very dilute, low-osmolarity urine (asthenuria).
Acidosis & Alkalosis
note: Anion gap decreases = Hypoalbuminemia
Renal Tubular Acidosis
| Type 1 | Type 2 | Type 4 | |
|---|---|---|---|
| Name | Distal | Proximal | Hypoaldosterone |
| Primary defect | ↓ H⁺ secretion | ↓ HCO₃⁻ reabsorption | ↓ Aldosterone effect |
| Acidosis | Normal AG | Normal AG | Normal AG |
| K⁺ | ↓ | ↓ | ↑ |
| Urine pH | >5.5 | <5.5 eventually | <5.5 |
| Stones | Yes | No | No |
| Classic association | Sjögren | Fanconi | Diabetes |
| Other clue | Nephrocalcinosis | HCO₃⁻ wasting | Hypoaldosteronism |
Nephrotic vs Nephritic
| Feature | Nephritic syndrome | Nephrotic syndrome |
|---|---|---|
| Main problem | Glomerular inflammation | Increased glomerular permeability |
| Proteinuria | Mild–moderate | Heavy >3.5 g/day ⭐ |
| Hematuria | Prominent ⭐ | Usually absent/minimal |
| RBC casts | Yes ⭐ | No |
| Dysmorphic RBCs | Yes | Usually no |
| Edema | Mild–moderate | Severe/generalized ⭐ |
| Hypoalbuminemia | Mild | Marked |
| Hyperlipidemia | Mild/absent | Marked ⭐ |
| Lipiduria | No | Yes ("oval fat bodies") |
| Hypertension | Common | Variable |
| GFR | ↓ | Usually preserved initially |
| Oliguria | Common | Less prominent |
GFR
| Change | Glomerular pressure | GFR | RBF |
|---|---|---|---|
| Afferent dilation | ↑ | ↑ | ↑ |
| Afferent constriction | ↓ | ↓ | ↓ |
| Mild efferent constriction | ↑ | ↑ | ↓ |
| Severe efferent constriction | ↑ initially, then ↓ effective filtration | ↓ eventually | ↓↓ |
| Efferent dilation | ↓ | ↓ | ↑ |
Forces
| Force | Effect |
|---|---|
| Capillary hydrostatic pressure (Pc) | Pushes fluid out of capillary |
| Interstitial hydrostatic pressure (Pi) | Pushes fluid into capillary |
| Plasma oncotic pressure (πc) | Pulls fluid into capillary |
| Interstitial oncotic pressure (πi) | Pulls fluid out of capillary |