Exam 6 · Week 11 · BIO 280 Pathophysiology
M11 · The Renal System & Renal Disorders
What the nephron actually does, the three places kidney injury starts, and how acute differs from chronic.
▸M11The Renal System & Renal DisordersWeek 11
💡 The one idea
The kidney is not just a filter — it is a pressure regulator, a bone hormone factory and a blood factory. That is why kidney failure causes hypertension, anemia and fractures, none of which sound renal.
Filter, balance, acid, blood pressure, red cells, vitamin D.
🫠 What the nephron does
Filtration at the glomerulus → reabsorption of what you want to keep → secretion of what you want gone → excretion as urine.
Normal GFR is about 125 mL/min. It is the single best measure of
kidney function.
- Creatinine — a muscle waste product, cleared almost entirely by the kidney. The most specific routine marker of kidney function.
- BUN — rises with kidney problems but also with dehydration, GI bleeding, high protein intake and steroids. Less specific.
- A BUN:creatinine ratio >20:1 points at a prerenal cause — dehydration rather than kidney damage.
Hormones the kidney makes: renin (blood pressure), erythropoietin (red cells), and it activates vitamin D (calcium and bone).
🚨 Acute kidney injury — the three places it starts
| Type | Problem | Causes | Reversible? |
|---|---|---|---|
| Prerenal | Not enough blood getting there. The kidney itself is fine. | Hypovolemia, hemorrhage, shock, heart failure, dehydration, NSAIDs | Yes — if perfusion is restored quickly. The commonest kind. |
| Intrarenal | Damage to the kidney tissue itself | Acute tubular necrosis, nephrotoxic drugs (aminoglycosides, contrast, NSAIDs), glomerulonephritis, prolonged ischemia, rhabdomyolysis | Sometimes |
| Postrenal | Obstruction to outflow | BPH, stones, tumor, blocked catheter, strictures | Yes — if the obstruction is relieved |
The phases: onset → oliguric (<400 mL/day, rising
BUN and creatinine, hyperkalemia, fluid overload, metabolic acidosis) →
diuretic (large urine volumes; the danger flips to dehydration and hypokalemia)
→ recovery, which can take months.
Hyperkalemia is what kills in the oliguric phase, and it does it through the heart. Peaked T waves and a widening QRS need treating immediately, not at the next round.
📊 Chronic kidney disease
Staged by GFR: stage 1 ≥90 with damage · 2
60–89 · 3 30–59 · 4
15–29 · 5 <15 — end stage, needing
dialysis or transplant.
| What fails | What happens |
|---|---|
| Excretion | Rising BUN and creatinine → uremia: nausea, itching, metallic taste, confusion, uremic frost |
| Potassium | Hyperkalemia — dysrhythmias |
| Acid | Metabolic acidosis → Kussmaul breathing |
| Erythropoietin | Normocytic anemia — treated with EPO, not iron alone |
| Vitamin D | Low calcium → high PTH → bone resorption → renal osteodystrophy. Phosphate rises as calcium falls. |
| Fluid / renin | Hypertension and edema — which damage the kidney further |
Diabetes and hypertension are the two leading causes, and together they account for most cases.
⭐ Nephrotic vs nephritic
| Nephrotic | Nephritic | |
|---|---|---|
| Problem | The filter is too leaky to protein | The glomerulus is inflamed |
| Protein | Massive —
>3.5 g/day | Mild to moderate |
| Blood in urine | Minimal | Yes — cola-colored |
| Edema | Severe — low albumin means no oncotic pull; often periorbital | Mild |
| Blood pressure | Normal or low | High |
| Also | High cholesterol; clotting risk from lost antithrombin | Often follows a streptococcal infection by 1–3 weeks |
NephrOtic = prOtein and Oedema. NephrItic = Inflammation and blood.
Kidney stones — excruciating flank pain radiating to the groin, hematuria, nausea, restlessness. Calcium oxalate is the commonest. Treatment is hydration, analgesia and straining all urine.
🎯 Module quiz
Questions for this module.
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