Urologic Anatomy, Physiology, and Terminology
This domain tests whether you can connect urinary structure to function and then describe a patient's complaint using standard urologic language. Items rarely ask for an isolated definition; they embed a term in a scenario and expect you to infer the anatomy or physiology driving it.
Anatomy you must be able to localize
- Kidney: nephron = glomerulus plus tubule. Daily filtrate is about 180 L, final urine 1-2 L, GFR roughly 125 mL/min.
- Ureter: peristaltic. Three physiologic narrowings - ureteropelvic junction, crossing of the iliac vessels, ureterovesical junction - are where stones lodge.
- Bladder: detrusor muscle and trigone. First desire to void around 150-250 mL; capacity 400-600 mL.
- Urethra: female about 4 cm (why women are UTI-prone), male about 20 cm, with the prostatic urethra passing through the prostate.
Neural control
- Parasympathetic (S2-S4, pelvic nerve): detrusor contraction - the void signal.
- Sympathetic (T10-L2, hypogastric): detrusor relaxation plus internal sphincter contraction - the store signal.
- Pudendal (S2-S4): external sphincter, voluntary. Storage therefore depends on sympathetic tone and pudendal contraction; voiding requires parasympathetic firing with sphincter relaxation.
Kidney functions beyond making urine
Erythropoietin (anemia of CKD), activation of vitamin D (renal osteodystrophy), hydrogen ion excretion and bicarbonate reabsorption, and volume/potassium regulation through the renin-angiotensin-aldosterone system.
Terminology precision
Oliguria is under 400 mL/24 h; anuria under 100 mL/24 h; polyuria above roughly 2.5-3 L/24 h. Distinguish frequency (many small voids), nocturia, urgency, dysuria, hesitancy, strangury, pneumaturia (gas in urine - think colovesical fistula), fecaluria, and gross versus microscopic hematuria.
Worked example
An 84-year-old reports constant leaking, and a bladder scan shows a 750 mL post-void residual. Reason stepwise: continuous leakage with incomplete emptying is overflow incontinence, not urge incontinence. The large residual suggests detrusor underactivity or outlet obstruction. Naming it correctly drives the plan - decompression and evaluation for obstruction - whereas labeling it overactive bladder and starting an anticholinergic would worsen retention. That is the typical exam chain: term, then physiology, then next action.
Traps that cost marks
- Reversing the sympathetic and parasympathetic bladder roles.
- Calling polyuria or nocturia 'frequency'.
- Applying standard 24-hour urine thresholds to a patient whose output comes from a urostomy or nephrostomy.
- Assuming hematuria in an older man is benign because he has BPH.