BS

Urinary System & Related Disorders – Vocabulary Review

Diuresis – Definition & Everyday Examples

  • Diuresis = production of a large volume of urine.
    • Triggered when water re-absorption in nephrons falls.
    • Everyday diuretics (non-drug):
    • Plain water ("milk-jug of water" illustration → constant restroom trips).
    • Iced tea or other caffeine-containing drinks.
    • Metaphor: Think of the kidney as a faucet—diuretics open the valve wider so more water exits.

Pharmacological Diuretics – Sites & Mechanisms

  • Goal: lower water re-absorption, ↑ urine output.
  • Key drug classes (know site + mechanism):
    • Furosemide (Lasix)
    • Loop diuretic; blocks Na⁺ re-uptake in the ascending loop of Henle.
    • \text{Less }Na^+ \Rightarrow \text{Less }H_2O \text{ reabsorbed} → potent diuresis.
    • Thiazides
    • Act on the distal convoluted tubule (DCT).
    • Keep Na⁺ inside the tubule → water follows → ↑ excretion.
    • Spironolactone
    • Aldosterone antagonist (collecting duct / DCT).
    • Prevents aldosterone-mediated Na⁺ re-uptake and K⁺ secretion → mild, “K⁺-sparing” diuresis.

Urine Composition & Odor

  • Varies with diet, hormones, and metabolism (e.g., asparagus).
  • Contains scores of solutes; ammonia chiefly responsible for characteristic smell (odor molecules become airborne, detected by nasal chemoreceptors).

Ureters – Structure & Peristalsis

  • Pair of muscular tubes from renal pelvis → bladder.
  • Peristalsis moves urine:
    • Circular smooth muscle contracts sequentially, propagating waves (toothpaste-tube analogy).
  • Histology:
    • Thick smooth-muscle coat.
    • Transitional epithelium lines lumen → stretches with volume.

Urinary Bladder – Anatomy & Histology

  • Hollow, muscular reservoir; male model identified by prostate inferior to bladder.
  • External supports:
    • Posterior inlets = ureters.
    • 3 round ligaments (left, midline, right) stabilize bladder.
  • Wall layers:
    • Detrusor muscle (unique, powerful smooth muscle).
    • Mucosa with rugae (pleated folds) → accommodates expansion.

Urethra & Sphincters – Sex Differences & Control

  • Two sphincters, both muscular rings:
    1. Internal urethral sphincter – involuntary (smooth muscle).
    2. External urethral sphincter – voluntary (skeletal muscle).
    • Learned during childhood “potty training.”
  • Length disparity:
    • Female urethra = short → ↑ risk of UTIs.
    • Male urethra = long, traverses prostate & penis.

Micturition (Voiding) Reflex – Neural Sequence

  • Filling phase
    • Stretch receptors in bladder wall → afferent signals.
    • Early signals elicit guarding reflex: detrusor relaxes while sphincters stay closed.
  • Urgency phase
    • Receptors fire more frequently → message to micturition center (pons).
    • Brain decides: contract detrusor or keep guarding.
  • Involuntary release if volume overwhelms external sphincter capacity → unavoidable urination.
  • Infants lack corticospinal connections → cannot voluntarily inhibit external sphincter. (Stories of “potty-trained 6-week-olds” = parental cueing, not true voluntary control.)

Urinary Tract Infections (Acute Cystitis)

  • Commonly caused by E. coli (fecal origin).
  • More frequent in women until ~60 yrs.
  • Symptoms: frequency, burning, incomplete emptying, possible hematuria & back pain.
  • Cranberry juice
    • Contains compounds that inhibit bacterial adhesion to mucosa—useful as prevention, not cure.

Urinary Incontinence – Etiologies & Lifestyle Triggers

  • Definition: inability to voluntarily control urination.
  • Causes:
    • Pelvic/abdominal trauma.
    • Pregnancy & childbirth (bladder compressed → sphincter misalignment).
    • CNS/PNS disorders (e.g., multiple sclerosis).
    • Age-related muscle weakening.
  • Exacerbating foods/drinks (“bladder irritants”):
    • Caffeine, carbonation (bubbles), artificial sweeteners, spicy foods.
  • Management → limit irritants, pelvic-floor exercises (Kegels), medical/surgical interventions.

Nephrolithiasis (Kidney Stones)

  • Composition: calcium oxalate, magnesium salts, or uric-acid crystals.
  • Pathway & pain points:
    1. Form on kidney’s inner surface.
    2. Dislodge → renal pelvis (minimal pain).
    3. Enter ureter → intense pain (↑ capsular pressure, ureter spasms).
    4. Ureter → bladder → urethra: each narrow region can be excruciating.
  • Treatment: hydration + analgesia; lithotripsy (ultrasonic shock waves) to fragment stones; surgery uncommon.

Renal Failure – Systemic Impact & Therapies

  • Hypertension major precipitant (glomeruli already under high pressure; renin–angiotensin system worsens load).
  • Consequences: disrupted H_2O & electrolyte balance, acid–base imbalance, neuromuscular & digestive dysfunction.
  • Interventions:
    • Diet ↓ Na⁺, ↓ protein, fluid management.
    • Dialysis – extracorporeal blood filtration (artificial kidney). Mechanism: diffusion of urea, creatinine, ions across semipermeable membrane, then blood is returned.
    • Transplant – often definitive; success rates improving.

Glomerulonephritis – Post-Infectious Inflammation

  • Trigger: large antigen–antibody complexes after infections (e.g., strep).
  • Complexes clog filtration membrane → inflammation, ↓ GFR.
  • Presents days–weeks after illness; monitor for hematuria, edema, hypertension.

Practical & Ethical / Developmental Connections

  • Pediatric care: Recognize neuro-developmental limits on continence → avoid premature potty-training expectations.
  • Geriatrics: Counsel on irritant avoidance & bladder training to maintain dignity and quality of life.
  • Public health: High prevalence of hypertension & diabetes → rising end-stage renal disease; importance of screening & lifestyle education.
  • Environmental health: Proper disposal of unused diuretic drugs to avoid water contamination.
  • Link diuretic site of action to nephron anatomy from previous lectures.
  • Remember: “Na⁺ pulls H₂O.” Any drug/pathology that leaves Na⁺ in tubule → more water lost.
  • Compare peristalsis in ureters to GI tract (Chapter 22) for muscle-layer similarities.
  • Recall transitional epithelium from histology lab—also lines bladder, not just ureters.
  • Ethics: Incontinence products & coverage—access, dignity, and cost considerations.