Urinary System Summary

Urinary System Overview

  • Functions of the Urinary System:
    • Contains two kidneys, two ureters, urinary bladder, urethra.
    • Functions include:
    • Blood filtration, waste excretion, blood volume and pressure regulation, electrolyte and acid-base balance, erythropoietin secretion, hormone clearance, detoxification, glucose synthesis in starvation.

Nitrogenous Wastes

  • Types of Nitrogenous Wastes:
    • Urea (from protein breakdown), uric acid (from nucleic acids), creatinine (from muscle metabolism).
    • Blood urea nitrogen (BUN) normal range: 10-20 mg/dL.
    • Azotemia indicates elevated BUN; uremia is toxicity from nitrogenous waste requiring dialysis.

Excretion and Waste Elimination

  • Excretion Systems:
    • Respiratory: CO₂ and water.
    • Integumentary: Sweat (urea, salts).
    • Digestive: Solid waste and some metabolic waste.
    • Urinary: Major contributor, eliminates metabolic waste, toxins, drugs.

Kidney Anatomy

  • Kidney Structure:
    • Retroperitoneal, located at T12-L3, protected by renal fascia, perirenal fat capsule, fibrous capsule.
    • Two zones: renal cortex (outer), renal medulla (inner) with pyramids and columns.
    • Flow: Renal artery → afferent arterioles → glomerulus → efferent arterioles → peritubular capillaries.

Nephron Structure

  • Nephrons:
    • Over 1 million per kidney, composed of renal corpuscle and renal tubule.
    • Renal Corpuscle Components: Glomerulus, glomerular capsule; contains podocytes.
    • Renal Tubule Sections: Proximal convoluted tubule (PCT), nephron loop, distal convoluted tubule (DCT), collecting duct.

Urine Formation

  • Stages of Urine Formation:
    • Glomerular filtration → tubular reabsorption → tubular secretion → urine excretion.

Urine Characteristics

  • Urine Composition:
    • 95% water, with urea, creatinine, electrolytes.
    • Normal volume: 1-2 L/day; conditions affecting urine output include diuresis, oliguria, anuria.

Storage and Elimination of Urine

  • Ureters:
    • Muscular tubes connecting kidneys to bladder, have three layers.
  • Urinary Bladder:
    • Muscular sac with three layers, features trigone region.
  • Urethra:
    • Conveys urine; variations in males (longer) and females (shorter).

Micturition Control

  • Urination Reflex:
    • Stretch receptors in bladder signal spinal cord causing detrusor muscle contraction and sphincter relaxation.
    • Voluntary control involves signals from the brain to retain or void urine.