Urinary System

Urinary System Overview

• Kidneys maintain blood purity and chemical balance.
• Primary function is filtering waste from blood and excreting it as urine.
• Organs include kidneys, ureters, urinary bladder, and urethra.

Kidney Anatomy and Function

• Location: posterior abdominal wall, superior lumbar region.
• Right kidney is slightly lower than the left due to the liver.
• Lateral surface is convex, medial surface is concave.
• Renal hilum is where vessels, ureters, and nerves enter/exit.
• Fibrous capsule: helps maintain shape and prevents infection.
• Internal Anatomy: two regions
  • Cortex: superficial, light-colored, granular appearance.
  • Medulla: deep to cortex, cone-shaped masses (renal pyramids).
  • Renal columns: inward projections of cortex separating pyramids.
  • Renal pelvis: expanded part of ureter; collects urine from calyces.

Kidney Vasculature and Nerve Supply

• Receive oxygenated blood from renal arteries from abdominal aorta.
• Renal arteries branch to: segmental, interlobar, arcuate, and interlobular arteries.
• Veins exit through hilum.
• Nerve supply is the renal plexus.

Microscopic Anatomy of the Kidney

• Nephron: structural and functional unit of the kidney
• Urine production involves three mechanisms:
  • Filtration: "cleaning" the blood: a strainer separating wastes from useful substances.
  • Reabsorption: reclaiming necessary substances from filtrate.
  • Secretion: removing additional wastes from blood into filtrate.

Nephron Structure

• Renal corpuscle: where filtration occurs.
  • Glomerulus: ball of capillaries.
  • Bowman's capsule: surrounding structure.
• Proximal convoluted tubule (PCT): initial reabsorption.
• Nephron loop (loop of Henle): vital for water and sodium balance.
• Distal convoluted tubule (DCT): "fine tuning" part; reabsorbs water based on body needs.
• Collecting ducts: final collection and passage of urine to renal pelvis.

Ureter Anatomy

• Thin-walled tubes.
• Carry urine from kidney to bladder.
• Oblique entry to bladder to prevent backflow.
• Microscopic layers: mucosa, muscularis, and adventitia.

Urinary Bladder Anatomy

• Collapsible muscular sac.
• Stores urine, inferior to peritoneal cavity.
• Expands when full; posterolateral angles receive ureters.
• Urethra: tube from bladder that expels urine.

Micturition

• Process of emptying the bladder (peeing).
• Controlled by the brain.
• Bladder's detrusor muscle contracts, internal/external sphincters relax.
• Stretching in bladder activates stretch receptors for control via lower pons (on/off switch).