Lecture Notes: The Urinary System

Overview

• The urinary system primarily functions to remove metabolic wastes from the bloodstream.
• It involves filtering blood, regulating blood volume and pressure, and balancing electrolytes and pH levels.

Functions of the Urinary System

• Removal of Metabolic Wastes: Urine contains solid wastes that are filtered from blood.
• Regulation of Blood Volume and Pressure:
  • Kidneys secrete hormones based on blood flow.
  • Regulation affects blood pressure and volume.
• Electrolyte Regulation: Controls plasma concentrations of minerals like sodium, potassium, and chloride.
• pH Stabilization: Maintains blood pH around 7.4 by managing H+ and bicarbonate ions.
• Nutrient Conservation: Retains valuable nutrients in the bloodstream.

Anatomy of the Urinary System

• Main Components:
  • Kidneys: Bean-shaped organs that filter blood and produce urine.
  • Ureters: Tubes that transport urine from kidneys to the urinary bladder.
  • Urinary Bladder: Temporary storage for urine.
  • Urethra: Tube through which urine exits the body.

Kidneys

• Located between the last thoracic vertebrae and the third lumbar vertebra.
• Left kidney is slightly higher than the right due to the liver.
• Major parts of a kidney:
  • Renal Cortex: Outer part of the kidney.
  • Renal Medulla: Inner part, contains renal pyramids.
  • Calyces: Minor and major calyces collect urine.
  • Renal Pelvis: Collects urine from the calyces before it enters the ureters.

Blood Flow in Kidneys

• Over 1 liter of blood flows through the kidneys each minute.
• Blood enters through renal arteries and exits via renal veins.
• Filtration occurs in the glomeruli, which are capillary networks.

Nephrons

• Nephrons: Functional filtering units of the kidney, approximately 1.25 million per kidney.
• Key Structures:
  • Glomerulus: Capillary bundle where filtration begins.
  • Bowman's Capsule: Surrounds the glomerulus; collects filtrate.
  • Proximal Convoluted Tubule (PCT): Reabsorption of nutrients and water.
  • Loop of Henle: Further concentrates urine through active transport.
  • Distal Convoluted Tubule (DCT): Final adjustments of urine composition.
  • Collecting Duct: Final collection of urine before exiting the kidney.

Urine Formation Process

1. Filtration: Occurs in the glomeruli; blood pressure forces solutes into the Bowman's capsule.
2. Reabsorption: Nutrients and water are reabsorbed back into the bloodstream from the renal tubules.
3. Secretion: Additional wastes are secreted back into the tubules from the peritubular fluid.

Composition of Urine

• Urine is typically 95% water.
• Other components include:
  • Urea: From amino acid breakdown.
  • Creatinine: From muscle metabolism.
  • Uric Acid: From RNA breakdown.
  • Urobilin: Contributes to urine color.
• Urine is generally sterile unless infected.

Ureters and Bladder

• Ureters: Muscular tubes that transport urine via peristalsis.
• Urinary Bladder: Holds about 1 liter of urine; lined with rugae that allow expansion.
• Internal Urethral Sphincter: Involuntary control, allows urine to exit bladder.
• Urethra: Longer in males than females; leads to the external environment.

Urinary Conditions and Disorders

• UTIs: More common in women due to shorter urethra.
• Kidney Stones: Hard deposits that can block urine flow; treated with sound wave therapy.
• Kidney Dialysis: Temporary filtering of blood when kidneys fail.
• Incontinence: Loss of bladder control, more common in older adults and pregnant women.
• Glomerulonephritis: Infection affecting kidney filtration capabilities.