Chapter 26: The Urinary System

Introduction

• Focus on kidneys and bladder
• Important processes and cell types
• Encouragement to ask questions if needed

Major Organs of the Urinary System

• Kidneys: Produce urine, located in the posterior abdominal cavity
• Ureters: Tubes transporting urine from kidneys to urinary bladder
• Urinary Bladder: Stores urine, located in the pelvic cavity
• Urethra: Eliminates urine from body, also passage for semen in males

Related Structures

• Adrenal Gland: Above kidneys, helps regulate fluid balance and blood pressure
• Renal Artery & Vein: Blood supply to kidneys for filtration

Functions of the Urinary System

1. Excretion of Metabolic Waste

   • Filters waste products like urea, creatinine, and uric acid from the blood
   • Urea is converted from ammonia in the liver
   • Dialysis mimics kidney function

2. Regulation of Water-Salt Balance

   • Maintains fluid and electrolyte balance
   • Important for blood volume and pressure
   • Involves hormones like ADH and aldosterone

3. Regulation of Acid-Base Balance

   • Maintains blood pH around 7.4
   • Excretes excess acids/bases

4. Secretion of Hormones

   • Erythropoietin (EPO): Stimulates red blood cell production
   • Renin: Regulates blood pressure and fluid balance
   • Calcitriol: Active form of Vitamin D for calcium absorption

Anatomy and Blood Supply of Kidneys

• Retroperitoneal Location: Behind the peritoneum

• Gross Anatomy

  • Hilum: Entry/exit point for renal artery, vein, and ureter
  • Renal Capsule: Protective outer layer
  • Cortex and Medulla: Filtration and concentration of urine occur here
  • Renal Pyramids and Columns: Structures within the medulla
  • Calices and Renal Pelvis: Drain urine into ureter

• Blood Flow

  • Pathway: Renal artery -> Segmental arteries -> Interlobar arteries -> Arcuate arteries -> Cortical radiate arteries -> Glomerular capillaries
  • Peritubular Capillaries and Vasa Recta: Support reabsorption and secretion

Nephron: Functional Unit of the Kidney

• Components

  • Renal Corpuscle: Glomerulus and Bowman’s capsule, site of filtration
  • Renal Tubule: Includes PCT, Loop of Henle, DCT, and Collecting Duct

• Processes

  • Glomerular Filtration: Blood filtration in renal corpuscle
  • Tubular Reabsorption: Reclaiming essential substances
  • Tubular Secretion: Eliminating additional wastes

Urine Transport and Excretion

• Ureters: Transport urine from kidneys to bladder
• Urinary Bladder: Stores urine, made of detrusor muscle
• Urethra: Difference in length and function between males and females

Reflexes and Control

• Storage Reflex: Sympathetic nervous system controls continence
• Voiding Reflex: Parasympathetic nervous system triggers urination
• External Urethral Sphincter: Voluntary control developed during childhood

Age-Related Changes

• Decrease in functional nephrons
• Changes in urine control (incontinence)
• Risks of benign prostatic hyperplasia in males

Conclusion

• Importance of the urinary system in maintaining homeostasis
• Encouragement to revisit the material and ask questions if necessary

Next Chapter

• Focus on the male reproductive system