Urinary System Overview

Urinary System

• Functions:
  • Removes waste products, including toxins
  • Regulates water and electrolyte balance, impacting blood pressure
  • Regulates blood pH (acid-base balance)
  • Secretes hormones:
    • Renin: Controls blood pressure through the Renin-Angiotensin-Aldosterone-System (RAAS)
    • Erythropoietin (EPO): Stimulates red blood cell production

Kidney Structure

• Components:
  • Cortex: Outer layer
  • Medulla: Inner layer
  • Pelvis: Funnel-shaped structure that collects urine
  • Hilum: Entry/exit point for:
    • Renal artery
    • Renal vein
    • Ureter
    • Nerves and lymph vessels

Nephron: Functional Unit of the Kidney

• Location: Partially in the cortex, partially in the medulla
• Components:
  • Glomerulus: Capillary loop, important for filtration
  • Proximal tubule: Reabsorbs nutrients, proteins, water, and electrolytes; also secretes substances
  • Loop of Henle: Creates a salt concentration gradient in the medulla, concentrating urine
  • Distal tubule: Reabsorbs electrolytes

Renal Corpuscle

• Components:
  • Glomerulus: Capillary loops enclosed by Bowman’s capsule
  • Bowman’s capsule: Surrounds the glomerulus and collects filtrate

Filtration Barrier

• Components:
  • Fenestrated endothelium of glomerular capillaries: Allows fluid and small molecules to pass through
  • Podocytes: Cells that cover the glomerular capillaries with projections, forming a filtration barrier
  • Basement membrane: Acts as a filter, preventing larger molecules from passing through

Glomerular Filtration Rate (GFR)

• Represents the amount of filtrate produced by the kidneys per unit of time.
• Approximately 180 L/day, indicating that the kidneys filter the entire blood volume 60 times per day

Proximal Convoluted Tubule

• Functions:
  • Reabsorption: Recovers valuable nutrients, proteins, water, and electrolytes
  • Secretion: Removes waste products like bile salts, creatinine, ammonia, and drugs from the blood into the filtrate

Loop of Henle

• Located in the medulla
• Functions:
  • Creates a salt concentration gradient in the medulla through a process called “countercurrent multiplication,” which concentrates urine

Distal Convoluted Tubule

• Functions:
  • Reabsorption: Recovers electrolytes
  • Juxtaglomerular apparatus (JGA): Specialized structure near the glomerulus that regulates blood pressure

Juxtaglomerular Apparatus (JGA)

• Components:
  • Macula densa: Cells in the distal tubule that sense salt concentration in the filtrate
  • Juxtaglomerular (JG) cells: Located in the afferent arteriole, produce and release renin, a hormone that increases blood pressure

Collecting Ducts

• Location: Cortex and medulla
• Functions:
  • Reabsorbs water under the influence of antidiuretic hormone (ADH), leading to concentrated urine

Urothelium (Transitional Epithelium)

• Found in the urinary bladder, ureters, and urethra
• Specialized epithelium designed to withstand the cytotoxic effects of hypertonic urine
• Layers:
  • Basal layer: Provides structural support
  • Intermediate layer: Cuboidal or columnar cells, forming a multilayered structure
  • Superficial layer: Contains large “umbrella cells” that provide a protective barrier

Ureters

• Structure:
  • Lumen: Lined with transitional epithelium
  • Muscle layer: Thick muscle layer for peristaltic contractions that transport urine to the bladder

Bladder

• Structure:
  • Lumen: Lined with urothelium
  • Muscle layers: Provide elasticity and contractility for urine storage and expulsion

Urethra

• Differences between males and females: Males have a significantly longer urethra than females
• Structure:
  • Lumen: Transitional epithelium in the proximal part, transitions to stratified squamous epithelium (like skin) in the distal part.
  • Sphincter: Circular muscle tissue that controls urine flow

This quiz covers the functions and structure of the urinary system, including kidney components and the nephron, the functional unit of the kidney. Test your knowledge on how the kidneys regulate body processes and filter waste. Perfect for biology students studying human anatomy.