Renal+PowerPoint+AU

The Urinary System

• Composition: Composed of kidneys, ureters, urinary bladder, and urethra.

• Function: Maintains fluid purity and health by:

  • Removing unwanted substances

  • Recycling necessary substances

• Homeostasis: Regulates plasma composition via:

  • Elimination of metabolic wastes

  • Toxins

  • Excess ions and water

Functions of the Kidney

• Regulation of Body Fluids: Adjusts volume, composition, and pH.

• Acid-Base Homeostasis: Produces ammonia to maintain pH.

• Energy Metabolism: Engages in gluconeogenesis (glucose production) during fasting.

• Plasma Osmolarity: Through aquaporin control in collecting ducts.

• Detoxification: Excretes metabolic wastes.

• Vitamin D Activation: Converts vitamin D3 to active form.

• Hormone Synthesis: Produces erythropoietin and renin.

Anatomy of the Kidney

• Main structures include:

  • Renal sinus, adipose tissue, renal lobe, renal pyramid, cortex, and fibrous capsule.

• Renal Regions: Includes hilus, renal pelvis, major and minor calyxes.

• Nephron Types:

  • Cortical Nephrons: 80-85% of nephrons, shorter loops.

  • Juxtamedullary Nephrons: 15-20% of nephrons, longer loops extending into the renal medulla.

Nephron Structure

• Components:

  • Renal corpuscle (Bowman's capsule + glomerulus)

  • Renal tubule (Proximal convoluted tubule, Loop of Henle, Distal convoluted tubule)

• Filtration: Occurs in glomerulus, where blood is filtered into the glomerular capsule.

Mechanism of Urine Production

1. Filtration: Occurs in renal corpuscle. Produces approximately 180L/day of filtrate (water, electrolytes, organic molecules).

2. Reabsorption: Moves substances from renal tubules back into blood via:

   • PCT: Major site for Na+, water, glucose, amino acids reabsorption.

   • Loop of Henle: Water (descending limb), Na+ and Cl- (ascending limb) reabsorption.

   • DCT: Further Na+ and water reabsorption.

3. Secretion: Moves substances from capillaries into renal tubules (e.g., hydrogen ions, ammonium, drugs).

Glomerular Filtration

• Definition: Initial urine formation stage through very porous capillary endothelium.

• Filtration Components:

  • Potent filtration coefficient, hydrostatic pressures, and oncotic pressures affect GFR (Glomerular Filtration Rate).

• Significance of GFR: Indicates renal function efficiency.

Renal Tubules

• Proximal Convoluted Tubule (PCT):

  • Contains cuboidal epithelial cells with microvilli for increased surface area for reabsorption and high energy (ATP) due to active transport.

  • Reabsorbs: Glucose, amino acids, water, and major electrolytes.

Loop of Henle

• Counter-current Multiplication: Mechanism that concentrates urine.

• Functionality:

  • Ascending limb pumps out Na+ (impermeable to water).

  • Descending limb (permeable to water) allows water to passively diffuse out into high osmolarity interstitial fluid.

Collecting Duct

• Reabsorbs: Na+, Cl-, HCO3-, some water.

• Aldosterone Regulation: Influences sodium reabsorption and water retention.

• ADH (Antidiuretic Hormone): Increases water reabsorption, affecting urine concentration.

Urinary Bladder and Micturition

• Bladder Function: Stores urine until release.

• Micturition Process: Controlled by internal (involuntary) and external (voluntary) sphincters.

• Volume Indicators:

  • Full sensation at 150-200 mL

  • Urgency at 300-400 mL

  • Involuntary urination at >600 mL.

Clinical Applications

• Renal Calculi (Kidney Stones):

  • Symptoms: Severe pain, risk factors include dehydration and high-salt diets.

  • Treatment: Lithotripsy to break up large stones.

• Urinary Tract Infections (UTIs):

  • Common in sexually active women and the elderly.

  • Symptoms: Burning sensation, increased urgency, confusion in the elderly.