In-Depth Notes on The Urinary System

Chapter 25: The Urinary System

• Overview of the Urinary System
  • Consists of:
  • Kidneys
  • Ureters
  • Urinary bladder
  • Urethra

Kidney Functions

• Filtration of Blood and Urine Production
  • Filter approximately 200 liters of blood daily
  • Functions include:
  • Regulating water volume, blood pressure, and blood volume
  • Regulating ion levels
  • Maintaining acid-base balance
  • Eliminating waste products (drugs, toxins, urea)
  • Producing hormones like erythropoietin and renin

Kidney Structure

• Location: Retroperitoneal space, partially protected by ribcage
• Anatomy:
  • Supportive layers:
  • Renal fascia (anterior and posterior)
  • Perirenal fat capsule
  • Fibrous capsule
  • Internal structure:
  • Renal cortex
  • Renal medulla (includes renal pyramids, renal columns)
  • Renal hilum: entry/exit point for renal artery, vein, ureter
  • Contains nephrons as functional units

Nephrons

• Functional unit of the kidney:
  • Composed of:
  1. Renal Corpuscle: filters blood
  2. Renal Tubule: processes filtrate
• Types of Nephrons:
  • Cortical Nephrons (80% of nephrons)
  • Juxtamedullary Nephrons (20% of nephrons)

Urine Formation Processes

1. Glomerular Filtration: fluid moves from blood into capsular space
2. Tubular Reabsorption: substances move from tubular fluid back into blood
3. Tubular Secretion: substances move from blood into tubular fluid

Filtration Membrane Anatomy

• Layers:
  • Visceral layer: forms the filtration membrane
  • Parietal layer: outer layer
  • Podocytes: create filtration slits assisting in selective filtration.
• Substances Filtered:
  • Water, glucose, ions, urea, amino acids, vitamins (B and C), hormones and small proteins can pass
  • Not filtered: formed elements (e.g., red blood cells, large proteins)

Factors Affecting Glomerular Filtration

• Net Filtration Pressure (NFP):
  • Formula: NFP = HPg - (OPg + HPc)
  • Controls the Glomerular Filtration Rate (GFR)
  • GFR: volume of filtrate formed per minute by all glomeruli (> 2 million in kidneys)

Regulation of GFR

• Intrinsic Mechanisms (autoregulation):
  • Juxtaglomerular Complex: regulates afferent arteriole diameter
  • Myogenic Mechanism: responds to systemic blood pressure changes
• Extrinsic Mechanism:
  • Renin-Angiotensin System involved in blood pressure control

Transport Mechanisms for Reabsorption

1. Transcellular Route: involves active transport and diffusion across tubular cells
2. Paracellular Route: movement between tubule cells through leaky junctions

• Uses processes like active transport for glucose, Na+, and nutrients, and osmosis/water follows solutes

Composition of Plasma, Filtrate, and Urine

• Comparison of concentration of key substances (mEq/L and mg% for plasma, filtrate, urine)
  • e.g., Sodium concentrations:
  • Plasma: 142
  • Filtrate: 142
  • Urine: 128
• Reabsorption Summary:
  • 100% glucose, amino acids, protein
  • 60-70% water
  • 80% Na+, K+, Cl-

Secretion Process

• Selected substances (e.g., urea, uric acid) move from blood into tubules for excretion
• Important for regulating blood pH and excess K+ removal

Concentration Gradient and Osmolality in Urine Formation

• Medulla: establishes salinity gradient, influencing urine concentration
• ADH role in increasing water permeability in collecting ducts; Diabetes Insipidus effects ADH regulation and urine concentration

Summary of Urinalysis and Other Disorders

• Tests can diagnose diseases (e.g., proteinuria for kidney inflammation)
• Disorders like kidney stones and uremia result from solute imbalances

Ureters and Bladder Anatomy

• Ureters transport urine from kidneys to the urinary bladder, featuring mucosal folds and muscular layers
• Bladder structure supports urination:
  • Detrusor muscle for contraction
  • Trigone area for ureteric orifices

Micturition Reflex

• Involuntary reflex controlled by autonomic and somatic nervous systems
  • Bladder control and urinary incontinence issues

Renal Failure Treatment

• Managed through dialysis (hemodialysis) or kidney transplant to support function.