Excretory System and Kidney Function

Excretory System Overview

• The excretory system removes metabolic waste from the body.
• This is distinct from defecation (undigested food removal) and secretion (release of useful substances).
• Key organs include kidneys, lungs, liver, and skin.

Kidney Structure and Function

• The kidney is composed of cortex, medulla, and pelvis.
• The cortex contains nephrons, the kidney's functional units.
• Each nephron includes glomerulus (filters blood), Bowman's capsule (collects filtrate), and renal tubules (reabsorb vital nutrients).
• The medulla contains loops of Henle and collecting ducts for urine concentration.
• The pelvis collects urine and directs it to the ureter.

Urine Formation Process

• Urine formation has three stages: filtration, reabsorption, and augmentation.
• Filtration (glomerular): Small molecules (water, glucose, salts, urea) pass from blood into Bowman's capsule, forming primary urine. Protein and blood cell leakage indicates potential kidney damage.
• Reabsorption (tubular): Essential substances (glucose, amino acids, ions, water) are reabsorbed from the filtrate into the blood. High glucose levels in urine might suggest diabetes mellitus.
• Augmentation (tubular): The final urine composition (water, salts, urea, waste products like urea, uric acid, ammonia, creatinine) is adjusted in the distal convoluted tubules and collecting ducts. Urine travels from the ureter → bladder → urethra for excretion.

Excretory Disorders

• Uremia: High levels of nitrogenous waste products in blood (urea, uric acid, creatinine); treated using hemodialysis.
• Renal failure: Kidney malfunction; advanced cases require a transplant.
• Renal calculi (Kidney stones): Solid crystal formations within kidney.
• Glomerulonephritis (Bright's disease): Glomerulus inflammation causing protein or RBC leakage to urine.

Other Excretory Organs

• Lungs: Remove carbon dioxide and water vapor via exhalation.
• Liver: Processes waste, converting ammonia into urea. It also breaks down toxins.
• Skin: Removes waste via sweat and helps maintain body temperature.

Skin Sensory Functions

• The skin acts as a sensory organ, detecting:
  • Cold (Krause's corpuscles)
  • Heat (Ruffini's corpuscles)
  • Pressure (Pacinian corpuscles)
  • Touch (Meissner's corpuscles)
  • Pain (free nerve endings)