• Purpose: A device used to remove waste and excess water from the blood artificially.
• Usage: Employed when kidneys fail to filter urea, excess salts, or water from the blood.
• How It Works:
  • Principle: Operates on diffusion of solutes and ultrafiltration across a semi-permeable membrane.
  • Process: Blood flows from the renal artery into the machine and back to the patient via the renal vein. Waste and excess water are removed through dialysis fluid.
  • Machine Features: The machine’s tube is long and narrow to increase surface area. The temperature matches the patient’s body temperature. The tube’s walls are semi-permeable, allowing diffusion of solutes (e.g., urea, glucose, amino acids) while retaining blood components.

Similarities and Differences Between Dialysis Machines and Kidneys

Similarities:

1. Both purify blood of wastes.
2. Both regulate the concentration of substances in the blood.
3. Both use principles of osmosis and active transport.

Differences:

• Usage Duration: Dialysis is used for short periods, often intermittently, while kidneys function continuously throughout life.

• Ultrafiltration: Dialysis does not involve ultrafiltration. In contrast, kidneys perform ultrafiltration in the Bowman’s capsule.

• Blood Processing: In dialysis, all blood passes through the machine. Kidneys process only glomerular filtrate.

• Selective Reabsorption: Dialysis does not have selective reabsorption, whereas kidneys reabsorb specific substances during urine formation.

• pH Regulation: Dialysis does not regulate urine pH. Kidneys actively regulate the pH of urine.

• Waste Levels: Dialysis may leave more waste in the blood compared to kidneys, which are more effective in removing waste.

• Hormones: Dialysis does not involve hormones, while kidneys use hormones such as ADH and aldosterone for regulation.

Summary of Physiological Processes in Urine Formation

1. Ultrafiltration:
   • Blood is filtered in the glomerulus. Glucose, water, ions, salts, and urea are forced into the tubules, while blood proteins and cells remain in the plasma.
2. Selective Reabsorption and Active Transport:
   • Most reabsorption occurs in the proximal tubules for solutes and ions.
3. Osmosis:
   • Water is reabsorbed from the nephron and collecting duct by osmosis.
4. Secretion:
   • Hydrogen ions (H⁺) or bicarbonate (HCO₃⁻) are secreted from the blood into the urine in the distal convoluted tubule.