Urinary System

• The process by which the wastes of cellular metabolism are removed from the organism is called excretion
• Excretory organs regulate the chemical makeup of the blood and other body fluids by removing metabolic wastes and excess materials
• Excretory organs also remove excess heat to maintain a constant body temperature
• Excretory organs function together with the circulatory, nervous and endocrin systems to maintain homeostasis
• Major metabolic wastes


  • CO2
  • H2O
  • Nitrogenous wastes
  • Mineral salts
• Role of Liver in Excretion

  1. Detoxification: Harmful or toxic substances are converted into inactive or less toxic forms

  2. Excretion of bile

  3. Urea formation
• NH3 is converted to carbon skeleton which is used as energy source or converted to glycogen or fat
• Kidneys


  The most important organ that performs the excretory event in humans. It ensures that waste materials such as water, urea, uric acid and mineral salts are filtered out of the blood and excreted in the form of urine
• Kidneys


  • Located behind the abdominal cavity and at waist level, on either side of the lumbar vertebrae (spine), one on the right and one on the left
  • Have a transparent, thin and durable kidney membrane
  • Have a thick fat layer around them for protection
  • Have adrenal glands that secrete hormones on the upper part
  • Have a hollow middle part with kidney artery, kidney vein and urinary tube (ureter)
• Parts of the kidneys

  • Crust area (Cortex)
  • Core region (Medulla)
  • Pool (Pelvis)
• Cortex


  • Located just under the kidney membrane, where harmful and waste materials such as water, urea, uric acid and mineral salts in the blood are filtered
• Medulla


  • Where harmful and / or waste materials such as urea, uric acid and mineral salts are transported to the pool (pelvis) of the nephrons through the urinary canals
• Nephron


  The smallest unit of the kidney, located in the core region, that filters waste materials from the blood
• Structure of a nephron

  • Glomerul: Ball formed by capillaries
  • Bowman Capsule: Membrane structure surrounding the Glomerula
  • Urinary Canal: Continuation of the Bowman capsule
• Filtration in the nephron

  Under the influence of blood pressure, substances (water, minerals, glucose, vitamins, urea ...) in the glomerulus capillaries pass through the cell membrane, out of the capillary and into the Bowman capsule
• Reabsorption in the nephron


  Useful substances found in the filtrate are absorbed back by the tube cells and given to the capillaries
• Reabsorption processes in different parts of the nephron

  • Proximal tube: Most water, all glucose, amino acid, fatty acid and glycerol, most sodium are reabsorbed
  • Descending arm of Henle handle: Water, sodium and chlorine are reabsorbed
  • Emerging arm of Henle handle: No water absorption, chlorine is reabsorbed, sodium is absorbed back
  • Distal tube: Sodium, chlorine and water are reabsorbed, potassium is excreted
  • Urine collection channels: Water and 50% of urea are reabsorbed
• Secretion in the nephron

  Harmful wastes such as ammonia, antibiotics, H+, creatinine are given to the tube ducts with active transportation
• The urine is composed of substances such as water, minerals, vitamins B and C, urea, ammonia, creatinine, H+
• Urinary tube (ureter)


  • Carries the urine collected in the pool into the bladder
• Bladder


  • Made of strong muscles and expands when needed to store urine for a while
• Kidneys receive 1 L of blood per minute, 1500 L per day. 12% of this blood is absorbed from the glomerulus (180 L). 98% of the absorbed liquid returns to the blood
• Man produces 4 times more concentrated urine than his blood
• Formation and Excretion of Urine

  1. Water, mineral salts, carbon dioxide gas and ammonia are given to blood

  2. Blood is converted into ammonia, urea and uric acid in the liver

  3. Water, urea, uric acid and mineral salts in dirty blood coming to kidneys are filtered by nephrons

  4. Filtrate is collected in the pool by passing through the urinary canals in the medulla

  5. Most of the water, glucose and other nutrients in the filtrate are absorbed by the collection channels in the core region and passes back into the blood

  6. The liquid remaining in the pool after absorbing the water and nutrients in the filtrate is called "urine"

  7. Urine is transported through the urinary tube to the bladder and is then expelled
• Those that are filtered

  • Amino acids
  • Glucose
  • Various ions
  • Urea and uric acid
• Those who can not be filtered

  • Blood Cells
  • Plasma
  • Protein and fat