Excretory system

• Excretory system


  • Regulates the chemical composition of body fluids by removing metabolic wastes and retaining the proper amounts of water, salts, and nutrients
  • Components include the kidneys, liver, lungs, and skin functioning at the organ level
• Deamination of amino acids in the liver

  1. Produces urea

  2. Urea is transported to the kidneys for removal
• Nephrons in the kidney

  Facilitate three basic processes: filtration, reabsorption and secretion during urine formation to maintain the composition of body fluids

  
• Homeostatic Functions of the Urinary System

  • Regulate blood volume and blood pressure
  • Regulate blood pH
  • Excrete metabolic wastes
  • Conserve valuable nutrients
  • Regulate body temperature

  
• Body water content


  • Infants have low body fat, low bone mass, and are 73% or more water
  • Total water content declines throughout life
  • Healthy males are about 60% water; healthy females are around 50% (reflects females' higher body fat)
• Fluid compartments


  • Intracellular fluid (ICF) - about two thirds by volume, contained in cells
  • Extracellular fluid (ECF) - consists of two major subdivisions

  
• Solutes in body fluids

  • Water (universal solvent)
  • Ions (Na+, Cl-, HCO3-, Mg2+, K+, HPO42-)
  • Proteins
• Extracellular and intracellular fluid have different solute compositions
• 1450 cm3 of blood flows through the liver every minute
• Functions of the liver

  • Amino acids to glucose (gluconeogenesis)
  • Metabolism of fat (production of lipids from excess glucose)
  • Synthesis of triglycerides (from breakdown of lipids)
  • Synthesis & regulation of cholesterol
  • Deamination (removal of amino group)/Transamination (convert one amino acid to another)/urea formation (linked to deamination)
  • Production of bile (from breakdown of haemoglobin)
  • Detoxification (e.g. metabolising alcohol)
• Deamination


  • Removes the amine group (-NH2) from excess amino acids, with the rest of the molecule being converted to fat
  • The amine group (NH2) is converted to ammonia (NH3) which is then combined with CO2 using ATP to produce urea (CO(NH2)2)
• Kidneys


  • Made up of two important tissues - blood vessels and tubules
  • Responsible for controlling ion, urea and water content

  
• Kidney function


  1. Ultrafiltration - water and products of digestion are squeezed out of the blood and into tubules under pressure

  2. Waste - excess water, excess ions and any urea are removed through the ureter

  3. Selective reabsorption - the blood takes back the things it wants (e.g. glucose and ions) even though this means going against a concentration gradient

  
• Aldosterone


  • Affects the Ascending limb to the Distal convoluted tubule
  • Causes an increase of Na+ and K+ into blood
• Antidiuretic hormone (ADH)


  • Affects the Distal convoluted tubules to the Collecting duct
  • Makes the DCT and CD more permeable to water
• ADH controls water content

  The amount of water reabsorbed into the blood vessels in the kidney is controlled by the hormone ADH