Excretory System

• Three excretory systems in simple organisms

  • Contractile vacuoles
  • Flame cells
  • Malpighian tubules
• Contractile vacuoles


  Found in unicellular organisms like bacteria and protists, used for excretion of cellular waste and excess water through exocytosis

  
• Flame cells (protonephridia)


  • Found in flatworms and roundworms, have a cluster of cilia that propel waste matter down tubules and out through excretory pores
• Malpighian tubules


  • Found lining the gut of some arthropods like insects, remove nitrogenous wastes and other solutes from the hemolymph, are convoluted with microvilli for reabsorption and osmotic balance
• Malpighian tubules reabsorb water and electrolytes when organisms are in low-water environments, and excrete uric acid as a thick paste or powder
• Kidney


  A pair of bean-shaped structures located below and posterior to the liver, filter blood and purify it, use up 25% of oxygen absorbed through the lungs

  
• Kidney structure


  • 3 layers: renal fascia, perirenal fat capsule, renal capsule

  3 main regions: renal cortex, renal medulla, renal pelvis

  
• Renal cortex


  • Granular due to presence of nephrons, space for arterioles, venules, and glomerular capillaries, where erythropoietin is produced

  
• Renal medulla


  • Inner region, consists of renal pyramids and renal columns, tips of pyramids are renal papillae

  
• Renal pelvis


  • Branches into major and minor calyces, contains the hilum where blood vessels, nerves, and ureters enter/exit

  
• Nephron


  • Functional unit of the kidney, over 1 million in each kidney, two types: cortical and juxtamedullary

  
• Parts of a nephron

  • Renal corpuscle, renal tubule, associated capillary network

  
• Kidney filtration process


  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion

  
• Nitrogenous wastes


  Formed during catabolism of nitrogen-containing macromolecules, need to be excreted to avoid toxicity
• Types of nitrogenous waste excretion

  • Ammonia (aquatic animals)
  • Urea (mammals)
  • Uric acid (reptiles, birds, terrestrial invertebrates)
• Urea is made in the liver and excreted in urine
• Kidney diseases


  • Kidney stones
  • Chronic kidney disease
  • Urinary tract infections
  • Kidney infections
  • Glomerulonephritis