Module 2: Regulation of Body Fluids

• Homeostasis must be achieved both in plants and animals.
• In animals, the principal metabolic wastes are water, carbon dioxide and nitrogenous wastes.
• Excretory organs such as kidneys, remove and excrete most of the water and nitrogenous wastes.
• There are two processes for maintaining homeostasis of fluids: osmoregulation and excretion of metabolic wastes.
• Osmoregulation is the process by which an animal regulates the osmotic pressure of its body fluids, so that they do not become too dilute or too concentrated.
• Excretion is the process of ridding the body excess water, salts, metabolic wastes, and harmful substances.
• Excretory systems maintain homeostasis by selectively adjusting the concentration of salts and other substances in blood and other body fluids.
• Nitrogenous wastes include ammonia, uric acid, and urea.
• Ammonia is produced through the breakdown of amino acids, wherein the nitrogen containing amino group is being removed.
• Ammonia is highly toxic in some aquatic animals that is why it must be excreted into their surrounding water before it can build up into toxic concentrations in their tissues.
• Uric acid is the product of ammonia and the breakdown of nucleotides from nucleic acids.
• Uric acid forms crystals and can be excreted as a crystalline paste with little fluid loss.
• Urea is the principal nitrogenous waste product of amphibians and mammals, produced in the liver from ammonia.
• urea - less toxic than ammonia and can accumulate in higher concentrations without damaging tissues, thus can be excreted in concentrated form
• osmotic conformers - concentration of their body fluids varies along with the changes in the seawater
• Marine sponges and cnidarians do not need a specialized excretory structure because their wastes pass by diffusion from their cells to the external environment and are washed away by water currents.
• nephridial organs - an organ consists of simple or branching tubes; usually open to the outside of the body through pores
• The protonephridia of flatworms are specialized for osmoregulation.
• The excretory system of insects and spiders consists of Malpighian Tubules which consists of two to several hundred tubules depending on the species.
• Malpighian tubules - have blind ends that lie in the body cavity (hemocoel) where they are bathed in blood.
• malpighian tubules - collect wastes and empty them into the intestine
• kidney - main osmoregulatory and excretory organ in vertebrates
• In most vertebrates, the skin, the lungs, or gills and digestive system also help maintain fluid balance and dispose of metabolic wastes.
• bile - emulsifies fats and neutralises stomach acid
• The liver also produces both urea and uric acid.
• urinary system of mammals

  • kidneys
  • urinary bladder
  • associated ducts
• renal medulla - overall portion of the urinary system of mammals
• The urinary bladder can hold up to 800 ml of urine.
• renal pelvis - a funnel shaped chamber
• ureters - ducts that connect the kidney with the urinary bladder
• The urethra in male is lengthy and passes through the penis and the semen, as well as urine, is transported through the urethra.
• In the female, the urethra is short and transport only urine and its opening to the outside is just above the opening of the vagina.
• nephron - the functional unit of kidney
• Each kidney consists of more than one million functional units, called nephrons.
• nephrons - consists of a cuplike Bowman’s capsule connected to long, partially coiled renal tubule
• three main regions of renal tubule

  • proximal convoluted tubule - which conducts the filtrate from the Bowman’s capsule
  • loop of Henle - an elongated hairpin-shaped portion
  • distal convoluted tubule - which conducts the filtrate to a collecting duct