osmo-regulation

• Osmoregulation


  The process of maintenance of salt and water balance (osmotic balance) across membranes within the body's fluids

  
• Ions that contribute to osmotic balance

  • Sodium (Na+)
  • Potassium (K+)
  • Calcium (Ca2+)
  • Magnesium (Mg2+)
  • Chloride (Cl-)
  • Carbonate (CO3 2-)
  • Bicarbonate (HCO3-)
  • Phosphate (PO3-)
• Cells in a hypertonic environment

  Tend to shrink due to loss of water
• Cells in a hypotonic environment

  Tend to swell due to intake of water
• Types of nitrogenous waste products

  • Ammonia
  • Uric acid
  • Urea
• Organisms that excrete different types of nitrogenous waste


  • Mammals, most amphibians, sharks, some bony fishes (urea)
  • Most aquatic animals, including most bony fishes (ammonia)
  • Many reptiles, birds, insects, land snails (uric acid)
• Protonephridia


  • A network of dead-end tubules connected to external openings in flatworms
  • These tubules excrete a dilute fluid and function in osmoregulation
• Metanephridia


  • Tubules that collect coelomic fluid and produce dilute urine in earthworms
• Malpighian tubules


  • Remove nitrogenous wastes from hemolymph and function in osmoregulation
  • Relatively dry waste produced
• Osmoregulators


  Employ various mechanisms to adapt to a variety of environments
• Osmoconformers


  • Internal environment is osmotic (same osmotic pressure) in relation to the external environment
  • Restricted to certain environments but expend less energy on osmoregulation
• Marine environment


  High concentration of dissolved salts, tends to promote the osmotic loss of water, and the gain of ions by drinking water
• Freshwater environment


  Tends to promote a gain of water by osmosis, and a loss of ions as excess water is excreted

  
• Elasmobranch osmoregulation


  • Blood contains enough urea to match the tonicity of sea water

  
• Terrestrial osmoregulation


  • Animals lose water through excretion and respiration, must drink water to make up for loss
  • Some reduce water loss by excreting nitrogen as relatively insoluble uric acid
  • Certain animals have a highly convoluted nasal passage with a mucous membrane surface (salt excretion)
• Body fluid regulation


  • Water can enter the body through drinking, food, and metabolism
  • An excretory system regulates body fluid concentrations, dependent upon concentration of mineral ions such as sodium and potassium
• Human kidneys


  • Located on either side of vertebral column, just below the diaphragm
  • Each connected to a ureter that conducts urine from the kidney to the urinary bladder
  • Urine voided through urethra

  
• Renal cortex


  • Outer region, granular appearance
• Renal medulla


  • Cone-shaped renal pyramids
• Renal pelvis


  • Hollow-chambered innermost part of the kidney

  
• Nephron anatomy


  • Glomerulus
  • Proximal convoluted tubule
  • Loop of Henle (descending and ascending limbs)
  • Distal convoluted tubule
  • Collecting duct
• Urine formation


  1. Glomerular filtration in glomerular capsule

  2. Tubular reabsorption at the proximal convoluted tubule

  3. Tubular secretion at the distal convoluted tubule
• Proximal tubule


  • Reabsorption of ions, water, and nutrients takes place
  • Molecules are transported actively and passively
  • Some toxic materials are secreted into the filtrate
  • The filtrate volume decreases
• Descending limb of the loop of Henle


  • Reabsorption of water continues through channels (aquaporins)
  • Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate
  • The filtrate becomes increasingly concentrated
• Ascending limb of the loop of Henle


  • Salt but not water is able to diffuse from the tubule into the interstitial fluid
  • The filtrate becomes increasingly dilute
• Distal tubule


  • Regulates the K+ and NaCl concentrations of body fluids
  • The controlled movement of ions contributes to pH regulation
• Collecting duct


  • Carries filtrate through the medulla to the renal pelvis
  • Water is lost as well as some salt and urea, and the filtrate becomes more concentrated
  • Urine is hyperosmotic to body fluids
• Reabsorption of sodium & water


  Regulated by hormones (aldosterone, renin, atrial natriuretic peptide hormone)
• pH adjustment


  By the reabsorption of bicarbonate ions, or the secretion of hydrogen ions
• Hormones that affect osmoregulation

  • Epinephrine and Norepinephrine
  • Renin
  • Angiotensin
  • Aldosterone
  • Anti-diuretic hormone (vasopressin)
  • Atrial natriuretic peptide
• Hemodialysis


  A type of dialysis
• Peritoneal dialysis


  A type of dialysis
• The kidneys are responsible for regulating the water balance, electrolyte concentration, and acid-base balance.
• Baroreceptors monitor blood pressure and adjust cardiac output and peripheral resistance accordingly.
• Antidiuretic hormone (ADH) is released by the posterior pituitary gland in response to increased osmotic pressure or decreased blood volume.
• Osmoreceptors detect changes in blood plasma osmolarity and stimulate thirst or release antidiuretic hormone (ADH) from the hypothalamus to increase reabsorption of water by the kidney tubules.