osmoregulation

• what will happen if the concentration of water in the blood is too high?

  water will move into the body cells by osmosis. If too much water moves into the cells then the cells may burst.
• what will happen if the concentration of water in the blood is too low?

  water will move out of the cells by osmosis. This causes cells to shrink.
• how do kidneys help to regulate water content?

  by controlling how much water is reabsorbed and how much is lost in urine.
• what are the 3 main roles of the kidneys?

  1. removal of urea from the blood. Urea is produced in the liver from the breakdown of excess amino acids.
  2. adjustment of ion levels in the blood.
  3. adjustment of water content in the blood.
• how do the kidneys act as a part of the urinary system?

  by filtering stuff out of the blood under high pressure, and then reabsorbing the useful things. The end product is urine.
• why do animal cells burst when they contain too much water?

  they don't have rigid cell walls (unlike plant cells).
• what happens to the liquid part of the blood (containing water, urea, ions and glucose) in the nephrons?


  forced out of the glomerulus and into the Bowman's capsule at high pressure (ultrafiltration). Bigger molecules (proteins) and blood cells can't pass through the membranes and are not forced out.
• as the liquid flows along the nephron, which useful substances are reabsorbed?

  • all the glucose is selectively reabsorbed, it's moved back into the blood against the concentration gradient.
  • sufficient ions are reabsorbed.
  • sufficient water is reabsorbed, according to the level of the hormone ADH.
• what happens to the substances that aren't reabsorbed in the nephrons (urea, excess water, excess ions)?


  they continue out of the nephron via the collecting duct. It then passes into the ureter and down to the bladder as urine. Urine is released through the urethra.
• why must water levels in the body be kept constant?

  to controlt the amount of water and ions diffusing in and out of cells.
• which factors affect the balance of water in the body?

  • eating too much salt: can make the blood ion concentration too high.
  • exhalation: water in the lungs leaves the body in a person' breath.
  • illness: fever, vomitting + diarrohea can result in dehydration.
  • sweating: water, ions + urea are all lost in sweat.
• what is lost during sweating?

  water, ions + urea
• what is a hypertonic solution?

  it has low water concentration and a higher ion concentration than cells.
• what happens if the blood becomes hypertonic?

  cells lose water by osmosis and shrink.
• what is an isotonic solution?

  has the same water and ion concentrations as cells.
• homeostasis works to regulate the blood's water and ion concentration so that it remains isotonic.
• what is a hypotonic solution?

  it has a higher water concentration and a lower ion concentration than cells.
• what happens if the blood becomes hypotonic?

  cells gain water by osmosis and burst.
• why must the body's ion levels be kept constant?

  to control osmosis and diffusion between cells in the body.
• what is the volume of water in the blood monitored by?

  the hypothalamus
• what is the main function of the kidney?

  to filter the blood and produce urine in order to remove unwanted substances such as urea, and excess water from the body.
• when is urea formed?

  when the digestion of proteins result in an excess of aminoa acids, which can't be stored in the body.
• what happens to amino acids in the liver?

  they undergo a process called deamination, and the waste product is ammonia.
• what happens to the ammonia produced by deamination?

  it's converted into urea and msut be excreted from the body as urine.
• why does urea need to be removed from the body?

  it's toxic. When there is too much of it in the bloodstream, it can harm cells and tissues.
• what are the 2 stages in urine production?

  1. ultrafiltration
  2. selective reabsorption
• what is the first stage in selective reabsorbtion?

  useful substances including glucose and some water, are reabsorbed from the tubule back into the bloodstream.
• what is the second stage in selective reabsorbtion?

  this leaves all urea, excess salts, and excess water in the nephron tubule.
• what is the third stage of selective reabsorption?

  this mixture forms urine, which is collected by the kidneys and travels to the bladder to be stored and excreted.
• what is the first stage of ultrafiltration?

  the blood capillaries form a knotted cluster called a glomerulus in a part of a nephron called the Bowman's capsule.
• what is the second stage of ultrafiltration?

  the blood is filtered and all water, urea, and salts move into the nephron tubule.
• what is the third stage of ultrafiltration?

  blood cells and proteins remain in the blood as they are too big to move across the capillary walls.
• what happens when there is too much water in the blood?

  The hypothalamus triggers the pituitary gland to stop the release of ADH (anti-diuretic hormone). This reduces the permeability of the kidney tubules, meaning less water is reabsorbed back into the bloodstream, resulting in a large volume of dilute urine.
• what happens when there is too little water in the blood?

  The hypothalamus triggers the pituitary gland to release ADH which increases the permeability of the kidney tubules meaning more water is reabsorbed back into the bloodstream. This results in a small volume of concentrated urine.
• what is urine made up from?

  urea and excess water
• where does urine production take place?

  in nephrons