excretory system

• the excretory system is responsible for removing waste products and excess water from the body. it plays a crucial role in maintaining homeostasis by regulating the body's fluid balance and salt levels
• defecation: the process of getting rid of solid wastes (faeces)
• faeces: undigested material that has passed from the digestive tract
• excretion: getting rid of wastes your body produces
• the lungs, skin, liver and kidney are all involved excretion
• respiration produces carbon dioxide and water, and these are carried to the lungs and exhaled.
• the lungs are part of the respiratory system and the excretory system
• the end products of protein digestion are amino acids (used by body to make proteins for growth and repair).

  they cannot be stored , so if you have more than needed, they will be broken down by the liver into a substance called urea. it will then be excreted
• the liver can break down poisonous substances from the digestive tract into harmless substances, which are then returned to the blood and from there are passed to the kidneys
• the liver breaks down old red blood cells
• any unwanted haemoglobin is added to bile, and passes with the bile into the intestines
• you usually produce more heat than needed, so excess heat is lost through your skin by sweating
• sweat contains a very small amount of urea
• kidneys are bean shaped organs about the size of a fist, and process about 50 litres of blood every hour
• the kidneys:

  • excrete urea
  • control the level of water in your body
  • will take extra water out of the blood as it is filtered through > very dilute urine is produced if you have drunk more water than required
  • will take out less water and produce more concentrated urine if your body is short of water
  • control salt levels in the blood (e.g. excess salt is removed in urine)
• urine: the waste material that has been filtered out of the blood by the kidneys (95% water, 5 % urea, small amounts of salts and pigments)
• the breakdown of haemoglobin gives a pigment, and gives urine its yellow colour
• urine passes from the kidneys down narrow tubes called ureters and into the bladder, where it is stored
• the bladder is a muscular bag that can expand to hold about 500 mL - 1 L of urine
• the urethra is a tube that carries urine to the outside of the body. at the end of the urethra is a sphincter muscle that controls the emptying of the bladder
• the kidneys, bladder, ureters and urethra are all part of the urinary tract
• ureters are 20 cm long
• kidneys have tiny filtration units called nephrons. each kidney contains over a million nephrons
• blood from the heart travels a relatively short distance to the kidneys, so very little pressure from the heartbeat is lost. the blood that enters the kidneys is therefore under pressure, which can help the filtering process, but abnormally high pressures can easily damage capillaries where blood is filtered, affecting the function of the kidneys
• when chemicals normally present in urine combine, they can create hard crystals. small ones can pass through with urine, but larger ones can cause pain and prevent the flow of urine. these hard crystals are called kidney stones

  substances present in urine usually prevent this from happening, however, these substances don't work in some people.

  the best way to avoid them is to drink a healthy amount of water