Excretion

• Excretion is the removal of metabolic waste from the body.
• The excretory system plays a role in regulating body temperature and controlling osmosis.
• Lungs excrete water and carbon dioxide. The skin excretes sweat and the kidneys excrete urea.
• The Urinary system

  
• The ureter brings urine from the kidneys to the bladder while the urethra brings urine out of the body.
• Vertical section of a kidney

  
• Aorta and renal arteries carry blood rich in waste products to the kidney.
• Each kidney contains more than a million nephrons. A nephron is a tube about 3cm long. They are in the cortex and medulla of the kidney and they make urine.
• Blood supply to nephron

  
• Urine is composed of 96% water.
• In filtration, blood entering the kidneys is filtered in the outer cortex. Small substances are forced out of the bloodstream into the kidney. These materials are called the glomerular filtrate.
• In reabsoption, useful materials are taken back into the blood. 99% of the glomerular filtrate is reabsorbed.
• The proximal tubule is thin walled and long with lots of mitochondria to allow for active transport.
• The collecting duct is permeable to water which is reabsorbed due to osmosis.
• ADH travels to kidneys to make the walls of the distal tubule and the collecting ducts more permeable to water. ADH allows for reabsoprion of more water from the nephron.