Excretion

• What is the role of the kidneys?


  - Removal of urea from the blood

  - Adjustment of ion (salt) levels in the blood

  - Adjustment of water content
• How is urea taken out of the blood?


  The kidneys do this by filtering stuff out of the blood under high blood pressure and then reabsorbing the useful stuff

  
  

  The end product is urine
• How do urea produced?


  Urea is produced in the liver from excess amino acids .
• What makes us the urinary system?


  - Ureter

  - Kidneys

  - Bladder

  - Urethra

  - Sphincter muscle
• What makes up the kidney?


  - Cortex

  - Medulla

  - Pelvis

  - Ureter

  - Renal vein

  - Renal artery
• What does each kidney contain thousands of?


  Nephrons
• Renal artery


  Blood is brought to the kidney
• Renal vein


  Blood is taken away from the kidney
• What is a nephron made up of?

  - Glomerulus

  - Bowman's capsule

  - Proximal convoluted tubule

  - Loop of henle

  - Distal convoluted tubule

  - Collecting duct
• Glomerulus


  Salt, glucose, urea and water leave the blood
• Bowman's capsule


  Protein and blood cells remain in the blood
• Proximal convoluted tubule


  Glucose is reabsorbed into the blood
• Loop of henle


  Most salt and water are reabsobed into the blood
• Distial convoluted tubule


  Some salt and water are reabsorbed into the blood
• Collecting duct


  Water is reabsorbed into he blood
• Ultrafiltration


  - Blood from the renal artery flows through the glomerulus (a bundle of capillaries at the start of the nephron)

  - A high pressure is built up which squeezes water, urea, ions and glucose of of the blood and into the bowman's capsule

  - The membranes between the blood vessels in the glomerulus and the Bowman's capsule act like a filter, so big molecules like proteins and blood cells are not squeezed out, they stay in the blood
• Glomerulus filtrate


  Filtered materials passing through glomerulus and into Bowman's capsule
• Selective reabsorption


  - All the glucose is reabsorbed from the proximal convoluted tubule so that it can be used in respiration, the reabsorption of glucose involves the process of active transport against the concentration gradient

  - Sufficient ions are reabsorbed, excess ions aren't

  - Sufficient water is reabsorbed from the collecting duct into the hood stream by osmosis
• Osmoregulation


  The control of water balance
• How many different ways is water lost from the body?

  3
• What are the different ways that water is lost from the body?


  - Sweating

  - Urinating

  - Breathing
• What is osmoregulation?


  The body has to constantly balance the water coming in against the water going out - this is osmoregulation
• What 1 way that the body can remove water?

  1 way that it can do this is by adjusting the amount of water that is excreted by the kidneys in the urine
• What happens when we drink lots of water?

  When the kidneys reabsorb more water, the urine has a smaller volume and is more concentrated
• What are hormones?


  They are chemical messages that travel in the blood
• What does ADH stand for?

  Antidiuretic hormone
• Where is ADH produced?

  Pituitary gland
• What does ADH do?


  It causes the collecting ducts of the kidney to become permeable to water, reducing the volume of urine and concentrating the urine
• If water levels are too high


  - Water levels in blood increase

  - Hypothalamus detects low salt evels in me blood

  - Pituitary gland doesn't produce/ producess less ADH

  - Collecting duct becomes less permeable

  - Collecting duct reabsorbs less water

  - More water remains in the filtrate

  - Large amount of dilated urine is produced

  - Water levels in the blood return to normal
• The receptor here is the ____

  Hypothalamus
• The effecter here is the ___

  Collecting duct
• ADH Helps to Control Water Content


  - The amount of water reabsorbed in the kidney nephrons is controlled by a hormone called anti-diuretic hormone (ADH).

  - ADH makes the collecting ducts of the nephrons more permeable so more water is reabsorbed back into the blood.

  - The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed.

  - The whole process of osmoregulation is controlled by a mechanism called negative feedback. This means that if the water content gets too high or too low a mechanism will be triggered that brings it back to normal.