Kidneys

• The kidneys are responsible for carrying out two very important functions they are responsible for the removal of waste products from the blood and the regulation of the water content of the blood.
• As an osmoregulatory(water) organ - they regulate the water content of the blood (vital for maintaining blood pressure)
• As an excretory organ - they excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts).
• Renal artery- carries oxygenated blood (containing urea and salts) to kidneys.
• Renal vein- carriers deoxygenated blood (that has had urea and excess salts removed) away from kidney.
• Kidney- regulates water content of blood and filter blood.
• Ureter-carriers urine from kidneys to bladder.
• Bladder- stores urine(temporarily)
• urethra-release urine outside of the body.
• Stages of urine formation 1- filtration 2- reabsorption 3-secretion
• • Filtration blood enters afferent arteriole - glomerulus- blood pressure forces water and small solutes such as salts, sugars, animo acids and nitrogenous waste into bowman's capsule - large components such as cells and serum albumins are carried away by efferent arteriole.
• Reabsorption- water and useful solutes such as glucose, salts and animo acids are absorbed from the filtrate back into the body.
• Secretion- solutes, such as excess salt and toxins, are added to the filtrate in the distal convolutes tubule.
• Arterioles branch off the renal artery and lead to each nephron, forming a knot of capillaries known as the glomerulus, which sits inside the cup-shaped Bowman’s capsule.
• The capillaries in the glomerulus get narrower as they get further into the knot, increasing the pressure on the blood moving through them.
• This increased pressure eventually causes smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, forming what is known as the filtrate.
• Ultra filteration-

  •  The substances forced out of the capillaries are glucose, water, urea, salts​
  •  Some of these are useful and will be reabsorbed back into the blood further down the nephron​
• Reabsorption ​Reabsorption of water & salts​

  • As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion​
  • As salts are reabsorbed back into the blood, water follows by osmosis​
  • Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time​
• Selective Reabsorption​-

  • After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule​​
  • This takes place by active transport​
  • The nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules​
  • Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule​
• Ultrafiltration occurs in the bowman's capsule and small molecules (including animo acids, water, glucose, urea and inorganic ions) are filtered out of the blood capillaries of the glomerulus and into the bowman's capsule to form filtrate known as glomerular filtrate.
• Selective reabsorption occurs in the proximal convoluted tubule where useful molecules are taken back (reabsorbed) from the filtrate and returned to blood as the filtrate flows along the nephron.
• Osmoregulation​- The control of the water potential of body fluids is known as osmoregulation​

  Osmoregulation is a key part of homeostasis
• Osmoregulation-

  • Specialised sensory neurones, known as osmoreceptors, monitor the water potential of the blood (these osmoreceptors are found in hypothalamus)​
  • If the osmoreceptors detect a decrease in the water potential of the blood, nerve impulses are sent along these sensory neurones to the posterior pituitary gland (another part of the brain just below the hypothalamus)​
  • These nerve impulses stimulate the posterior pituitary gland to release antidiuretic hormone (ADH)​
  • ADH molecules enter the blood and travel throughout the body​
  • ADH causes the kidneys to reabsorb more water​
• The effect of ADH on the kidneys​-

  • ADH causes the collecting ducts of the nephron to become more permeable to water by increasing the number of aquaporins (water permeable channels)​
  • Water moves from the high water potential in the collecting ducts to the low water potential in the medulla ​
• • Water is reabsorbed by osmosis from the filtrate in the nephron​​
  •  This reabsorption occurs as the filtrate passes through structures known as collecting ducts​
  •  ADH causes the membranes of the collecting duct cells to become more permeable to water​
  •  ADH does this by causing an increase in the number of aquaporins (water-permeable channels) in the membranes of the collecting duct cells. This occurs in the following way:​
  • of the membrane to water​
  • ADH molecules bind to receptor proteins​
  • This activates the aquaporins, causing ​
  • This increases the permeability ​
• The end result is reduced production and concentrated Urine ​

  • As the filtrate in the nephron travels along the collecting duct, water molecules move from the collecting duct (high water potential), through the aquaporins, and into the tissue fluid and blood plasma in the medulla (low water potential)​
  • As the filtrate in the collecting duct loses water it becomes more concentrated​
  • As a result, a small volume of concentrated urine is produced. This flows from the kidneys, through the ureters and into the bladder​
• Osmoregulation ​The control of the water potential of body fluids is known as osmoregulation​

  Osmoregulation is a key part of homeostasis
• Osmoregulation 

  • Specialised sensory neurones, known as osmoreceptors, monitor the water potential of the blood (these osmoreceptors are found in the hypothalamus)​
  • If the osmoreceptors detect a decrease in the water potential of the blood, nerve impulses are sent along these sensory neurones to the posterior pituitary gland (another part of the brain just below the hypothalamus)​
  • These nerve impulses stimulate the posterior pituitary gland to release antidiuretic hormone (ADH)​
  • ADH molecules enter the blood and travel throughout the body​
  • ADH causes the kidneys to reabsorb more water​
• What is the name of the hormone which stimulates the reuptake of water in the kidney?

  ADH
• The kidneys removes waste we don't want by urea (which in made in the liver during a process deamination) this is where excess animo acids are converted to fats and carbohydrates for storage.
• ways are body loses water is by sweating, lungs when we breathe and urine.
• water regulation is important as our cells lose or gain water from osmosis therefore if our body has too much water it causes the cells to swell.
• the tubule absorbs anything small such as water, glucose, animo acids, urea, everything expect large things e.g: proteins and cells. This process is called filtration.
• The tubule reabsorbs anything we need such as all glucose, some water. This process is called selective reabsorption.
• The hypothalamus detects the water concentration of the blood if the water concentration is too low then the hypothalamus sends a signal to the pituitary gland to release ADH, ADH travels around the body and reaches the kidneys telling the tubules to reabsorb water into the blood meaning that the amount of water in the blood increases. therefore producing less urine.
• The hypothalamus detects the water concentration of the blood if the water concentration is too high the hypothalamus will stop sending signals to the pituitary gland so it won't releases as much ADH, less ADH will travel to the kidneys and the tubules will reabsorb less water into the blood meaning more water will stay in the tubules producing more urine to get rid of the extra water.
• First part of the nephron is the glomerulus, which is the part of the kidney that filters blood.
• The glomerulus is surrounded by the bowman's capsule.
• Blood pressure forces fluid from the blood in the glomerulus into the Bowman's capsule. Once the fluid is in the bowman's capsule, the fluid is called the filtrate .
• What's in filtrate?


  Glucose, animo acids, salts, water, H+ ions, Bicarbonate ions, medications and vitamins, urea.