The kidneys

• Kidneys act as a filter to clean the blood
• if the receptors in the brain detect a high water content the pituitary gland releases less ADH causing the kidney tubules to become less permeable and therefore less water is reabsorbed and so more water is lost
• if the receptors in the brain detect low water content the pituitary gland releases more ADH which makes the kidney tubules become more permeable and more water is reabsorbed and therefore less water is lost
• dialysis can be used to keep concentrations of dissolved substances normal levels in people whose kidneys don't work and to remove waste products
• in a dialysis machine the persons blood flows between partially permeable membranes surrounded by dialysis fluid
• how is water lost from the body?

  sweating, urination and exhalation (breathing)
• what makes up sweat and is lost from the body during sweating?

  water, ions and urea
• do we have control over how much water is lost from our body via sweating and breathing?

  no we only have control over how much water is lost when we urinate
• what is removed from the body during urination?

  excess water, ions and urea
• what happens if the water concentration outside our body cells is greater than inside our body cells?

  water enters the cell via osmosis and the cell may burst
• what happens if the water concentration inside our body cells is greater than outside our body cells?

  water will leave our cells via osmosis and cells may shrivel
• what is the problem with the concentration of water and mineral ions not being the same inside and outside of our body cells?

  if body cells gain or lose too much water by osmosis they do not function effectively
• what is deamination?

  proteins and amino acids can't be stored by the body so excess amino acids are converted into fats and carbohydrates in the liver via a process called deamination
• what is the waste product of deamination?

  ammonia
• why must the waste product of ammonia be converted into urea in the liver?

  Urea is less toxic than ammonia
• what happens to the ammonia after it has been converted into urea in the liver?

  urea is transported to the kidneys where is is filtered out of the blood and excreted from the blood in urine, also a small amount of urea is lost from the body in sweat
• what is the function of the kidneys?

  make urine by taking waste products and other unwanted substances out of the blood
• what is filtration in the kidneys?

  kidneys process of removing substances from the blood as they pass through the kidneys
• what is selective reabsorption?

  a mechanism in the kidneys that means that useful substances like glucose, some ions and the correct amount of water in reabsorbed into the blood
• why must the ion level in the blood be controlled?

  ions such as sodium can affect how much water is drawn into the cells via osmosis which can affect how effectively the cells can function
• what does the hormone ADH do?

  control how much water is reabsorbed via negative feedback
• what happens if your kidneys fail?

  waste substances build up in the blood and this means you lose the ability to control the levels of ions and water in the body which eventually results in death
• what are the two treatments for kidney failure?

  transplant or dialysis
• what are the advantages of dialysis?


  Removes waste and excess fluid from the blood, can buy are patient with kidney failure time until a donor organ is found
• what are the disadvantages of dialysis?

  expensive for the NHS to run, painful, time consuming (three times a week for three to four hours) and can cause blood clots or infections
• what are the advantages of a kidney transplant?

  actual cure, relatives can be donors as we have two kidneys and do not need both and cheaper in the long run
• what are the disadvantages of kidney transplants?

  small risk for person donating kidney (if they are alive), long waiting lists, risk of the immune system rejecting the new kidney and the person must take drugs to prevent the kidney being rejected
• how does dialysis treatment work?

  unfiltered blood is taken from a blood vessel in the arm and mixed with blood thinners to prevent clotting, pumped into a dialysis machine, Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane which is only permeable to ions and waste substances but not big molecules like proteins, blood flows in the opposite direction to dialysis fluid to maintain a steep concentration gradient
• why does the dialysis fluid contain the same concentration of dissolved ions as healthy blood?

  If the patient's blood is too low in ions, they will diffuse from the dialysis fluid into the blood, restoring the ideal level in the blood and if the patient's blood is too high in ions, the excess ions will diffuse from the blood to the dialysis fluid.
• label this diagram:

  A) partially permeable membrane

  B) clean blood

  C) unfiltered blood from patient

  D) used dialysis fluid containing waste

  E) fresh dialysis fluid

  
• why does the dialysis fluid not contain urea?

  there is a large concentration gradient - meaning that urea moves across the partially permeable membrane, from the blood to the dialysis fluid, by diffusion. This is very important as it is essential that urea is removed from the patients' blood.
• why does the dialysis fluid contain glucose levels similar to that of healthy blood?

  the is no concentration gradient so glucose can be returned to the blood and used by the body
• Osmosis is the diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane. This membrane allows water to pass through but not the solute (like sugar or salt). When glucose is dissolved in water, it creates a concentrated solution. Water will move towards this higher concentration of glucose to balance the concentrations on both sides of the membrane. If cells are in a solution with high glucose concentration, water will move out of the cells, causing them to shrink. Conversely, if cells are in a dilute glucose solution, water will move into the cells, causing them to swell. In the kidneys, glucose is reabsorbed to maintain osmotic balance. If blood glucose levels are high, more water is reabsorbed to dilute the glucose.
• Osmotic changes in body fluids can significantly affect cells: Cells gain or lose water through osmosis, depending on the concentration of the surrounding fluid. If the fluid is more concentrated (hypertonic), water moves out of the cell, causing it to shrink. If the fluid is less concentrated (hypotonic), water moves into the cell, causing it to swell. When cells lose too much water, they may become less effective at carrying out their functions. For example, red blood cells can shrivel, which affects their ability to transport oxygen. The kidneys help maintain osmotic balance by adjusting the amount of water and ions excreted in urine. If the body is dehydrated, the kidneys conserve water, affecting urine concentration. Maintaining the right osmotic conditions is crucial for homeostasis. If osmotic balance is disrupted, it can lead to health issues, such as dehydration or overhydration.
• Water leaves the body via the lungs during exhalation
• If body cells lose or gain too much water by osmosis they do not function efficiently.
• What is the function of the kidneys?

  Filtration and excretion of waste products
• Before Filtration: The blood entering the kidneys contains glucose, ions (like sodium and potassium), and urea. These substances are at higher concentrations in the blood. After Filtration: During filtration, the kidneys remove waste products like urea and excess ions from the blood. Glucose is usually reabsorbed back into the bloodstream, so its concentration decreases in the urine. Interpreting Data: When looking at tables or bar charts: Glucose: Should show high levels in blood before filtration and low levels in urine after filtration. Ions: May show a decrease in concentration in the blood after filtration, depending on the body's needs. Urea: Should show high levels in blood before filtration and significant levels in urine after filtration.