Biology

• Factors disrupting water balance

  • Exhaling
  • Sweating
  • Illness
  • Eating too much salt
• Kidneys control water and ion levels in the blood
• The body's ion levels must be kept relatively constant to control osmosis and diffusion between cells in the body
• Volume of water in blood is controlled by the hypothalamus in the brain
• Urea must be removed from the bloodstream because it is toxic. When there is too much urea in the bloodstream, it can harm cells and tissues.
• Amino Acids

  Urea is formed when the digestion of protein results in an excess of amino acids which cannot be stored in the body.
• Deamination

  In the liver, the excess amino acids undergo deamination and the waste product is ammonia
• The ammonia from deamination is then converted into urea and must be excreted from the body as urine.
• Each kidney contains millions of very small structures called nephrons. There are two stages in the process of urine production. These stages happen in every nephron.
• Ultrafiltration

  The blood is filtered and all water, urea and salts move into the nephron tubule. Blood cells and proteins remain in the blood as they are too big to move across the capillary walls.
• Selective Reabsorption

  Useful substances, including some water, are reabsorbed from the tubule back into the bloodstream. This leaves all urea, excess salts and excess water in the tubule. This mixture forms urine, which is collected by the kidneys and travels to the bladder to be stored and then excreted.
• Too little water in the blood

  The hypothalamus triggers the pituitary gland to release anti diuretic hormone (ADH). This increases the permeability of the kidney tubules, meaning that more water is reabsorbed back into the bloodstream. This results in a small volume of concentrated urine.
• Too much water in the blood

  The hypothalamus triggers the pituitary gland to stop the release of ADH. This reduces the permeability of the kidney tubules, meaning that less water is reabsorbed back into the bloodstream. This results in a large volume of dilute urine.
• Dialysis is a possible treatment for kidney failure. It is an essential treatment for people whose kidneys cannot keep the concentrations of urea and salt at an optimum level to ensure that tissue damage does not occur.
• Dialysis Machine

  Patient is linked up to the dialysis machine and their blood flows into the machine. Machine contains a fluid that is designed to have the optimum concentrations of salts and glucose, like a healthy person's blood.
• Dialysis Fluid

  Patient's blood flows over a partially permeable membrane in the machine designed to replicate kidney tubules. Dialysis fluid is on the other side of the membrane. A concentration gradient is established allowing excess ions and urea to diffuse from and area of high concentration in patient's blood to low concentration in the dialysis fluid.
• Advantages of Dialysis

  • Life saving
  • Gives patient more time to find a donor kidney
• Disadvantages of Dialysis

  • Lasts 3-4 hours and is needed 3 times a week
  • Expensive
  • Increases risk of blood clots and infections
• Advantages of Kidney Transplants

  • No need for dialysis which is time consuming
  • Cheaper than dialysis
• Disadvantages of Kidney Transplants

  • Kidney may be rejected by body
  • Can be long waiting lists
  • Patient must take immunosuppressant drugs which can make a patient more prone to other infections
• Puberty in males

  • Testosterone levels rise, stimulating sperm production
  • Underarm, facial and pubic hair grow
  • Voice deepens
• Puberty in females

  • Oestrogen rises and triggers menstrual cycle
  • Underarm and pubic hair grow
  • Breasts enlarge
• Menstrual cycle is controlled by 4 hormones:

  • Follicle stimulating hormone (FSH)
  • Oestrogen
  • Luteinising Hormone (LH)
  • Progesterone
• Follicle stimulating hormone (FSH)

  Released by the pituitary gland and causes an egg in the ovary to mature, and also encourages production of oestrogen.
• Oestrogen

  Produced in the ovaries and causes the development of the thick spongy uterus lining. Also stimulates production of LH and inhibits production of FSH.
• Luteinising Hormone (LH)

  Produced by pituitary gland and stimulates release of a mature egg on day 14 of cycle, also known as ovulation.
• Progesterone

  Produced in ovaries after ovulation, responsible for maintaining uterus lining for days 14-28. When progesterone levels drop, the lining breaks down, marking day 1 of the cycle. Also inhibits release of LH and FSH.
• Combined Pill

  Contains both oestrogen and progesterone. By taking it daily, enough oestrogen builds up to inhibit FSH production so no eggs mature.
• Progesterone-only Pill

  Stimulates the production of thick mucus which is difficult for any sperm to penetrate. Inhibits release of FSH so eggs don't mature. Just as effective as combined pill but with fewer side effects,
• Contraceptive Patch

  Woman places the patch onto the skin, which only has to be changed once a week. It steadily releases progesterone.
• Contraceptive Implant

  Lasts for 3 years, placed under skin (usually an arm) and continuously releases a small amount of progesterone.
• Contraceptive Injection

  Contains progesterone and can last up to 3 months.
• Intrauterine Devices (IUDs)

  AKA the coil, small T shaped devices which are inserted into the uterus, they stop the implantation of a fertilised egg, some of them release progesterone.
• Diaphragm

  A shallow plastic cup, inserted into vagina before sex and sits at entrance to uterus. Designed to prevent sperm from reaching the egg, can also be covered in spermicide to kill the sperm.
• Condoms stop STIs and prevent the sperm from entering the female. They are worn by the male and often contain a spermicide to kill the sperm.
• Sterilisation

  Women - the fallopian tubes are cut so the egg cannot reach the uterus

  Men - sperm ducts are cut
• Natural Contraception Methods

  • Abstinence (refraining)
  • Timing (not having sex when the woman is ovulating)
• Some women don't have high enough levels of FSH to stimulate the maturing of their eggs, meaning that they are infertile
• Fertility drugs contain a mixture of LH and FSH and are given to the woman by a doctor. Boosting LH and FSH levels can cause an egg to be released in the ovaries.
• IVF

  FSH and LH are given to stimulate the growth of lots of eggs. Eggs are collected before being fertilised in a petri dish in a lab, using sperm from the father. The fertilised eggs grow into embryos and are implanted into the woman's uterus.