Chapter 12

• The thermoregulatory centre, a part of the brain, controls your core body temperature. To do this, it receives information about body temperature from receptors. These include

  -Receptors in the the thermoregulatory centre that are sensitive to the temperature of the blood flowing through the brain

  -Receptors in the skin that send information about skin temperature via nervous impulses
• The temperature of the body is kept around a constant level due to a negative feedback system - If it gets too high or too low, the body responds to bring the temperature back to optimum
• responding to a rise in body temperature-

  1)When the temperature receptors detect that core body temperature is too high, they send impulses to the thermoregulatory centre, which acts as a coordination centre

  2)The thermoregulatory centre processes the information from the temperature receptors and triggers the effectors automatically

  3)The effectors produce a response that increases the amount of heat lost from the body and the body cools down
• optimum body temperature

  ->

  rise in body temperature

  ->

  receptors detect change

  ->

  thermoregulatory centre receives and processes information and sends impulses to effectors

  ->

  effectors respond
• responses that reduce body temperature

  -Hairs on the skin lie flat. This means less air is trapped near the surface of the skin, so there isn't a layer of insulating air surrounding the skin. This allows heat to be transferred to the environment easily

  -Sweat is produced by sweat glands. When sweat evaporates from the skin, it transfers energy to the environment, helping to reduce body temperature

  -The blood vessels supplying the skin capillaries dilate so more blood flows close to the surface of the skin. This is called vasodilation. It helps transfer energy from the skin to the environment
• Some effectors work antagonistically e.g. one effector heats and another cools - they'll work at the same time to achieve a very precise temperature. This mechanism allows a more sensitive response.
• Responses that increase core body temperature

  -Hairs on the skin stand up. This traps an insulating layer of air next to the skin, reducing the amount of energy transferred to the environment

  -No sweat is produced

  -The blood vessels supplying the skin capillaries constrict to reduce the skin's blood supply. This is called vasoconstriction. It reduces the amount of blood that flows close to the surface of the skin and so less energy is transferred from the skin to the environment

  -Shivering. This needs respiration, which transfers some energy to warm the body
• -The kidneys make urine by taking waste products out of your blood

  -Filtration is when substances are filtered out of the blood as it passes through the kidneys

  -Selective reabsorption is when useful substances including all the glucose, some ions and the right amount of blood are absorbed back into the blood

  -The substances that are removed from the body in urine include urea and excess ions and water
• -The body has to constantly balance the water coming in against the water going out

  -We lose water from the skin in sweat and from the lungs when we exhale

  -We can't control how much we lose in these ways, so the amount of water is balanced by the amount we consume and the amount removed by the kidneys in urine
• Adjustment of ion content-

  -Ions are taken into the body in food, and then absorbed into the blood

  -If the ion/water content is wrong, this could upset the balance between ions and water, meaning too much or too little water is drawn into cells by osmosis

  -Some ions are lost in sweat. However, this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount of ions is reabsorbed into the blood after filtration and the rest is removed from the body in urine.
• Removal of urea-

  -Proteins (amino acids) can't be stored by the body - so any excess amino acids are converted into fats / carbohydrates which can be stored

  -This occurs in the liver and involves a process called deamination. Ammonia is produced as a waste product from this process

  -Ammonia is toxic, so it's converted to urea in the liver

  -Urea is then transported to the kidneys, where it's filtered out of the blood and excreted from the body in urine
• Kidney tubules are where filtration and selective reabsorption take place
• -The kidney can let more or less water move out of the tubules to change the water content of the blood - the more water that leaves the tubules and is reabsorbed into the blood, the more concentrated the urine will be

  -This process is controlled by a hormone called ADH (anti-diuretic hormone). It does this by acting on cells in the kidney tubules, causing them to be more / less permeable to water and so changing the volume of water that can be reabsorbed
• ADH is released into the bloodstream by the pituitary gland. 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 process of water content regulation is controlled by 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
• A receptor in the brain detects that the water content is too high

  ->

  The coordination centre in the brain receives the information and coordinates a response

  ->

  The pituitary gland releases less ADH, so the kidney tubules become less permeable and less water is reabsorbed from the kidney tubules
• -If the kidneys don't work properly, waste substances build up in the blood and you loose your ability to control the levels of ions and water in your body.

  -If left untreated, kidney failure will eventually result in death
• people with kidney failure can be kept alive by-

  -Having dialysis treatment - where machines do the job of the kidneys

  -Having a kidney transplant - where the diseased kidney is replaced by a healthy one

  
• Dialysis treatment-

  -The partially permeable membrane allows ions and waste products through, but not big molecules like proteins

  -The dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood. This means that useful dissolved ions and glucose won't be lost from the blood during dialysis

  -Only waste substances and excess ions and water diffuse across the membrane
• Problems with dialysis-

  -Dialysis is not a pleasant experience and many patients have to have a dialysis session three times a week. Each session takes 3-4 hours

  -Can lead to infections and cause blood clots

  -Dialysis patients have to be careful about what they eat to avoid too much of a particular ion building up between sessions

  -Patients have to limit the amount of fluid they take in. When the kidneys aren't functioning properly, fluid can build up in the body, which can be dangerous

  -expensive for the NHS to run
• Rejection of Kidney transplants-

  -A problem of kidney transplants is that the donor kidney can be rejected by the recipient's immune system

  -This happens when antigens on the donor kidney aren't recognised as being part of the body by the recipients white blood cells. The white blood cells produce antibodies to attack the donor cells as a result
• Preventing rejection-

  -A donor with a tissue-type that closely matches the patient's is chosen. The more similar the tissue types of the donor and the patient, the more similar the antigens. This reduces the chance of the patient's white blood cells identifying the antigens as 'foreign'

  -Drugs that supress the immune system. They reduce production / release of antibodies by the White blood cell's, so that the immune system won't attack the transplanted kidney
• Problems with kidney transplants-

  -Long waiting list for kidneys

  -Even if a kidney with a matching tissue type is found, there is still a possibility that it'll be rejected

  -taking drugs that supress the immune system means that the person is vulnerable to other illnesses and infections

  -major operation, risky
• Advantages of kidney transplants-

  -relatively normal life, no endless hours by dialysis machine

  -cheaper than dialysis