Animal Coordination, Control & Homeostasis

• Hormones are chemicals released directly into the blood. They are carried in the blood to other parts of the body, but only affect particular cells in particular organs - target organs.
• Hormones are produced in various glands, called endocrine glands - these glands make up the endocrine system.
• What does the Pituitary Gland do ?

  Produces many hormones that regulate body conditions.
• What does the Thyroid Gland do ?

  Produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature.
• What do the Ovaries do ?

  Produce oestrogen, which is involved in the menstrual cycle.
• What do the Testes do ?

  Produce testosterone, which controls puberty and sperm production in males.
• What do the Adrenal Glands do ?

  They produce adrenaline, which is used to prepare the body for a 'fight or flight' response.
• What does the Pancreas do ?

  This produces insulin, which is used to regulate the blood glucose level.
• Neurones:

  • very fast action
  • act for a very short time
  • act on a very precise area
• Hormones:

  • slower action
  • act for a long time
  • act in a more general way
• Adrenaline 'fight or flight' method:

  1. Adrenaline binds to specific receptors in the heart. This causes the heart muscle to contract more frequently and with more force, so heart rate and blood pressure increase.
  2. This increases the blood flow to the muscles, so the cells receive more oxygen and glucose for increased respiration.
  3. Adrenaline also binds to receptors in the liver. This causes the liver to break down its glycogen stores to release glucose.
  4. This increases the blood glucose levels, so there's more glucose in the blood to be transported to the cells.
• Negative Feedback System:

  • When the blood thyroxine level is lower than normal, the hypothalamus is stimulated to release Thyrotropin releasing hormone (TRH).
  • TRH stimulates the pituitary gland to release thyroid stimulating hormone (TSH).
  • TSH stimulates the thyroid gland to release thyroxine, so the blood thyroxine level rises back towards normal.
  • When the blood thyroxine level becomes higher than normal, the release of TRH from the hypothalamus is inhibited, which reduces the production of TSH, so the blood thyroxine level falls.
• The Menstrual Cycle:

  Stage 1 -> Day 1 is where menstruation starts.

  The lining of the uterus breaks down and is released.

  Stage 2 -> The uterus lining is repaired.

  From day 4 to 14, until it becomes a thick spongy layer full

  of blood vessels ready for a fertilised egg to implant there.

  Stage 3 -> An egg develops and is released.

  It is released from the ovary at around day 14.

  Stage 4 -> The lining is then maintained.

  If no fertilised egg has landed on the uterus wall by day

  28, the spongy lining starts to break down again and the

  whole cycle starts over.
• What does FSH (follicle-stimulating hormone) do ?

  released by the pituitary gland

  causes follicle to mature in one of the ovaries

  stimulated oestrogen production
• What does Oestrogen do ?

  released by the ovaries

  causes the lining of the uterus to thicken and grow

  a high level stimulates a rapid increase of LH
• What does LH (luteinising hormone) do ?

  Released by the pituitary gland.

  The LH surge stimulates ovulation at day 14- the follicle ruptures and the egg is released.

  Stimulates the remains of the follicle to develop into a structure called a corpus luteum.
• What does Progesterone do ?

  Released by the corpus luteum after ovulation.

  Maintains the lining of the uterus.

  Inhibits the release of FSH and LH.

  When the level of progesterone falls, and there's a low oestrogen level, the uterus lining breaks down.

  A low progesterone level allows FSH to increase and then the whole cycle starts again.
• Clomifene Therapy:

  • some women are infertile because they don't ovulate regularly, these women can take a drug called clomifene
  • this works by causing more FSH and LH to be released by the body, which stimulate egg maturation and ovulation
  • by knowing when the woman will be ovulating, the couple can have intercourse during this time period to improve the chance of becoming pregnant
• IVF:

  • involves collecting eggs from the woman's ovaries and fertilising them in the lab using the man's sperm
  • they are then grown into embryos
  • once the embryos are tiny balls of cells, one or two of them are transferred to the woman's uterus to improve the chance of pregnancy
  • FSH and LH are given before egg collection to stimulate egg production
• What are the different types of contraception ?

  the combined pill, the contraceptive patch, the mini-pill, contraceptive injection
• What does Homeostasis mean ?

  maintaining the right condition inside your body so that everything works properly
• What is Osmoregulation ?

  Regulating water content.

  You have to keep a balance between the water you gain and the water you urinate, sweat and breathe out.
• What is Thermoregulation ?

  Regulating body temperature.

  You need to reduce your body temperature when you are hot but increase it when the environment is cold.
• What is Blood Glucose regulation ?

  You need to make sure the amount of glucose in your blood doesn't get too high or too low.
• If blood glucose concentration are too high, insulin is added.

  If blood glucose concentration is too low, glucagon is added.
• Eating foods containing carbohydrate puts glucose into the blood from the small intestine.

  The normal metabolism of cells removes glucose from the blood. Vigorous exercise removes much more glucose from the blood. Excess glucose can be stored as glycogen in the liver and in the muscles.

  When these stores are full then the excess glucose is stored as lipid (fat) in the tissues.

  Changes in blood glucose are monitored and controlled by the pancreas.
• Type 1 diabetes:

  • A condition where the pancreas produces little or no insulin. the result is that a person's blood glucose can rise to a level that can kill them.
  • They have to be treated with insulin therapy - this usually involves injecting insulin into the fatty tissue under the skin, where it enters the bloodstream. They have to ensure that glucose is removed from the blood quickly once food has been digested. This stops the level of glucose in the blood from getting too high. The amount of insulin that needs to be injected depends on the person's diet and how active they are.
• As well as insulin therapy, people with type 1 diabetes also need to think about:

  • limiting the intake of foods rich in simple carbohydrates
  • taking regular exercise - this helps to remove excess glucose from the blood
• All enzymes have an optimum temperature - this is the temperature at which they work best at.
• The enzymes in the human body work best at 37 degrees celcius. Below this temperature enzyme activity slows down and above this temperature enzymes may start to denature.
• Homeostasis maintains our core body temperature at a steady 37 degrees celcius. Any change in body temperature triggers a response that counteracts it.
• The thermoregulatory centre in the hypothalamus acts as your own personal thermostat.

  It contains receptors that are sensitive to the blood temperature in the brain. It also receives impulses from receptors in the skin that provide information about the external temperature. These receptors are located in the epidermis and the dermis.

  When the hypothalamus detects a change, it causes a response in the skin.
• When you are too hot:

  • Erector muscles relax, so hairs lie flat
  • Lots of sweat is produced in sweat glands in the dermis. The sweat is released onto the surface of the skin through pores in the epidermis. When the sweat evaporates it transfers energy from your skin to the environment, cooling you down.
  • Blood vessels close to the surface of the skin dilate. This is called vasodilation. It allows more blood to flow near the surface, so it can transfer more energy into the surroundings, which cools you down.
• When you are too cold:

  • Erector muscles contract. Hairs stand on end to trap an insulating layer of air near the surface of the skin, which helps you keep warm.
  • Very little sweat is produced.
  • Blood vessels near the surface of the skin constrict. This means that less blood flows near the surface, so less energy is transferred to the surroundings.
  • When you are cold you also shiver. This increases your rate of respiration, which transfers more energy to warm the body.
• It is very important to keep the water content of the blood controlled to keep cells functioning normally.

  If the concentration of water in the blood is too high then water will move into the body cells by osmosis. If too much waste moves into the cells then the cells may burst.

  If the concentration of water in the blood is too low then water will move out of the cells into the blood by osmosis. This causes the cells to shrink.

  The kidneys help to regulate the water content by controlling how much water is reabsorbed and how much is lost in urine.
• Kidneys have 3 main roles:

  • Removal of urea from the blood. Urea is produced in the liver from the breakdown of excess amino acids.
  • Adjustment of ion levels in the blood.
  • Adjustment of water content of the blood.

  They do this by filtering things out of the blood under high pressure and then reabsorbing the useful things. The end product is urine.
• What happens in a nephron ?

  The liquid part of the blood is forced out of the glomerulus and into the Bowman's Capsule at high pressure. Bigger molecules and blood cells can't pass through the membranes and aren't forced out.

  As the liquid flows along the nephron, useful substances are reabsorbed: all the glucose is moved back into the blood against a concentration gradient, ions are reabsorbed, water is reabsorbed according to the level of ADH.

  Whatever isn't reabsorbed continues out of the nephron via the collecting duct. It then passes into the ureter and down to the bladder as urine.
• The amount of water reabsorbed in the kidney nephrons is controlled by anti-diuretic hormone (ADH).

  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. ADH makes the collecting ducts of the nephrons more permeable so that more water is reabsorbed back into the blood. This stops the body from becoming dehydrated.
• Patients who have kidney failure can't filter their blood properly - but a dialysis machine can be used to filter their blood for them.

  Dialysis can be done regularly to keep dissolved substances at the right concentrations, and to remove waste.

  Dialysis fluid has the same concentration of salts and glucose as blood plasma.

  The barrier is permeable to things like ions and waste substances, but not big molecules like proteins. So the waste substances, plus excess ions and water from the blood, move across the membrane into the dialysis fluid.

  Cells and proteins stay in the blood.
• Currently, the only cure for kidney disease is a kidney transplant.

  A donor kidney can be rejected by the patient's immune system.

  To help prevent this from happening, precautions are taken:

  • a donor with a tissue type that closely matches the patient is chosen.
  • the patient is treated with drugs that suppress the immune system, so that their immune system won't attack the transplanted kidney.