homeostasis

• homeostasis is the regulation of internal conditions of a cell or organism to maintain optimum conditions for functions in response to internal and external changes.
• describe the general features of an automatic control system

  • receptor cells detect changes in the environment (body's condition)
  • receptor cells pass information into the co-ordination centre.
  • it receives and processes the information from the receptor cells.
  • the coordination centre sends instructions to the effector (muscle or gland)
  • effector carries out a response to the stimulus and restores the optimum level
• the nervous system is the communication system of the body and is made up of the brain, spinal cord and nerves
• • receptors detect stimulus and send electrical impulses down neurones to the CNS.
  • coordination centre (CNS) sends electrical impulses down the other neurones to effectors
  • effectors bring about a response
  • (either a muscle which contracts or gland which secretes hormones)
• Reflex arc occurs when touching a hot object:

  • Stimulus (heat) is detected by receptor (skin)
  • Electrical impulses pass from receptor along sensory neurone to CNS
  • At the end of the sensory neurone, there is a junction called the synapse
  • The synapse releases a chemical which diffuses into the relay neurone in the CNS
  • Electrical impulse passes across the relay neurone
  • At the end of the relay neurone, there is another synapse where another chemical is diffused, triggering the electrical impulses in the motor neurone
  • These electrical impulses are passed along the motor neurone to the effector
  • Effector (muscle) brings out a response which would be to take the hand away from the candle (source of heat)
• endocrine system

  • consists of glands that secrete hormones directly into the bloodstream.
  • blood carries the hormones equally.
  • each hormone acts to a specfic target organ
• endocrine vs nervous

  • NS uses electrical impulses which travel through neurones
  • ES uses hormones which are chemicals and are carried in the blood stream
  • NS signalling is extremely fast, ES tends to produce at a more slower rate but the effect lasts longer
• pancreas

  releases hormones and are often involved in controlling the concentration of glucose in the blood
• ovaries and testes

  release hormones involved in puberty and reproduction
• thyroid gland

  produces hormones which are involved in growth and regulates the body's basal metabolic rate (how rapidly the body's reactions take place)

  releases thyroxine makes the body's chemical reactions take place at a faster rate

  controlled by negative feedback

  monitored by the brain, when the thyroxine levels fall, the pituitary gland releases the hormone TSH into the bloodstream, triggers thyroid to release more thyroxine.

  detected by the brain so prevents more release of TSH, less thyroxine.
• adrenal glands

  release the hormone adrenaline which is produced in times of fear or stress

  released into the blood

  increases the heart rate, more oxygen and glucose are delivered to the brain and muscles

  both oxygen and glucose are needed for aerobic respiration, preparing it to "fight or flight"
• pituitary gland

  • located in the brain
  • master gland
  • releases a number of different hormones into the blood depending on the conditions
  • that they act on other glands and cause other hormones to be released
  • can trigger a range of different effects in the body
• glucose is needed by every cell to release energy through respiration, needs to be kept as constant as possible.
• • the rise in glucose is detected by the pancreas, which produces a hormone called insulin.
  • insulin travels in the bloodstream and trigger body cells to take up glucose from the blood.
  • also triggers liver and muscle cells tp store excess glucose as glycogen
• diabetes type 1

  • pancreas doesn't produce enough insulin.
  • the glucose level in the blood will stay risen as pancreas cannot produce sufficient insulin and will not return to normal.
  • when they inject insulin, their blood glucose levels decrease.
• diabetes type 2

  • the body cells stop responding to insulin produced by the pancreas
  • often treated with a diet with a controlled level of carbohydrates
  • advised to take exercise
• blood glucose concentration too low

  • pancreas releases glucagon which triggers liver cells to convert glycogen stores into glucose and it releases glucose into the blood
• if the blood glucose concentration levels rise, insulin is released by the pancreas. however, if the blood glucose concentration levels fall, the pancreas releases glucagon.
• negative feedback cycle

  if the level of thyroxine falls, events are triggered which causes it to increase.

  if the level of thyroxine are too high, events are triggered which causes it to decrease.
• testes produce testosterone causing the testes to produce sperm

  ovaries produce oestrogen
• menstrual cycle

  • every 28 days ovulation takes place where the ovaries releases an egg
  • in preparation the uterus lining becomes thick and spongy
  • egg makes its way down to the uterus
  • if sperm is present, egg is fertilised
  • if not both egg and uterus lining is released as a period
• FSH causes an egg to mature in the ovary
• LH causes the egg to be released (ovulation)
• Oestrogen and progesterone maintain the uterus lining, incase the egg is fertilised and implants.
• FSH is released by the pituitary gland and travels in the blood to the ovaries where it causes an egg to mature
• FSH triggers the ovaries to produce oestrogen, causes lining to be thick and stops the pituitary gland from releasing FSH but now it releases the hormone LH which triggers ovulation. once the ovary has released its egg, it produces progesterone. it stops the pituitary gland from releasing FSH and LH. This prevents more eggs from maturing or being released. it also keeps the lining thick. if fertilisation doesn't take place the level of progesterone will drop and the lining and egg will be released and the woman will have a period
• interpret the graph of these hormones during the menstrual cycle

  • level of FSH rises, triggers the ovaries to release oestrogen
  • as the level of oestrogen increases, the level of FSH falls
  • oestrogen triggers the ovaries to release LH so the LH level rises around day 14
  • LH triggers ovulation which increases the level of progesterone
  • if the egg is not fertilised the level of progesterone decreases
• contraceptive pills

  • AD = Highly effective if taken correctly
  • DS= must be taken every day if not there is a risk of pregnancy
  • side effect = risk of breast cancer or blood clots
• implant, skin plant or injection

  • contains progesterone
  • AD = more convenient than takin a daily pill (lasts for weeks)
• forms of contraception

  none of these protect against sexually transmitted infections (STIs)

  eg. HIV
• Barrier method

  • condom or diaphragm
  • effective if used correctly
  • AD = don't have side effects, condoms can reduce risk of STIs
  • DS = slip off or break
  • more effective if used with spermicide gel which kills or disables sperm and reduce chances of fertilisation
• IUD

  • sometimes called the coil
  • prevent embryo from implanting
  • release hormones reduce chances of fertilisation
  • highly effective can prevent pregnancy for up to 10 yrs
  • does not protect against STIs
  • very few side effects
• surgical forms (sterilisation)

  • woman = prevents egg from reaching the uterus
  • men = prevents the sperm from leaving the penis
  • highly effective
  • difficult to reverse
  • don't protect against STIs
• natural contraception

  • does not protect against STIs
  • very hard to tell when a woman is ovulated so it makes it difficult
• Hormones like FSH and LH are used to treat infertility by causing a woman to ovulate more than usual, increasing her chances of getting pregnant
• In IVF treatment, FSH and LH are used to help eggs mature, which are then collected and fertilized with sperm in a laboratory, resulting in embryos that are inserted into the mother's uterus for development
• IVF treatment can be emotionally stressful and physically demanding on the mother, with risks of multiple births, destruction of unused embryos, and high costs
• The benefit of using hormones for infertility treatment is that it gives women a chance to have a baby of their own