5-Homeostasis and response

• homeostasis is the regulation of the conditions inside the body to maintain a stable internal environment in response to changes in internal and external conditions
• homeostasis can regulate conditions and keep everything at around the right levels but it will not always be constant such as temperature and glucose levels which fluctuate
• automatic control systems recognise a change from optimal conditions and send signals to reverse it:

  1. receptor
  2. coordination centre
  3. effector
• automatic control system functions

  1. receptors- detect a change
  2. coordination centres- interprets the change and organises a response
  3. effectors- carry out the change
• automatic control systems- how signals are sent

  • nervous system - fast and precise electrical impulses through nerves, allows for quick responses
  • endocrine system - slower, longer lasting and more generalised, hormones released into the bloodstream, travel throughout the body, only affect certain cells
• homeostasis relies on a system of negative feedback so if the levels of something get too high they're brought back down, and if the levels of something get too low, they're brought back up
• the nervous system - neurons (nerve cell)

  • carry electrical impulses
  • they are long, thin, have branched connections on each side
  • they link with other nerve cells
  • there are synapses (gaps) between neurons that allow chemicals to travel through them from the electrical impulses
• central nervous system consists of:

  • brain
  • spinal chord
• reflex arcs' function are to avoid us getting hurt and are:

  • fast
  • automatic
• pathway of a reflex arc:

  1. stimulus is detected by receptors
  2. sensory neurone is stimulated and carry an impulse from finger to cns (spinal chord)
  3. cns transfers the impulse to the relay neurone
  4. relay neurone transfers impulse to the motor neurone
  5. motor neurone transfers impulse to the effector which will contract and move away from stimulus
• the endocrine system consists of:

  • glands that secrete hormones
• types of glands

  • pituitary - 'master gland', produces multiple different hormones, can tell the body or other glands to release hormones, is near the brain
  • thyroid - produces thyroxine (regulates rate of metabolism), is in the neck
  • adrenal - produces adrenaline (fight or flight response), on top of kidneys
  • pancreas - produces insulin (regulates blood glucose concentrations), in front of kidneys
  • testes - produces testosterone and sperm, found in testes
  • ovaries - produces oestrogen and hold egg cells
• thyroid stimulating hormone - negative feedback

  1. pituitary gland detects low levels of thyroxine and releases TSH
  2. TSH stimulates the thyroid to produce more thyroxine
  3. level of thyroxine is brought back to normal
• blood glucose concentration needs to be regulated so that there is enough glucose for our cells for respiration but not too much to damage tissues
• hormones that regulate blood sugar concentration:

  • insulin
  • glucagon
• hormone insulin

  • rise in glucose levels is detected by pancreas
  • pancreas releases insulin into the bloodstream
  • insulin binds to receptors on certain cells to tell them to take in glucose from the blood (liver, muscle)
  • liver and muscle cells take in glucose to form glycogen
  • the blood glucose concentration decreases
• hormone glucagon

  • drop in glucose levels is detected by pancreas
  • pancreas releases glucagon into the bloodstream
  • glucagon mainly binds to liver cells
  • liver breaks down glycogen into glucose molecules and release them into the blood
  • the blood glucose concentration increases
• two types of diabetes that cause the body to not regulate the blood glucose properly

  • type 1 - can't produce enough insulin
  • type 2 - resistant to insulin
• type 1 diabetes

  • more common in children and teenagers
  • lifelong condition
  • pancreas stops producing insulin or produces small amounts
  • if blood glucose levels get too high it can cause: feeling ill, death
  • managed by injecting with insulin into the abdomen or thigh after a meal, exercising regularly and not having too much sugary food
• type 2 diabetes

  • more common in older people
  • have had unhealthy diet for a long time so the cells become resistant to insulin so don't respond to the insulin and therefore don't take in glucose from the blood stream
  • managed by having a healthy low sugar diet and regular exercise
• puberty is the period in which adolescents start to develop secondary sexual characteristics and is triggered by reproductive hormones:

  • in men: testosterone - testes
  • in women: oestrogen - ovaries
• the menstrual cycle

  • prepares the lining of the uterus for pregnancy but if implantation of a fertilised egg does not occur the lining is shed
  • lasts around 28 days
  • has four stages
• the four stages of the menstrual cycle

  1. menstruation
  2. lining of uterus starts to build up
  3. ovulation
  4. maintaining of lining of uterus
• stages of the menstrual cycle - menstruation

  • menstruation is the first stage
  • period of bleeding due to the breakdown of the uterus lining
  • lasts 4 days (0-4)
• stages of the menstrual cycle - lining starts to build up

  • this is the second stage
  • the uterus lining starts to build up again and becomes a thick spongy layer with lots of blood vessels in it
  • prepares the uterus lining for a fertilised egg
  • lasts 10 days (4-14)
• stages of the menstrual cycle - ovulation

  • this is the third stage
  • the egg is released from one of the ovaries
  • takes one day (14)
• end of the menstrual cycle

  • by day 28, if no fertilised egg has been implanted into the uterus, the uterus wall starts to break down and the menstrual cycle would repeat
  • if there was a fertilised egg, it would implant into the uterus lining and develop into a foetus. This stops the menstrual cycle
• hormones responsible for the menstrual cycle

  1. oestrogen - inhibits FSH production, repairs thickens and maintains the uterus lining, stimulates production of LH
  2. progesterone - maintains the lining of the uterus
  3. luteinising hormone - triggers ovulation (the release of mature egg)
  4. follicle stimulating hormone - causes an egg to mature in an ovary, stimulates the ovaries to release oestrogen
• hormones - oestrogen

  • produced in the ovaries
  • stimulates uterus lining to grow - levels increase in stage 2 and decrease in stage 3
• hormones - progesterone

  • produced in the ovaries
  • progesterone levels increase in stage 4 and maintain the lining of the uterus but if these progesterone levels drop then the uterus lining breaks down and restarts the cycle
• hormones - luteinising hormone LH

  • produced in the pituitary gland
  • LH stimulates the release of the egg on day 14 - levels of LH increase in stage 3
• hormones - follicle stimulating hormone FSH

  • produced in the pituitary gland
  • FSH stimulates one of the eggs to mature in the ovaries - levels increase in stage one, decrease in stage 2, increase in stage 3 and decrease in stage 4
• menstrual cycle - how hormones interact

  1. FSH stimulates the ovaries to produce oestrogen
  2. as oestrogen levels start to increase they inhibit FSH (negative feedback)
  3. when oestrogen levels get high, they stimulate the release of LH
  4. progesterone inhibits LH and FSH
• contraception is an artificial method used to prevent pregnancy
• contraception can be:

  hormonal - combined oral contraceptive pill (the pill), progesterone only pill, contraceptive patch, contraceptive injection, contraceptive implant, plastic intrauterine device (IUD)

  non-hormonal - copper IUD, condom, female condom, diaphragm, spermicide, sterilisation, natural methods, abstinence
• hormonal contraceptive - the pill

  • short for combined oral contraceptive pill
  • contains both progesterone and oestrogen
  • progesterone - stimulates the production of thick mucus in the cervix so prevents the sperm from reaching the egg
  • oestrogen - inhibits FSH if released steadily every day so no egg will be developed or released
  • 99 % effective
  • side effects include - nausea or headaches
• hormonal contraceptive - progesterone only pill

  • progesterone - stimulates the production of thick mucus in the cervix so prevents the sperm from reaching the egg
  • 99 % effective
  • has less side effects than the pill
• hormonal contraceptive - contraceptive patch

  • slowly releases oestrogen and progesterone
  • small sticker placed on the upper arm
  • a patch lasts one week
• hormonal contraceptive - contraceptive implant

  • small device placed under the skin of the arm
  • slowly releases progesterone
  • lasts up to 3 years
• hormonal contraceptive - plastic intrauterine device IUD

  • placed inside the uterus
  • releases progesterone
  • lasts 3 years