What is being taught lesson by lesson:

Key Terms for this topic (Tier 3 vocabulary)

Homeostasis – optimum – negative feedback – coordination – central nervous system – effectors – sensory neurone – relay neurone – stimuli – synapse – reflex arc – reaction time – hormone – endocrine – oestrogen – progesterone – testosterone – adrenaline – thyroxine – insulin – diabetes – menstrual cycle – fertility – contraception – in vitro fertilisation (IVF).

Homeostasis & Response

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What everyone needs to know:

Explain that homeostasis if the process of keeping conditions the same. This includes blood glucose levels, body temperature and levels of hydration. These are crucial for enzymes to work optimally. This is maintained by a series of receptor cells that detect conditions, coordination centres like the brain or spinal cord and effectors which are muscles or glands that make the change.

Our nervous system allows us to sense the environment around us. The central nervous system (CNS) is the brain and spinal cord. The CNS receives information and instructs a muscle of gland to react.

Stimulus → Receptor → Coordinator → Effector → Response

The reflex arc ignores the brain and just passes the spinal cord, these reflexes are essential for self preservation and so your brain does not get a chance to stop this “involuntary reaction”.

Required practical 6 – plan and investigate the effect a factor may have on a human’s reaction time.

Homeostasis is not only controlled by the fast acting/short lived nervous system, it is controlled by slow acting/long lived hormones. The endocrine system secretes chemical messages called hormones, the master gland is the pituitary gland in the brain, the glands are:

  • Pituitary gland
  • Pancreas
  • Thyroid
  • Adrenal glands
  • Ovaries
  • Testes.

You need to be able to describe how blood glucose levels are managed with the hormone insulin. You also need to know about type 1 and type 2 diabetes, what are the causes, effects and treatments. You may be asked to translate data or graphs of blood glucose levels.

The menstrual cycle is controlled by a series of hormones. You need to be able to describe their roles. During puberty, these hormones start the development of secondary sexual characteristics. You need to know about testosterone, oestrogen, FSH and LH.

Be prepared to evaluate different forms of contraception, both hormonal and non-hormonal methods. These methods control fertility. These include:

  • The pill which contains hormones to stop FSH maturing an egg.
  • Implants with slow release progesterone to inhibit egg release.
  • Barrier methods lick condoms and diaphragms.
  • Intrauterine devices which prevent egg implantation.
  • Spermicides which kill sperm cells.
  • Abstinence when eggs are available to be fertilised.
  • Surgery – vasectomy and tying fallopian tubes.

Extra topics needed for the Higher papers:

As well as insulin, the pancreas produces glucagon which converts glycogen into glucose if the blood glucose levels fall too low. You need to explain the negative feedback relationship between glucagon and insulin during blood glucose level control.

You not only need to know the roles of progesterone, LH and FSH, you need to know how these interact with each other during the menstrual cycle. You may be expected to interpret data of hormone levels and uterus wall thickness.

Infertility can be treated by administering hormones like FSH and LH in a fertility drug to become pregnant in a natural way. If this fails, In Vitro Fertilisation (IVF) may be considered which involves:

  • Give the mother FSH and LH to mature and release sever eggs.
  • These eggs are harvested in a clinic.
  • The eggs are fertilised in the lab using the father’s sperm cells.
  • The fertilised eggs develop into embryos.
  • The small ball of developing cells are inserted into the mother’s uterus.

This is not always successful and is very emotional and stressful, the success rates are not very high and if the embryos implant, it may lead to multiple births which is a higher risk to babies and mother. Due to the low success rate, usually 6 or 7 embryos are implanted in order to improve the chances of a successful birth.

Finally, you need to know about feedback systems. Thyroxine controls the basal metabolic rate of the body and is important in growth and development. Thyroxine is produced in the thyroid gland.. Thyroxine levels are controlled by negative feedback.

Adrenaline is produced in the adrenal glands. Adrenaline speeds up the heart rate so more oxygen and glucose is pumped around the body to prepare for a “flight or fright” response.