homeostasis

• what is homeostasis?

  homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
• Homeostasis maintains optimal conditions for enzyme action and all cell functions.

  In the human body, these include control of:

  • blood glucose concentration
  • body temperature
  • water levels.
• These automatic control systems may involve nervous responses or chemical responses.

  All control systems include:

  • cells called receptors, which detect stimuli (changes in the environment)
  • coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
  • effectors, muscles or glands, which bring about responses which restore optimum levels.
• the human nervous system

  The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
• Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.
• stimulus receptor → coordinator → effector → response
• reflex actions

  Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
• Motor neurone carries nerve impulse away from the CNS towards an effector
• Sensory neurone carries nerve impulse away from the receptor towards the CNS
• Aim: Investigate the effect of practice/repetition on the reaction time of a ruler drop test
• human endocrine system

  The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream.The blood carries the hormone to a target organ where it produces an effect.Compared to the nervous system the effects are slower but act for longer.
• The pituitary gland in the brain is a 'master gland' which secretes These lomones into tacind iner gands to simaoions.

  hormones to be released to bring about effects.
• human endocrine system

  
• blood glucose concentration

  Blood glucose concentration is monitored and controlled by the pancreas.

  If the blood glucose concentration is too high, the pancreas

  produces the hormone insulin that causes glucose to move from the blood into cells.In the liver and muscle cells excess glucose is converted into glycogen for storage.
• type 1 diabetes

  Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels and is normally treated with insulin injections.
• type 2 diabetes 


  in type 2 diabetes the body cells no longer respond to insulin produced by the pancreas.A carbohydrate controlled diet and exercise regime are common treatment.Obesity is a risk factor of type 2 diabetes.
• if the blood glucose concentration is too low,the pancreas produces the hot glucagon that causes glycogen to be converted into glucose and released into the bod.
• Oestrogen is the main female reproductive hormone produced in the ovary. At puberty eggs begin to mature and one is released approximately every 28 days. This is called ovulation.
• Testosterone is the main male reproductive hormone produced by the testes and it stimulates sperm production.
• Several hormones are involved in the menstrual cycle of a woman.

  • Follicle stimulating hormone (FSH) causes maturation of an egg in the ovary.
  • Luteinising hormone (LH) stimulates the release of the egg.
  • Oestrogen and progesterone are involved in maintaining the uterus lining.
• contraception

  • oral contraceptives that contain hormones to inhibit FSH

  production so that no eggs mature

  • injection, implant or skin patch of slow release progesterone to inhibit the maturation and release of eggs for a number of months or years

  • barrier methods such as condoms and diaphragms which prevent the sperm reaching an egg

  • intrauterine devices which prevent the implantation of an embryo or release a hormone

  • spermicidal agents which kill or disable sperm abstaining from intercourse when an egg may be in the oviduct

  • surgical methods of male and female sterilisation.
• the use of hormones to treat infertility

  This includes giving FSH and LH in a 'fertility drug' to a woman. She may then become pregnant in the normal way.

  In Vitro Fertilisation (IVF) treatment.

  • IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs.

  The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.

  The fertilised eggs develop into embryos.

  • At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus (womb).
• disadvantages of IVF

  • it is very emotionally and physically stressful
  • the success rates are not high
  • it can lead to multiple births which are a risk to both the babies and the mother
• Adrenaline

  Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the 

  body for ‘flight or fight’.
• Thyroxine

  Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and 

  development.

  Thyroxine levels are controlled by negative feedback.