Biology

• Homeostasis maintains optimal conditions for enzyme action and all cell functions
• Receptors

  Cells that detect stimuli (changes in the environment)
• Automatic control systems may involve nervous responses or chemical responses
• Effectors

  Muscles or glands that bring about responses which restore optimum levels
• Coordination centres

  Receive and process information from receptors
• Components of control systems

  • Cells called receptors
  • 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
• Examples of homeostasis in the human body

  • Control of blood glucose concentration
  • Body temperature
  • Water levels
• Homeostasis

  Regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• CNS

  Coordinates the response of effectors which may be muscles contracting or glands secreting hormones
• Information from receptors

  Passes along cells (neurones) as electrical impulses to the central nervous system (CNS)
• Reflex arc

  Automatic and rapid; they do not involve the conscious part of the brain
• Reflex actions are important
• Relay neurone

  Transmits information from the sensory neurone to the motor neurone
• CNS

  Central nervous system (CNS) is the brain and spinal cord
• Structures in a reflex arc

  • Sensory neurone
  • Synapse
  • Relay neurone
  • Motor neurone
• Nervous system

  Enables humans to react to their surroundings and to coordinate their behaviour
• Sensory neurone

  Transmits sensory information from the receptor to the CNS
• Motor neurone

  Transmits information from the CNS to the effector
• Pituitary gland

  A 'master gland' which secretes several hormones into the blood in response to body conditions
• Hormonal coordination and control by the human endocrine system

  • Endocrine system
  • Hormones
  • Bloodstream
  • Target organ
  • Pituitary gland
  • Effects
  • Nervous system
  • Longer acting
• Hormones

  Chemicals that are carried by the blood to a target organ where it produces an effect
• Compared to the nervous system, the effects of the endocrine system are slower but act for longer
• Target organ

  The organ where the hormone produces an effect
• Endocrine system

  Composed of glands which secrete chemicals called hormones directly into the bloodstream
• Glycogen

  Excess glucose is converted to glycogen for storage in liver and muscle cells
• High blood glucose concentration

  1. Pancreas produces hormone insulin

  2. Glucose moves from the blood into the cells

  3. Excess glucose is converted to glycogen for storage in liver and muscle cells
• Type 2 diabetes

  • Body cells no longer respond to insulin produced by the pancreas
  • A carbohydrate controlled diet and an exercise regime are common treatments
  • Obesity is a risk factor
• Insulin

  Hormone produced by the pancreas that causes glucose to move from the blood into the cells
• Blood glucose concentration is monitored and controlled by the pancreas
• Type 1 diabetes

  • Disorder in which the pancreas fails to produce sufficient insulin
  • Characterised by uncontrolled high blood glucose levels
  • Normally treated with insulin injections
• Hormones in human reproduction

  • During puberty reproductive hormones cause secondary sex characteristics to develop
  • 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
• Hormones in human reproduction

  Hormones that play a role in human reproduction
• Menstrual cycle

  1. Follicle stimulating hormone (FSH) causes maturation of an egg in the ovary

  2. Luteinising hormone (LH) stimulates the release of the egg

  3. Oestrogen and progesterone are involved in maintaining the uterus lining
• Barrier methods

  Condoms and diaphragms prevent the sperm reaching an egg
• Methods of fertility control

  • Oral contraceptives
  • Injection, implant or skin patch
  • Barrier methods
  • Intrauterine devices
  • Spermicidal agents
  • Abstaining from intercourse when an egg may be in the oviduct
  • Surgical methods of male and female sterilisation
• Spermicidal agents

  Kill or disable sperm
• Oral contraceptives

  Contain hormones to inhibit FSH production so that no eggs mature
• Intrauterine devices

  Prevent the implantation of an embryo or release a hormone
• Fertility control

  Methods of contraception
• Injection, implant or skin patch

  Slow release progesterone to inhibit the maturation and release of eggs for a number of months or years