Topic 5 - Homeostasis and Response

• Homeostasis is the regulation of conditions inside the body to maintain a stable internal environment in response to change
• Automatic control systems are used to maintain a constant internal environment
• Examples of automatic control systems :

  • nervous and hormonal communication
  • body temperature
  • blood glucose level
  • water content
• Receptors detect a stimulus, they can form part of larger complex organs like the retina of the eye is covered in like receptor cells
• Effectors respond to nervous impulses and bring about a change in the body. For example, muscles contracting or glands secrete hormones
• Sensory neurones 


  The neurones that carry information as electrical impulses from the receptors to the CNS
• Motor Neurones 


  The neurones that carry electrical impulses from the CNS to effectors
• Central Nervous System


  The CNS is connected to the body by sensory neurones and motor neurones
• Homeostasis is important because cells and enzymes need the right conditions to function properly
• Negative feedback


  When the level of something in the body (like water or temp) is either too high or low so the body needs to return it to back to normal
• Stimulus


  A change in environment

  e.g. Sound, hot objects, bright lights
• When body is too hot it has many responses:

  • Sweat is produced by the sweat glands
  • Through vasodilation which is when the blood vessels supplying the skin dilate so more blood flows close to surface of the skin to help energy transfer
• When the body is cold it responds with:

  • Hair stands up to trap an insulated layer of air
  • No sweat is produced
  • Vasoconstriction, when skin capillaries constrict to close off the skin supplies
  • Shivering, for energy transfer
• A tropism is the growth towards a particular stimulus, such as light or gravity.
• A positive tropism is when the plant grows towards a stimulus. For example, a stem grow towards light
• A negative tropism is when the growth is away from a stimulus. For example, roots grow away from a light.
• Auxins are a group of plant hormones, which are produced in the tips of the stem and roots and diffuse to other areas
• Phototropism is growth towards a light stimulus
• The shaded side of the plant stem contains more auxins and cells elongate, which causes them to grow towards the light
• Geotropism or gravitropism is a stimulus of gravity
• Stems and leaves show negative geotropism as they grow against the force of gravity
• Roots show positive geotropism as they grow in the direction of gravity.
• Gibberellin is a plant hormone involved in seed germination, flowering, fruit formation and seedling growth.
• Auxins diffuse through plant tissue from the tips where it was made
• Plant hormones help stimulate growth in specific areas of the plant
• Hormones are chemical messengers that are produced by glands and travel through the bloodstream to target organs
• Testosterone is produced in the testes and is the main male hormone
• Oestrogen is produced by the ovaries and is the main female hormone.
• Menstrual cycle


  Recurring series of events in the female reproductive system
• Oestrogen repairs and thickens the uterus lining, preparing it for implantation
• FHS stimulates oestrogen production and the growth of follicles in the ovary. It is a secreted by the pituitary system
• LH is secreted by the pituitary gland, which stimulates ovulation
• Hormones can be used to control fertility to prevent unwanted pregnancies
• Oral contraception uses oestrogen or progesteron, to prevent FSH being released and eggs cannot mature
• Injections, implants or patches release progesteron, which inhibit maturation and release of eggs for many months and years
• Intrauterine devices (IUD)


  prevent the implantation of an embryo
• Spermicidal agents 


  Kill sperm
• Physical barriers can be used as contraception like condoms
• the endocrine system:

  • pituitary gland - regulates body conditions
  • ovaries - produces oestrogen
  • testes - produces testosterone
  • thyroid - produces thyroxine
  • adrenal gland - produces adrenaline
  • pancreas - produces insulin to regulate blood glucose levels
• Nerves:

  • very fast action
  • act for a short time
  • act on precise area