Homeostasis and Response

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

  •• blood glucose concentration

  •• body temperature

  •• water levels.
• The order of automatic response systems is:

  stimulus-> receptor-> coordinator-> effector-> response
• Reflex actions are automatic and rapid; they do not involve the

  conscious part of the brain.
• What factors affect reaction time?

  Amount of sleep, caffeine intake, intoxication
• To focus on a near object:

  •• the ciliary muscles contract

  •• the suspensory ligaments loosen

  •• the lens is then thicker and refracts light rays strongly.
• To focus on a distant object:

  •• the ciliary muscles relax

  •• the suspensory ligaments are pulled tight

  •• the lens is then pulled thin and only slightly refracts light rays.
• Accommodation is the process of changing the shape of the lens to

  focus on near or distant objects.
• Label the eye

  A) Iris

  B) Pupil

  C) Cornea

  D) Lens

  E) Retina

  
• Short-sightedness is called myopia
• Long-sightedness is called hyperopia
• Body temperature is monitored and controlled by the thermoregulatory

  centre in the brain.
• The thermoregulatory centre contains receptors

  sensitive to the temperature of the blood.
• The skin contains temperature

  receptors and sends nervous impulses to the thermoregulatory centre
• If the body temperature is too high, blood vessels dilate (vasodilation)

  and sweat is produced from the sweat glands.

  Both these mechanisms cause a transfer of energy from the skin to the environment.
• If the body temperature is too low, blood vessels constrict

  (vasoconstriction), sweating stops and skeletal muscles contract (shiver).
• The endocrine system is composed of glands which secrete chemicals

  called hormones directly into the bloodstream.
• The blood carries hormones to a target organ where it produces an effect.
• The pituitary gland in the brain is a ‘master gland’ which secretes

  several hormones into the blood in response to body conditions.

  These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.
• Endocrine system

  A) Ovaries

  B) Testes

  C) Pancreas

  D) Pituary

  E) Thyroid

  F) Adrenal

  
• If the blood glucose concentration is too high, the pancreas produces

  the hormone insulin that causes glucose to move from the blood into the cells. In liver and muscle cells, excess glucose is converted to glycogen for storage.
• If the blood glucose concentration is too low, the pancreas

  produces the hormone glucagon that causes glycogen to be converted

  into glucose and released into the blood.
• Different ways water moves through the body by osmosis:

  • Water leaves the body via the lungs during exhalation.
  • Water, ions and urea are lost from the skin in sweat.
  • There is no control over water, ion or urea loss by the lungs or skin.
  • Excess water, ions and urea are removed via the kidneys in the urine.
• The digestion of proteins from the diet results in excess

  amino acids which need to be excreted safely. In the liver these amino

  acids are deaminated to form ammonia. Ammonia is toxic and so it is

  immediately converted to urea for safe excretion
• The water level in the body is controlled by the hormone ADH

  which acts on the kidney tubules. ADH is released by the pituitary

  gland when the blood is too concentrated and it causes more water

  to be reabsorbed back into the blood from the kidney tubules. This is

  controlled by negative feedback.
• 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.
• 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.
• Fertility


  Can be controlled by a variety of hormonal and non-hormonal methods of contraception
• Methods of 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
• Oral contraceptives


  • Contain hormones to inhibit FSH production so that no eggs mature
• Injection, implant or skin patch of slow release progesterone


  • Inhibit the maturation and release of eggs for a number of months or years
• Barrier methods


  • Prevent the sperm reaching an egg
• Intrauterine devices


  • Prevent the implantation of an embryo or release a hormone
• Spermicidal agents


  • Kill or disable sperm
• Abstaining from intercourse


  • When an egg may be in the oviduct
• Surgical methods


  • Male and female sterilisation
• 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).
• Although fertility treatment gives a woman the chance to have a baby of

  her own:

  •• 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.