B5 - Homeostatis

• What is homeostatis?

  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.
• What do all control systems include

  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.
• How is the structure of the nervous system adapted to its functions?

  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
• Why are reflex actions important?

  They are automatic, rapid, and do not involve the conscious part of the brain to protect the human body.
• The brain

  The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.Neuroscientists have been able to map the regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques. The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult.
• What is the function of the cerebral cortex?

  Higher cognitive functions, such as perception, memory, language, and decision-making.
• What is the function of the cerebellum?


  The cerebellum is responsible for coordinating voluntary movements, maintaining posture, and regulating balance.
• What is the function of the medulla?


  Regulating vital bodily functions.
• How does the eyes structure change to accomodate focus on near or distant objects?

  Lens shape changes.
• How does the eye structure change to adapt to dim light?

  Dilation
• What is the eye?


  A sense organ containing receptors sensitive to light intensity and colour
• What is the function of the retina?


  Vision
• What is the function of the optic nerve?


  The optic nerve is responsible for transmitting visual information from the eye to the brain, allowing us to perceive and interpret the images we see.
• What is the function of the sclera?


  Protection and support for the eyeball.
• What is the function of the cornea?


  To refract light.
• What is the function of the iris?


  Regulating the amount of light entering the eye.
• What is the function of the ciliary muscles?


  Controls accomodation for viewing objects at varying distances by changing lens shape
• What is the function of suspensory ligaments?


  To support the lens in the eye.
• What is accomodation?


  The process of changing the shape of the lens to focus on near or distant objects
• What happens to focus on a near object?

  • the ciliary muscles contract
  • the suspensory ligaments loosen
  • the lens is then thicker and refracts light rays strongly.
• What happens 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.
• What are two common defects of the eyes and how are they treated?

  Two common defects of the eyes are myopia (short sightedness) and hyperopia (long sightedness) in which rays of light do not focus on the retina.

  • Generally these defects are treated with spectacle lenses which refract the light rays so that they do focus on the retina.
  • New technologies now include hard and soft contact lenses, laser surgery to change the shape of the cornea and a replacement lens in the eye.
• body temperature


  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.
• How is body temperature controlled?


  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).
• 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 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.
• Control of 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 the cells, where excess glucose is converted to glycogen for storage.
• 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.In Type 2 diabetes the 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 for Type 2 diabetes.
• Maintaining water and nitrogen balance in the body

  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.If body cells lose or gain too much water by osmosis they do not function efficiently.
• Digestion of proteins

  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.
• What is the function of kidneys in maintaining water balance?


  The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water.
• What is the effect of ADH on the permeability of the kidney tubules?


  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.
• People who suffer from kidney failure may be treated by organ transplant or by using kidney dialysis
• What are the basic principles of dialysis?


  Filtration and diffusion.
• Hormones

  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.
• Women menstrual cycle hormones

  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.
• How do FSH, oestrogen, LH and progesterone interact in the control of the menstrual cycle?

  Feedback loop

  FSH Produces egg

  As egg develops, oestrogen is produced

  Oestrogen causes growth and repair, inhibiting FSH

  When oestrogen rises to a high enough level, LH surges from the pituitary, causing ovulation

  Produces oestrogen and progresterone which inhibit FSH and LH

  Progesterone maintains lining

  If egg not fertilised, progesterone level drops, causing menstruation
• Contraception

  • Fertility can be controlled by a variety of hormonal and non-hormonal methods of contraception.
• 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).
• Fertility treatment - pros and cons

  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.
• What is the role of thyroxine in the body?

  Metabolism