homeostasis and response

• 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, and 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, and effectors, muscles or glands, which bring about responses which restore optimum levels.
• 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.
• Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
• The endocrine system is composed of glands that 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 of hormones 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.
• 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.
• In liver and muscle cells excess glucose is converted to glycogen for storage.
• 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.
• 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.
• 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, a process 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 the 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 nonhormonal methods of contraception.
• These include 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 several months or years, barrier methods such as condoms and diaphragms which prevent the sperm from reaching an egg, intrauterine devices that 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 sterilization.
• In Vitro Fertilisation (IVF) treatment involves giving a mother FSH and LH to stimulate the maturation of several eggs, collecting the eggs from the mother and fertilizing them by sperm from the father in the laboratory, and developing the fertilized eggs 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.
• Adrenaline is produced by the adrenal glands in times of fear or stress, 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 from the thyroid gland stimulates the basal metabolic rate, plays an important role in growth and development, and its levels are controlled by negative feedback.
• 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 involves keeping the blood glucose concentration, body temperature, and water levels constant in the human body.
• Homeostasis consists of automatic control systems making sure that the internal conditions of the body stay as constant as possible.