Homeostasis

• Homeostasis

  • The regulation of conditions in the body to maintain a stable internal environment in response to changes both internal and external conditions.
  • Maintains optimal conditions for enzyme action and all cell functions.
• Control systems

  • Nervous system
  • Endocrine system
• The human nervous system

  • Organisms must response to stimuli (changes in the environment) in order to survive.
• Central nervous system

  • The CNS is connected to the body by sensory neurones and motor neurones.
• Sensory neurones

  • The neurones that carry out electric impulses from the receptors to the CNS.
• Motor neurones

  • The neurones that carry the electrical impulses from the CNS to the effectors.
• Receptors

  • Are cells that detect stimuli
  • Such as taste receptors on the tongue and sound receptors in the ear.
• Effectors

  • Respond to the nervous impulses and bring about the change
  • For example, Muscles contract and glands secrete hormones.
• Hormones

  • Are chemical messengers sent into the blood.
  • Carry through the blood to other parts of the body but only affect particular cells and organs.
• Where do hormones produce?

  • Endocrine glands
• The Pituitary gland

  • Produces many hormones that regulate body conditions.
• Thyroid

  • Produces thyroxine which involves regulating the rate of metabolism, heart rate and temperature.
• Adrenal gland

  • Produces adrenaline which is used to prepare the body for a 'fight or flight' response.
• Pancreas

  • This produces insulin, which is used to regulate the blood glucose levels.
• Ovaries

  • Produce oestrogen which is involved in the menstrual cycle.
• Regulating blood glucose

  • Glucose is needed by cells for respiration
  • Insulin is produced by the pancreas which regulates glucose concentrations in the blood.
• Type 1 diabetes

  • Occurs when the pancreas fails to produce sufficient insulin
  • Uncontrolled high blood glucose levels.
  • Usually treated with insulin injectors.
• Type 2 diabetes

  • Occurs when the body no longer responds 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.
• What happens if blood glucose concentration is too high?

  • The pancreas produces the hormone insulin that causes glucose to move from the blood into the liver and muscle cells where excess glucose is converted to glycogen for storage.
• Oestrogen

  • Is the main female reproductive hormone. 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 and it stimulates sperm production.
• Hormones that control the menstrual cycle

  • FSH
  • Oestrogen
  • LH
  • Progesterone
• FSH

  • Causes an egg to mature in an ovary and stimulates the ovaries to release oestrogen.
• Oestrogen

  • Stops FSH being produced.
  • Repairs, thickens and maintains the uterus lining.
  • Stimulates the pituitary gland to produce LH.
• LH

  • Triggers ovulation (the release of mature egg)
• Progesterone

  • Maintains the lining of the uterus during the middle part of the menstrual cycle and pregnancy.
• IVF

  • Involves giving a mother FSH and LH in a 'fertility drug' to a woman>
  • Stimulates 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.
• Reflex actions are automatic and quick
• The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
• The endocrine system is composed of glands that secrete chemicals called hormones directly into the bloodstream.
• Compared to the nervous system, the endocrine system is slower but act for longer.
• Blood concentration is monitored and controlled by the pancreas.
• Barrier methods such as condoms and diaphragms which prevent the sperm reaching the egg.
• Oral contraceptives that contain hormones to inhibit FSH production so no eggs mature.
• IVF

  • It is 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. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for 'fight and flight'
• Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development.

  Thyroxine levels are controlled by negative feedback.