B5 - Homeostasis and Response

• Homeostasis is the maintenance of a constant internal environment despite changes in the external environment.
• In the human body, homeostasis controls:

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Receptors are cells which detect stimuli (changes in an environment)
• Coordination centres process the information received from the receptors.

  Examples: brain, spinal cord, pancreas
• 1. Receptor cells convert a stimulus into an electrical impulse
  2. These impulses travel along sensory neurones to the central nervous system
  3. Information is processed and an electrical impulse in response is sent along motor neurones to effectors
  4. The effectors carry out the response
• A synapse is the gap between 2 neurons that allows the transmission of information.
• 1. When impulse reaches the end of the first neuron, a chemical is released into the synapse
  2. The chemical diffuses across the synapse
  3. When the chemical reaches the second neuron, it triggers the impulse to begin again in the next neuron
• The endocrine system sends hormones around the body, when they reach a target tissue it produces a response
• Pituitary Gland:

  • The master gland
  • Secretes hormones into the blood
  • Either have an effect on the body or other glands to stimulate hormone production
• Pancreas:

  • Secretes insulin
  • Controls blood glucose levels
• Thyroid:

  • Secretes Thyroxine
  • Controls metabolic rate, heart rate and temperature
• Adrenal Gland:

  • Secretes adrenaline
  • Involved in the 'fight-or-flight' response
• Ovary:

  • Secretes oestrogen
  • Involved in the menstrual cycle and in the development of female secondary sex characteristics
• Testes:

  • Secretes testosterone
  • Involved in the production of sperm and the development of male secondary sex charcteristics
• Hormones are transported through the blood to target organs or tissue where it has an effect
• If glucose levels are too high, the pancreas produces insulin
• Insulin binds to the cell in target organs, this causes:

  1. Glucose to move from blood into muscle cells
  2. Excess glucose to be converted into glycogen which is stored in the liver
• If glucose levels decrease, pancreas produces the hormone glucagon
• Glucagon binds to liver cells causing glycogen to be broke down into glucose
• Glucose made from the glycogen is released into the blood, increasing the blood glucose concentration
• A negative feedback loop is a system which allows blood glucose concentration to remain constant.

  When blood glucose levels increase/decrease, a hormone is secreted to oppose the change and bring the level back to normal
• Type 1 diabetes is when the pancreas cannot produce enough insulin

  Type 2 diabetes is when body cells no longer respond to insulin
• With type 1 diabetes, glucose is excreted with urine and lots of urine is produced, leaves the individual very thirsty
• With type 2 diabetes, treatments include reducing the number of simple carbohydrates in your diet, and increasing exercise
• With type 1 and type 2 diabetes, blood glucose can rise to a fatal amount
• Testosterone:

  • Produced by the testes
  • Stimulates sperm production
• Oestrogen:

  • Produced in the ovaries
  • Produces physical changes and is involved in the menstrual cycle
  • Secreted as a result of FSH
  • Stimulates production of LH and inhibits the secretion of more FSH
• Follicle Stimulating Hormone (FSH):

  • Produced in the pituitary gland
  • Stimulates the ovaries to produce oestrogen
  • Causes the maturation of an egg in the ovaries
• Luteinising Hormone (LH):

  • Produced in the pituitary gland
  • Produced as a result of the hormone oestrogen
  • Its release results in ovulation
• Progesterone:

  • Produced in the ovaries and secreted from egg follicle
  • Maintains lining of the uterus and supports pregnancy if egg is fertilised
  • Inhibits the release of FSH and LH