School resources

• What is homeostasis?

  Homeostasis is the regulation of a constant internal environment. The conditions are maintained to ensure optimum conditions for metabolism and changes in response to both internal and external fluctuations
• What does homeostasis regulate in humans?

  • Temperature
  • Blood glucose levels
  • Temperature
  • CO2
  • Water levels
• Homeostasis

  The levels are monitored and regulated by automatic control systems which can be either nervous responses (coordinated by the nervous system) or chemical responses (coordinated by the endocrine system). Information about the environment is called a stimulus and is detected by a receptor. The information is processed by a central coordination system and a response is initiated by an effector.
• What is a synapse?

  A synapse is the gap where the ends of two neurons meet.
• The message is transmitted by chemical neurotransmitters. When the electrical impulse arrives at the terminal of the first neuron, it causes a release of neurotransmitter chemicals into the synapse. They travel across the gap and bind to receptor sites on the terminal of the next neuron. The receptor sites are specific for each type of neurotransmitter. A nerve impulse will only be created in the second neuron when a complimentary chemical binds.
• The nervous system allows a fast, short-lived response to a stimulus in the surroundings. The information is received by a receptor, passed along the neurons (nerve cells) as an electrical impulse and results in a response.
• Label the diagram

  a = myelin sheath

  b = axon terminal

  c = axon

  d = dendrites

  e = cell body

  f = nucleus

  
• Reflexes

  A reflex is a fast and automatic response to a particular stimulus which may be harmful to the organism. They are quick because there is no conscious thought or process to deliver the response (they are an involuntary action). The pathway which carries the information about a reflex action is called a reflex arc.
• Reflex arc

  A reflex arc begins with the stimulus e.g. a bee sting or a hot object on the skin. The stimulus is detected by the receptor cells and an electrical impulse is transmitted along the sensory neuron. The impulse is passed through relay neurons in the spinal cord or the unconscious areas of the brain. The response is coordinated automatically and sent along the motor neuron to the effector cells.
• Hormones

  Hormones are chemical messengers transported in the bloodstream to an effector where they can activate a response. They are produced and released from glands around the body which all make up the endocrine system. Hormones do a similar job to the neurons of the nervous system but there are some differences.
• Neurones vs hormones

  Neurones Hormones

  Speed fast slow

  Duration short long

  Target

  Area specific I general
• Pituitary gland

  The pituitary gland produces a range of hormones including FSH and LH which help to regulate the menstrual cycle. The pituitary gland acts as a master gland because many of the hormones it releases control and coordinate the release of other hormones from other glands in the body
• Type 1 diabetes

  • Type 1 diabetes is a disorder affecting the pancreas.
  • pancreas does not produce enough insulin to control the blood sugar level and so the levels become higher than normal.
  • usually treated by injections of insulin.
• Type 2 diabetes

  • disorder of effector cells which no longer respond to the hormones released from the pancreas.
  • can usually be managed through lifestyle choices such as maintaining a carbohydrate-controlled diet and regular exercise.
• Oestrogen

  • main reproductive hormone in females.
  • produced in the ovaries
  • this hormone increases and it stimulates an egg to be released from an ovary each month. This process is called ovulation and happens, on average, every 28 days.
• Testosterone

  • the main reproductive hormone in males. It is produced in the testes.
  • This hormone stimulates the production of sperm.
• Pancreas

  The pancreas is the organ and gland which monitors and regulates the blood glucose concentration.
• If blood glucose is too low

  • Pancreas releases glucagon, causing the cells to release glucose
  • Liver and muscles convert glycogen into glucose to be released
  • Normal blood glucose concentration
• If blood glucose is too high

  • Pancreas releases insulin, so cells can absorb glucose
  • Liver and muscles convert the glucose into glucagon to be stored
• The whole menstrual cycle is controlled by four main reproductive hormones:

  • follicle stimulating hormone (FSH) • oestrogen • luteinising hormone (LH) • progesterone
• Where is FSH produced

  Pituitary gland
• Response caused by FSH

  An egg to develop in one of the ovaries.
• FSH Interaction with Other Hormones

  Stimulates the production of oestrogen.
• Where is oestrogen produced?

  In the ovaries
• Response caused by oestrogen

  The lining of the uterus builds up and thickens.
• Interaction with other hormones - oestrogen

  Stimulates the production of LH. Inhibits the production of FSH.
• Where is LH produced?

  The pituitary gland
• What does LH cause?

  Ovulation
• LH Interaction with Other Hormones

  Indirectly stimulates the production of progesterone.
• progesterone

  It is produced in the ovaries
• Response caused by progesterone

  The uterus lining to maintain.
• Interaction with Other Hormones - progesterone

  Inhibits the production of LH.
• oral contraceptives (‘the pill’) (hormonal)

  Pill taken which contains hormones to inhibit FSH so that an egg does not mature.

  PRO - Easily self-administered. Short-term effects. Can easily be reversed. Very reliable.

  CON - May have mild side-effects associated. Could lead to pregnancy if missed. Does not protect from STIs
• injection, implant or skin patch (hormonal)

  Contains progesterone which is slowly released to inhibit the release of eggs for months or even years.

  PROS - Administered through routine appointment at GP surgery. Requires little to no aftercare or maintenance

  • Very reliable

  CONS - May take some time for effects to be reversed once removed. Does not protect from STIs
• condoms or diaphragm (female condom) - non hormonal

  Creates a physical barrier to prevent the sperm from reaching the egg.

  PROS - Easy to use. Short-term effects. Very reliable. Provides protection from most STIs.

  CONS - can fail
• intrauterine devices (coil) (hormonal)

  The device is attached to the lining of the uterus and releases hormones or prevents the implantation of an embryo.

  PROS - Requires little to no aftercare or maintenance. Very reliable.

  CONS - May take some time for effects to be reversed once removed. Does not protect from STIs
• Spermicidal agents - non hormonal

  Contains chemicals to kill or immobilise sperm cells.

  P - Easy to use. Short-term effects. N - Does not protect from STIs. Less effective when used as the only method.
• abstaining from intercourse (around the time of ovulation) - non hormonal

  Avoiding sexual intercourse when there is a likelihood of an egg being present in the oviduct.

  P - inexpensive

  N - not always reliable
• Surgery - non hormonal

  A surgical procedure carried out in men or women. In males, the vas deferens tubes are sealed or blocked to prevent the passage of sperm from the testes. In females, the fallopian tubes (oviducts) are sealed or blocked to prevent the passage of the egg from the ovaries.
• cons of surgery

  • risks associated with surgery eg, infection
  • Difficult to reverse
  • Can take several months to be reliable