Homeostasis and Response

• What is the definition of homeostasis?

  The regulation of internal conditions in a cell or organism to give optimum conditions for it to function in response to internal and external changes.
• What is it in cells and organisms that needs optimal conditions?

  Enzymes work best in their optimum conditions, and most reactions inside cells and organisms involve enzymes.
• What exactly is controlled during homeostasis in humans?

  Blood glucose concentration, body temperature and water levels.
• What are the automatic control systems in the body for homeostasis?

  The nervous system and the endocrine (hormonal) system.
• What three parts do all control systems have?

  Receptor cells, coordination centres and effectors.
• What is the role of a receptor?

  To detect a stimulus
• What is a coordination centre?

  An area of the body that receives and processes the information from the receptors.

  Eg, brain, spinal cord, pancreas.
• What is an effector?

  Effectors cause the response to happen so that the body is returned to optimum levels.

  Eg. Muscles and glands.
• What is a neurone?

  A nerve cell.

  They are quite long and thin, and they can transmit information as electrical impulses.
• What is the CNS?

  The central nervous system. It is made of two parts, the brain and the spinal cord.
• What happens at the CNS?

  the CNS receives impulses from the receptor cells and then sends impulses out to the effectors.

  The effect would be a muscle contracting or a gland secreting hormones.
• What is the order of the pathway of a reflex arc

  stimulus ➔ receptor ➔ sensory neurone➔ relay neurone ➔ motor neurone ➔ effector ➔ response
• What are the three neurones called in a reflex arc?

  Sensory neurone, Relay neurone and Motor neurone.
• What is the role of a sensory neurone?

  To transfer a signal from a receptor to the CNS
• What is the role of a relay neurone?

  To transmit a signal from a sensory neurone to a motor neurone

  Relay neurones are found in the CNS, usually in the spinal cord.
• What is the role of a motor neurone?

  To transmit a signal from the CNS to an effector (a muscle or a gland).
• What is a synapse?

  Synapses are tiny gaps between neurones. As the electrical signal can't pass across the gap, the information is converted into chemicals called neurotransmitters.
• How do neurotransmitters cross a synapse?

  Neurotransmitters diffuse across a synapse. When they reach the next neurone, they cause a new electrical impulse to be sent.
• Why does the speed slow down when an impulse reaches a synapse?

  The electrical impulse is much faster than the chemical neurotranmitter, so every synapse slows the speed of the overall reaction.
• Why do reflexes help reduce damage by injury?

  They are automatic and rapid so they don't involve the conscious part of the brain.

  The response is quicker than if the impulse travelled to the brain, so less damage happens.
• What sort of factors slow down reaction times?

  Alcohol, depressant drugs, tiredness and dehydration can all slow down the speed of a reaction.

  Stimulant drugs can speed up reactions.
• What is the endocrine system?

  The system of glands that release hormones directly into the bloodstream. This leads to slower responses than the nervous system, but the effects last for longer.
• What is a hormone?

  A chemical that travels in the blood to a target organ where it produces an effect.
• What is a target organ?

  The organ of the body where the chemical hormone will have an effect.

  Each hormone has it's own target organ.
• Why is the pituitary gland so important?

  The pituitary gland is a "master gland" as it produces several different hormones that can then make other glands produce hormones too, which cause effects.
• Which glands do I need to know/label?

  The pituitary gland, the pancreas, the thyroid, the adrenal gland, the ovaries and the testes.
• Which hormonal controls do I need to know for GCSE?

  The control of blood glucose levels, and the control of human reproduction (including how we develop contraceptives).
• What does the pancreas do?

  It monitors and controls blood glucose levels.
• What are the hormones produced by the pancreas?

  Insulin (when blood glucose is too high) and glucagon (when blood glucose is too low.)
• When is insulin produced?

  When levels of glucose in the blood get higher than they should be, the pancreas produces insulin.
• What does insulin do?

  Insulin travels in the bloodstream to the liver (it's target organ) where it causes liver and muscle cells to take in glucose and convert it to glycogen for storage.
• What does glucagon do? HT

  Glucagon causes glycogen stores to be converted back to glucose which is then released back into the blood.
• What is negative feedback in blood glucose control? HT

  The pancreas is constantly monitoring glucose levels in the blood, and the two hormones insulin and glucagon are constantly causing their own inhibition.
• What is diabetes?

  A disorder where the blood glucose levels are not properly controlled. There are two types of diabetes.
• What is Type 1 diabetes?

  A disorder where the pancreas does not produce sufficient insulin. Blood glucose levels can get extremely high.
• How is Type 1 diabetes treated?

  Regular insulin injections and careful diet control are needed to treat Type 1 diabetes.
• What is Type 2 diabetes?

  A disorder where liver and muscle cells no longer respond to insulin produced by the pancreas.

  Obesity increases the risk of developing Type 2 diabetes.
• When do people get diabetes?

  Type 1 is usually diagnosed in childhood.

  Type 2 occurs in older people who have become obese.
• What are the hormones in the human reproductive system?

  Testosterone in men, and oestrogen, progesterone, follicle stimulating hormone (FSH) and luteinising hormone (LH) in women.
• When do humans start making reproductive hormones?

  During puberty, and they cause secondary sex characteristics to develop (breasts, pubic hair etc).