'Fight or Flight' Response

• When an organism is threatened (e.g. by a predator) it responds by preparing the body for action (e.g. for fighting or running away). This response is called the 'fight or flight' response. Nerve impulses from sensory neurones arrive at the hypothalamus, activating both the hormonal (endocrine) system and the sympathetic nervous system.
• The pituitary gland is stimulated to release a hormone called ACTH.

  This causes the cortex of the adrenal gland to release steroidal hormones, which have a range of effects on the body, helping it to respond to stress both in the short and long-term
• Sympathetic nervous system activation

  Release of adrenaline from the medulla region of the adrenal gland
• Sympathetic nervous system and adrenaline

  Produce a faster response than the hormones secreted by the cortex of the adrenal gland
• Effects of sympathetic nervous system and adrenaline

  1. Heart rate is increased and the heart contracts with more force, causing blood to be pumped around the body faster

  2. Muscles around the bronchioles relax, causing the airways to widen, so breathing is deeper

  3. Intercostal muscles and diaphragm contract faster and with more strength, increasing the rate and depth of breathing

  4. Glycogen is converted into glucose via glycogenolysis, so more glucose is available for muscles to respire

  5. Muscles in the arterioles supplying the skin and gut constrict, and muscles in the arterioles supplying the heart, lungs and skeletal muscles dilate, so blood is diverted from the skin and gut to the heart, lungs and skeletal muscles, increasing blood flow to skeletal muscles (e.g. in the legs), making them ready for action

  6. Erector pili muscles in the skin contract, making hairs stand on end so the animal looks bigger