Hormonal control

• What is the endocrine system?

  A network of glands that produce and secrete hormones into the bloodstream
• What is a hormone?

  • A cell signalling molecule produced by endocrine glands and released into the blood

  • Travels to a target organ and binds to receptors on effectors initiating a response
• Compare the endocrine and nervous system

  Endocrine system :

  • Uses hormones

  • Hormones travel in the bloodstream to the target organ

  • Slower response

  • Lasts until all hormones have broken down which takes a long amount of time

  Nervous system :

  • Uses nerve impulses

  • Nerve impulses travel via neurones to the effectors

  • Faster response

  • Lasts until the nerve impulse stops which takes a short amount of time
• What is the pituitary gland?

  • Described as the ‘master gland’

  • Endocrine gland that produces hormones which control other glands (e.g. adrenal glands)
• What are the adrenal glands?

  Endocrine glands that produce adrenaline
• Where are the adrenal glands located?

  Above the kidneys
• What is adrenaline?


  A hormone produced by the adrenal glands that is involved in the ‘fight or flight’ response (where the body prepares to confront danger of flee from it)
• State the effects of adrenaline on the body

  • Increases heart rate

  • Increases blood pressure

  • Increases blood flow to muscles

  • Increases blood glucose levels
• Describe how adrenaline increases heart rate and blood pressure

  • Secreted by adrenal glands, travels in the blood to the heart

  • Binds to specific receptors on cells in the heart

  • Causes heart muscle to contract more forcefully and frequently

  • Therefore heart rate and blood pressure increase
• Describe how adrenaline increases respiration at muscle tissues

  • Adrenaline binds to specific receptors on cells in the liver

  • Triggers breakdown of glycogen stores and release of glucose so blood glucose levels increase

  • Increased heart rate causes greater blood flow to muscles

  • Therefore, muscle cells receive more oxygen and glucose for respiration
• What is negative feedback?


  • A corrective mechanism that allows only small shifts from a set point

  • It reverses a change in conditions e.g. if the concentration of a hormone increases, negative feedback systems work to reduce the concentration back to normal level
• What is the thyroid gland?

  Endocrine gland that produces thyroxine
• Where is the thyroid gland located?

  In the neck
• What is thyroxine?


  A hormone secreted by the thyroid gland that controls metabolic rate, heart rate and temperature
• What is metabolic rate?


  The rate at which biochemical reactions occur in cells
• Describe how thyroxine is released

  • Hypothalamus secretes TRH

  • TRH stimulates secretion of TSH from pituitary gland

  • TSH stimulates the release of thyroxine from the thyroid gland
• What does TRH stand for?

  Thyrotropin releasing hormone
• What does TSH stand for?

  Thyroid stimulating hormone
• Describe how a negative feedback system controls blood thyroxine levels

  • If blood thyroxine levels increase above a set point, TRH and TSH secretion is inhibited. Less thyroxine is produced by the thyroid gland. Thyroxine levels return to normal

  • If blood thyroxine levels decrease below a set point, TRH and TSH secretion is increased. More thyroxine is produced by the thyroid gland. Thyroxine levels return to normal
• How do the ovaries act as an endocrine gland?


  They secrete oestrogen in the bloodstream