Endocrine System

• Endocrine System

  • a network of glands throughout our bodies that manufacture and secrete chemical messengers known as hormones
  • works alongside the nervous system to regulate physiological processes in the human body
• Glands

  • produce and secrete hormones
  • each gland produces and secretes different hormones
  • the endocrine system is regulated by the hypothalamus, which signals a target gland to increase levels of a hormone
  • when sufficient levels are reached the hypothalamus shuts down
• Hormones

  • chemicals that circulate in the bloodstream and carried to target sites throughout the body
  • each hormone excites or stimulates a particular part of the body
  • a hormone only effects a given number of cells, known as target cells
  • a target cell receives a hormone via receptors, that are specific to that hormone
• The Pituitary Gland

  • controlled by the hypothalamus
  • the hypothalamus helps regulate basic functions within the body
  • it is a master gland that helps produce hormones that are then sent in the blood stream and received by target cells
• Anterior and Posterior gland

  • produces different hormones that target different parts of the body
  • ACTH - stress hormone, stimulates the adrenal gland to produce cortisol
  • produces LH and FSH, important in the control of reproductive functions and releases oestrogen and progesterone
  • oxytocin stimulates contractions
• Adrenal Glands

  • on top of kidneys
  • each gland is made up of two distinct parts of the adrenal cortex and adrenal medulla
  • the adrenal cortex releases hormones that are necessary for life (e.g. cortisol which regulates cardiovascular and anti-inflammatory functions)
  • adrenal medulla - noradrenaline (constricts blood vessels and BP increase) and adrenaline (increases heart rate and blood flow to muscles and brain)
• Ovaries

  • key structures in the female reproductive system
  • ovaries are responsible for the production of eggs and for progesterone and oestrogen
• Testes

  • male reproductive glands produce testosterone
  • important for the development of growth of facial hair, deepening voice and growth spurts
  • it is vital for the overall health and wellbeing in men
  • the production of testosterone is controlled by the hypothalamus and pituitary gland
• The fight or flight response

  • a sequence of activity within the body part that is triggered when the body prepared itself for defending or attacking (fight) or running away (flight)

  1. threat
  2. amygdala mobilises, associating sensory signals with emotions associated with the fight of flight response
  3. it then sends a distress signal to the hypothalamus that then communicates with the rest of the body via the nervous system

  • in response to stressors, the body has two major systems within the sympathetic nervous system - acute and chronic
• Acute (sudden) stressors

  1. adrenaline
  2. heart rate increases - blood to muscles, heart and vital organs
  3. blood pressure increases
  4. blood rate increases
  5. it also increases the release of fats and blood sugar providing energy to body parts associated with fight or flight
• Chronic (ongoing) stressors

  • hypothalamus - releases a chemical messenger - corticotrophin release hormone in response to the continued threat
  • CRH causes the pituitary gland to release ACTH - which is transported in the bloodstream to its target site in the adrenal glands
  • the adrenal glands cortex gets stimulated by the ACTH to release several stress relieving hormones such as cortisol
  • is levels rise above threshold, the hypothalamus and pituitary gland initiate a reduction in CHR and ACTH levels
• Evaluation

  • Taylor et al (2000) suggested that females respond by tending through nurturing and protecting behaviours and perform protective alliances with other women. Fleeing to early would put their offspring at risk
  • Lee and Harley (2012) - the SRY gene found on the male Y chromosome (aggression) primes the male to respond to to stress in a different way
  • Gray (1988) - proposed that the initial response is to avoid confrontation. Most animals freeze/display the "freeze-response" to stop, look and listen to consider their next move