Homeostasis and endocrine system

• Hypothalamus; Major link between the nervous and endocrine systems

  • Neuroendocrine organ
  • Controls the function of the endocrine glands
  • Releases stimulating and inhibiting hormones
  • Influences the pituitary gland
• Hypothalamus


  Releases - corticotrophin-releasing hormone, dopamine, growth hormone-releasing hormone, somatostatin, gonadotrophin-releasing hormone and thyrotropin-releasing hormone
• Pituitary gland


  • Attached to the hypothalamus by the Infundibulum
  • Two lobes - Posterior lobe and Anterior lobe
  • Has a rich blood supply which is vulnerable to damage following a major obstetric haemorrhage
• Posterior pituitary gland


  • Downgrowth of the hypothalamus
  • Does not produce hormones
  • Stores hormones produced by hypothalamus (oxytocin and ADH)
  • Neural impulses stimulate release
• Anterior pituitary gland


  • "Master endocrine gland"
  • No direct neural communication
  • Controlled by stimulating and inhibiting hormones released by hypothalamus
  • Tropic hormones (act on other endocrine glands) – TSH, ACTH, FSH, LH
  • Direct hormones – GH and prolactin
• Thyroid Gland


  • Lies in front of the trachea and below the larynx
  • Two lateral lobes joined by medial isthmus
  • Largest adult endocrine gland weighing 10-20g
  • Produces thyroxine (t4) and triiodothyronine (t3)
• Adrenal Glands


  • Adrenal medulla produces the catecholamines: Adrenaline (epinephrine) and Noradrenaline (norepinephrine)
  • Adrenal cortex produces three groups of steroid hormones: Mineralocorticoids, Glucocorticoids, Androgens
• ACTH rises progressively in pregnancy


  Cortisol rises in response
• Myometrium and decidua convert cortisone to cortisol


  Feedback mechanism seems to change during pregnancy - cortisol remains high
• Homeostasis


  The automatic process of maintaining equilibrium in the body – maintaining a stable environment
• Systems involved in homeostasis

  • Nervous system
  • Endocrine system
  • Respiratory system
  • Cardiovascular system
  • Digestive system
  • Urinary system
• Homeostasis at an Organismic Level


  • Maintenance of a stable internal environment within the body despite changes in the external environment
  • Components: Osmoregulation, Excretion, Thermoregulation
• Homeostasis at Cellular Level


  • Maintenance of a stable internal environment within the cells, despite changes in the extracellular environment
  • Processes: Osmosis, Diffusion, Active transport, Exocytosis, Endocytosis
• Homeostasis Feedback Mechanism


  • 3 Components: A receptor, The control Centre, The effector
  • Negative Feedback - Restores equilibrium
  • Positive Feedback - A deliberate increase in output
• Examples of homeostasis


  • Temperature regulation
  • Blood sugar regulation
  • Water balance
  • Electrolyte balance
  • pH balance
  • Blood pressure regulation
  • Respiration
  • Immunity
  • Digestion
  • Metabolism