Hormonal Communication

• what is an endocrine gland?

  a group of cells which are specialised to secrete chemicals known as hormones, and are secreted directly into the bloodstream e.g. pancreas
• what is an exocrine gland?

  a group of cells which are specialised to secrete chemicals through ducts into organs, or to the surface of the body
• what is the anterior pituitary gland responsible for?

  • growth hormone - controls growth of bones/muscles
  • gonadotrophins - controls development of ovaries and testis
• what is the posterior pituitary gland responsible for?

  • anti-diuretic hormone - increases reabsorption of water in kidneys
• what is the pineal gland responsible for?

  • melatonin - affects reproductive development and daily cycles
• what is the thyroid gland responsible for?

  • thyroxine - controls rate of metabolism and rate that glucose is used up in respiration, and promotes growth
• what is the thymus responsible for?

  • thymosin - promotes production and maturation of white blood cells
• what is the adrenal gland responsible for?

  • adrenaline - increases heart breathing rate and raises blood glucose levels
• what is the pancreas responsible for?

  • insulin - convert excess glucose into glycogen
  • glucagon - converts glycogen back to glucose in liver
• what is the ovary responsible for?

  • oestrogen - controls ovulation and secondary sexual characteristics
  • progesterone - prepares uterus lining for receiving an embryo
• what are the testis responsible for?

  • testosterone -controls sperm production and secondary sexual characteristics
• what is the endocrine function of the kidneys?

  produces erythropoietin - stimulating production of erythrocytes in bone marrow
• why aren't kidneys considered endocrine gland?

  have many other non-endocrine roles
• what chemicals can hormones be derived from?

  • steroids
  • proteins
  • glycoproteins
  • polypeptides
  • amines
  • tyrosine derivatives
• what is the mode of action of steroid hormones?

  • non-polar lipid-soluble steroid hormone passes through plasma membrane
  • receptor protein in cytoplasm
  • hormone-receptor complex attaches to DNA
  • instructions for synthesis of polypeptide
  • polypeptide synthesised by ribosomes and mRNA
• why don't steroid hormones require receptors on cell membrane?

  lipid-soluble so can pass through (diffuse) phospholipid bilayer
• why do only small quantities of steroid hormones be secreted?

  stimulates gene expression (production of many copies of mRNA) so very little needed
• what is the mode of action of a non-steroid hormone?

  • polar and hydrophilic so can't diffuse directly through membrane
  • binds to specific receptors on plasma membrane of target cell
  • triggers a cascade reaction mediated by chemicals called secondary messengers (adenylyn cyclase (apoenzyme) to holoenzyme after binding)
  • e.g. adrenaline
• what are pros and cons of endocrine system?

  • pro - needs less ATP
  • con - slower response
• what are pros and cons of nervous system?

  • pro - faster response
  • con - needs more ATP
• what is the structure of adrenal glands?

  • outer region - produces hormones vital to life controlled by hormones from pituitary gland
  • inner region - produces non-essential hormones, released when sympathetic n.s. is stimulated, when body is stressed, flight/fight response
• what hormones does adrenal cortex produce?

  • glucocorticoids - cortisol (regulate metabolism controlling how body converts fats/carbs into energy, regulate blood pressure in response to stress), corticosterone (regulate immune response and supress inflammatory reactions)
  • mineralocorticoids - aldosterone (control blood pressure by maintaining balance between salts and water)
  • androgens - small amount male/female sex hormone released, important in menopause
• what hormones does the adrenal medulla produce?

  • adrenaline - increase heart rate, rapidly raises blood glucose concentration by converting glycogen to glucose
  • noradrenaline - works with adrenaline in response to stress, increases heart rate, widens pupils, wides air passages, increase blood pressure