5.4.1 endocrine communication

communication system using hormones as signalling molecules

molecules (proteins/steroids) that are released by endocrine glands directly into blood - act as messengers which carry signal from glands to specific target organ/tissues

for non-steroid hormones, cells which possess specific receptor on plasma membrane - shape of receptor complementary to hormone molecule –> many similar cells together form target tissue

• protein & peptide hormones, and derivatives of amino acids - eg. adrenaline, insulin, glucagon • steroid hormones eg. oestrogen, testosterone

• proteins not soluble in phospholipid membrane & don’t enter cell • need to bind to cell surface membrane & release second messenger inside cell

• pass through membrane & enter cell/nucleus • have direct effect on dna in nucleus (if enter it)

ductless = consist of groups of cells that manufacture/release hormone directly into bloodstream via capillaries running through gland

• endocrine gland = secrete hormones • exocrine glands = don’t secrete hormones & consist of group of cells surrounding small duct where the products are secreted from cells eg. salivary gland

cells receiving endocrine signal

• must possess specific receptor on plasma membrane with complementary shape to signalling molecule (hormone) • hormone binds to receptor & initiates changes in cell

first messengers

• signalling molecules outside cell • bind to cell surface membrane • initiate effect in cell • usually cause release of another signalling molecule in cell = second messenger

• stimulates change in activity of cell eg. cAMP

• non-steroid hormones act via G protein in membrane • G protein activated when hormone binds to receptor • G protein then activates effector molecule - usually enzyme which converts inactive molecule into active second messenger • many cells, effector is enzyme adenyl cyclase, which converts ATP to cyclic AMP (cAMP) - cAMP is second messenger • second messenger may act directly on another protein (eg. ion channel) or initiate cascade of enzyme-controlled reactions which alter cell activity