Hormonal communication

• Endocrine communication

  • glands that is responsible for hormonal communication
  • secrete hormones which are transported in the blood + bind to their target cell causing a response
• What glands are involved?

  • pituitary gland
  • thyroid
  • adrenal
  • pancreas
  • ovary
  • testis
• what is a chemical messenger?

  widespread + longer lasting effect

  travels through the blood

  e.g. steroids, proteins, glycoprotein, polypeptide, amines and tyrosine
• what are steroid hormones?

  lipid soluble + can diffuse across the cell surface membrane into their target cells to bind to a receptor often located within the cytoplasm
• what are non steroid hormones?

  Insoluble in lipids and cannot diffuse across the cell surface membrane

  • they bind to complementary shaped receptors on cell surface membrane (target cell)
  • this is binding to a receptor causes a cascade within the cell that how the hormone causes a response
• Features of adrenal glands

  • endocrine gland
  • humans have two on top of each kidney
  • made up of adrenal cortex + adrenal medulla surrounded by a capsule
  • adrenal cortex +medulla both secrete hormones
• Adrenal cortex

  • controlled by hormones secreted by pituitary gland (in brain)

  types of hormones secreted

  • Glucocorticoids
  • Mineralocorticoids
  • Androgens
• Adrenal medulla

  • controlled by the nervous system

  when sympathetic nervous system is stimulated it causes the release of adrenaline

  • adrenaline - increases heart rate + raise blood glucose concentration
  • noradrenaline - increases heart rate + pupils dilate + widens airways in lungs + narrows blood vessels in non essential organs = higher BP
• Pancreas

  • gland in stomach
  • releases hormones to control blood glucose levels
  • endocrine gland + exocrine gland (digestion enzymes)
  • creates amylases, proteases + lipases
  • islets of Langerhans = alpha +beta cells which secrete insulin
• what happens when the blood glucoses concentration increases?

  ingestion of food or drink containing carbohydrates
• what happens when blood glucose concentration decreases?

  following exercise or if you have not eaten
• How is the pancreas involved in the blood glucose concentration?

  • detects changes in the blood glucose levels
  • Islets of Langerhans cells release insulin + glucagon to bring blood glucose to bring blood glucose back to normal
• insulin


  released when blood glucose levels are too high and cause the blood glucose levels to decrease
• glucagon


  released when blood glucose levels are too low and causes a increase in blood glucose levels
• adrenaline 


  released by adrenal glands when body anticipates danger + results in more glucose being released from hydrolysis of glycogen in liver
• Blood glucose levels increase

  • Detected by the beta cells in the islets of Langerhans (pancreas)
  • beta cells release insulin
  • Liver cells become more permeable to glucose + enzyme are activated to convert glucose to glycogen
  • glucose is removed from the blood + stored as glycogen in cells
  • normal blood glucose levels
• Blood glucose levels decrease

  • detected by alpha cells in islets of Langerhans (pancreas)
  • alpha cells release glucagon adrenal gland release adrenaline
  • second messenger model occurs to activate enzymes to hydrolyse glycogen
  • Glycogen is hydrolysed to glucose + more glucose is release back into the blood
  • normal blood glucose levels
• The control of insulin secretion

  • normal blood glucose conc + potassium ion channels in beta cells remain open = -70mV resting potential
  • glucose blood conc increase = glucose enter via glucose transporter
  • glucose used in respiration = ATP binds to potassium ion channels
  • causes them to close no more potassium diffuses out of cell = depolarisation
  • Voltage-gated calcium ion channels open
  • calcium ions enter = secretory vesicles = insulin = exocytosis
• Actions of Insulin

  1. attaches to receptors on surface of target cells = more glucose absorbed (facilitated diffusion)
  2. protein carrier = more glucose is absorbed from blood into cells
  3. activating enzyme involved in conversion of glucose to glycogen = glycogenesis in liver
• Actions of Glucagon

  1. attaching receptors on surface of target cells (liver cells)
  2. glucagon binding = protein to be activated into adenylate cyclase = ATP converted to cAMP
  3. cAMP activate enzyme protein kinase = hydrolysis of glycogen to glucose
  4. activating enzymes convert glycerol + amino acids into glucose
• Second messenger

  1. glucagon binds to glucagon receptors
  2. once bound it changes in shape to the enzyme adenyl cyclase which activates it
  3. activated adenyl cyclase enzymes converts ATP into cyclic AMP (cAMP)

  • cAMP = second messenger

  
• Role of adrenaline

  1. adrenaline attaches to receptors on the surfaces of target cells = (G protein) activated and convert ATP into cAMP
  2. cAMP activates enzyme hydrolyse glycogen into glucose
  3. Second messenger model of adrenaline + glucagon due to cAMP formation = second messenger
• Glycogenesis 


  converting glucose into glycogen this occurs in the liver and is catalysed by enzymes there
• Glycogenolysis 


  hydrolysis of glycogen to glucose this occurs in the liver due to the second messenger model
• Gluconeogenesis 


  creating of glucose from other molecules such as amino acids and glycerol in the liver
• feature of type I diabetes

  • unable to produce insulin
  • starts in childhood could be result of an autoimmune disease where beta cells are attacked
  • treatment injections of insulin
• features of type II diabetes

  • receptors on target cells lose their responsiveness to insulin
  • develops in adults due to obesity + poor diet
  • controlled by regulating carbs + increasing exercise + sometimes insulin injections