5.1.4 Hormonal Communication

• Protein Hormones

  • not soluble in the phospholipid membrane
  • do not enter the cell
  • bind to receptor on target cell and initiate changes in the cell
  • first messengers which trigger the release of second messangers
• How do non-steroid hormones work

  1. Act via a G protein
  2. activates effector molecule - enzyme that converts inactive molecules into secondary messangers
  3. adenyl cyclase - converts ATP --> cAMP
  4. cAMP - acts directly on another protein or initiates a cascade of enzyme-controlled reactions
• Steroid Hormones

  Can pass through the membrane and have a direct effect on DNA molecules
• How do steroid hormones work

  1. pass through the cell membrane of target cells
  2. bind to a receptor, that's complementary to the hormone, in the cytoplasm
  3. receptor-steroid hormone complex enters the nucleus
  4. binds to receptor on the chromosomal material
  5. stimulates production of mRNA - codes for proteins
• Adrenal Medulla

  1. inner layers
  2. secretes adrenaline
• Adrenaline

  1. polar molecule made of tyrosine so cannot enter the cell
  2. detected by receptors on the membrane
  3. many cells and tissues have these receptors so adrenaline has a widespread effect

  • increase in stroke volume, heart rate and mental awareness.
  • Vasoconstriction
  • glycogen --> glucose
  • dilate the pupils
• Adrenal Cortex

  1. Aldosterone - (mineralcorticoids) controls the concentration of Na+ and K+
  2. Cortisol - (glucocorticoids) controls the metabolism of carbohydrates, fats and proteins. in response to stress
• Structure of pancreas

  1. exocrine cells are in small groups - acinus
  2. grouped to form lobules which are seperated by connective tissues
  3. secrete enzymes into tubules which join to form interlobular duct and then pancreatic duct which leads to the duodenum
• Islets of Langerhans

  1. alpha cells - secrete glucagon
  2. Beta cells - secrete insulin
• Regulating blood glucose - too high

  1. Hyperglycaemia
  2. beta cells secrete insulin
  3. can't pass through the membranes of the target cells so binds to receptors which activate tyrosine kinase
  4. causes the phosphorylation of inactive enzyme - more transporter proteins in the membrane caused by vesicles binding

  • glucose enters the cell
  • glycogenesis
  • glucose used in respiration
• Glycogenesis

  Glucose is converted to glycogen. When glucose levels are too high
• How is insulin released

  Cell membranes contain K+ and Ca2+ channels, with K+ flowing out, inside of the cell is negative

  1. glucose levels increase and then glucoses enters the cell
  2. metabolised and converted into ATP
  3. this closes the K+ channel - K+ accumulates and inside becomes more positive. The change in potential difference opens the Ca2+ channel
  4. this causes a vesicle containing insulin to fuse with the membrane. insulin secreted via exocytosis
• Regulating blood glucose - too low

  1. hypoglycaemia
  2. detected by alpha cells and glucagon secretes
  3. binds to receptors on the hepatocytes and stimulates a G protein which activates adenyl cyclase
  4. ATP --> cAMP

  • Glycogenolysis
  • gluconeogensis
  • fatty acids used in respiration
• Glycogenolysis

  glycogen is converted to glucose. when glucose concentration is too low
• Glyconeogenesis

  glycerol and amino acids converted into glucose. when glucose levels are too low
• Causes of Type 1 diabetes and how it can be controlled

  • body can't produce sufficient insulin, from childhood, autoimmune disease where Beta cells are attacked
  • treatment - injecting insulin, genetically modified bacteria, pancreas transplant, islet cell transplant, stem cells
• Causes of Type 2 diabetes and how it can be controlled

  1. Response to insulin decreases as receptors on liver and muscle cells become less responsive
  2. may be caused by obesity, lack of exercise and high sugar diet
  3. control diet and exercise regularly