Hormonal communication

• endocrine system

  made up of endocrine glands that secret hormones which are transported in the blood

  examples: thyroid and adrenal glands
• hormones

  chemical messenger

  widespread and have a longer lasting effect than nervous impulses
• steroid hormones

  lipid-soluble

  diffuse across the plasma membrane into the target cells

  bind to receptors located within the cytoplasm
• protein hormones

  polar and insoluble in lipids

  cannot diffuse across the membrane

  so they bind to complimentary receptors on the plasma membrane of the target cell

  this causes a secondary messenger to be activated which brings about the target response within the cell
• adrenal glands

  endocrine glands

  located atop of the kidneys

  three layers: adrenal cortex, adrenal medulla, and the capsule which surrounds them
• adrenal cortex

  controlled by hormones secreted by the pituitary gland

  it secrets three types of hormones: glucocorticoids, mineralocorticoids and androgens
• adrenal medulla

  controlled by the activation of the sympathetic nervous system

  releases adrenaline and noradrenaline
• adrenaline

  increases heart rate

  raises blood glucose concentration
• noradrenaline

  dilation of pupils

  widens the airway into the lungs

  narrows blood vessels to non-essential organs to create a higher blood pressure
• pancreas

  located behind the stomach

  can act as both an endocrine gland (control of blood glucose) and exocrine (release of digestive enzymes)
• structure of the pancreas

  mostly made up of exocrine tissue which contains acinar cells which secret digestive enzymes and pancreatic juices

  there are regions of endocrine glands called the islet of langerhans which are made up of alpha and beta cells

  pancreatic islet cells secret hormones

  alpha cells secret glucagon

  beta cells secret insulin
• blood glucose control - increasing blood glucoselevels

  after exercise blood glucose decreases

  this change is detected by the alpha cells in the islet of langerhans

  these cells then release glucagon as the adrenal glands secret adrenaline

  this causes secondary messengers to be released to active the enzymes responsible for hydrolysing glycogen into glucose

  this increases blood glucose levels
• blood glucose control - lowering blood glucose levels

  after eating carbohydrates blood glucose concentration increases

  detected by the beta cells in the islet of langerhans inside the pancreas these cells release insulin causing the liver to become more permeable to glucose as glucose is then converted into glycogen to be stored this decreases blood glucose
• control of insulin secretion

  at normal blood glucose concentration the K+ channels within the plasma membrane of the beta cells remains open to maintain the -70 mV

  when blood glucose levels increase, glucose enters the cell via a glucose transporter

  this is used in respiration to form ATP which then binds to the K+ channels causing them to close resulting in depolarisation

  this causes voltage-gated Ca2+ channels to open causing vesicles containing insulin to fuse with the plasma membrane and released by exocytosis
• action of insulin

  1. attach to receptors on the surfaces of target cells changing their tertiary structure resulting in more glucose being absorbed by facilitated diffusion
  2. more protein carriers are present in the plasma membrane to ensure more glucose is absorbed from the blood
  3. activation of enzymes to convert glucose into glycogen via glycogenesis in the liver
• insulin as a primary messenger

  binds to insulin receptors

  this binding causes intracellular chemicals to be released which stimulates vesicles containing glucose channel proteins to fuse with the plasma membrane

  causing more facilitated diffusion of glucose
• action of glucagon

  1. attaches to receptors of liver cells
  2. causes adenyl cyclase to convert ATP into cAMP which activates a secondary protein kinase which hydrolyses glycogen into glucose known as glycogenolysis
  3. actives enzymes which convert amino acids and glycerol into glucose known as gluconeogenesis
• role of adrenaline

  1. attaches to receptors on the surface of target cells which activates g-proteins causing the conversion of ATP into cAMP
  2. cAMP acts as a secondary messenger to activate the enzymes that hydrolyze glycogen into glucose
• glycogenesis

  conversion of glucose into glycogen
• gluconeogenesis

  formation of glucose from amino acids and glycerol
• glycogenolysis

  hydrolysis of glycogen into glucose
• type 1 diabetes

  where the beta cells are unable to produce insulin

  autoimmune disease

  treatment involves insulin injections

  islet cell or pancreas transplant -> immunosuppressant dugs
• type 2 diabetes

  receptors on target cells loose their responsiveness to insulin

  permanently raised glucose levels

  treated with a change in life style and dieting
• hypoglycemia symptoms

  tiredness and irritability
• hyperglycemia

  weight loss and increased full bladder
• glucocorticoids

  cortisol -> regulates stress and blood glucose levels
• mineralocorticoids

  regulate the immune system
• androgens

  oestrogen and testosterone