Hormonal communication

• a gland is an organ that secretes a chemical
• an endocrine gland secretes a chemical directly into the bloodstream
• an exocrine gland secretes a chemical via a duct onto an epithelial surface
• a hormone is a chemical messenger secreted by an endocrine gland
• two types of hormones are steroid hormones and amine hormones
• steroid hormones are lipid-based, can go into cells (through membrane - lipid soluble)

  e.g. cortisol, progesterone, testosterone, oestrogen
• amine hormones are protein based (made from amino acids)

  e.g. FSH, LH, Melatonin, adrenaline, insulin
• pathway of an endocrine gland:

  stimulus --> gland --> hormone --> blood --> target cell --> response
• steroid hormones can enter cells and the nucleus so have a direct effect on transcription and there gene expression
• non-steroid hormones cause changes in reactions/activity/metabolism in the cell by binding to cell-membrane receptors
• steroid hormones are involved in transcription of mRNA:

  1. steroid hormones pass through the cell membrane of the target cell

  2) the hormone bind with a specific receptor in the cytoplasm

  3) the receptor bound steroid hormone travels into the

  nucleus and binds to another specific receptor on the chromatin

  4) the steroid hormone-receptor complex calls for the production of mRNA molecules which code for the production of proteins
• the adrenal gland is situated above the kidneys
• non-steroid hormones are made in the medulla of the adrenal gland e.g. adrenaline
• steroid hormones are made in the the cortex of the adrenal gland e.g. cortisol
• the pancreas is a small organ lying below the stomach

  has both exocrine and endocrine functions
• the two main secretions of the pancreas are:

  • pancreatic juices containing enzymes which are secreted into the small intestine
  • hormones which are secreted from the islets of Langerhans into the blood
• the exocrine function of the pancreas:

  • secrete digestive enzymes
  • exocrine cells in small groups (acinus) surrounding tiny tubules, acini grouped together into small lobules separated by connective tissue
  • acini secrete enzymes into the tubule, tubules join to form intralobular ducts that combine to forms pancreatic duct - carries enzymes into duodenum (small intestine)
• fluid from the pancreatic duct contains:

  Pancreatic amylase - a carbohydrate which digests amylose to maltose.

  Trypsinogen - an inactive protease, converted to the active form trypsin when it enters the duodenum.

  Lipase - digests lipid molecules.

  Some hydrogen carbonate which makes it alkaline, helping to neutralise the contents of the digestive system.
• the endocrine function of the pancreas:

  • dispersed in small patches among the lobules of acini are the islets of Langerhans
  • the islets of Langerhans contain the alpha cells and beta cells that make up the endocrine tissue in the pancreas
  • the alpha cells secrete glucagon and the beta cells secrete insulin
• bile breaks down fat into smaller fat droplets - easier for lipase to digest
• The Islet of Langerhans makes and releases hormones in the pancreas
• Beta cells make insulin, Alpha cells make glucagon
• Acini( Acinus – singular) are the group of cells that make and secrete enzymes
• enzymes are secreted into ducts
• groups of many acini are arranged into lobules within the pancreas
• the mode of adrenaline cell response (cAMP pathway/ second messenger pathway):

  1. adrenaline is the first messenger which arrives at the hormone receptor on the plasma membrane and binds

  2) this triggers a response inside the cell, the G-protein is activated and binds to the enzyme - Adenylyl cyclase

  3) Adenylyl cyclase catalyses the formation of cAMP from ATP

  4) cAMP then causes the activation of another enzyme via the phosphorylation of protein kinases

  5) this enzyme catalyses a reaction the cell such as breaking down glycogen to glucose
• Diabetes Mellitus is:

  • condition in which the body is no longer able to produce sufficient insulin to control its blood glucose concentration
  • leads to hyperglycaemia (very high glucose) after a meal and hypoglycaemia (very low glucose) after exercise
• type 1 diabetes:

  • typically appears in children approx. 14 years old
  • it is caused by either: an autoimmune response where the body's immune system attacks and destroys beta cells or due to a viral attack
  • blood glucose concentrations are not controlled because the person cant synthesise sufficient insulin and cant store excess glucose as glycogen
• type 2 diabetes:

  • typically appears in over 40's, however recently younger
  • it is caused by the glycoprotein insulin receptor no longer being functional so cells cannot take up glucose. this could be due to age, health and genetics
  • blood glucose concentrations are not controlled because the body doesn't respond to insulin
  • risks are increased due to: obesity, lack of exercise, diet high in sugars, Asian or Afro-Caribbean, family history
• treatments for type 1 diabetes:

  • Insulin injections - blood glucose concentration must be monitored and correct dose of insulin administered to keep concentration fairly stable
  • Insulin pumps - small device constantly pumps insulin at a controlled rate into bloodstream via a needles under skin
  • Islet or pancreas transplantation healthy beta cells from pancreas of donor implanted into patient, or whole pancreas transplanted
  • Stem cells - used to grow new islets of Langerhans to produce new beta cells
• glycolysis is breaking down glucose
• glycogenesis is forming glycogen from glucose
• glycogenolysis is breaking down glycogen into glucose
• gluconeogenesis is forming new glucose from lipids and proteins (amino acids)
• ectotherms are organisms that cant control their body temperature internally - they control their temperature by changing their behaviour. their internal temperature depends on the external temperature
• ectotherms have variable metabolic rates and generate very little heat themselves
• endotherms are organisms that control their body temperature internally by homeostasis, can also control their temperature behaviourally
• endotherms have a constantly high metabolic rate and generate a lot of heat from metabolic reactions
• mechanisms in endotherms to reduce body temprature:

  • Sweating - secreted from sweat glands and evaporates from skin, taking heat from the body, cooling it
  • Hair lies flat - erector pili muscles relax, less air is trapped, so skin is less insulated and heat lost more easily
  • Vasodilation - arterioles near the skin dilate so more blood flows through the capillaries so more heat is lost by radiation
• mechanisms in endotherms to increase body temperature:

  • Shivering - muscles contract in spasms, shivering makes more heat via increased respiration
  • Less sweat - reduces heat loss
  • Hairs stand up - erector pili muscles contract, hairs trap more air, preventing heat loss
  • Vasoconstriction - less blood flows through capillaries, reducing heat loss
  • Hormones - adrenaline and thyroxine released, increase metabolism, producing more heat