Hormonal communication

• endocrine system is a communication system that uses hormones as signalling molecules
• hormone = chemical messenger
• hormones are secreted into the bloodstream by endocrine glands, which travel to target cells where they bind to receptors on their surface or inside the cell.
• the binding of a hormone to its receptor triggers a response within the target cell.
• protein/peptide hormones e.g: adrenaline, insulin and glucagon are not soluble in cell membrane so cant enter cell. They bind to receptors on cell surface membrane to release second messenger inside
• steroid hormones e.g: oestrogen, testosterone and cortisol are soluble so pass through cell bilayer. They enter nucleus effecting DNA directly.
• non steroid hormones bind to complementary receptors on target cells plasma membrane
• Adrenal glands divided into outer adrenal cortex and inner adrenal medulla
• Both outer adrenal cortex and inner adrenal medulla well supplied with blood and produce hormones directly into blood vessels
• Adrenal cortex - zona glomerulosa secretes mineralcorticoid, aldosterone

  aldosterone increases Na+/ water retention and decreases K+ absorption in collecting duct in kidney
• Adrenal cortex - zona fasciculata secretes the glucocorticoid, cortisol

  .Cortisol stimulates Glycogenolysis and controls metabolism
• Adrenal cortex - zona reticularis secretes androgens to make sex hormones

  .androgens regulate gamete production and development of sexual characteristics
• Adrenal medulla secretes adrenaline and noradrenaline

  .Adrenaline prepares body for fight/flight responses: increased HR and BP, pupil dilation and Glycogenolysis
• How insulin is released from Beta cells:

  1> Na+ and K+ channels are open in cell membrane

  2> blood glucose conc. is high so glucose moves in cell

  3> glucose metabolised to ATP which closes K+ channels

  4> accumulation of K+ alters potential difference across membrane as inside becomes less negative

  5> change in potential difference opens Ca2+ channels

  6> Ca2+ cause vesicles of insulin to fuse with cell membrane, releasing insulin by exocytosis
• Hypoglycaemia is when blood glucose concentration remains too low for a long time period
• Hyperglycaemia is when blood glucose concentration remains too high for a long time period
• How is a low blood glucose concentration reversed by coordination of first messenger hormone?

  1> High blood glucose concentration detected by Alpha cells which secrete glucagon which binds to specific membrane-bound receptor on target cells (hepatocytes)

  2> this stimulates G protein inside membrane

  3> this activates adenyl cyclase inside cell

  4> ATP is converted to cAMP

  5> which activates chain of enzyme controlled reactions in cell
• What are the effects of glycogen in the body?

  Glycogenolysis and Gluconeogenesis occurs and more fatty acids are used in respiration
• How is a high blood glucose concentration reversed by the coordination of a first messenger hormone?

  1> Low blood glucose concentration is detected by Beta cells which secrete insulin which binds to specific membrane - bound receptor on target cells

  2> this activates enzyme tyrosine kinase

  3> kinase activates receptor on inside of membrane and causes phosphorylation of inactivate enzymes in cell

  4> which activates a chain of enzyme controlled reactions in cell
• What are the effects of insulin in the body?

  >Glycogenesis takes place.

  >More vesicles containing 'glucose transporter proteins' fuse with membrane.

  >More glucose enters cells, turned to fats and used in respiration.
• What is the difference between Type 1 and 2 diabetes mellitus?

  >Type 1 starts in childhood as a result of an autoimmune disease which destroys Beta cells.

  > Type 2 is a result of specific surface receptors on hepatocytes becoming less responsive to insulin due to age, lack of exercise, high sugar diet, obesity.
• What are the treatments for Type 1 diabetes mellitus?

  > Insulin injections

  > Pancreas or islet cell transplant

  > Insulin pump therapy (pumps insulin into pancreas at controlled rate)
• What are the treatments for Type 2 diabetes mellitus?

  > Changes in life style

  lose weight, exercise regularly, monitor diet

  > Use drugs that boost amount of insulin released from pancreas
• What is diabetes mellitus?

  Chronic disorder where blood glucose concentration cannot be controlled effectively due to insufficient insulin release.
• What are some potential treatments for diabetes mellitus?

  > Stem cells: can be used to grow new islets of Langerhans in pancreas as they are undifferentiated cells

  sourced from bone marrow and embryonic cells

  > using insulin from genetically modified bacteria:

  E.coli bacteria modified to manufacture human insulin
• What are the advantages of using insulin from genetically modified bacteria?

  > it is an exact copy of human insulin so less chance of rejection from immune system

  > lower risk of infection

  > cheaper to manufacture from than animals

  > people less likely to have ethical objections
• What is an exocrine gland?

  Glands that secrete hormones via a duct
• What is an endocrine gland?

  A gland that secretes hormones directly into bloodstream i.e: islet of langerhans
• Histology of the Pancreas:

  exocrine tissue-

  >acini grouped in small lobules separated by connective tissue surround tubules

  >acini secrete enzymes into tubule

  >tubules join forming intralobular ducts, which join to make pancreatic duct

  >duct carries fluid containing enzymes into small intestines

  
• What are the endocrine glands in the body?

  Pituitary gland

  Thyroid gland

  Thymus

  Adrenal gland

  Pancreas

  Ovaries

  Testis

  
• How do Non-steroid hormones activate second messenger?

  1> Non steroid hormone binds to receptor on target cell

  2> This activates a G protein, which then activates effector molecule adenyl cyclase

  3> enzyme converts ATP into cyclic AMP (cAMP)

  4> cAMP acts on protein ion channel or initiates chain of enzyme controlled reactions in cell
• Why do Non-steroid hormones need to activate a 2nd messenger inside target cell?

  Non-steroid hormones are not soluble as they are made from proteins so cannot diffuse through phospholipid bilayer unlike steroid hormones which are lipid - soluble and can diffuse through cell by binding to receptors in cytoplasm.
• How do Steroid hormones stimulate protein synthesis (transcription) inside target cells?

  1> Steroid hormones pass through cell membrane of target cell

  2> this binds to specific complementary receptor in cytoplasm

  3> 'receptor steroid complex' enters nucleus of target cell

  4> binds to specific receptor on chromosomal material

  5> binding stimulates mRNA production, coding proteins
• What happens in Glycogenolysis?

  Glycogen-ol-yisis (hydrolysis)

  glycogen is broken down to glucose
• What happens in Gluconeogenesis?

  New-glucose-genesis(made)

  Glucose is made from non-carbohydrate sources e.g: fats
• What happens in Glycogenesis?

  Glyco-genesis(to make)

  Glucose is turned into Glycogen
• What type of diabetes mellitus would be most likely be improved by stem cell therapy?

  Type 1 as it is a result of a shortage in beta cells in the pancreas
• What is a signalling molecule?

  Hormone/Protein/enzyme that carries information between cells
• The endocrine tissue, Islets of Langerhans, contain Alpha and Beta cells. Alpha cells secrete glucagon.

  Beta cells secrete insulin.

  A) Islet of langerhans

  B) Alpha cells

  C) Beta cells

  D) Blood vessel

  E) Pancreatic acini