Hormonal communication

• What is endocrine communication?


  Specialised glands secrete hormones into the bloodstream.

  Circulatory system carries hormone to target cell/ tissue.

  Lipid-soluble steroid hormones diffuse into cell & bind to complementary receptor in cytoplasm. Peptide hormones bind to complementary receptor on cell-surface membrane.
• Describe the structure of the adrenal glands?

  Located above kidneys.

  
• What hormone does the medulla secrete?

  Adrenaline in response to danger, stress or excitement as part of the fight or flight response.
• Which hormones does the cortex secrete?

  ● Mineralocorticoids e.g. aldosterone, which targets kidney & gut to control concentration of Na+ & K+ ions in blood.

  ● Glucocorticoids e.g. cortisol & corticosterone, which stimulate an increase in blood glucose concentration.
• Describe the histology of the pancreas?

  Pancreas:

  
• Why is it important that blood glucose concentration remains stable?

  ● Maintain constant blood water potential: prevent osmotic lysis/ crenation of cells.

  ● Maintain constant concentration of respiratory substrate: organism maintains constant level of activity regardless of environmental conditions.
• Define negative feedback?


  Self-regulatory mechanisms return internal environment to optimum when there is a fluctuation.

  Different mechanisms are responsible for dealing with an increase/ decrease in normal level for greater control.
• Define glycogenesis, glycogenolysis and gluconeogenesis?

  Glycogenesis: liver converts glucose into the storage polymer glycogen.

  Glycogenolysis: liver hydrolyses glycogen into glucose which can diffuse into blood.

  Gluconeogenesis: liver converts glycerol & amino acids into glucose.
• Outline the role of glucagon when blood glucose concentration decreases?

  1.Alpha cells in Islets of Langerhans in pancreas detect decrease & secrete glucagon into bloodstream.

  2. Glucagon binds to surface receptors on liver cells & activates enzymes for glycogenolysis & gluconeogenesis.

  3. Glucose diffuses from liver into bloodstream.

  4. 𝛼 cells detect that blood glucose concentration has returned to

  optimum & stop producing glucagon. (negative feedback).
• Use the secondary messenger model to explain how glucagon works?

  1.Hormone-receptor complex forms.

  2. Conformational change to receptor activates G-protein.

  3. Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP).

  4. cAMP activates protein kinase A pathway.

  5. Results in glycogenolysis.
• Outline what happens when blood glucose concentration increases?


  1.Beta cells in Islets of Langerhans in pancreas detect

  increase & secrete insulin into bloodstream.

  2. Insulin binds to surface receptors on target cells to:

  increase cellular glucose uptake.

  activate enzymes for glycogenesis (liver & muscles).

  stimulate adipose tissue to synthesise fat.
• Describe how insulin leads to a decrease in blood glucose concentration?

  ● Increases permeability of cells to glucose.

  ● Increases glucose concentration gradient.

  ● Triggers inhibition of enzymes for glycogenolysis.
• How is insulin secretion controlled?

  1.Beta cells have K+ & Ca2+ ion channels to maintain p.d. -70mV.

  2. As glucose concentration increases, glucose enters beta cells via facilitated diffusion.

  3. Respiration of glucose produces ATP. ATP-gated K+ ion channels close, so K+ ions no longer diffuse out of cell.

  4. P.d. in cell becomes more positive = depolarisation. Ca2+ ion channels open. Ca2+ triggers exocytosis of insulin.
• Describe the exocrine function of the pancreas?

  Secretes digestive enzymes e.g. amylase, trypsin & lipase to the duodenum via the pancreatic tract.
• Explain the causes of Type 1 diabetes mellitus and how it can be controlled?

  Body cannot produce insulin e.g. due to autoimmune response which attacks beta cells of Islets of Langerhans.

  Treat by injecting insulin from animal source or genetically modified bacteria. Possible future treatment: use stem cells to produce new beta cells.
• Explain the causes of Type 2 diabetes mellitus and how it can be controlled?

  ● Glycoprotein receptors are damaged or become less responsive to insulin.

  ● Strong positive correlation with poor diet / obesity.

  ● Treat by controlling diet and exercise regime.