5.1.4 - Hormonal Communication

• How does the endocrine system work?

  Glands secrete hormones when stimulated by neurons or a change in concentration of a chemical substance. These hormones travel in the blood stream to target organs.
• What do target cells possess?

  Complementary receptors on their cell surface membranes, allowing it to respond to the hormone and triggering a response in the cell.
• List four properties of the endocrine system.

  Slower, longer-lasting, widespread response and involves use of chemicals rather than electrical impulses.
• Why are second messengers used?

  Hormones can't get inside target cells to exert their effects directly, so second messengers activate reactions inside cells.
• Where are the adrenal glands located, and what is it made up of?

  They sit on top of the kidneys, and are made up of the medulla and the cortex.
• What does the medulla secrete?

  Adrenaline and noradrenaline
• When are catecholamines (adrenaline + noradrenaline) secreted?

  In times of stress
• How do catecholamines increase energy levels?

  By increasing heart rate, increasing breathing rate, glycogenolysis, vasoconstriction of blood vessels to organs
• What is glycogenolysis?

  Converting glycogen into glucose
• How does vasoconstriction increase energy levels?

  It diverts blood flow to the brain and muscles
• What does the cortex secrete?

  Steroid hormones which are also released in times of stress
• List three effects of steroid hormones

  Suppression of the immune system, increasing blood pressure by stimulating the kidneys to take up more sodium ions and Water, gluconeogenesis.
• What is gluconeogenesis and how does it aid times of stress?

  It converts proteins and fats into glucose, and it increases the amount of glucose available for respiration.
• What is the endocrine part of the pancreas called?

  The islets of Langerhans, clusters of cells that are surrounded by capillaries.
• What are the islets of Langerhans made up of?

  Alpha and beta cells
• What do alpha cells do?

  Secrete glucagon directly into the bloodstream
• What do beta cells do?

  Release insulin into the blood.
• Recal what happens when blood glucose is too high:

  Cells in the pancreas detect high blood glucose and stimulate beta cells in the islets of Langerhans to secrete insulin. Insulin travels in the bloodstream to liver and muscle cells, where it binds to insulin receptors on their cell surface membrane. Insulin increases the permeability of the membrane to glucose, so more glucose is moved from the bloodstream into cells. When insulin binds to its receptor, vesicles containing glucose transporters move and fuse with the plasma membrane.It also stimulates glycogenesis and an increase in the rate of respiration, which helps to lower blood glucose.
• Recall what happens when blood glucose is too low:

  Cells in the pancreas detect low blood glucose and stimulate alpha cells in the islets of Langerhans to secrete glucagon. Glucagon travels in the bloodstream to liver cells, where it binds to glucagon receptors on their cell surface membrane. Glucagon stimulates the breakdown of glycogen into glucose (glycogenolysis) and a decrease in the rate of respiration, which helps to increase blood glucose. It also triggers the production of glucose from non-carbohydrates, such as lipids and amino acids, in a process called gluconeogenesis.
• When do beta cells release insulin?

  In response to membrane depolarisation
• Recall the depolarisation of beta cells

  High blood glucose causes increases glucose uptake into cells by facilitated diffusion. Respiration rates increase, causing a rise in ATP. Increased ATP causes potassium ion channels in the membrane to close. Potassium ions are blocked from leaving the cell, so intracellular potassium ion levels rise. The inside of the beta cell becomes less negative compared to the outside – the membrane is depolarised. This triggers voltage-gated calcium ion channels to open and calcium ions move into the beta cell. This stimulates the fusion of insulin-containing vesicles with the plasma membrane. Insulin is released by exocytosis.
• What is diabetes?

  A condition resulting from the inability to control blood glucose levels.
• What occurs in type 1 diabetes?

  The immune system destroys the beta cells of the islets of Langerhans so they can no longer produce insulin
• How can type 1 diabetes be treated?

  With insulin injections or an insulin pump
• What happens in type 2 diabetes?

  Body cells stop responding properly to insulin, as their insulin receptors stop working and cells stop absorbing glucose, leading to elevated blood glucose levels.
• How can type 2 diabetes be managed?

  Through a managed diet and regular exercise. In more severe cases, glucose-lowering drugs or insulin injections
• What are genetically modified organisms?

  organisms which have had their DNA changed, so they synthesise proteins that can be used as drugs
• What are restriction enzymes used for?

  To cut DNA at specific sites to extract a gene of interest, then cut plasmid DNA to create complementary sticky ends.
• What does DNA ligase do?

  Join the two pieces of DNA together, meaning that the gene of interest is contained within a plasmid, kown as recombinant DNA
• What happens to this recombinant DNA?

  It is either placed in a virus, infecting organisms with the recombinant DNA, or the plasmid will be taken up by bacteria.
• Recall the process used for the production of insulin.

  The insulin gene is removed from human DNA using restriction enzymes. A plasmid is also cut with restriction enzymes. DNA ligase joins the complementary sticky ends to form the recombinant DNA. The recombinant plasmid is taken up by bacteria. The transgenic bacteria are grown in large fermenters to produce large amounts of insulin, which can then be extracted.
• How can stem cells be used to cure diabetes?

  Using transcription factors to convert stem cells into pancreatic beta cells, whichh would be implanted into the pancreas to allow a person to synthesise insulin.