Module 5 Hormonal Communication

Question 1

The Endocrine System

Answer 1

• Hormones are chemical messengers produced by endocrine glands and carried in the blood that transmit information and bring about changes. They alter the activity of target organs in non-instant responses.
• Glands are a group of cells that produce and secrete substances. Endocrine glands have a good blood supply as they secrete hormones into the blood plasma for transport to target cells, where they bring about a response, as they are complimentary to receptors.
• Hormones are the first messengers that bind to receptors on the cell surface membrane. A second messenger acts inside the cell and brings about the change.
• Adrenaline is a first messenger hormone that binds to receptors on the cell surface membrane. This activates adenylyl cyclase, the second messenger that converts ATP to cAMP. The protein kinase converts glycogen to glucose phosphate.
• The adrenal glands are located above the kidneys. They are made up of two areas. The outer cortex secretes steroid hormones. Aldosterone controls salt levels and the water balance of blood. Cortisol is the primary stress hormone that promotes the metabolism of glucose, proteins and fats to release energy. The central medulla secretes adrenaline, which is produced in times of stress and excitement, to initiate the fight or flight response.

Question 2

The Pancreas

Answer 2

• The pancreas is an organ found in the abdomen that acts as both an endocrine and exocrine gland. Endocrine glands secrete hormones directly into the blood, while exocrine glands secrete substances via a duct.
• The pancreas acts as an exocrine gland as most cells secrete pancreatic juices containing digestive enzymes to the small intestines.
• Areas of the pancreas called islets of Langerhans are endocrine tissue which secrete the hormones glucagon and insulin into the blood. Alpha cells secrete glucagon and beta cells secrete insulin. Differential staining can be used to visualise the endocrine and exocrine tissue, which are separated by connective tissue.

Question 3

Control of blood glucose concentration

Answer 3

• Blood glucose concentration can be affected by absorption of carbohydrates in the small intestine, the hydrolysis of glycogen and the conversion of non-carbohydrates to glucose.
• Blood glucose concentration is controlled by a negative feedback loop, where alpha and beta cells are the receptors.
• If blood glucose concentration becomes too low, this is detected by alpha cells which secrete glucagon in response. Glucagon binds to receptors on the cell surface membrane of liver cells, causing a confirmational change that activates G proteins. These G proteins activate adenylyl cyclase, which converts ATP to the second messenger cAMP. cAMP binds to protein kinase enzymes, that activate kinase phosphorylase enzymes by adding phosphate groups. These enzymes activate glucose phosphorylase which catalyses the hydrolysis of glycogen to glucose by glycogenolysis. Adrenaline also increases the blood glucose concentration in the same way and promotes the breakdown of glycogen stores in the muscles.
• If blood glucose concentration becomes too high, this is detected by beta cells. Glucose enters the beta cells by facilitated diffusion, and ATP is produced by aerobic respiration. This causes potassium ion channels to close and the membrane potential difference changes. This change causes voltage gated calcium ion channels to open, and calcium ions enter the cell, causing the cell to secrete insulin. Insulin binds to receptors on target cells, causing more glucose transporter proteins to fuse to the cell surface membrane, so the rate of facilitated diffusion increases. This stimulates glycogenesis as glucose is converted to glucose phosphate and glycogen, ensuring a low concentration of glucose in liver cells.
• The liver plays a role in glycogenesis, the synthesis of glycogen, triggered by insulin. Glycogenolysis the conversion of glycogen to glucose triggered by glucagon. Glucogenesis is the synthesis of glucose from non-carbohydrate molecules triggered by glucagon.

Question 4

Diabetes

Answer 4

• Diabetes results in the disrupted insulin function, causing blood glucose concentration to rise. Kidneys are unable to filter this excess glucose and it often appears in the urine. Low water potential of urine can lead to dehydration.
• Type 1 diabetes is caused when the pancreas doesn’t secrete sufficient insulin. This is generally caused by an autoimmune system response where the body immune system attacks beta cells. The lack of insulin effects glycogenesis. It is treated by regular blood tests, insulin injections and diabetes suitable diets.
• Type II diabetes is caused by reduced sensitivity to insulin in liver and fat storage tissues. This causes reduced glucose uptake and a high glucose concentration. It is treated by controlling sugar and fat intake and an exercise regime. It can be caused by genetics, obesity and high blood pressure.
• Diabetes can cause high blood pressure. An increased blood glucose concentration decreases the water potential of the blood, causing more water to enter blood vessels, and increase blood pressure.
• Genetically modified bacteria can be modified to synthesise human insulin. Restriction endonucleases and DNA ligase are used to insert the gene for insulin into bacterial plasmids. The insulin produced is identical to human insulin, reliable, cheap to produce, and has fewer moral objections.
• Stem cells could be used to differentiate into pancreatic beta cells and transplanted into the pancreas to replace damaged beta cells.