Hormonal Communication

• What is the endocrine system?


  The endocrine system uses hormones to send information about changes in the environment around the body to bring about a designated response. It consists of endocrine glands that secrete hormones directly into the bloodstream.

  
• Give examples of endocrine glands


  Pancreas

  Adrenal glands

  Pituitary gland
• What is the role of hormones?


  Hormones act as chemical messengers. They bind to specific receptors on target cells

  
• What are target cells?


  Target cells are cells that have specific receptors for a hormone.

  
• Describe how hormones can act as chemical messengers


  1) Hormones are produced by endocrine gland cells.

  2) When stimulated, glands release hormones into the bloodstream.

  3) The blood carries hormones to their target cells.

  4) They attach to receptors on or inside the target cells.

  6) The cells then respond to the hormones.
• What are the two types of hormones?


  Steroid hormones

  Non-steroid hormones

  
• Steroid hormones


  Steroid hormones are lipid-soluble and can diffuse across the phospholipid bilayer.

  Steroid hormones bind to receptors molecules in the cytoplasm or the nucleus, forming a hormone-receptor complex that acts as a transcription factor

  Examples of a steroid hormones include oestrogen and cortisol
• Non-steroid hormones


  Non-steroid hormones are hydrophilic and cannot diffuse across the phospholipid bilayer.

  Non-steroid hormones bind to receptors on the cell-surface membrane of their target cells to activate second messengers: cyclic AMP (cAMP). This triggers a cascade of reactions

  Examples of non-steroid hormones include adrenaline, insulin, glucagon

  
• Comparison of hormonal and neuronal communication

  
• What are adrenal glands?


  A pair of small, endocrine glands that sit above each kidney

  
• What are two main regions of adrenal glands (surrounded by a capsule)?


  -> Adrenal cortex: Outer region of the gland - it is responsible for producing vital steroid hormones (such as cortisol)

  -> Adrenal medulla: Inner region of the gland - produces non-essential hormones such as adrenaline (which responds to stress)
• What hormones are produced by the adrenal cortex?


  Glucocorticoids

  Mineralocorticoids

  Androgens

  
• Glucocorticoids


  Glucocorticoids regulate metabolism by controlling the conversion of fats, proteins, and carbohydrates to energy.

  -> They also control blood pressure and stress responses

  -> Regulate immune response and suppress inflammation

  Example: Cortisol
• Mineralocorticoids


  Maintain blood pressure by balancing salt and water in the blood and body fluids.

  Example: Aldosterone
• Androgens


  Regulation of sexual characteristics and cell growth.

  Example: Testosterone
• What are the hormones produced by the adrenal medulla?


  Adrenaline

  Noradrenaline

  These are released when the sympathetic nervous system is stimulated

  
• Adrenaline


  -> Increases heart rate and blood pressure to increase blood flow to the muscles and brain.

  -> Increases blood glucose levels.

  -> Increases breathing rate.
• Noradrenaline


  -> Increases heart rate.

  -> Expands air passages.

  -> Dilates pupils.

  -> Narrows blood vessels in organs like the gut to reduce blood flow to regions that aren't helpful in the stress response.
• What is an example of the second messenger model?


  The action of adrenaline in the fight or flight response
• What are the two functions of the pancreas


  Exocrine function -> Produce enzymes and release them via a duct into the duodenum

  Endocrine function -> Produce hormones and release them into the blood

  
• What is the role of the pancreas as an exocrine gland?


  -> The pancreas predominately consists of exocrine tissue (made up of pancreatic acini)

  -> The acini contain cells that produce digestive enzymes such as amylase, protease, lipase, alkaline pancreatic juice

  -> These substances travel through the pancreatic duct and are released into the duodenum

  
• Why is the exocrine secretion alkaline?


  Pancreatic fluid contains sodium hydrogencarbonate (which is alkaline). This helps to neutralise the contents of the digestive system (which are acidic)
• What is the role of the pancreas as an endocrine gland?


  The pancreas uses special cell clusters called islets of Langerhans to secrete different hormones into blood vessels directly.
• What are the two types of cells in the islets of Langerhans?


  Beta (β) cells - They secrete the hormone insulin

  Alpha (α) cells - They secrete the hormone glucagon

  Insulin and glucagon are crucial in controlling blood glucose concentration

  
• What are the differences in structure between alpha and beta cells?


  Alpha cells are larger and more numerous than beta cells
• Stained section of pancreas (1)

  
• Stained section of pancreas (2)

  
• What are the roles of alpha and beta cells?


  Receptors

  Effectors

  
• What is the normal blood glucose concentration?


  90 mg 100cm^-3
• How does blood glucose concentration increase?


  After ingestion of food/drink containing carbohydrates

  
• How does blood glucose concentration decrease?


  Following exercise or if you have not eaten

  
• What happens to cells if blood glucose levels drop below 90 mg 100cm^-3?


  -> Cells may run short of glucose for respiration, and be unable to carry out normal activities
• What happens if blood glucose concentrations are too high?


  -> Changes the osmotic balance of cells and upsets their normal behaviour
• What blood glucose sugar detected by?


  Alpha and beta cells in the islet of Langerhans in the pancreas
• What is insulin?


  A globular protein made up of 51 amino acids -> Contains disulfide bonds
• What is glycogenesis?


  The synthesis of glycogen from glucose molecules.

  Insulin triggers this process after it detects an increased blood glucose concentration

  -> The synthesis of glycogen removes glucose molecules from the bloodstream and decreases the blood glucose concentration to within a normal range

  -> Glycogen acts as a compact and efficient carbohydrate storage molecule

  
• What is glycogenolysis?


  The breakdown of glycogen to produce glucose molecules.

  Glucagon triggers this process after it detects a decreased blood glucose concentration

  -> It activates enzymes within the liver that breakdown glycogen molecules into glucose

  -> The breakdown of glycogen releases more glucose molecules to the bloodstream and increases the blood glucose concentration to within the normal range

  
• What is gluconeogenesis?


  The synthesis of glucose molecules from non-carbohydrate molecules.

  Glucagon also triggers this by activating enzymes within the liver

  -> These enzymes convert other molecules, such as fatty acids and amino acids, into glucose molecules

  -> Glucose molecules are released into the bloodstream which increases the blood glucose concentration to within the normal range

  
• Give examples of target cells


  -> Hepatocytes (liver cells)

  -> Muscle cells

  -> Adipose (fat) cells

  
• What happens when blood glucose concentration is too high?


  High blood glucose (hyperglycemia) is detected by beta cells in the islet of Langerhans

  -> Beta cells secrete insulin into the blood

  -> Insulin reaches target cells (e.g., muscle cells, liver cells, adipose cells)

  -> Insulin binds to complementary receptors on plasma membranes, and second messenger (cAMP) brings about the response

  -> The liver cells become more permeable to glucose by causing protein channels in the membrane to open (more glucose enters the cell), and enzymes are activated to convert glucose to glycogen (glycogenesis)

  -> Glucose is converted to fats

  -> More glucose is used in respiration