The Hormonal System and Glands

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  • The Hormonal System
    • What is the hormonal system?
      • Sends information as chemical signals.
        • Made up on endocrine glands and hormones.
          • Endocrine glands are groups of cells that are specialised to secrete hormones e.g. the pancreas secretes insulin.
          • Hormones are chemical messengers. Many are proteins or peptides e.g. insulin. or some are steroids e.g. progesterone.
          • Hormones are secreted when an endocrine gland is stimulated.
            • Glands can be by stimulated by a change in concentration of a specific substance or electrical impulses.
      • Hormonal Communication
        • Hormones diffuse directly into the blood, then they're taken around the body by the circulatory system.
          • They diffuse out of the blood all over the body but each hormone will only bind to specific receptors found on cell membranes- target cells.
            • Tissues that contain target cells are called target tissue.
              • The hormones trigger a response in the target cell (effectors)
    • Glands
      • There are 2 types of gland: endocrine and exocrine.
        • Endocrine glands secrete hormones directly into the blood.
        • Exocrine glands are groups of cells specialised to secrete chemicals through ducts into cavities or onto the surface of the body.
          • They usually secrete enzymes. Some organs have exocrine tissue and endocrine tissue so act as both types of gland. e.g. pancreas.
    • Action of Hormones
      • A hormone is called a first messenger because it carries the chemical message the first part of the way, from the endocrine gland to the receptor on the target cell.
        • When a hormone binds to its receptor it activates an enzyme in the cell membrane.
          • The enzyme catalyses the production of a molecule inside the cell called a signalling molecule.
            • The signalling molecule is called a second messenger because it carries the chemical message the second part of the way. from the receptor to other parts of the cell.
              • Secondary messengers activate a cascade inside the cell.
      • Adrenaline
        • Adrenaline is a hormone secreted from your adrenal glands.
          • Its secreted when there's a low concentration of glucose in your blood, when you're stressed or exercising.
            • Adrenaline gets the body ready for action by making more glucose available for muscles to respire. e.g. by activating glycogenolysis (breakdown of glycogen to glucose.
              • It is a first messenger. It binds to specific receptors in the cell membranes of many cells.
                • When adrenaline binds it activates an enzyme in the membrane called adenylate cyclase.
                  • Activated adenylate cyclase catalyses the production of a second messenger called cyclic AMP.
                    • cAMP activates a cascade.
    • Adrenal Glands
      • The adrenal glands are endocrine glands that are found just above your kidneys.
        • Each adrenal gland has an outer part called the cortex and an inner part called the medulla.
          • The cortex secretes steroid hormones. e.g. it secretes glucocorticoids such as cortisol when stressed.
          • The medulla secretes catecholamine hormones. e.g. it secretes adrenaline when stressed.
    • The Pancreas
      • The pancreas is an endocrine and exocrine gland that's found below the stomach.
        • The areas of endocrine tissue are called the islets of Langerhans.
          • They're found in clusters around blood capillaries and they secrete hormones directly into the blood.
            • They're made up of two types of cells: alpha cells and beta cells. Alpha secrete glucagon. Beta secrete insulin. They both help to control blood glucose concentration.
        • Most of the pancreas is exocrine tissue. The exocrine cells are called acinar cells.
          • They're found in clusters around the pancreatic duct- a duct that goes to the duodenum.
            • The acinar cells secrete digestive enzymes into the pancreatic duct. The enzymes digest food in the duodenum.


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