Introduction to Hormones

What are hormones?

Endocrine glands secrete chemicals, or hormones directly into the blood, where they travel to specific target cells where they are required.

How do hormones get into their target cells?

  • Protein based hormones, otherwise known as peptide hormones (for example insulin, glucagon and oxytocin) bind with specific receptors in the plasma membrane of their target cells. Peptide hormones tend to act more quickly than lipid-soluble hormones.
  • Steriods are lipid-soluble hormones, these can pass straight through the plasma membrane.

Exocrine glands secrete substances into a duct, making them different to endocrine glands.

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  • Secreted by the adrenal medulla in the adrenal glands.
  • Is a first messenger (a molecule that bids to a receptor in the plasma membrane and causes changes to happen in the cell).

How does adrenaline work?-

1. Adrenaline is released into the blood by the adrenal medulla.

2. Adrenaline binds with receptors on its target cells, for example liver cells.

3. The G-protein is activated, and moves to the enzyme adenyl cyclase, which in turn is activated and produces cAMP (a second messenger) from ATP.

4. cAMP activates protein kinase, which prompts a series of reactions to produce glucose from glycogen (glycogenolysis).

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Insulin and Glucagon

The Pancreas-

  • The areas of endocrine tissue are the Islets of Langerhans, which contain alpha and beta cells. 
  • The areas of exocrine tissue produce digestive juices which are secreted into the pancreatic duct.

Alpha Cells-

  • Secrete glucagon.
  • Glucagon is secreted when blood sugar levels are low. This makes liver cells break down glycogen into glucose (glycogenolysis) and convert amino acids and fatty acids into glucose (gluconeogenesis).

Beta Cells-

  • Secrete insulin.
  • Insulin is secreted when blood sugar levels are high. This makes liver cells and muscle cells take up more glucose from the blood, and makes the liver convert glucose to glycogen (glycogenesis).
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Type One Diabetes-

  • Can occur at any age.
  • Happens whent the immune system attacks the Beta cells so that they no longer produce insulin.
  • Treated with insulin and careful planning of diet. 

Type Two Diabetes-

  • Usually occurs later in life.
  • Happens when insulin receptors don't properly respond to insulin.
  • Does not require treatment with insulin.

Genetically modified bacteria are currently used to produce insulin, but in the future this could be replaced by stem cells.

The heart rate is controlled by both the nervous and endocrine systems, Adrenaline increases the heartrate. 

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