endocrine communication

• The endocrine system is another system, in addition to the nervous system that is used for communication around the body. It uses the blood circulatory system to transport its signals, these signals are molecules called hormones.
• what are the two types of hormones?

  Protein, peptide hormones and derivative of amino acids

  Steroid hormones
• what are example of protein / peptide hormones?


  Insulin, adrenaline and glucagon
• What are examples of steroid hormones?


  Testosterone, estrogen, progesterone, cortisol, aldosterone.
• protein hormones are not soluble in the phospholipid membrane and do not enter the cell, protein hormones need to bind to the cell surface membrane and release a second messenger inside the cell
• Steroid hormones can pass through the membrane and enter the cell and nucleus, they have a direct effect on the DNA in the nucleus
• hormones are released directly into the blood from endocrine glands, these glands are ductless- they consist of groups of cells that manufacture and release hormones directly into the blood in capillaries which run through the gland.
• what are the major endocrine glands in the human body?

  Pituitary, thyroid, thymus, pancreas, ovaries in females and testes in males
• hormones always have a specific function, they are transported all over the body- they have an effect in one type of tissue only. The cells which receive an endocrine system are called target cells. They can be grouped together, or widely dispersed. For non steroid hormones, the target cells must possess a specific receptor on the plasma membrane that is complementary in shape to the shape of the hormone.
• Nonsteroid hormones are called first messengers. They are signaling molecules outside of the cell that bind to the cell surface membrane and initiate an effect inside of the cell. They usually cause the release of another signaling molecule in the cell called the second messenger which will stimulate a change in the activity of the cell.
• Many non steroid hormones act via a G protein in the membrane, this protein is activated when the hormone binds to the receptor. The G protein will activate an effector molecule, usually an enzyme that converts an inactive molecule into the active second messenger. In many cells the effector molecule is the enzyme called Adenyl cyclase, this converts ATP into cyclic AMP (cAMP) as another protein (like an ion channel) or it may initiate a cascade of enzyme controlled reactions.