Endocrine system

• What is a hormone?

  Chemical messenger
• Cells which are affected by a specific hormone have receptors for that specific cell either on the cell surface or inside the cell. Each receptor is only stimulated by that particular hormone and no other hormone. Individual cells will have receptors for more than one hormone
• Steroid hormones are based on cholesterol which is a type of lipid. They are secreted by steroid glands including the adrenal cortex, the testes and the ovary as well as the placenta during pregnancy.
• Protein hormones are made of amino acids which can be arranged as peptides or proteins. Examples of protein hormones include: insulin, gastrin, follicle stimulating hormone and growth hormone.
• Steroid hormones are lipid-based and can get through the cell membrane. Target cells for steroid hormones have receptors within the cytoplasm. The steroid hormone will pass through the cell membrane and stimulate the specific receptor.