Hormones

• Endocrine glands secrete hormones directly into the bloodstream
• Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a receptor-hormone complex
• The receptor-hormone complex promotes the transcription of specific genes
• Peptide hormones bind to receptors in the plasma membrane of the target cell
• Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside the cell
• The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland
• Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis
• The three types of hormones are steroid hormones, peptide hormones and amino acid derivatives
• Thyroxin contains iodine within its chemical structure and cannot be produced if iodine is deficient in the diet
• Individuals with an iodine deficiency will develop an enlarged thyroid gland – a condition known as goitre
• One strategy employed is to add iodine to common dietary products (e.g. iodised table salt)