Hormones • Chemical messenger secreted directly into the bloodstream • Secreted by endocrine cells or neurosecretory cells (specialized neurons) • Hormones are specific – they can only affect the actions of specific target cells. • Regulated by hormones binding to specific receptors
Types of Hormones Classified based on chemical structure: • Steroids hormones - derived from cholesterol • e.g. estrogen, testosterone • Protein (Peptide) hormones – hormones derived from different amino acids. • e.g. insulin, ADH • Tyrosine derivative hormones– derived from the amino acid tyrosin • e.g. Thyroxine
How Steroid Hormones Work • Steroids are lipid soluble and pass directly through the plasma membrane of their target cells. • Hormone binds to a receptor protein in the cytoplasm • Hormone-receptor complex moves into the nucleus and binds to recognition sites along the cell’s DNA • This induces or suppresses the expression of specific genes that code for specific proteins
How Steroid Hormones Work • Steroid hormones can have different effects in different target cells: e.g. – estrogen stimulates uterine lining growth and development of female secondary sex characteristics • How is this possible? • The hormone-receptor complex binds to different regulatory sites on the DNA and controls the expression of different genes.
How Protein Hormones Work • Amino acid hormones are unable to pass through the plasma membrane of their target cells. • Therefore they must work from OUTSIDE the cell. • Amino acid hormones use a signal-transduction pathway to produce a response. • This requires two messengers: • First messenger – hormone – extracellular • Second messenger – chemical signal - intracellular
How Protein Hormones Work • Hormone binds to receptor on plasma membrane of target cell (first messenger) • Hormone-receptor stimulates action of effector to produce a chemical signal inside the cell (second messenger) • The second messenger induces or suppresses enzyme action within the cell, thus producing a response.
Hypothalamus • Located in the Lower part of the brain • Integrates nervous and endocrine systems • Receives signal from neurons and initiates endocrine response. • Neurosecretory cells in hypothalamus produce hormones in response to nerve impulse • Regulates the activity of the pituitary gland
Pituitary Gland • The “master,” gland – controls function of many other endocrine glands Posterior Pituitary Gland: • Stores hormones produced in the hypothalamus – e.g. oxytocin and ADH Anterior Pituitary Gland: • Synthesizes own hormones • Tropic hormones – hormones that target and control other endocrine glands. • Only synthesizes hormones when signaled by releasing hormones from the hypothalamus
Antidiuretic Hormone (ADH) • Structure – it’s a protein hormone • Origin - produced in the hypothalamus by neurosecretory cells • Stored and released from the posterior pituitary gland • Function – increases re-absorption of water into blood stream through collecting duct • Regulation – osmotic changes in blood and osmoregulators in the hypothalamus