Hormones * A hormone is a chemical secreted by an endocrine gland, which brings about a response in an organ elsewhere in the body (target tissue) * A target tissue is a group of cells that contain receptors for a particular hormone and therefore affected by it. * A gland is a group of cells which produce and release one or more useful substances and we call that secretion. * An exocrine gland secretes something into a duct, carries the substance to a particular part of the body e.g. salivary grand and pancreas. * An endocrine gland is an organ that secretes hormones directly into the blood e.g. pancreas. They have no ducts e.g. pancreas secretes insulin and glucagon. * A duct is a tube leading from one part of the body to another.

Mammalian hormones * Mammalian hormones are relatively small molecules * There are two main types of hormones - steroids e.g. oestrogen, testosterone - Peptides/proteins/amino acid derivatives e.g. Insulin * Hormones are secreted in response to stimuli, such as a nervous stimulation, the secretion of another hormone, or change in the concentration of a substance in the blood. * Many hormones have a very short life in the body. They are broken down by enzymesin the blood or in cells or are lost in the urine. * After they have been secreted from an endocrine gland, hormones are transported in the blood plasma. * Conc. of hormones in human blood is very small. * Hormones only affect target cells. * Target cells possess receptors on the cell surface membrane with a complementary shape to the hormone. * Hormone binds to receptor and sets into action a series of events. This is called cell signalling. * Most endocrine glands can secrete hormones very quickly when appropriate stimulus arrives.

How hormones work * Steroid hormones are lipid soluble so can diffuse through phospholipid bilayer and can be found in cytoplasm. * The hormone-receptor complex diffuses across the cell surface membrane of target cells. * The hormones diffuse into the nucleus and act on DNA to switch on specific genes.

* Adrenaline is secreted by the adrenal glands in response to excitement, danger or stress. * Adrenaline’s target tissues are the sino-atrial node in the heart, smooth muscle in the wall of the alimentary canal and the muscles in the iris of the eye. * Adrenaline is sometimes known as the flight or fight hormone. This is because adrenaline brings about changes that prepare the body for vigorous activity, such as needing to escape from danger or fighting against it. * The adrenaline-receptor complex does not diffuse across the membrane because it is a protein and not lipid soluble. * A first messenger is a molecule that binds to a receptor in the plasma membrane and causes changes to happen in the cell. * A second messenger is a molecule that is affected by the binding of a first messenger to a receptor. * The adrenal medulla is found in the centre of the gland. The cells in the medulla manufacture and release adrenaline. * Adrenaline causes the smooth muscle in the bronchioles to relax. * It increases the heart rate, and causes vasoconstriction to raise the general blood pressure. * Adrenaline also inhibits the action of the gut and increases mental awareness. * The adrenal cortex uses cholesterol to produce certain steroid hormones. * These hormones are called the mineralocorticoids and the glucocorticoids. * The mineralocorticoids help to control the conc. of sodium and potassium in the blood. * The glucocorticoids help control the metabolism of carbohydrates and proteins in the liver.

Mechanism of adrenaline action on the liver

* Adrenaline is known as the first messenger in the process. * It binds with specific