ENDOCRINE SYSTEM Endocrine System Cells tissues and organs

ENDOCRINE SYSTEM

Endocrine System • Cells, tissues, and organs that secrete hormones directly into body fluids • EXOcrine: secrete into or onto a surface • Hormone: Hormone biochemical that affects the function of another cell – Regulate metabolic processes • Rate of reactions • Aid in transport across membranes • Help regulate water & electrolyte balance

Hormone action • Some hormones travel short distances • Others are carried by blood to target cells —those cells with receptors for the hormone • Chemically, many hormones are steroid or peptide products • Chemical composition determines how hormone will operate

Hormone Action • Steroid hormones • Move through cell membrane and can react with molecules inside the cell (DNA for example) • Nonsteroid hormones • Bind with a receptor molecule on membrane • The receptor molecule then triggers a change within cell

Actions • Read 294 -295 • Prostaglandins: Prostaglandins a group of biochemicals that regulate cells similarly to hormones • Often affect only organ that produces them and are not stored

Control of Hormonal Secretions • Negative Feedback – A gland (or system controlling a gland) is sensitive to concentrations of a substance that will reach a certain level and inhibit the gland – Changing the level of the inhibiting substance controls the gland – High levels—gland “off” – Low levels—gland “on”

Control Sources • Hypothalamus – Job as relay station means it is constantly receiving information and signal action • Nerve impulses – Glands can be stimulated directly by peripheral nerves • Directly to changes in internal environment – e. g. when blood sugar rises…pancreas secrete insulin