Chapter 6 The Endocrine System Endocrine Glands and Hormone Ac ons What are the organs of the endocrine system Func5onal Classes of Chemical Messengers Paracrine secreted by one cell and di use to a nearby target cell Synap5c secreted by neurons which then di uses a very short distance to bind receptors on a post synap5c cell Hormones secreted by endocrine cells which di uses into the blood stream for transport to target cells in the body Anatomical Direc5ons Anatomy of the Endocrine System Primary endocrine organs primary func5on is the secre5on of hormones Secondary endocrine organs also secrete hormones but it is secondary to some other func5on Hypothalamus and Pituitary Gland Together they regulate virtually every body system Most of the hormones the hypothalamus secretes a ect the pituitary gland Posterior Pituitary Posterior pituitary secretes two pep5de hormones from axon terminals origina5ng from cells residing in the hypothalamus ADH vasopressin and oxytocin Hypothalamus regulates the secre5on of 7 hormones from the anterior pituitary Summary of hormone ac5on Feedback lops control hormone secre5on Release of tropic hormones from the anterior pituitary inhibits the release of hypothalamic tropic hormones preven5ng the build up of excess anterior pituitary tropic hormone Pineal Gland Pineal gland secretes the hormone melatonin which helps to establish the circadian rhythm Sleep Wake Cycle Melatonin produc5on increases as light from the environment decreases reaching a maximum between 2 and 4 am Circadian Rhythms Human sleep occurs with circadian periodicity of about Even in the absence of cues to establish night and days human subjects s5ll display an internal biological clock to maintain a cycle of about 24 26 hours Circadian Rhythms and Jet Lag Jet lag occurs because the body s circadian rhythm is disrupted When travelers y across 5me zones their normal exposures to light are disrupted changing their circadian rhythms The use of medica5ons like melatonin is used by many to prevent jet lag Thymus Lies close to the heart and secretes thymosin which s5mulates the prolifera5on and func5on of T lymphocytes in the immune system The Thyroid Gland Bu er y shaped structure located on the ventral surface of the trachea Secretes two thyroid hormones tetraiodothyronine T4 and triiodothyronine T3 which regulate the body s metabolic rate and are necessary for normal growth and development Anatomy of the thyroid gland Anatomy of the Adrenal Gland Adrenal cortex secretes a number of hormones called adrenoco5coids that regulate kidney func5on the body s response to stress sex hormones Adrenal medulla secretes catecholamines 80 of which is adrenaline epinephrine in response to stress Anatomy of the Adrenal Gland Adrenal cortex secretes a number of hormones called adrenocor5ciods that regulate kidney func5on the body s response to stress sex hormones Adrenal medulla secretes catecholamines 80 of which is adrenaline epinephrine in response to stress Anatomy of the Pancreas Insulin secreted by beta cells and glucagon secreted by alpha cells Anatomy of the Pancreas Insulin secreted by beta cells and glucagon secreted by