Chapter 45 Hormones & the Endocrine System

Main Ideas 1.) A hormone is a chemical signal that is secreted into the circulatory system & communicates regulatory messages throughout the body. 2.) Hormones may be secreted throughout the body but only target cells contain the receptors that accept the hormone & respond to it. a.) Therefore, a hormone causes a specific response from its target cells & does not affect other cells.

Main Ideas 3.) Hormones coordinate processes such as responses to stress, dehydration & blood glucose levels. They also regulate development & growth of parts of the body as well as sex characteristics. 4.) Endocrine system: all of an animal’s hormone- secreting cells. a.) Hormone-secreting organs are called endocrine glands.

Main Ideas 5.) The endocrine system is not the only system functioning in regulation in your body – the nervous system also regulates processes. a.) The nervous system is responsible for fast responses to environmental stimuli.

Main Ideas 6.) The endocrine & nervous systems often function together… a.) The hypothalamus (a part of the brain) can also secrete hormones. b.) Some chemicals function as both hormones & neurotransmitters (the chemical signals that travel between nerve cells). c.) The nervous system can also trigger endocrine glands to speed up or slow down production of certain hormones.

Main Ideas Note: In addition to hormone signals, body cells also respond to local regulators: a.) These are chemicals secreted by cells that affect neighboring cells very quickly. b.) Neurotransmitters in the nervous systems, cytokines in the immune system & growth factors (which trigger cells to grow & divide) are all local regulators.

Main Ideas c.) An additional local regulator is nitric oxide. It is made and secreted by cells in the walls of blood vessels in response to low oxygen levels. Causes the walls of blood cells to vasodilate = increased blood flow. It typically breaks down shortly after release. i.) The action of nitric oxide is what increases blood flow to the penis during erection in males – the drug Viagra works by interfering with the breakdown of nitric oxide.

Main Ideas d.) Prostaglandins are local regulators with numerous functions... i.) Prostaglandins in semen trigger muscles in uterine wall to contract to help sperm reach the egg, during childbirth they are secreted by the placenta inducing more contractions of the uterus, also function in blood clotting and immune function.

Main Ideas 7.) Basic endocrine system pathways: a.) A receptor/sensor detects a stimulus (such as a change in blood glucose) and sends this information to a control center & the control center sends out a signal that directs an effector to respond. i.) In endocrine pathways, the signal is a hormone. The effector is whatever responds to that hormone. b.) Don’t forget – many endocrine pathways exhibit negative or positive feedback!

Overview of Hormone Function 1.) There are 3 major types of hormones: a.) Protein & peptide hormones i.) Peptides: small polypeptides containing up to 30 amino acids. ii.) Soluble in water b.) Amines – derived from amino acids i.) Soluble in water c.) Steroids i.) Insoluble in water

Overview of Hormone Function 2.) Hormone signaling to target cells has 3 main steps: a.) Reception: can be received by receptors on plasma membrane of target cells or inside target cells. b.) Signal transduction: often involving long signal transduction pathways

Overview of Hormone Function c.) Response: the result – the change in the cell. i.) Responses can include the activation of an enzyme, change in the uptake or secretion of some molecule, movement of cytoskeleton, or transcription of a gene.

Overview of Hormone Function 3.) A single hormone can cause different responses in different types of cells because they may trigger different signal transduction pathways that lead to different responses! 4.) Steroid hormones almost always bind to intracellular receptors in their target cells. a.) They also almost always bind to transcription factors inside cells resulting in the response of the transcription of a gene.

This is a diagram of all the organs that have endocrine function – meaning they release hormones.

Hormones & Their Functions 1.) The hypothalamus & pituitary gland control much of your endocrine system functioning. a.) The hypothalamus receives information from nerves throughout the body & other parts of the brain & initiates the correct endocrine signals. b.) The hypothalamus triggers the production/release of hormones from the pituitary gland (which has 2 parts: the anterior pituitary and the posterior pituitary).

Hormones & Their Functions 2.) Some hormones produced by the pituitary are tropic hormones: this means that they trigger other endocrine organs to release hormones. a.) Others act directly on nonendocrine organs – called nontropic hormones.

The hypothalamus & pituitary gland control much of your endocrine system functioning.

Additional Hormones/Notes 1.) Anterior pituitary also releases endorphins which dull pain perception. 2.) Abnormal production of growth hormone can lead to gigantism or dwarfism

Additional Hormones/Notes 3.) Thyroid hormones: a.) Produces 2 hormones T3 and T4 b.) Important in growth & development & maintaining homeostasis: thyroid deficiency can cause slowed growth & mental development. i.) Too much thyroid hormone in humans (hyperthyroidism) leads to high body temperature, weight loss, irritability, high blood pressure). Hypothyroidism causes the opposite.

Additional Hormones/Notes 4.) Parathyroid hormones control blood calcium levels which must be maintained for normal muscle contraction. a.) Parathyroid hormone: raises blood Ca by stimulating the breakdown of bone matrix and reabsorption of Ca in kidney b.) Calcitonin: lower blood Ca by doing opposite.

Additional Hormones/Notes 5.) Pancreas structure: a.) Has clusters of endocrine cells called islets of Langerhans – each of these “islets” has 2 types of cells: i.) Alpha cells: produce glucagon (raises blood glucose) ii.) Beta cells: produce insulin (lowers blood glucose)

Additional Hormones/Notes 6.) Adrenal glands are on top of the kidneys and have 2 parts: the adrenal medulla and the adrenal cortex. a.) Adrenal medulla secretes epinephrine & norepinephrine in response to positive or negative stress producing a short term response. b.) Adrenal cortex releases hormones that produce a more long term response to stress.

Additional Hormones/Notes 7.) Pineal gland (small, located near center of brain): a.) Produces melatonin which affects biological rhythms associated with day length & season. It is produced at night – longer periods of night = more melatonin.