<p> Chapter 9: The Endocrine System</p><p>Function: coordinates functions of body with nervous system Hormones: chemical substances that are secreted by endocrine cells into ECF  Mediator molecule released in one part of the body but regulates activity in other parts of the body  Regulate metabolic activity of other cells  Affects target cells/organs Endocrine vs. Nervous  Endocrine: release hormones as chemical signal, work more slowly, can target any cell in the body Control of Hormone Release  Negative feedback mechanisms: chief means of regulating blood levels of nearly all hormones o Stimulus triggers hormone secretion and rising levels inhibit further release o Maintaining homeostasis! (levels of hormones within a narrow range)  Positive feedback can also control (i.e. oxytocin)  Stimuli that activate endocrine organs: o Hormonal: stimulated by other hormones i.e. hypothalamic hormones stimulate anterior pituitary o Humoral: stimulated by changing blood levels of certain ions and nutrients i.e. blood calcium levels stimulate release of parathyroid hormone o Neural: stimulated by nerve fibers i.e. sympathetic nervous system stimulates adrenal medulla Endocrine & Exocrine Glands  Glandular tissue is epithelial tissue!  Endocrine gland: secrete hormones directly into internal environment o No ducts o Secrete hormones  Exocrine glands: secrete substances into external environment o Have ducts o Secrete substances such as sweat, oil, wax, enzymes, etc. Hormone Receptors  Receptor: protein on cell membrane of target cell o i.e. insulin (secreted by pancreas) – liver has insulin-specific receptors that receive insulin and tell liver to take sugar in and transfer to glycogen for storage  Two types of hormones: o Circulating: deposited into fluid/blood, circulates through body o Local: acts on neighboring cells or itself (paracrine – neighboring) or autocrine (targets itself) Water-soluble vs. Lipid-soluble  Chemical classes determine how easily the hormone gets into and moves through the blood stream and the cell membrane  Lipid-soluble: nonpolar o Hard to transport because fluids are water-based; need to be bound to transport protein (“chaperone”) that allows it to move around o Once it gets to target cell, can move across membrane without protein channel o i.e. steroid hormones  Water-soluble: polar o No help needed for transport o Cannot go through membrane of target cell – needs a protein receptor; binds to receptor and activates second messenger system o i.e. amines, peptide/protein, glycoproteins, eicosanoids Major Endocrine Organs  Hypothalamus: major link between nervous and endocrine system!  Pituitary Gland o Hangs from inferior surface of hypothalamus o Some hormones released are tropic hormones: stimulate other endocrine glands to release hormones o Two lobes: 1. Anterior pituitary (glandular tissue): “master endocrine gland” – controls so many others! 2. Posterior pituitary (nervous tissue): stores 2 hormones for hypothalamus and secretes them Hormones of the Anterior Pituitary o Hormones secreted with non-endocrine targets Growth hormone (GH): general metabolic hormone, growth of skeletal muscles and long bones of the body, promotes healing and increases ATP - Pituitary dwarfism: hyposecretion during childhood - Gigantism: hypersecretion during childhood - Acromegaly: hypersecretion after growth plates closed Prolactin (PRL): targets mammary glands in females to stimulate and maintain milk production after childbirth o Tropic hormones Adrenocorticotropic hormone (ACTH): regulates endocrine activity of the adrenal cortex Thyroid-stimulating hormone (TSH): influences growth & activity of thyroid, stimulates release of thyroid hormones (aka thyrotropic hormone or TH) Gonadotropic hormones (hyposecretion causes sterility) - Follicle-stimulating hormone (FSH): stimulates follicle development in ovaries and sperm development by testes - Luteinizing hormone (LH): triggers ovulation of egg from ovary and production of progesterone and estrogen; in men, stimulates testosterone production by testes Hormones of the Posterior Pituitary o Posterior pituitary does not make hormones – it stores them for the hypothalamus o Hypothalamus makes two hormones that are transported via neurosecretory cells to be stored in the posterior pituitary Oxytocin: released in significant amounts only during childbirth and in nursing women; contractions of uterus & milk ejection - Pitocin is synthetic form: used for inducing labor and to control hemorrhage and increase uterine muscle tone Antidiuretic hormone (ADH): inhibits or prevents urine production and causes kidneys to reabsorb more water from the forming urine  Thyroid Gland o Located at the base of the throat, inferior to the Adam’s apple Thyroid hormone - two active iodine-containing hormones thyroxine (T4) & triiodothyronine (T3) - targets all cells - controls rate at which glucose is converted to energy (increases basal metabolic rate) - Maintains body temperature - important for normal tissue growth and development; accelerates body growth - Goiter: enlarged thyroid gland resulting in diet deficient in iodine - Cretinism (hypothyroidism) - Graves’ disease (hyperthyroidism) Calcitonin: inhibits osteoclasts and decreases calcium level in the blood; causes calcium to be deposited in the bone  Parathyroid Glands o Glandular tissue found on posterior surface of thyroid gland (“piggybacks” the thyroid) Parathyroid hormone (PTH): regulates ions (calcium, magnesium, phosphate); antagonist to calcitonin - Most important regulator of blood calcium levels! - Increases blood calcium levels by promoting resorption of calcium from bone matrix into blood (increases activity of osteoclasts) - Also acts on kidneys – slows loss of ions from blood to urine  Adrenal Glands o Two bean-shaped glands that curve over the top of the kidneys o Functionally two organs in one: 1. Adrenal cortex (glandular) - Corticosteroids (mineralocorticoids, glucocorticoids, sex hormones) 2. Adrenal medulla (neural) - When stimulated by sympathetic nervous system, releases catecholamines epinephrine (adrenaline) norepinephrine (noradrenaline) o Stimulated in times of stress (“fight or flight”) o Allows body to better deal with short-term stressors Hormones of the Adrenal Cortex o Mineralocorticoids: regulate mineral (salt) content of the blood (Na+/K+ ions) – target kidney tubules to regulate electrolyte and water balance in body Aldosterone o Glucocorticoids: promote normal cell metabolism and help body to resist long-term stressors (increase blood glucose levels); anti-inflammatory properties Cortisone Cortisol - PTSD – stress hormones produced after traumatic event</p><p> o Sex hormones Androgens (male - testosterone) Estrogens (female) o Disorders Addison’s Disease (hyposecretion of adrenal cortex hormones) Cushing’s Syndrome (hypersecretion of cortisol) Congenital Adrenal Hyperplasia (CAH): genetic disorder (don’t make cortisol)  Pancreatic Islets o Pancreas is a mixed gland - Pancreatic islets (endocrine – also called the islets of Langerhans) - Pancreas also produces enzymes for the digestive system (exocrine) Insulin – released by beta cells in response to high levels of glucose (acts on all body cells) – decreases blood glucose levels - Diabetes mellitus (hyposecretion) Glucagon – antagonist of insulin; released by alpha cells; helps regulate blood glucose levels by increasing them (primarily targets liver, stimulating it to break down stored glycogen)  Pineal Gland o Small, cone-shaped gland that hangs from roof of third ventricle of brain (diencephalon - epithalamus) Melatonin – “sleep trigger” that plays an important role in establishing the body’s day-night cycle; sets “biological clock” and rhythms o Light can affect gland – Seasonal Affective Disorder (SAD) & Jet Lag  Thymus o Located in upper thorax, posterior to sternum (lymphatic organ) Thymosin – promotes normal development of T lymphocytes (immunity); may slow aging process  Gonads o Produce sex hormones identical to those produced by adrenal cortex o Release of hormones stimulated by anterior pituitary gonadotropins Hormones of the ovaries Estrogens: development of sex characteristics in women (growth and maturation of reproductive organs) and the appearance of secondary sex characteristics at puberty Progesterone: acts with estrogen to bring about menstrual cycle, prepares mammary tissue for lactation, maintains pregnancy Hormones of the testes Androgens (testosterone): promotes growth and maturation of the reproductive system organs at puberty; causes secondary sex characteristics to appear; necessary for production of male gametes o Hyposecretion of these hormones causes sterility  Other Tissues/Organs o Hormone-producing cells are found in fatty tissue and in walls of small intestine, stomach, kidneys, and heart (Table 9.2, page 331) o Placenta: organ formed temporarily in uterus of pregnant women that acts as a respiratory, excretory, and nutrition-delivery system for fetus - Produces several hormones that help to maintain the pregnancy and prepare for delivery of the baby Human chorionic gonadotropin (hCG): stimulates the ovaries to continue producing estrogen and progesterone so that the lining of the uterus is not sloughed off in menses Human placental lactogen (hPL) – works with estrogen and progesterone in preparing the breasts for lactation Relaxin: causes mother’s pelvic ligaments and the pubic symphysis to relax and become more flexible, which eases birth passage</p>