Chapter 17- The Endocrine System
Chapter 17- The Endocrine System BIOL 20214
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This 12 page Study Guide was uploaded by Marlee Porter on Wednesday February 3, 2016. The Study Guide belongs to BIOL 20214 at Texas Christian University taught by Mrs. Crenshaw in Spring 2016. Since its upload, it has received 32 views. For similar materials see Anatomy and Physiology in Biology at Texas Christian University.
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Date Created: 02/03/16
Chapter 17 The Endocrine System Endocrine Glands Ductless; release hormones into surrounding tissue; highly vascular Neuroendocrine Combined functions associate with both the nervous system and the endocrine system Adipose cells, cardiac cells, and epithelial cells in digestive organs also have minor endocrine functions Some endocrine organs also have exocrine functions Testes, ovaries, liver and pancreas Hormones Longdistance chemical signals that target cells all over the body Intracellular effects (exocrine extracellular effects) Regulate processes such as growth and development, reproduction, metabolism, blood composition, and mobilization of body defenses by cells Compared to: Autocrines chemicals that exert their effect on the same cells that secrete them Paracrines chemicals that exert their effect on the cells immediately neighboring them Three Classes: Steroid Hormones Derived from cholesterol Hydrophobic Not stored in cells Include: aldosterone, androgens, corticosterone, cortisol, estrogens, and progesterone Monoamines (Biogenic) Hormones Derived from amino acids Subclass= catecholamines Hydrophilic Include: epinephrine/norepinephrine, melatonin, and thyroid hormone Peptide Hormones Chains of 3200+ amino acids Hydrophilic Subclasses= Oligopeptides: ADH, GnRH, Oxytocin, and TRH Polypeptides: ACTH, Calcitonin, CRH, Glucagon, GH, GHRH, Insulin, PTH, PRL, Somatostatin (GHIH) Glycoproteins FSH, LH, TSH Secretion Source Organ an endocrine gland responsible for secreting a particular hormone Will secrete a hormone in response to one of three types of stimuli: 1. Humoral Stimulus changing solute concentration 2. Hormonal Stimulus hormone released by another organ 3. Neural Stimulus nervous system stimulation Most hormone secretion is regulated by negative feedback increasing levels of a particular hormone in the blood will automatically inhibit production of the hormone at the source Transport Most hydrophilic hormones travel freely through blood plasma Most hydrophobic hormones are bound the transport proteins in the blood to increase solubility Some hormones are secreted in an inactivated form, and must be activated in the blood or by the target cell Hormone activity is limited by: Halflife—length of time for a hormone’s blood level to decrease by ½ Transport proteins can prolong halflife Some are degraded by enzymes; most are removed from the blood by the liver or kidneys Binding Bind specifically to protein receptors of target cells Can be intracellular or extracellular Hormone chemistry dictates what kind of receptor a hormone will bind to The more receptors a cell has for a specific hormone, the stronger the response will be Up Regulation target cell increases sensitivity to a hormone by increasing the number of receptors Down Regulation target cell decreases sensitivity to a hormone by decreasing the number of receptors Location of Receptors: Hydrophilic bind to extracellular receptors Secondmessenger system These pathways can activate or inhibit metabolic pathways that already exist in the cell Effects are quick and shortlived Hydrophobic diffuse through the membrane to intracellular receptors Steroid hormones and thyroid hormone Hormone receptor complex is transported to the nucleus Results in direct gene activation Results in transcription (production of mRNA) and translation (production of proteins) Effects are slow and require several hours to days to show Actions Amplification cascade one hormone can trigger the synthesis/activity of a “downstream” of chemicals Hormones interact with one another by: Permissiveness one hormone is not fully effective without another hormone being present Synergism more than one hormone produces the same effects at the target cell and their combined effects are amplified Antagonism one hormone opposes the action of another hormone Specific Hormone Examples Hypothalamus and the Pituitary Gland Infundibulum connects the hypothalamus to the pituitary gland Hypothalamus “master endocrine gland” Produces 8 hormones Pituitary Gland two separate structures Posterior Pituitary (neurohypophysis) Neurons and neuroglia HypothalamoHypophyseal Tract 2 neurohormones: Oxytocin Stimulated by: stretching of the cervix and uterus, suckling of an infant at the breast Inhibited by: Lack of stimulus Target and Effects: 1. Stimulates smooth muscle contraction of the uterus during labor and nursing 2. Stimulates milk ejection during nursing (positive feedback) 3. Cuddle hormone Antidiuretic hormone (ADH) Aka= Vasopressin Stimulated by: when bloodsolute concentration increases due to dehydration or fluid loss Inhibited by: Alcohol, caffeine, high water intake Target and effects: 1. Decrease urination to conserve water and prevent dehydration 2. Minor role in stimulation of peripheral vasoconstriction in order to increase systemic BP Diabetes Insipidus hyposecretion of ADH Output large amounts of dilute urine ADHmediated water retention—hypersecretion Associated with meningitis, anesthesia, neurosurgery or hypothalamic surgery Can lead to edema, headache, disorientation Anterior Pituitary (adenohypophysis) Glandular tissue similar to other endocrine organs HypophysealPortal System 6 neurohormones (FLAT PG) Follicle Stimulating Hormone (FSH) Gonadotropin Stimulated by: GnRH Inhibited by: increased levels of gonadal hormones (negative feedback) Targets and Effects: Males testes to produce sperm (spermatogenesis) Females ovaries to induce growth of ovarian follicles and produce estrogens Luteinizing Hormone (LH) Gonadotropin Stimulated by: GnRH Inhibited by: increased levels of gonadal hormones (negative feedback) Targets and Effects: Males testes to produce testosterone Females ovaries to trigger ovulation and production of progesterone by the corpus luteum Adrenocorticotropic Hormone (ACTH) Stimulated by: CRH Inhibited by: increased levels of ACTH (negative feedback) Target and Effects: 1.Stimulates the adrenal cortex to release corticosteroid hormones (some reduce the stressresponse) 2. Part of the HPA axis Thyroid Stimulating Hormone (TSH) AKA= thyrotropin Stimulated by: TRH Occurs when energy needs of the body increase or when TH levels begin to drop Inhibited by: High bloodTSH levels (negative feedback) High glucocorticoid levels Target and Effect stimulates normal development and secretory activity of thyroid gland *Hypothyroid individuals often exhibit high levels of TSH Growth Hormone (GH) Stimulated by: GHRH Inhibited by: GHIH (Somatostatin), high blood levels of GH (negative feedback) and decreased GHRH Target and effects: Induces widespread tissue growth Indirectly promotes growth by stimulating the release of Insulin Like Growth Factors (IGFs) Targets cartilage, bone, muscle, fat Stimulates lipid breakdown for energy Prevents metabolism of proteins & glucose Increases levels of Na+, K+, Cl, and Ca2+ *GH is highest during the first two hours of sleep and following vigorous exercise; also following trauma, stress, and hypoglycemia Pituitary Gigantism hypersecretion of GH before growth plates fuse; people are abnormally tall Acromegaly hypersecretion of GH after the growth plates fuse; overgrowth of cartilage and bones Pituitary Dwarfism hyposecretion of GH in children Psychosocial Dwarfism stress and emotional disorders suppress the hypothalamic release of GHRH and GH Prolactin (PRL) Stimulated by: high estrogen levels Inhibited by: prolactin inhibiting hormone (PIH) Target and effect: Breast tenderness during menstrual cycle Milk production after birth In males, can increase sensitivity to LH Hypersecretion of PRL can cause inappropriate lactation, lack of menses, infertility and impotence (in males) Other Endocrine Organs Thyroid Gland Follicles Site of TH production Follicle cells cuboidal or squamous epithelium, and produce the glycoprotein thyroglobulin Colloid stores thyroglobulin Parafollicular cells Epithelial cells embedded in the CT between follicles Produce calcitonin Thyroid Hormone (TH) Source follicle cells and colloid Stimulated by: TSH from the anterior pituitary Inhibited by: decreased TSH levels (negative feedback) Target and Effects: Development of multiple body systems (nervous, reproductive, musculoskeletal) Promote alertness and quicken reflexes Stimulates protein synthesis in hair, skin, nails and teeth Increases respiratory rate, heart rate, and contractility Calorigenic effect increased metabolism stimulates hunger and nutrient catabolism, increases the catabolism of fats and glucose Synthesis: 1. Iodide from the bloodstream is oxidized to Iodine 2. Iodine and thyroglobulin are assembled into both forms of TH 3. Colloid releases some T3 and mostly T4 in response to TSH 4. T4 and T3 are transported through the blood bound to Thyroxinebinding globulins (TBGs) and produced by the liver 5. T4 an T3 reach target cells most cells will use T3, and then convert T4 to T3 Imbalances Myxedema (mucous swelling) Prolonged hyposecretion of TH Low metabolic rate, lethargy, chills, constipation, thick dry skin, puffy eyes, edema Endemic Goiter Enlargement of the thyroid gland due to iodide deficiency Associated with hyposecretion of TH Cretinism Extreme hypothyroidism in infants Results in short stature, mental retardation, thick tongue and neck; may be caused by insufficient thyroid gland or maternal dietary deficiencies Grave’s Disease (Toxic Goiter) Abnormal antibody production mimics TSH and stimulates TH release from the thyroid gland Elevated metabolic rate, sweating, rapid irregular heartbeat, nervousness, weight loss Exophthalmos protrusion of eyeballs due to edema in the eye socket, which eventually causes the tissue to become fibrous Calcitonin Source: Parafollicular cells Stimulated by: excessive bloodcalcium levels Inhibited by: declining bloodcalcium levels Target and Effect: Stimulates calcium uptake and storage into bone matrix Osteoclast activity is inhibited Parathyroid Hormone Source: Parathyroid gland Stimulated by: decreased bloodcalcium levels Inhibited by: rising bloodcalcium levels Targets and effects: Stimulates bone resorption (osteoclasts) and inhibits bone deposit Increases reabsorption of Ca2+ from the kidneys Increases activation of Vitamin D (calcitriol) to increase absorption of Calcium from the intestines Hyperparathyroidism Often from a parathyroid tumor Bones soften, kidney stone formation Metastatic calcification of soft organs Hypoparathyroidism Often due to trauma Leads to fatal tetany within 34 days Adrenal Cortex Regions: Zona Glomerulosa Thin, superficial; cluster of cells Produce mineralocorticoids Zona Fasciculata Cells arranged in parallel cords separated by capillaries Secretes glucocorticoids and androgens Zona Reticularis Thin, deep layer Cells form branching network Secretes glucocorticoids and androgens Aldosterone Source: Zona Glomerulosa Accounts for 95% of mineralocorticoids Stimulated by: decreasing blood volume and pressure, and by rising levels of K+ Inhibited by: increasing blood volume/pressure Target and effects: 1. Promotes Na+ reabsorption (water retention) and K+ elimination by the kidneys 2. Maintains blood volume, blood pressure and pH Cortisol and Corticosterone Source: Zona Fasciculata Stimulated by: Rhythmic release of ACTH from the Anterior Pituitary Inhibited by: Rising cortisol levels “shut off” CRH release at the hypothalamus (negative feedback) Target and Effects: 1. Regulate daily glucose levels 2. Increase catabolism of lipids, proteins and promote hyperglycemia 3. Helps the body respond to stress and repair damaged tissue 4. Can inhibit inflammatory and immune response 5. Longterm secretion can disrupt normal activity of the cardiovascular and GI systems and can deplete protein stores, and cause retention of water and electrolytes Gonadocorticoids Source: Zona Reticularis Produces Androgens DHEA is most abundant Triggers and release are unclear Target and effects: 1. DHEA is the precursor to Testosterone in males and females 2. Indirectly responsible for male secondary sex characteristics (bone growth, pubic and axillary hair growth, apocrine gland activation) and libido 3. In adult females, it contributes to libido and estrogen production following menopause Adrenal Disorders Aldosteronism Hypersecretion of aldosterone Typically results from adrenal tumors Can result in hypertension and edema (due to increased Na+ reabsorption) Accelerated excretion of K+ can result in hypokalemia Addison’s Disease Hyposecretion of mineralocorticoids and glucocorticoids Causes hypoglycemia, hypotension, and electrolyte imbalances Weight loss and muscle weakness Corticosteroid replacement therapy is successful Cushing’s Syndrome Usually caused by a pituitary tumor (increased ACTH release) Results in hypersecretion of glucocorticoids Prolonged hyperglycemia, hypertension, depletion of muscle and bone proteins, water and salt retention, and edema Abnormal fat deposition between shoulders or in the face Androgenital Syndrome Congenital adrenal hyperplasia hypersecretion of Gonadocorticoids Obscured by testosterone production of gonads in adult males Can result in precocious puberty in young males Masculinization of features in females—hirsutism, ambiguous genitalia, and failure to menstruate Stress Management Short Term Stress Autonomic nervous system—sympathetic neurons target the adrenal medulla Triggers release of epinephrine and norepinephrine into the body’s bloodstream—fight or flight response Long Term Stress Sympathetic neurons and the HPA axis (Hypothalamicpituitary adrenal cortex) Surges in ACTH target the adrenal cortex Induces cortisol release and causes aldosterone release Effects: 1. Heart palpitations and Hypertension (and atherosclerosis) 2. Susceptibility to infection and cancer formation 3. Suppressed secretion of sex hormones 4. Severe tissue wasting and organ failure Pineal Gland Melatonin Stimulated by: absence of light Inhibited by: presence of bright light Target and Effects: 1. Linked to activities like sleep, appetite and body temperature 2. Powerful antioxidant 3. Inhibits Gonadotropin release Thymic Hormones Functions of the Thymus: Associated with the endocrine, lymphatic and immune systems Site of maturation of T Cell Lymphocytes Grows until the age of 56, then undergoes atrophy into adulthood Hormones: Thymopoietin, Thymosin and Thymulin Functions of Thymic Hormones: 1. Stimulate the development of lymphatic organs 2. Regulate the development and activity of T Cell Lymphocytes The Pancreas Capable of both exocrine and endocrine functions Exocrine Secretions are digestive enzymes from Acinar Cells Endocrine Secretions are Insulin from Beta (β) Cells, and Glucagon from Alpha (α) Cells– both amino acidbased hormones Pancreatic Islets contain clusters of α and β cells Insulin Source: Pancreatic β Cells Stimulated by: High blood levels of glucose, amino acids and fatty acids during and immediately following a meal Parasympathetic Activity Inhibited by: decreased levels of Glucose in the blood (hypoglycemia) Increased Sympathetic Activity Targets and Effects: 1. Lowers circulating amounts of glucose, amino acids and fat by promoting cellular uptake of them 2. Some of these molecules are immediately used for cellular activities 3. Some of these molecules are stored for later use as glycogen, protein and fat Diabetes Mellitus Hyposecretion or hypoactivity of insulin Type I DM Insulin Dependent Diabetes Mellitus (IDDM) More than 1 million Americans Beta cells are destroyed by the immune system Type II DM NonInsulin Dependent Diabetes Mellitus (NIDDM) approx. 12 million Americans Insulin resistant insulin receptors are unable to respond Most are overweight and sedentary Glucagon Source: Pancreatic α Cells Stimulated by: Bloodglucose levels drop Sympathetic Nervous System can induce glucagon release Inhibited by: Rising bloodglucose levels (hyperglycemia) Insulin and GHIH can inhibit glucagon release Targets and Effects: 1. Promotes Glycogen breakdown (glycogenolysis) and the formation of glucose from amino acids (gluconeogenesis) 2. Increases circulating bloodglucose 3. Promotes release of fat from Adipose cells (lipolysis) 4. Promotes amino acid absorption following a highprotein meal Endocrine Functions of Other Tissues -The Skin produces: cholecalciferol, the precursor for calcitriol -The Liver produces: -Calcidiol, another precursor to calcitriol -Angiotensin to regulate blood volume and pressure -Erythropoietin to stimulate erythrocyte production -Hepcidin to stimulate iron homeostasis -Insulin-Like Growth Factors -The Kidneys produce: calcitriol and Renin to regulate angiotensin production -The Heart produces: Natriuretic Peptides to regulate blood pressure -The Stomach and Small intestine produce: -Cholecystokinin -Gastrin -Ghrelin -Peptide YY -Adipose Tissue produces: Leptin to regulate appetite and puberty -Osseous Tissue produces Osteocalcin to regulate pancreatic production of insulin -The Placenta secretes estrogens to maintain pregnancy and fetal development
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