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Transcript
Lecture Outline The Endocrine System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endocrine Glands o o Endocrine glands are ductless Secrete hormones • Chemical signals that influence: • Metabolism Growth and development Homeostasis Categories of hormones Peptides (proteins, glycoproteins, and modified amino acids) – most hormones Steroid hormones PEPTIDE Hormones Endocrine Glands o How Peptide Hormones Function • Second messenger system Peptide hormone binds to a receptor Peptide hormone “first messenger” activates a “second messenger” (cyclic AMP and calcium) Second messenger sets in motion an enzyme cascade that leads to: Change in cellular behavior Formation of an end product that leaves the cell STEROID Hormones Endocrine Glands • Intracellular mechanism of steroid hormone function Steroid hormones (lipids) diffuse across the plasma membrane Once inside the cell, steroid hormones bind to receptor proteins Hormone-receptor complex binds to DNA, activating particular genes Gene activation leads to production of cellular enzymes that cause cellular changes Endocrine Glands o Hormone Control • Release of hormones controlled by: The nervous system The action of other hormones Negative feedback mechanisms Hypothalamus and Pituitary Gland o Hypothalamus • Controls secretions of the pituitary gland • Produces Neurosecretory cells: Antidiuretic hormone (ADH) Oxytocin Hypothalamus and Pituitary Gland Hypothalamus and Pituitary Gland o Posterior pituitary • Stores hypothalamic hormones ADH and oxytocin ADH • Released in response to elevated blood salt concentrations Causes more water reabsorption into kidney capillaries Raises blood pressure Malfunction-Diabetes insipidus Hypothalamus and Pituitary Gland o Posterior pituitary • Oxytocin Causes uterine contraction Causes milk letdown controlled by positive feedback Hypothalamus and Pituitary Gland o Anterior pituitary • • • Controlled by hypothalamic hormones Contains hormones that: Affect other glands • Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Gonadotropic hormones Effects of other hormones Prolactin (PRL) Growth hormone (GH) Hypothalamus and Pituitary Gland • Effects of growth hormone Affects the height of an individual Pituitary dwarfism- too little GH during childhood Gigantism- too much GH produced during childhood Acromegaly- too much GH is secreted in adulthood Thyroid o Thyroid Gland • Two forms of thyroid hormone • Triiodothyronine (T3) Thyroxine (T4) contains Effects of thyroid hormone Increase the metabolic rate Stimulate all cells of the body Effects of Thyroid Hormones Simple Goiter- lack of iodine Effects of Thyroid Hormones Myxedema Congenital hypothyroidism Effects of Thyroid Hormones • Hyperthyroidism (Grave’s Disease) Oversecretion of thyroid hormone Symptoms include Hyperactivity Nervousness and irritability Insomnia Thyroid • Thyroid Gland • Calcitonin Helps control blood calcium levels Secreted when the blood calcium levels rise Brings about the deposit of calcium in the bones Parathyroid o Parathyroid Glands • • Posterior surface of the thyroid gland Produces parathyroid hormone (PTH) Causes blood phosphate levels to decrease Causes blood calcium (Ca2+) levels to increase Promotes the release of calcium from the bones Promotes the reabsorption of calcium by the kidneys Activates vitamin D in the kidneys, which stimulates the reabsorption of calcium from the intestines Adrenal Glands o Adrenal Medulla • • • • • Inner portion Under nervous control Secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) Causes “fight or flight” responses Provide a short-term response to stress Adrenal Glands o Adrenal Cortex • • • 3 layers Under the control of ACTH Hormones Provide a long-term response to stress Mineralcorticoids(i.e.aldosterone)promotes renal absorption of sodium and water Atrial natriuretic hormone (ANH) Glucocorticoids- raises blood glucose levels Male and female sex hormones Adrenal Glands • Malfunction of the Adrenal Cortex Addison Disease Hyposecretion of adrenal cortex hormones Excessive (but ineffective) ACTH causes bronzing of the skin Adrenal Glands • Malfunction of the Adrenal Cortex Cushing Syndrome Hypersecretion of adrenal cortex hormones Tendency towards diabetes mellitus Excess aldosterone Pancreas o Composed of two types of tissue • • Exocrine – secretes digestive juices Endocrine tissue (pancreatic islets or islets of Langerhans) produces: Insulin Secreted when blood glucose level is high Stimulates the uptake of glucose by most body cells Glucagon Secreted when blood glucose levels are low Targets liver and adipose tissue Stimulates liver to break down glycogen to glucose Pancreas o Diabetes Mellitus • Insulin-sensitive body cells are unable to take up and/or metabolize glucose Blood glucose level is elevated (hyperglycemia) Symptoms: • • Polyphagia – extreme hunger Glycosuria – glucose in the urine Polyuria – excessive water loss through urine Polydipsia – extreme thirst Pancreas • Two forms of diabetes mellitus Type I – insulin-dependent diabetes mellitus Pancreas does not produce insulin Immune cells destroy the pancreatic islets Type II – non-insulin-dependent diabetes mellitus Normal or elevated amounts of insulin are present in the blood Receptors on the cells do not respond to insulin Other Endocrine Glands o Testes and ovaries • • • Testes produce androgens (testosterone) Ovaries produce estrogens and progesterone Secretion is controlled by the hypothalamus and the pituitary Other Endocrine Glands • Androgens Increased testosterone secretion during puberty stimulates the growth of the penis and the testes Brings about and maintains the male secondary sex characteristics Facial, axillary, and pubic hair Enlargement of larynx and the vocal cords Muscular strength Stimulates oil and sweat glands of the skin Other Endocrine Glands • Estrogen and Progesterone Required for breast development Regulation of the uterine cycle Estrogens Stimulate the growth of the uterus and the vagina during puberty Necessary for egg maturation Responsible for secondary sex characteristics Female body hair Fat distribution Other Endocrine Glands o Thymus Gland • • • o Most active during childhood Transforms lymphocytes into thymusderived lymphocytes (T-lymphocytes) Epithelial cells secrete hormones called thymosins Pineal Gland • • • Located in the brain Produces the hormone melatonin Melatonin is involved in daily sleepwake cycle Other Endocrine Glands o Hormones from Other Tissues • Leptin • Produced by adipose tissue Signals satiety in hypothalamus Growth Factors – stimulate cell division and mitosis Granulocyte and macrophage colonystimulating factor Platelet-derived growth factor Epidermal growth factor and nerve growth factor Tumor angiogenesis factor Other Endocrine Glands • Prostaglandins Potent chemical signals Act locally Some effects of prostaglandins include: Uterine contractions Mediate the effects of pyrogens Reduce gastric secretion Lower blood pressure Inhibit platelet aggregation The Importance of Chemical Signals o Cells and organs communicate with one another using chemical signals Chemical signals between individuals o • • Called pheromones Humans produce airborne chemicals from a variety of areas Effects of Aging o Thyroid disorders • • o Hypothyroidism Hyperthyroidism Diabetes Homeostasis o The endocrine system and the nervous system work together to maintain homeostasis The endocrine system helps regulate the following: o • • • • • Digestion Fuel metabolism Blood pressure and volume Calcium balance Response to the external environment