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Ch 16 The Endocrine System: Part A
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Acts with nervous system to coordinate and integrate activity of body cells
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Endocrinology:
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Controls and integrates
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Exocrine glands
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Endocrine glands
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Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands
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Hypothalamus is Neuroendocrine organ
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Some have exocrine and endocrine functions
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Other tissues and organs that produce hormones
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Pancreas, gonads, placenta
Adipose cells, thymus, and cells in walls of small intestine, stomach, kidneys, and heart
Chemical Messengers
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Hormones: long-distance chemical signals; travel in blood or lymph
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Autocrines: chemicals that exert effects on same cells that secrete them
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Paracrines: locally acting chemicals that affect cells other than those that secrete them
Two main classes of Hormones
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Amino acid-based hormones
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Steroids
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Mechanisms of Hormone Action
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Target cells
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Hormone action on target cells may be to
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Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location
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Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
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Lipid-soluble hormones (steroid and thyroid hormones)
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Target cells must have specific receptors to which hormone binds, for example
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Target Cell Activation
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Target cell activation depends on three factors
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Hormones influence number of their receptors
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Up-regulation—
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Down-regulation—
Control of Hormone Release
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Blood levels of hormones
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Endocrine gland stimulated to synthesize and release hormones in response to
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Humoral Stimuli
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Changing blood levels of ions and nutrients directly stimulate secretion of hormones
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Example: Ca2+ in blood
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PTH causes Ca2+ concentrations to rise and stimulus is removed
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Neural Stimuli
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Hormonal Stimuli
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Hormones stimulate other endocrine organs to release their hormones
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Nervous System Modulation
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Nervous system can override normal endocrine controls
Hormones in the Blood
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Hormones circulate in blood either free or bound
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Concentration of circulating hormone reflects
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Hormones removed from blood by
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Half-life—time required for hormone's blood level to decrease by half
Onset of Hormone Activity
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Pituitary gland (hypophysis) has two major lobes
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Posterior pituitary (lobe)
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Anterior pituitary (lobe) (adenohypophysis)
Posterior pituitary (lobe)
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Posterior Pituitary and Hypothalamic Hormones
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Oxytocin and ADH
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Oxytocin
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ADH (Vasopressin)
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Syndrome of inappropriate ADH secretion (SIADH)
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Anterior Pituitary Hormones
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Growth hormone (GH)
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Thyroid-stimulating hormone (TSH) or thyrotropin
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Follicle-stimulating hormone (FSH)
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Luteinizing hormone (LH)
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Prolactin (PRL)
CH 16 The Endocrine System: Part B
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Thyroid Gland
-Parafollicular cells produce the hormone calcitonin
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Thyroid Hormone (TH)
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Actually two related compounds
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T4 (thyroxine); has 2 tyrosine molecules + 4 bound iodine atoms
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T3 (triiodothyronine); has 2 tyrosines + 3 bound iodine atoms
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Affects virtually every cell in body
Thyroid Hormone
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Regulation of tissue growth and development
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Homeostatic Imbalances of TH
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Hyposecretion in adults—myxedema; goiter if due to lack of iodine
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Hyposecretion in infants—cretinism
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Hypersecretion—Graves' disease
Parathyroid Glands
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PTH—most important hormone in Ca2+ homeostasis
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Parathyroid Hormone
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Functions
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Negative feedback control: rising Ca2+ in blood inhibits PTH release
Homeostatic Imbalances of PTH
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Hyperparathyroidism due to tumor
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Hypoparathyroidism following gland trauma or removal or dietary magnesium deficiency
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Adrenal (Suprarenal) Glands
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Paired, pyramid-shaped organs atop kidneys
Structurally and functionally are two glands in one
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Adrenal medulla—nervous tissue; part of sympathetic nervous system
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Adrenal cortex—three layers of glandular tissue that synthesize and secrete corticosteroids
Mineralocorticoids
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Regulate electrolytes (primarily Na+ and K+) in ECF
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Aldosterone most potent mineralocorticoid
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Homeostatic Imbalances of Aldosterone
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Aldosteronism—hypersecretion due to adrenal tumors
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Glucocorticoids
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Cortisol (hydrocortisone)
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Homeostatic Imbalances of Glucocorticoids
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Hypersecretion—Cushing's syndrome/disease
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Hyposecretion—Addison's disease
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Gonadocorticoids (Sex Hormones)
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Hypersecretion
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Females and prepubertal males
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Adrenal Medulla
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Adrenal Medulla
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Hypersecretion
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Hyposecretion
Pineal Gland
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Pinealocytes secrete melatonin, derived from serotonin
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Pancreas
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Glucagon
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Effects
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Glycogenolysis—breakdown of glycogen to glucose
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Gluconeogenesis—synthesis of glucose from lactic acid and noncarbohydrates
Effects of insulin
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Factors That Influence Insulin Release
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Homeostatic Imbalances of Insulin
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Diabetes mellitus (DM)
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Glycosuria – glucose spilled into urine
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Diabetes Mellitus: Signs
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Three cardinal signs of DM
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Polyuria—huge urine output
Polydipsia—excessive thirst
Polyphagia—excessive hunger and food consumption
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Homeostatic Imbalances of Insulin
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Hyperinsulinism:
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Ovaries and Placenta
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Ovaries produce estrogens and progesterone
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Estrogen
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Testes produce testosterone
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Other Hormone-producing Structures
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Adipose tissue
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Leptin –
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Resistin –
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Adiponectin –
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Other Hormone-producing Structures
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Enteroendocrine cells of gastrointestinal tract
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Gastrin
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Secretin
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Cholecystokinin
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Serotonin acts as paracrine
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Other Hormone-producing Structures
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Heart
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Kidneys
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Atrial natriuretic peptide (ANP)
Erythropoietin
Skeleton (osteoblasts)
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Osteocalcin
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Skin
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Cholecalciferol,