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The Endocrine System Endocrinology = the study of the endocrine system Unlike the nervous system with which the endocrine works similarly to and in some cases with, the endocrine system sends messages to cells to perform a necessary action. Hormones are messenger molecules. The endocrines system is comprised of small organs dispersed throughout the body and secrete hormones into the extracellular space to then be picked up by nearby capillaries into the general circulation to be delivered throughout the body. If the hormone finds a “lock and key” fit on the surface of a cell membrane, it will fuse at that point and the message will be delivered. Therefore, cells that don’t have a receptor protein for a particular hormone, it will have no effect. Hormones only act on “target” cells. © 2014 Pearson Education, Inc. Figure 17.1 Location of the major endocrine organs. Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Gonads Ovary (female) Testis (male) © 2014 Pearson Education, Inc. Three types of endocrine gland stimuli. Humoral Stimulus Hormone release caused by altered levels of certain critical ions or nutrients Neural Stimulus Hormone release caused by neural input Hormonal Stimulus Hormone release caused by another hormone (a tropic hormone) Hypothalamus CNS (spinal cord) Capillary (low Ca2+ in blood) Thyroid gland (posterior view) Parathyroid glands Preganglionic sympathetic fibers Anterior pituitary gland Thyroid gland Adrenal cortex Gonad (Testis) Medulla of adrenal gland Parathyroid glands PTH Capillary Stimulus: Low concentration of Ca2+ in capillary blood Response: Parathyroid glands secrete parathyroid hormone (PTH), which increases blood Ca2+ © 2014 Pearson Education, Inc. Stimulus: Action potentials in preganglionic sympathetic fibers to adrenal medulla Response: Adrenal medulla cells secrete epinephrine and norepinephrine Stimulus: Hormones from hypothalamus Response: Anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones The pituitary gland (hypophysis). Corpus callosum Thalamus Pineal Hypothalamus Mammillary body Brain stem Pituitary (hypophysis) Anterior lobe Optic chiasma Median eminence of hypothalamus Anterior lobe Pars tuberalis Pars intermedia Pars distalis Mammillary body Tuber cinereum Posterior lobe Infundibulum Pars nervosa Chromophobe cells Basophil cells Acidophil cells Pituicytes (neuroglia) © 2014 Pearson Education, Inc. Posterior lobe Figure 17.4a The hypothalamus controls release of hormones from the pituitary gland in two different ways. Anterior Pituitary: Hypothalamic hormones released into special blood vessels (the hypophyseal portal system) control the release of anterior pituitary hormones. Hypothalamus Hypothalamic neurons synthesize releasing and inhibiting hormones Anterior lobe of pituitary Superior hypophyseal artery 1 When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus. 2 Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary. Hypophyseal portal system Primary capillary plexus Hypophyseal portal veins 3 In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation. Growth Hormone (GH) Prolactin (PRL) Thyroid-Stimulating Hormone (TSH) Luteinizing Hormone (LH) Adrenocorticotropic Hormone (ACTH) Follicle-Stimulating Hormone (FSH) © 2014 Pearson Education, Inc. Secondary capillary plexus Anterior lobe of pituitary A portal system is two capillary plexuses (beds) connected by veins. Figure 17.4b The hypothalamus controls release of hormones from the pituitary gland in two different ways. Posterior Pituitary: Nerve impulses travel down the axons of hypothalamic neurons, causing hormone release from their axon terminals in the posterior pituitary. Paraventricular nucleus Hypothalamus 1 Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH). Posterior lobe of pituitary Optic chiasma Supraoptic nucleus Infundibulum (connecting stalk) Hypothalamohypophyseal tract Inferior hypophyseal artery 2 Oxytocin and ADH are transported down the axons of the hypothalamohypophyseal tract to the posterior pituitary. Axon terminals Posterior lobe of pituitary 3 Oxytocin and ADH are stored in neurosecretory bodies in the posterior pituitary. Oxytocin Antidiuretic Hormone (ADH) 4 When associated hypothalamic neurons fire, nerve impulses arriving at the neurosecretory bodies cause oxytocin or ADH to be released into the blood. © 2014 Pearson Education, Inc. Figure 17.6 The parathyroid glands. Pharynx (posterior aspect) Capillary Thyroid gland Esophagus Parathyroid glands Photomicrograph of parathyroid gland embedded within the thyroid gland (2) © 2014 Pearson Education, Inc. Trachea Illustration of parathyroid glands embedded within the thyroid gland, posterior view Parathyroid cells (secrete parathyroid hormone) Oxyphil cells Photomicrograph of parathyroid gland (205) Figure 17.7 The adrenal gland, gross and microscopic structure. Hormones secreted Adrenal gland Medulla Cortex Cortex Capsule Zona glomerulosa Aldosterone Zona fasciculata Cortisol and androgens Kidney Medulla Zona reticularis Adrenal medulla Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla © 2014 Pearson Education, Inc. Epinephrine and norepinephrine Photomicrograph (120) Figure 17.8 Stress and the adrenal gland. Short-term stress Prolonged stress Stress Nerve impulses Hypothalamus CRH (corticotropinreleasing hormone) Spinal cord Corticotropic cells of anterior pituitary Preganglionic sympathetic fibers To target in blood Adrenal medulla (secreted amino acid– based hormones) Catecholamines (epinephrine and norepinephrine) Short-term stress response • Heart rate increases • Blood pressure increases • Bronchioles dilate • Liver converts glycogen to glucose and releases glucose to blood • Blood flow changes, reducing digestive system activity and urine output • Metabolic rate increases © 2014 Pearson Education, Inc. Adrenal cortex (secretes steroid hormones) ACTH Mineralocorticoids Glucocorticoids Long-term stress response • Kidneys retain sodium and water • Blood volume and blood pressure rise • Proteins and fats converted to glucose or broken down for energy • Blood glucose increases • Immune system suppressed Figure 17.9 Photomicrograph of a pancreatic islet. Pancreas Pancreatic islet (Glucagonproducing) cells (Insulinproducing) cells Pancreatic acinar cells (exocrine) © 2014 Pearson Education, Inc. Figure 17.10 Disorders of pituitary growth hormone. © 2014 Pearson Education, Inc. Figure 17.11 Thyroid disorders. Protrusion of the eyeballs; symptom of hyperthyroidism © 2014 Pearson Education, Inc. An enlarged thyroid (goiter); due to iodine deficiency Figure 17.12 The effects of excess glucocorticoid. Patient before onset © 2014 Pearson Education, Inc. Same patient with Cushing’s syndrome. The white arrow shows the characteristic “buffalo hump” of fat on the upper back. Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (1 of 4) © 2014 Pearson Education, Inc. Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (2 of 4) © 2014 Pearson Education, Inc. Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (3 of 4) © 2014 Pearson Education, Inc. Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (4 of 4) © 2014 Pearson Education, Inc.