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Transcript
ENDOCRINE SYSTEM ENDOCRINE GLANDS • Are ductless and secrete hormones directly into the bloodstream • Target Cells – the cells that a hormone directly affects; if a cell does not have receptors or the receptors don’t respond, the hormone has no effect. Human Endocrine Glands • Most hormones operate by a negative feedback system – an excess of a hormone will cause the gland to stop producing it THE PITUITARY GLAND • Often called the “master gland” because it secretes so many hormones (9 total!) • Has two parts: Anterior Pituitary and Posterior Pituitary • The pituitary sits just below the hypothalamus • The hypothalamus regulates the anterior pituitary by secreting neurosecretory hormones that can stimulate or inhibit the actions of it Hormones of the hypothalamus and pituitary glands Nerve cells that release hormones into the blood Remember the acronym: “MAP TO FLAG” to remember the nine pituitary hormones ANTERIOR PITUITARY • Secretes six hormones: –Growth Hormone (GH) – stimulates bone and muscle growth –Adrenocorticotropic Hormone (ACTH) stimulates the adrenal cortex to secrete hormones (corticosteroids) Anterior Pituitary Gland: Thyroid-Stimulating Hormone (TSH) • Stimulates the thyroid to secrete thyroxine Follicle-Stimulating Hormone • Stimulates the follicle to grow in females, oogenesis, and spermatogenesis Anterior Pituitary Gland: Luteinizing Hormone • Causes the release of the ovum during the menstrual cycle in females and testosterone production in males Anterior Pituitary Gland: Prolactin • Stimulates the mammary glands to produce milk Anterior Pituitary Gland Melanocyte-Stimulating Hormone: Regulates skin color in lower vertebrates, although its function In humans is unknown Posterior Pituitary Gland: • Secretes Two Hormones: (made by hypothalamus) • Antidiuretic Hormone (ADH) – acts on the kidneys, increasing water retention and thus decreasing urine volume. Posterior Pituitary Gland •Oxytocin – is secreted by the stimulation of the nipples during breast feeding and sexual intercourse; it also stimulates uterine contractions during labor ADRENAL GLANDS • Adrenal Medulla – secretes epinephrine (adrenaline) and norepinephrine(noradrenaline) “fight-or-flight” response – increase HR, BP, metabolism, etc ADRENAL CORTEX • ACTH – causes the adrenal cortex to produce its different hormones •Glucocorticoids – target the liver and promote the release of glucose Adrenal Cortex: • Mineralcorticoids – target the kidney and promote the retention of water • Ex: Aldosterone – increases recovery of Na and increases excretion of K and H ions into the urine THYROID GLAND • Located in the neck, is the target gland of thyroidstimulating hormone (TSH) • When the thyroid is stimulated by TSH it releases the hormones Triiodothyronine (T3) and Thyroxine (T4), which regulates the metabolic rate of your body tissues • The thyroid also increases the concentration of calcitonin which decreases the blood’s concentration of calcium PARATHYROID GLANDS • These are four pea-shaped organs that rest on the thyroid They secrete parathyroid hormone which increases blood calcium levels – the opposite effect of what calcitonin does An example of how feedback regulation maintains homeostasis THE PANCREAS • Glucagon – stimulates the liver to convert glycogen into glucose and to release that glucose into the blood • Insulin – has the opposite effect of glucagon Major Vertebrate Endocrine Glands and Some of Their Hormones Major Vertebrate Endocrine Glands and Some of Their Hormones (Pancreas–Thymus) Glucose homeostasis maintained by insulin and glucagon Feedback control loops regulating the secretion of thyroid hormones T3 and T4