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Transcript
ENDOCRINE SYSTEM Mechanisms of Chemical Signaling: a Review Water-Soluble/Nonsteroid Hormones Lipid-Soluble/Steroid Hormones Control Pathways and Feedback Loops • There are three types of hormonal control pathways Pathway Example Low blood glucose Stimulus Receptor protein Pancreas secretes glucagon ( ) Endocrine cell Blood Response Example Stimulus Suckling Sensory neuron Example Pathway Stimulus Sensory neuron Hypothalamus/ posterior pituitary Hypothalamus Neurosecretory cell Posterior pituitary secretes oxytocin Blood ( ) vessel vessel Target effectors Pathway Neurosecretory cell Blood vessel Hypothalamic neurohormone released in response to neural and hormonal signals Hypothalamus secretes prolactinreleasing hormone ( ) Liver Glycogen breakdown, glucose release into blood (a) Simple endocrine pathway Target effectors Response Smooth muscle in breast Milk release Endocrine cell Blood vessel Anterior pituitary secretes prolactin ( ) (b) Simple neurohormone pathway Target effectors Response Figure 45.2a–c Mammary glands Milk production (c) Simple neuroendocrine pathway One Chemical Signal, Different Effects 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 or feedback inhibition – a stimulus produces a response that opposes the original stimulus; an environmental change “feeds back” to inhibit the original stimulus. The Reproductive Cycle of the Human Female 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 Feedback control loops regulating the secretion of thyroid hormones T3 and T4 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 PITUITARY GLAND • Often called the “master gland” because it secretes so many hormones (9 total!) • Has two parts: Anterior Pituitary and Posterior Pituitary Remember the acronym: “MAP TO FLAG” to remember the nine pituitary hormones • The pituitary sits just below the hypothalamus which 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 ANTERIOR PITUITARY • Secretes seven hormones: –Growth Hormone (GH) – stimulates bone and muscle growth –Adrenocorticotropic Hormone (ACTH) stimulates the adrenal cortex to secrete hormones (corticosteroids) 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 Anterior Pituitary Gland: Thyroid-Stimulating Hormone (TSH) • Stimulates the thyroid to secrete thyroxine Follicle-Stimulating Hormone (FSH) • 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 (MSH) : 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 Glucose homeostasis maintained by insulin and glucagon 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) What is the advantage of having both a nervous system and an endocrine system? What does the hormone thyroxine affect? What is one effect of an iodine deficient diet? Insulin stimulates cell to remove sugar from the blood while ___________ stimulates the release of glucose from cells. A shortage of dietary iodine makes it impossible for the thyroid gland to produce thyroxine. What would happen to blood levels of thyroxine and the thyroid gland as a result? The role of ADH is to: What is the difference between Type I and Type II diabetes? • The thyroid also increases the concentration of calcitonin which decreases the blood’s concentration of calcium.