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Transcript
Chapter 17 The Endocrine System and Development Endocrine system Mostly comprised of glands Other organs and tissues also produce and secrete hormones Secretes hormones that move through the bloodstream to target cells o Allows communication between different parts of the body o Results in a slow but prolonged response Hormones Hormones are chemical signals that promotes communication between cells, body parts, and even individuals Steroid hormones - lipids that enter a cell to affect gene activity and thus protein synthesis Nonsteroid hormones - bind to a receptor in the plasma membrane causing the formation of cAMP which activates a cascade of enzymes o Regardless of whether it is a steroid or nonsteroid hormone, the target cell must have the proper receptor for the hormone to have an effect Major glands of the endocrine system Hypothalamus Regulates the internal environment through the autonomic nervous system o Helps control heartbeat o Helps control body temperature o Helps control water balance o Controls glandular secretions Posterior pituitary gland Stores antidiuretic hormone (ADH) and oxytocin that are produced by the hypothalamus o ADH - regulates water balance by reabsorbing water into the bloodstream o Oxytocin - causes uterine contractions during childbirth and allows milk to be released during nursing Anterior pituitary gland Controlled by hypothalamic-releasing and hypothalamic-inhibiting hormones Hormones produced by the anterior pituitary o Thyroid-stimulating hormone (TSH) - stimulates the thyroid to produce thyroid hormones o Adrenocorticotropic hormone (ACTH) - stimulates the adrenal cortex to produce cortisol o Gonadotropic hormones - stimulate the gonads to produce sex cells and hormones o Prolactin (PRL) - stimulates the mammary glands to develop and produce milk after childbirth o Melanocyte-stimulating hormone (MSH) - causes skin cells to produce melanin o Growth hormone (GH) - promotes skeletal and muscular growth What happens when the body produces too much or too little GH? Pituitary dwarfism – too little GH is produced during childhood resulting in small stature Giantism – too much GH is produced during childhood resulting in large stature but overall poor health Acromegaly – overproduction of GH as an adult that results in larger than normal feet, hands, and face Adrenal glands Glands that sit on top of the kidneys 2 parts of each gland o Adrenal medulla - controlled by the nervous system o Adrenal cortex - portions are controlled by ACTH from the anterior pituitary Adrenal medulla o Inner portion of the adrenal glands o Hypothalamus initiates stimulation of hormone secretion in the adrenal medulla o Produces hormones that allow a short-term response to stress (“fight or flight” response) Epinephrine (adrenaline) Norepinephrine Adrenal cortex o Outer portion of the adrenal glands o Produces hormones that provide a longer-term response to stress o 2 major types of hormones Mineralocorticoids regulate salt and water balance e.g. aldosterone (targets the kidney) Glucocorticoids regulate carbohydrate, protein, and fat metabolism Suppress the body’s inflammatory response e.g. cortisol and cortisone Adrenal glands can malfunction Addison’s disease – hyposecretion of glucocorticoids by the adrenal cortex characterized by bronzing of the skin Cushing syndrome – hypersecretion of glucocorticoids by the adrenal cortex characterized by weight gain in the trunk of the body but not the arms and legs Thyroid gland A large gland located below the larynx o Iodine is needed in the diet to allow the thyroid gland to produce its hormones o Thyroid hormone (TH) - regulates overall metabolism o Calcitonin - helps lower blood Ca2+ levels by stimulating the deposition of calcium in the bones Thyroid abnormalities o Simple goiter – thyroid enlarges due to lack of iodine in the diet o Hypothyroidism – low blood levels of thyroid hormones o Congenital hypothyroidism - thyroid does not develop properly and is characterized in a short, stocky person that may be mentally retarded o Myxedema - hypothyroidism in adults characterized by lethargy, weight gain, loss of hair, cold intolerance, and thick, puffy skin o Hyperthyroidism – excess thyroid hormones in the blood o Exophthalmic goiter - such as seen in Graves' disease and is characterized by enlargement of the thyroid gland, protrusion of the eyes, hyperactivity, and insomnia o Thyroid tumor - can also cause hyperthyroidism Parathyroid glands o Small glands embedded in the surface of the thyroid gland o Produce parathyroid hormone (PTH) o Causes blood Ca2+ level to increase by promoting osteoclast activity o Promotes reabsorption of Ca2+ by the kidneys Thymus gland o Lies beneath the sternum o This gland is largest and most active during childhood o T lymphocytes mature here o Secretes hormones called thymosins that aid in differentiation of lymphocytes Pineal gland o Located in the brain o Secretes melatonin that regulates the sleep/wake cycle (circadian rhythm) o May also regulate sexual development Pancreas o Fish-shaped organ behind the stomach o Composed of 2 tissues o Exocrine produces and secretes digestive juices o Endocrine (islets of Langerhans) produces and secretes hormones Insulin – secreted when blood glucose is high and stimulates the uptake of glucose by muscle and liver cells Glucagon – secreted when blood glucose is low and stimulates the breakdown of glycogen in the liver Diabetes o Inability to control blood glucose levels o There are two types: Type 1 and Type 2 o 18 million people in the US have diabetes o General symptoms: o Frequent urination o Unusual hunger and/or thirst o Unexplained change in weight o Blurred vision o Sores that heal slowly or not at all o Excessive fatigue o Long-term effects are blindness, loss of limbs, nerve deterioration, kidney and cardiovascular disease Type 1 o Usually early-onset o Autoimmune disorder that tends to run in families o Pancreatic cells are attacked and cannot produce insulin o Require insulin injections Type 2 o Usually adult-onset and the most common type o Tends to occur in obese, sedentary people o Cells do not respond to insulin o Usually diet and exercise are important for controlling this and may even prevent this Hormones from other tissues o Erythropoietin - secreted by the kidney to increase red blood cell production o Leptin - produced by fat cells and acts on the hypothalamus to give a feeling of being satiated o Prostaglandins o A group of potent chemicals that work locally on neighboring cells o Some cause smooth muscle contraction o Major impact on reproductive organs o Many other roles in the body o Aspirin and ibuprofen block the synthesis of these Homeostasis o The nervous and endocrine systems are important in maintaining homeostasis o The hypothalamus bridges the regulatory functions of both systems o Both systems are able to respond to changes in the external environment Development o Hormones signal and control the sequential growth and maturation from the neonatal period and infancy, through childhood, adolescence, adulthood, and senescence Aging o There are 3 hypotheses for aging o Limits on cellular division o Accumulated cell damage o Demise of organ systems