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Body control systems Endocrine system Endocrine system Controls body activities by releasing hormones Slower responses Broader influence Hormones are carried by the blood to target cells Endocrine glands release hormones into bloodstream Hormones are carried to all cells of the body, but only affect certain cells Regulate the metabolism of target cells Hormones alter activities of cells in different parts of the body Endocrine cell How do hormones know which cells to communicate with? Membraneenclosed sacs Blood vessel Hormone molecules Hormone Receptor Target cell Adrenal glands (type of endocrine gland), which sit atop the kidneys Receptor protein Each hormone has a receptor that fits it like a key into a lock. “Target Cells” Target cells have receptors for particular hormones. Figure 25.1 How do hormones travel to target cells? In the blood! Why do hormones only affect certain cells? Water soluble hormones: Dissolved in blood Hormones only affect target cells, cells that have receptors for that specific hormone Target cell Receptor protein Lipid soluble hormones: Attached to transport proteins (blood is watery, so fat soluble chemicals can’t mix well on their own) Steroid Hormone Hormones have a wide range of targets There are two main classes of hormones Some, like sex hormones, affect most of the tissues of the body Others, like glucagon, have only a few target cells (in this case, liver and fat cells) Some target other endocrine glands Peptide hormones the pituitary targets the ovaries, testes, thyroid gland Most common type of hormone Short chains of amino acids Water soluble, circulate in a “free” form (not attached to plasma proteins) Some hormones have different responses in different target cells Copyright 2009, John Wiley & Sons, Inc. There are two main classes of hormones There are two main classes of hormones Steroid hormones The main difference is their solubility Fat-soluble Can diffuse thru cell membranes Bind to transport proteins in blood Peptide hormones Steroid hormones Steroid Hormone water-soluble cannot penetrate the cell membrane lipid-soluble pass directly through the phospholipid bilayer of cell membranes This single difference translates into completely different modes of action Action of steroid hormones Action of peptide hormones Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Hormone binds to a receptor in the plasma membrane. Hormone binds to a receptor in the plasma membrane Activates a second messenger in the target cell Alters cell functions peptide hormone 1. receptor protein 2. 2. Binding leads to activation of an enzyme that changes ATP to cAMP . plasma membrane ATP 3. cAMP (second messenger) 3. cAMP activatesan enzyme cascade. 4. Many molecules of glycogen are broken down to glucose, which enters the bloodstream. glucose (leaves cell and goes to blood) glycogen Action of glucagon on liver steroid hormone 1. Hormone diffuses through plasma membrane because it is lipid soluble. capillary 4. Diffuse thru membrane Bind to receptors inside target cells The hormone-receptor complex binds to the DNA and alters gene expression New proteins are made → changes the cell’s activity plasma membrane cytoplasm nucleus 2. Hormone binds to receptor inside nucleus. protein DNA receptor protein mRNA 3. Hormone-receptor complex activates gene and synthesis of a specific mRNA molecule follows. ribosome mRNA 4. mRNA moves to ribosomes, and protein synthesis occurs. Mechanism of action: Estrogen Estrogen binds to estrogen receptors in the cell nucleus Switches on/off transcription of specific genes Hormones need tight controls Most hormones are released in short bursts Hormone secretion is controlled by 1. Signals from the nervous system TSH 2. Changes in blood chemicals (glucose, calcium) 3. Other hormones Most hormone secretion is regulated by negative feedback “Master” endocrine glands: the hypothalamus and pituitary Hypothalamus – major link between nervous and endocrine system The hypothalamus Hypothalamus and pituitary secrete hormones These hormones regulate all aspects of growth, development, metabolism, and homeostasis Copyright 2009, John Wiley & Sons, Inc. The pituitary Infundibulum (stalk) It controls secretion of hormones by the pituitary gland Copyright 2009, John Wiley & Sons, Inc. The posterior pituitary is actually an extension of the hypothalamus Anterior pituitary Receives information from the nervous system Secretes hormones Anterior pituitary hormones Posterior pituitary Is the main control center of the endocrine system. Integrates nervous and endocrine control Human growth hormone (hGH) It stores and secretes hormones made in the hypothalamus Acts in water regulation and childbirth The anterior pituitary secretes 7 hormones which in turn stimulate other endocrine glands Thyroid stimulating hormone (TSH) Infundibulum Anterior pituitary Follicle stimulating hormone (FSH) Luteinizing hormone (LH) Prolactin (PRL) Adrenocorticotropic hormone (ACTH) Melanocyte-stimulating hormone (MSH) Human Growth Hormone (hGH) Human growth hormone ↑ Growth of bones & muscles Has a broad effect on the body Causes cells in liver, muscles, bones and other tissues to grow and multiply Increases breakdown of fat in adipose tissue Immune System Stimulated Breakdown of stored nutrients (ex. release of sugars to blood) Numerous growth diseases involve hGH Low hGH Pituitary Dwarfism Releases fatty acids for ATP production High hGH in Childhood Gigantism Hormones regulate the rate of metabolism High hGH in Adulthood Acromegaly Thyroxine (T3/T4) Secreted by the thyroid gland Increases the metabolic rate hGH Insulin In adults, arm/leg bones have finished growing, but facial bones can be stimulated to grow more Regulation of T3 and T4 secretion Thyroxine Secreted by the thyroid Thyroid produces thyroid hormones T4 = Thyroxine T3 = Triiodothyronine Both stimulate cell metabolism Copyright 2009, John Wiley & Sons, Inc. 1 Low blood levels of T3 and T 3 or low metabolic rate stimulate release of Low blood T3/T4 or low metabolic rate Hypothalamus TRH 2 TRH, carried Release of TRH Release of TSH Synthesis of T3 and T4 by thyroid gland ↑ T3/T4 in blood Negative feedback by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs 5 Elevated T3inhibits release of TRH and TSH (negative feedback) TSH 3 TSH released into blood stimulates thyroid follicular cells Anterior pituitary 4 T3 and T4 Thyroid follicle released into blood by follicular cells Thyroid Gland Disorders: hypothyroidism Actions of T3/T4 Affect most body cells If have receptors for thyroid hormones Increased metabolism Growth and development Stimulate protein synthesis Increase use of glucose and fatty acids for ATP production Why does the thyroid gland enlarge? X Congenital hypothyroidism during fetal life or infancy → severe mental retardation (cretinism) Excess thyroid hormones The most common form of hyperthyroidism is Graves’ disease X enlargement of the thyroid gland Hyperthyroidism X Too little thyroid hormone Due to dietary deficiency of iodine or from a defective thyroid gland Sx: Goiter an autoimmune disease. Produce antibodies that mimic the action of TSH and continually stimulate the thyroid gland Sx: enlarged thyroid, protruding eyes (exophthalmos) Copyright 2009, John Wiley & Sons, Inc. The pancreas has a dual role Blood glucose homeostasis Insulin Glucagon It secretes • digestive enzymes • hormones insulin & glucagon regulate body’s energy supplies Pancreatic Beta cells secrete insulin Insulin Regulation of Blood Glucose After a meal, blood sugar levels rise Pancreas secretes insulin Insulin lowers blood sugar by stimulating liver, muscle and fat cells to take up glucose Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucagon is a peptide hormone It binds to receptors on the membrane of target cells Supplies energy to the brain and active muscle Insulin and glucagon have opposite effects Why does glucagon stimulate liver and not stomach cells? When blood glucose levels are low, the pancreas secretes glucagon Glucagon stimulates liver and muscle cells to break down stores of glycogen, releasing glucose into the blood Glucagon increases blood sugar between meals Target cell Receptor protein Both insulin and glucagon regulate the body’s energy supplies Insulin Glucagon ↓ blood sugar levels ↑ blood sugar levels Copyright 2009, John Wiley & Sons, Inc. How insulin stimulates glucose uptake Glucose transporters In the absence of insulin, only a few glucose transporters are on the cell surface Insulin binds to its receptor Insulin recruits glucose transporters from inside the cell to the cell surface Glucose is transported into cells Pancreatic Disorders Diabetes mellitus is a common and serious impairment of glucose homeostasis the body loses control of the level of glucose in the blood One of the most serious chronic diseases in the US $92 billion a year in health care costs ~7% of the U.S. population has diabetes The sixth leading cause of death Type I Diabetes Insulin and type 1 diabetes (4:03) Type 2 diabetes Autoimmune disease Destroys cells that make insulin Most common form Occurs most often in children and young adults The patient must monitor the level of glucose in the blood and inject insulin when it climbs Complications: damage to blood vessels in retina and kidneys Rx: insulin injections Insulin resistance 90% of diabetics 55% are obese Cells don’t respond to insulin Can’t absorb glucose properly Can be controlled by diet, exercise and weight loss http://www.youtube.com/watch?v=OYvav8aDGCc Gestational diabetes Calcium Homeostasis Pregnant women who have never had diabetes before but who have high blood glucose levels during pregnancy Affects about 4% of all pregnant women It may precede development of type 2 diabetes Calcitonin and PTH have opposing actions These hormones have opposite effects on blood calcium levels Calcitriol (vitamin D) Figure 25.10 Three hormones regulate blood calcium levels Calcitriol (vitamin D) Calcitonin Parathyroid hormone (PTH) Calcitriol (vitamin D)