1/29/2015 Endocrine System | Principles of Biology from Nature Education contents Principles of Biology 139 Endocrine System The endocrine system interacts with the nervous system to maintain homeostasis, regulate growth and development, and modulate behavior. A mother spotted hyena (Crocuta crocuta) and cubs. This mother hyena cares for her cubs, a behavior that is modulated by the endocrine system. © 2010 Nature Publishing Group Höner, O. et al. The fitness of dispersing spotted hyaena sons is influenced by maternal social status. Nature Communications 1, (2010) doi:10.1038/ncomms1059. Used with permission. Topics Covered in this Module Endocrine System Function Major Organs of the Endocrine System The Hypothalamus and Pituitary Glands The Thyroid and Parathyroid Glands The Gonads The Adrenal Gland The Pineal Gland The Pancreas Major Objectives of this Module Give examples of how the endocrine system uses hormones to regulate homeostasis. Explain how certain behaviors are triggered by hormones. Describe how hormones regulate reproduction and the development of sex characteristics. Describe the major glands of the endocrine system. page 710 of 986 8 pages left in this module http://www.nature.com/principles/ebooks/principles­of­biology­104015/29145735 1/1 1/29/2015 Endocrine System | Principles of Biology from Nature Education contents Principles of Biology 139 Endocrine System Endocrine System Function The endocrine system produces a variety of complex responses to stimuli. Some responses are immediate and temporary, such as the increases in heart, respiratory, and metabolic rates associated with an "adrenaline rush," while others are long term, such as the testosterone­ and estrogen­associated development of secondary sexual characteristics during puberty. Organs of the endocrine system are ductless glands called endocrine glands. In addition to dedicated glands, specialized hormone­producing cells within non­endocrine organs such as the intestines, heart, and kidney are also part of the endocrine system. In response to certain stimuli, endocrine cells secrete hormones into the bloodstream. From there, hormones travel to their target cells in tissues throughout the body. Major Organs of the Endocrine System The location of major endocrine glands in the human body is summarized in Figure 1. Three of these glands, the hypothalamus, the pituitary gland, and the pineal gland, are found in the brain. The thyroid and parathyroid are located in the neck. The pancreas is located beneath the stomach. The adrenal glands sit on top of the kidneys. The ovaries are located on either side of the uterus, and the testes are located in the scrotum. Endocrine cells are also associated with the thymus (which is part of the immune system), heart, liver, stomach, kidneys, and small intestine. Figure 1: Location of major endocrine organs in the human body. © 2014 Nature Education All rights reserved. Some hormones, called tropic hormones, regulate the secretion of hormones by another endocrine gland or cell. The hypothalamus, which is the regulatory center of the endocrine system, releases two types of tropic hormones that regulate hormone production by the anterior pituitary: releasing hormones that stimulate hormone production and inhibiting hormones that repress hormone production. Non­tropic hormones are hormones that directly produce an effect on target cells. The hormones produced by the major endocrine glands are summarized in Table 1. http://www.nature.com/principles/ebooks/principles­of­biology­104015/29145735/1 1/3 1/29/2015 Endocrine System | Principles of Biology from Nature Education Table 1: Hormones produced by major organs of the endocrine system. © 2014 Nature Education All rights reserved. IN THIS MODULE Endocrine System Function Major Organs of the Endocrine System http://www.nature.com/principles/ebooks/principles­of­biology­104015/29145735/1 2/3 1/29/2015 Endocrine System | Principles of Biology from Nature Education The Hypothalamus and Pituitary Glands The Thyroid and Parathyroid Glands The Gonads The Adrenal Gland The Pineal Gland The Pancreas Summary Test Your Knowledge WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cutting­edge research lead to prevention and treatment strategies that could make cancer obsolete? PRIMARY LITERATURE Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download Classic paper: Breakthrough enables tiny measurements of ion channel activity (1976) Single­channel currents recorded from membrane of denervated frog muscle fibers. View | Download How can nematodes help reduce obesity in humans? A whole­organism screen identifies new regulators of fat storage. View | Download page 711 of 986 7 pages left in this module http://www.nature.com/principles/ebooks/principles­of­biology­104015/29145735/1 3/3 1/29/2015 Endocrine System | Principles of Biology from Nature Education contents Principles of Biology 139 Endocrine System The Hypothalamus and Pituitary Glands Most activities of the endocrine system are directly or indirectly regulated by the hypothalamus, a region in the brain critical for maintaining homeostasis. Importantly, the hypothalamus also serves as the primary link between the nervous system and the endocrine system. The pituitary gland, which hangs beneath the hypothalamus, has anterior and posterior lobes. The posterior pituitary is an extension of the hypothalamus. Specialized neurons, called neurosecretory neurons, extend from the hypothalamus into the posterior pituitary. These neurons produce two hormones, oxytocin and vasopressin (also called antidiuretic hormone, or ADH). Oxytocin promotes maternal bonding and milk production and stimulates contractions during labor. Vasopressin regulates water and salt balance. The anterior pituitary, which is regulated by releasing and inhibiting hormones secreted from the hypothalamus, produces both tropic and non­tropic hormones. Thyroid­stimulating hormone (TSH) is considered a tropic hormone because it stimulates the production of thyroid hormones by the thyroid gland. Thyrotropin­releasing hormone (TRH), a releasing hormone produced by the hypothalamus, stimulates TSH secretion. Growth hormone (GH), which directly stimulates growth and cell division in a wide variety of cells, is an example of a non­tropic hormone. Pituitary hormones and behavior. Some hormones secreted by the pituitary affect behavior. For example, oxytocin, which is secreted by the posterior pituitary, and prolactin, which is secreted by the anterior pituitary, are both involved in parental bonding. Recent studies indicate that prolactin may even be involved in parental bonding in non­mammals. For example, a study of the male North American bluegill fish (Lepomis macrochirus) indicates that disruption of prolactin signaling alters behavior associated with paternal care. Male bluegills take exclusive responsibility for care of eggs. When a prolactin antagonist (a drug that prevents prolactin from binding its receptor) was administered to male fish caring for eggs, behavior associated with paternal care, such as fanning eggs, diminished. IN THIS MODULE Endocrine System Function Major Organs of the Endocrine System The Hypothalamus and Pituitary Glands The Thyroid and Parathyroid Glands The Gonads The Adrenal Gland The Pineal Gland The Pancreas Summary Test Your Knowledge WHY DOES THIS TOPIC MATTER? Cancer: What's Old Is New Again Is cancer ancient, or is it largely a product of modern times? Can cutting­edge research lead to prevention and treatment strategies that could make cancer obsolete? PRIMARY LITERATURE Adaptor proteins regulate cell signaling Structural basis for regulation of the Crk signaling protein by a proline switch. View | Download Classic paper: Breakthrough enables tiny measurements of ion channel activity (1976) Single­channel currents recorded from membrane of denervated frog muscle fibers. View | Download How can nematodes help reduce obesity in humans? A whole­organism screen identifies new regulators of fat storage. View | Download page 712 of 986 6 pages left in this module http://www.nature.com/principles/ebooks/principles­of­biology­104015/29145735/2 1/2 1/29/2015 Endocrine System | Principles of Biology from Nature Education http://www.nature.com/principles/ebooks/principles­of­biology­104015/29145735/2 2/2 1/29/2015 Endocrine System | Principles of Biology from Nature Education contents Principles of Biology 139 Endocrine System The Thyroid and Parathyroid Glands The thyroid gland, located in the neck in humans, plays an important role in metabolism. The thyroid secretes two thyroid hormones, triiodothyronine (T3) and thyroxine (T4), which increase the metabolic rate of most cells in the body. The thyroid also produces calcitonin, a hormone that reduces the concentration of calcium ions in the blood. Calcitonin inhibits calcium ion absorption in the intestines and calcium ion reabsorption by the kidneys. Calcitonin also inhibits the action of osteoclasts, cells that reabsorb (break down) bone tissue. However, in humans, calcitonin appears to play a relatively minor role in calcium ion homeostasis. Parathyroid hormone (PTH), which is produced by four small glands, called parathyroid glands, that are located on the surface of the thyroid, increases serum calcium ion levels. PTH promotes calcium ion absorption by the intestines and reabsorption by the kidneys and stimulates bone reabsorption