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All Multicellular Organisms Must Coordinate Their Functions • The many cells, tissues, and organs in the animal body need to communicate so that the whole organism can develop and function effectively • The endocrine system consists of different types of secretory cells that release a variety of signaling molecules called hormones The Endocrine System • Animal hormones are produced by specialized cells that are often organized into discrete organs called endocrine glands • Endocrine glands release hormones into body fluids, which then carry these chemical messengers throughout the body • Some endocrine cells are embedded as single cells or clusters of cells within other specialized tissues and organs The Endocrine System • The hypothalamus is responsible for coordinating the endocrine system and integrating it with the nervous system • The hypothalamus contains both neurons that interact with the brain and also endocrine cells that produce hormones The Endocrine System • The hypothalamus makes releasing and inhibiting hormones that direct the pituitary to release another set of hormones • These hormones from the pituitary will travel through the circulatory system to regulate the various endocrine glands. The Endocrine System • Hormones are often distributed through the body by the circulatory system and therefore move only as fast as blood is circulated • Hormones are effective in small amounts because they bind to target cells with great specificity and tenacity Hormones and their Target Cell • A hormone released by one cell causes one or more specific responses in the target cells, which may lie in more than one type of tissue • Hormones can act on target cells by binding to plasma membrane receptors or intracellular receptors Hormones and their Target Cell • A single hormone can produce a diversity of effects in a variety of potential target cells Hormonal Signals to the Cell • Hormonal signals are amplified inside the target cell and alter key cellular processes • There are four main categories of cellular responses produces by a hormonal signal: – Changes in protein production – Changes in metabolism – Changes in the activity of the cytoskeleton – Changes in plasma membrane transport Hormonal Signals to the Cell • Animals usually produce hormones in tiny amounts measured in micrograms • When hormone molecules bind to receptors in the target cell, they set in motion a chain of events that may activate thousands of protein molecules in that cell • Through signal amplification, just a few hormone molecules can have a substantial impact on the whole body Hormonal Signals to the Cell • Signal transduction is the process in which a signal received by a membrane receptor is relayed within the cytoplasm to produce responses from the target cell • Notice the amplification of the singnal Hormonal Signals to the Cell • Some hormones bind to receptors on the plasma membrane • Others, like steroids, are able to cross the plasma membrane and deliver the hormonal message within the cell Specific Hormonal Processes we will Cover Glucose homeostasis The fight-or-flight response Growth Menstruation Glucose Homeostasis • Hormones that regulate homeostasis must act quickly to maintain a constant internal environment • Glucose homeostasis is controlled by the pancreas • The pancreas, function as endocrine glands and also as exocrine (ducted) glands • The pancreas contains clusters of endocrine cells called islet cells that produce and release insulin and glucagon Glucose Homeostasis • Insulin and glucagon are hormones that act in opposite ways to maintain homeostasis in blood glucose levels • Insulin acts on target cells throughout the body, but especially in the liver, fat tissue, and skeletal muscles, signaling these cells to increase their uptake of glucose from the blood • Insulin= into cell out of blood • Causes decrease blood sugar • Glucagon= gone from cell into blood • Causes increased blood sugar Disruption in Glucose Homeostasis: Diabetes • Too much glucose in the blood results in diabetes • Most cases of type 1 diabetes result from: – autoimmune damage to the islet cells preventing insulin production or – production of a defective form of insulin by the pancreas • Type 2 diabetes occurs when: – too little insulin is produced or – the receptors on target cells respond poorly to insulin Short Term Control: Fight-or-Flight Response • The adrenals regulate the fight-or-flight response • The adrenal glands are a pair of endocrine glands that sit on top of the kidneys and release epinephrine and norepinephrine, which coordinate our response to sudden stress Short Term Control: Fight-or-Flight Response • Epinephrine stimulates glycogen breakdown in liver and skeletal muscle cells, which raises blood glucose levels and in turn increases the speed and force with which the heart contracts Regulating Long-Term Processes: Growth • The pituitary gland produces growth hormone (GH), which promotes the growth of bones and stimulates increases in muscle mass • Too much or too little GH can have lifelong consequences on an individual, resulting in a variety of conditions Regulating Long-Term Processes: Reproduction • Animals rely on hormones to regulate nearly all aspects of reproduction • In humans, hormones influence nearly all aspects of sexual development and reproduction, including sperm production in males and the menstrual cycle of women Sex Hormones Play a Role in Sexual Development before Birth • It is through the action of the hormones that a fetus develops into a male or a female • By the seventh week of the fetus’s development, the sex glands, or gonads, are producing the sex hormones • These sex hormones signal genes in their target cells to begin the process of sexual development • The gonads of both sexes produce estrogens, progestogens, and androgens in varying amounts Sex Hormones Play a Role in Sexual Development before Birth • Estrogen produces female characteristics, while progestogens, including progesterone, create a suitable environment for a developing fetus • Androgens, such as testosterone, stimulate cells to develop the characteristics of maleness Sex Hormones Coordinate Sexual Maturation at Puberty • During puberty, the hypothalamus makes Gonadotropin Releasing Hormone (GnRH) that activates the production of gonadatropins made in the pituitary gland • These gonadatropins, Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) coordinate the development of sperm in males and play a role in regulating the menstrual cycle in females GnRH Sex Hormones Coordinate the Menstrual Cycle • In humans females, individual eggs mature and are released in a hormone-driven sequence of events known as the menstrual cycle • The menstrual cycle is marked by a succession of hormones that stimulate the release of an egg and prepare the uterine lining to grow and thicken in preparation for a potential pregnancy • Between 40 and 50 years of age, a drop in the levels of estrogen and progesterone results in menopause, in which the menstrual cycle ceases permanently Sex Hormones Coordinate the Menstrual Cycle • The menstrual cycle is marked by a succession of hormones that stimulate the release of an egg and prepare the uterine lining to grow and thicken in preparation for a potential pregnancy Sex Hormones Coordinate the Menstrual Cycle