Biological Sciences
Endocrine System
The endocrine system is a network of glands that produce and release hormones to regulate various bodily functions, such as metabolism, growth, and reproduction. These hormones are transported through the bloodstream to target organs and tissues, where they help maintain homeostasis and coordinate the body's responses to internal and external stimuli.
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9 Key excerpts on "Endocrine System"
eBook - PDF- Ian Peate, Suzanne Evans, Amy Byrne, Will Deasy, Michele Dowlman, Pauline Gillan, Siva Purushothuman, Dan Wadsworth(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Owing to its rapid onset of action, the nervous system is responsible for the control of rapid bodily processes such as breathing and movement. The Endocrine System is often responsible for the regulation of longer-term processes. The major functions it coordinates are: • homeostasis — maintains the internal body environment • storage and utilisation of energy substrates (carbohydrates, proteins and fats) • regulation of growth and reproduction • control of the body’s responses to external stimuli (particularly stress). It should be noted, however, that though these two systems are separate, they often act together and complement each other in the maintenance of homeostasis. The Endocrine System is made up of a collection of small organs that are scattered throughout the body, each of which releases hormones into the blood supply (‘endo’ = within, ‘crine’ = to secrete). These hormone-releasing organs can be split into three main categories (Jenkins & Tortora 2013). • Endocrine glands — organs whose only function is the production and release of hormones. These include: – pituitary gland – thyroid gland – parathyroid gland – adrenal gland • Organs that are not pure glands (as they have other functions as well as the production of hormones) but contain relatively large areas of hormone-producing tissue. These include: – hypothalamus – pancreas • Other tissues and organs that also produce hormones — areas of hormone-producing cells are found in the wall of the small intestine and the stomach. There are no cell types, organs or processes that are not influenced by the Endocrine System in some way, and while there are many hormones that we know of, there are probably many more that are yet to be discovered. 16.1 The endocrine organs LEARNING OBJECTIVE 16.1 Name the endocrine glands in the body and the hormones they secrete. Figure 16.1 shows the endocrine organs and their position within the body.
eBook - PDF- George Spilich(Author)
- 2023(Publication Date)
- Wiley(Publisher)
We will then describe the many structures that make up the Endocrine System in the brain and else- where in the body. With that basic knowledge in hand, we will take a closer look at how the Endocrine System controls our response to stress. 8.1 An Introduction to the Endocrine System LO 8.1 Understand the advantages of a slow-acting, generalized control system. In our discussion of the biological basis of human behavior, it would be easy to assume that our nervous system controls everything that happens in our bodies, but that would not be accurate. It may come as a surprise to you to discover that there is a second network that is responsible for a different set of functions such as stimulating growth during development, initiating sexual behavior, regulating blood pressure, maintaining blood glucose levels, and preparing you to fight or flee. That second and equally important network is the Endocrine System. We begin our exploration of the Endocrine System with a brief history of its discovery. The Discovery of Hormones as Messengers MCAT The first medical practitioners did not have the luxury of MRI or blood work to help them diag- nose and treat maladies, but they were astute observers of their patients. Aristotle (4th century BCE) noted that castration of an animal or a person, although a relatively small change, led to significant changes in behavior. Hippocrates (a contemporary of Aristotle) proposed that human behavior was dictated by the proportion of four humors, or vital bodily fluids, in the blood and that these were responsible for the proper functioning of the body (Figure 8.1). The theory that disease was caused by a humor imbalance in the blood was eventually discarded when microscopes allowed scientists to visualize germs. Nonetheless, the idea that there were 202 C H A P T E R 8 The Endocrine System chemical messengers in the blood was a valuable insight.
eBook - PDF- Cecie Starr, Beverly McMillan(Authors)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Reproductive system The hypothalamus regulates the release of sex hormones that govern the development and functioning of ovaries and testes (the gonads). Oxytocin triggers uterine muscle contractions during labor and (with prolactin) for milk release for a nursing infant. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) also have key roles in reproduction. Digestive system Insulin and GH support the delivery of nutrients to all cells by stimulating cells to take up glucose from the bloodstream. The Endocrine System The Endocrine System produces hormones, signaling molecules that travel in the bloodstream to nearly all body cells. Each kind of hormone influences the activity of its target cells. Along with signals of the nervous system, these changes adjust body functions in ways that maintain homeostasis in the body as whole. In general, responses to hormones take longer and last longer than responses to nerve impulses. Hormones govern long-term events such as bodily growth and metabolism. The Endocrine System in Homeostasis Skeletal system Growth hormone stimulates the growth of bones. Parathyroid hormone (PTH) is the main regulator of blood calcium levels. Calcitonin stimulates uptake of calcium from blood as needed to form bone tissue. Nervous system Epinephrine supports the sympathetic nervous system in the fight–flight response and helps the CNS regulate blood pressure. Hormones that regulate blood sugar ensure adequate fuel for brain cells. Urinary system Aldosterone and ANP support the urinary system’s management of salt–water balance by promoting or reducing the reabsorption of sodium. Muscular system Growth hormone stimulates development of skeletal muscle mass.
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
The science of the structure and function of the endocrine glands and the diagnosis and 18.1 Comparison of Control by the Nervous and Endocrine Systems OBJECTIVE • Compare control of body functions by the nervous system and Endocrine System. The nervous and Endocrine Systems act together to coordinate functions of all body systems. Recall that the nervous system acts through nerve impulses (action potentials) conducted along axons of neurons. At synapses, nerve impulses trigger the release of mediator (messenger) molecules called neurotransmitters (shown in Figure 12.23). The endo- crine system also controls body activities by releasing mediators, called hormones, but the means of control of the two systems are very different. A hormone (hormon = to excite or get moving) is a molecule that is released in one part of the body but regulates the activity of cells in other parts of the body. Most hormones enter interstitial fluid and then the bloodstream. The circulating blood delivers hormones to cells throughout the body. Both neurotransmitters and hormones ex- ert their effects by binding to receptors on or in their “target” cells. Several chemicals act as both neurotransmitters and hormones. One familiar example is norepinephrine, which is released as a neuro- transmitter by sympathetic postganglionic neurons and as a hormone by chromaffin cells of the adrenal medullae. Responses of the Endocrine System often are slower than re- sponses of the nervous system; although some hormones act within seconds, most take several minutes or more to cause a response. The effects of nervous system activation are generally briefer than those of the Endocrine System. The nervous system acts on specific muscles and glands. The influence of the Endocrine System is much broader; it helps regulate virtually all types of body cells.
eBook - PDF- Bryan H. Derrickson(Author)
- 2019(Publication Date)
- Wiley(Publisher)
447 CHAPTER 13 The Endocrine System The Endocrine System and Homeostasis • The hormones of the Endocrine System contribute to homeostasis by regulating the activity and growth of target cells in the body. LOOKING BACK TO MOVE AHEAD… • The body regulates controlled variables, such as blood pressure, blood glucose level, and stretch of the uterine cervix, through feedback systems; a negative feedback system reverses a change in a controlled variable, whereas a positive feedback system reinforces a change in a controlled variable (Section 1.4). • There are two types of glands in the body: (1) exocrine glands, which secrete substances into ducts that empty onto the body surface or into the lumen of an organ and (2) endocrine glands, which secrete hormones that enter interstitial fluid and then into the bloodstream without flowing through a duct (Section 3.8). • An extracellular chemical messenger is a molecule that is released by a cell, enters extracellular fluid, and then binds to a receptor on or in its target cell to cause a response; the three types of extracellular chemical messengers are hormones, neurotransmitters, and local mediators (paracrines and autocrines) (Section 6.2). • The hypothalamus is a region of the brain that performs a variety of functions, including production of hormones and regulation of circadian rhythms (Section 8.2). 448 CHAPTER 13 The Endocrine System 13.1 Overview of the Endocrine System Objectives • Identify the components of the Endocrine System. • Compare the two chemical classes of hormones. • Discuss the mechanisms of hormone action. • Explain the different types of hormone interactions. • Describe the ways by which hormone secretion can be controlled. The Endocrine System Consists of All Glands, Organs, and Tissues That Contain Hormone-Secreting Cells Endocrine glands are ductless glands that secrete hormones, chemical messengers that are carried by the blood to distant target cells.
eBook - PDF- Gerard J. Tortora, Bryan H. Derrickson(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
We will also have several opportunities to see how the ner- vous and Endocrine Systems function together as an interlocking “supersystem.” For example, certain parts of the nervous sys- tem stimulate or inhibit the release of hormones by the endo- crine system. Table 18.1 compares the characteristics of the nervous and Endocrine Systems. In this chapter, we focus on the major endocrine glands and hormone-producing tissues and exam- ine how their hormones govern body activities. Checkpoint 1. List the similarities among and differences between the nervous and Endocrine Systems with regard to the control of homeostasis. 18.2 Endocrine Glands OBJECTIVE • Distinguish between exocrine and endocrine glands. Recall from Chapter 4 that the body contains two kinds of glands: exocrine glands and endocrine glands. Exocrine glands (EKS-ō-krin; exo- = outside; krino = separate) secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body. Exocrine glands include sudoriferous, sebaceous, mucous, and digestive glands. Endocrine glands (EN-dō-krin; endo- = within) secrete their products (hormones) into the interstitial fluid surrounding the secretory cells rather than into ducts. From the interstitial fluid, hormones diffuse into blood capillaries and blood carries them to target cells throughout the body. Because of their dependence on the cardiovascular system to distribute their products, endocrine glands are some of the most vascular tissues of the body. Considering that most hormones are required in very small amounts, circulating lev- els typically are low. The endocrine glands include the pituitary, thyroid, parathyroid, suprarenal, and pineal glands (Figure 18.1). In TABLE 18.1 Comparison of Control by the Nervous and Endocrine Systems Characteristic Nervous System Endocrine System Molecules Neurotransmitters released locally in response to nerve impulses.
- Gerard J. Tortora, Bryan H. Derrickson, Brendan Burkett, Gregory Peoples, Danielle Dye, Julie Cooke, Tara Diversi, Mark McKean, Simon Summers, Flavia Di Pietro, Alex Engel, Michael Macartney, Hayley Green(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
CHAPTER 18 The Endocrine System LEARNING OBJECTIVES After studying this chapter, you should be able to: 18.1 compare control of body functions by the nervous system and Endocrine System 18.2 distinguish between exocrine and endocrine glands 18.3 compare the classes of hormones and describe how they interact with target-cell receptors 18.4 describe the two general mechanisms of hormone action 18.5 describe the mechanisms of control of hormone secretion 18.6 describe the properties of the hypothalamus and pituitary gland, and the relationships between them 18.7 describe the location, histology, hormones, and functions of the thyroid gland 18.8 describe the location, histology, hormone, and functions of the parathyroid glands 18.9 describe the location, histology, hormones, and functions of the adrenal glands 18.10 describe the location, histology, hormones, and functions of the pancreatic islets 18.11 describe the location, hormones, and functions of the male and female gonads 18.12 describe the properties of the pineal gland and its secretions 18.13 describe the hormonal properties of cells in tissues and organs that are not traditionally considered endocrine glands 18.14 describe how the body responds to stress 18.15 describe the development of endocrine glands 18.16 describe the effects of ageing on the Endocrine System. OPENING CASE The impact of COVID-19 on the Endocrine System The Endocrine System is a complex relationship of anatom- ical structures and physiological processes underpinning the body’s ability to communicate within and between sys- tems. As an intricate network of neuro-hormonal signalling, the body’s homeostasis relies heavily on the feedforward and feedback nature of the hormones travelling throughout the circulation. Disturbance of any of the pathways can ultimately result in acute and chronic pathophysiological conditions and impact on life expectancy.
eBook - PDF- Craig Freudenrich, Gerard J. Tortora(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
280CHAPTER9 TheEndocrineSystem THE PLANNER ✓ ✓ )ROOLFXODU FHOOV UHOHDVH WK\URLG KRUPRQHV LQWR WKH EORRG 5 7K\URLG IROOLFOH +\SRWKDODPXV $QWHULRU SLWXLWDU\ 76+ 75+ +\SRWKDODPXV VHQVHV ORZ WK\URLG KRUPRQH OHYHOV LQ WKH EORRG DQG UHOHDVHV 75+ 1 Summary Hormones Act on Target Cells 254 • The Endocrine System consists of both endocrine glands and endocrine cells of other organs. The Endocrine System regulates many physiological parameters chemically. • Endocrine cells secrete hormones that bind to receptors in target cells and cause some actions in the target cells to evoke physiological responses. • Hormones can be classified as steroid hormones or nonste- roid hormones. • Steroid hormones can go directly through the target cell membrane, and stimulate specific genes to make new pro- teins, which alter the activity of the target cell. • As shown, nonsteroid hormones, usually must bind to a hormone receptor on the surface of the cell membrane, and elicit the formation of a “second messenger” inside the cell (for example, cyclic AMP, calcium), which alters the target cell’s activity. Endocrine Glands Regulate Key Body Functions 257 • The endocrine glands and organs containing endocrine cells secrete approximately 30 different hormones that regu- late and control many body functions, including chemical composition and volume of blood, metabolism, contractions of smooth and cardiac muscles, secretions of endocrine glands, growth, development, and reproduction. • Endocrine disorders involve either hyposecretion or hyper- secretion of hormones. Causes of disorders can be either primary (within the affected gland) or secondary (within a gland that regulates the affected gland). • The hypothalamus and pituitary gland regulate many endocrine glands and body functions. The hypothalamus secretes hormones (ADH, oxytocin) directly into the blood- stream through the neurosecretory cells of the posterior pituitary.
eBook - PDF- Laurie Kelly McCorry(Author)
- 2008(Publication Date)
- Routledge(Publisher)
2 chapter ten The Endocrine System Study objectives Differentiate.between.the.primary.functions.of.the.nervous.system.and. the.endocrine.system Describe.the.biochemical.and.functional.distinctions.between.steroid. hormones,.protein/peptide.hormones,.and.amine.hormones Explain. the. beneficial. effects. of. the. binding. of. hormones. to. plasma. proteins Explain.how.hormones.are.eliminated Distinguish.between.a.trophic.and.a.nontrophic.hormone Describe.the.three.types.of.hormone.interactions Explain.the.two.primary.mechanisms.by.which.hormones.carry.out. their.effects Describe.how.the.effects.of.hormones.are.amplified Describe.how.the.pituitary.gland.is.formed.during.embryonic.devel-opment Describe. the. anatomical. and. functional. relationships. between. the. hypothalamus.and.the.pituitary.gland Explain.how.negative.feedback.mechanisms.limit.the.release.of.hor-mones.from.the.adenohypophysis List. the. functions. and. describe. the. mechanisms. that. regulate. the. release.of.hormones.from.the.neurohypophysis List. the. functions. and. describe. the. mechanisms. that. regulate. the. release.of.hormones.from.the.adenohypophysis Discuss.the.functions.and.the.factors.that.regulate.the.release.of.the.fol-lowing.hormones:.thyroid.hormones,.calcitonin,.parathyroid.hormone,. aldosterone,.cortisol,.adrenal.androgens,.insulin,.and.glucagon 0. Introduction There. are. two. major. regulatory. systems. that. contribute. importantly. to. homeostasis:.the. nervous system .and.the. Endocrine System . .In.order.to.main-tain.relatively.constant.conditions.in.the.internal.environment.of.the.body,. each.of.these.systems.influences.the.activity.of.all.of.the.other.organ.systems . . The. nervous. system. coordinates. fast,. precise. responses,. such. as. muscle. contraction. . As. such,. the. electrical. impulses. generated. by. this. system. are. very. rapid. and. of. short. duration. (msec) . . The. endocrine. system. regulates. • • • • • • • • • • • • • •
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