endocrine system hormone case study analysis answer key quizlet

17.1 An Overview of the Endocrine System

Learning objectives.

By the end of this section, you will be able to:

• Distinguish the types of intercellular communication, their importance, mechanisms, and effects
• Identify the major organs and tissues of the endocrine system and their location in the body

Communication is a process in which a sender transmits signals to one or more receivers to control and coordinate actions. In the human body, two major organ systems participate in relatively “long distance” communication: the nervous system and the endocrine system. Together, these two systems are primarily responsible for maintaining homeostasis in the body.

Neural and Endocrine Signaling

The nervous system uses two types of intercellular communication—electrical and chemical signaling—either by the direct action of an electrical potential, or in the latter case, through the action of chemical neurotransmitters such as serotonin or norepinephrine. Neurotransmitters act locally and rapidly. When an electrical signal in the form of an action potential arrives at the synaptic terminal, they diffuse across the synaptic cleft (the gap between a sending neuron and a receiving neuron or muscle cell). Once the neurotransmitters interact (bind) with receptors on the receiving (post-synaptic) cell, the receptor stimulation is transduced into a response such as continued electrical signaling or modification of cellular response. The target cell responds within milliseconds of receiving the chemical “message”; this response then ceases very quickly once the neural signaling ends. In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.In contrast, the endocrine system uses just one method of communication: chemical signaling. These signals are sent by the endocrine organs, which secrete chemicals—the hormone —into the extracellular fluid. Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones. For example, the hormones released when you are confronted with a dangerous or frightening situation, called the fight-or-flight response, occur by the release of adrenal hormones—epinephrine and norepinephrine—within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones.

Interactive Link

Visit this link to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?

In addition, endocrine signaling is typically less specific than neural signaling. The same hormone may play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone oxytocin promotes uterine contractions in people in labor. It is also important in breastfeeding, and may be involved in the sexual response and in feelings of emotional attachment in humans.

In general, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting—taking care of the internal environment of the body, maintaining homeostasis, and controlling reproduction ( Table 17.1 ). So how does the fight-or-flight response that was mentioned earlier happen so quickly if hormones are usually slower acting? It is because the two systems are connected. It is the fast action of the nervous system in response to the danger in the environment that stimulates the adrenal glands to secrete their hormones. As a result, the nervous system can cause rapid endocrine responses to keep up with sudden changes in both the external and internal environments when necessary.

Structures of the Endocrine System

The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function. The endocrine gland is the major player in this system. The primary function of these ductless glands is to secrete their hormones directly into the surrounding fluid. The interstitial fluid and the blood vessels then transport the hormones throughout the body. The endocrine system includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands ( Figure 17.2 ). Some of these glands have both endocrine and non-endocrine functions. For example, the pancreas contains cells that function in digestion as well as cells that secrete the hormones insulin and glucagon, which regulate blood glucose levels. The hypothalamus, thymus, heart, kidneys, stomach, small intestine, liver, skin, ovaries, and testes are other organs that contain cells with endocrine function. Moreover, adipose tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.

The ductless endocrine glands are not to be confused with the body’s exocrine system , whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. As just noted, the pancreas also has an exocrine function: most of its cells secrete pancreatic juice through the pancreatic and accessory ducts to the lumen of the small intestine.

Other Types of Chemical Signaling

In endocrine signaling, hormones secreted into the extracellular fluid diffuse into the blood or lymph, and can then travel great distances throughout the body. In contrast, autocrine signaling takes place within the same cell. An autocrine (auto- = “self”) is a chemical that elicits a response in the same cell that secreted it. Interleukin-1, or IL-1, is a signaling molecule that plays an important role in inflammatory response. The cells that secrete IL-1 have receptors on their cell surface that bind these molecules, resulting in autocrine signaling.

Local intercellular communication is the province of the paracrine , also called a paracrine factor, which is a chemical that induces a response in neighboring cells. Although paracrines may enter the bloodstream, their concentration is generally too low to elicit a response from distant tissues. A familiar example to those with asthma is histamine, a paracrine that is released by immune cells in the bronchial tree. Histamine causes the smooth muscle cells of the bronchi to constrict, narrowing the airways. Another example is the neurotransmitters of the nervous system, which act only locally within the synaptic cleft.

Career Connection

Endocrinologist.

Endocrinology is a specialty in the field of medicine that focuses on the treatment of endocrine system disorders. Endocrinologists—medical doctors who specialize in this field—are experts in treating diseases associated with hormonal systems, ranging from thyroid disease to diabetes mellitus. Endocrine surgeons treat endocrine disease through the removal, or resection, of the affected endocrine gland.

Patients who are referred to endocrinologists may have signs and symptoms or blood test results that suggest excessive or impaired functioning of an endocrine gland or endocrine cells. The endocrinologist may order additional blood tests to determine whether the patient’s hormonal levels are abnormal, or they may stimulate or suppress the function of the suspect endocrine gland and then have blood taken for analysis. Treatment varies according to the diagnosis. Some endocrine disorders, such as type 2 diabetes, may respond to lifestyle changes such as modest weight loss, adoption of a healthy diet, and regular physical activity. Other disorders may require medication, such as hormone replacement, and routine monitoring by the endocrinologist. These include disorders of the pituitary gland that can affect growth and disorders of the thyroid gland that can result in a variety of metabolic problems.

Some patients experience health problems as a result of the normal decline in hormones that can accompany aging. These patients can consult with an endocrinologist to weigh the risks and benefits of hormone replacement therapy intended to boost their natural levels of reproductive hormones.

In addition to treating patients, endocrinologists may be involved in research to improve the understanding of endocrine system disorders and develop new treatments for these diseases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction

• Authors: J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix
• Publisher/website: OpenStax
• Book title: Anatomy and Physiology 2e
• Publication date: Apr 20, 2022
• Location: Houston, Texas
• Book URL: https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction
• Section URL: https://openstax.org/books/anatomy-and-physiology-2e/pages/17-1-an-overview-of-the-endocrine-system

© Jun 13, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

17.1 An Overview of the Endocrine System

Learning objectives.

By the end of this section, you will be able to:

• Distinguish similarities and differences between neural and hormonal communication
• Identify the major organs of the endocrine system and their location in the body

Communication within the human body involves the transmission of signals to control and coordinate actions in an effort to maintain homeostasis.  There are two major organ systems responsible for providing these communication pathways: the nervous system and the endocrine system.

The nervous system is primarily responsible for rapid communication throughout the body.  As discussed in previous chapters, the nervous system utilizes two types of signals – electrical and chemical ( Table 17.1 ).  Electrical signals are sent via the generation and propagation of action potentials which move along the membrane of a cell.  Once the action potential reaches the synaptic terminal, the electrical signal is converted to a chemical signal as neurotransmitters are released into the synaptic cleft.  When the neurotransmitters binds with receptors on the receiving (post-synaptic) cell, a new electrical signal is generated and quickly continues on to its destination.  In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.

In contrast, the endocrine system relies on only a single method of communication: chemical signaling (Table 1).  Hormones are the chemicals released by endocrine cells that regulate other cells in the body.   Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, triggering a response.  Because of this dependence on the cardiovascular system for transport, this type of communication is much slower than that observed for neural signaling.  As such, hormonal communication is usually associated with activities that go on for relatively long periods of time.

External Website

Visit this link to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?

In general, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting—taking care of the internal environment of the body, maintaining homeostasis, and controlling reproduction. This does not mean, however, that the two systems are completely independent of one another.  Take for example the release of adrenaline from the adrenal medulla as part of the ‘fight-or-flight’ response.  Although adrenaline uses blood for transportation throughout the body, the effects are evident within seconds after the event has occurred;  how does the response happen so quickly if hormones are usually slower acting?   It occurs so rapidly because the nervous and endocrine system are both involved in the process: it is the fast action of the nervous system responding to the danger in the environment that stimulates the adrenal glands to quickly secrete their hormones.  In such a situation, the nervous system causes a rapid endocrine response to deal with sudden changes in both the external and internal environments when necessary.

Endocrine Organs

Hormones are released by secretory cells that are derived from epithelial tissue.  Often, these cells are clustered together, forming endocrine glands .  Unlike exocrine glands, which have a duct for conveying secretions to the outside of the body (e.g., sweat gland), endocrine glands secrete substances directly into the surrounding interstitial fluid.  From there, hormones then enter the bloodstream for distribution throughout the body.

The major endocrine glands found in the human body include the pituitary gland, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pineal gland, testes, and ovaries ( Figure 17.1.1 ). While some of the glands are pure endocrine (e.g., thyroid gland), others serve both endocrine and exocrine function. For example, the pancreas contains cells that secrete digestive enzymes and juices into the small intestine (exocrine function) and cells that secrete the hormones insulin and glucagon, which regulate blood glucose levels.

In addition to the endocrine glands, major organs of the body show endocrine function including the hypothalamus, heart, kidneys, stomach, small intestine, and liver.  Moreover, adipose tissue has long been known to produce hormones, and recent research has revealed a role for bone tissue in hormone production and secretion.

Other Types of Chemical Signals

In the classical definition of the endocrine system, hormones are secreted into the interstitial fluid and then diffuse into the blood or lymph for circulation throughout the body to reach target tissues.  However, in certain instances, target cells are local and do not require hormones to enter the blood.  If a chemical signal is released into the interstitial fluid and targets neighboring cells, then the activity is referred to as paracrine .  Neurotransmitter communication between a pre- and post-synaptic neuron is a good example of paracrine activity.  Alternatively, chemicals released by a cell elicit a response in the same cell that secreted it, demonstrating autocrine activity.  An example of this is type of activity is Interleukin-1, signaling molecule released in an inflammatory response that binds to receptors located on the surface of the cell releasing the molecule.

Career Connections –  Endocrinologist

Endocrinology is a specialty in the field of medicine that focuses on the treatment of endocrine system disorders. Endocrinologists, the medical doctors who specialize in this field, are experts in treating diseases associated with hormonal systems, ranging from thyroid disease to diabetes mellitus.

Patients who are referred to endocrinologists may have signs and symptoms or blood test results that suggest excessive or impaired functioning of an endocrine gland or endocrine cells. The endocrinologist may order additional blood tests to determine whether the patient’s hormonal levels are abnormal, or they may stimulate or suppress the function of the suspect endocrine gland and then have blood taken for analysis. Treatment varies according to the diagnosis. Some endocrine disorders, such as type 2 diabetes, may respond to lifestyle changes such as modest weight loss, adoption of a healthy diet, and regular physical activity. Other disorders may require medication, such as hormone replacement, and routine monitoring by the endocrinologist. These include disorders of the pituitary gland that can affect growth and disorders of the thyroid gland that can result in a variety of metabolic problems.

Some patients experience health problems as a result of the normal decline in hormones that can accompany aging. These patients can consult with an endocrinologist to weigh the risks and benefits of hormone replacement therapy intended to boost their natural levels of reproductive hormones.

In addition to treating patients, endocrinologists may be involved in research to improve the understanding of endocrine system disorders and develop new treatments for these diseases.

Chapter Review

The body coordinates its functions through two major types of communication: neural and endocrine. Neural communication includes both electrical and chemical signaling between neurons and target cells. Endocrine communication involves chemical signaling via the release of hormones which travel through the bloodstream, where they elicit a response in target cells. Endocrine glands are ductless glands that secrete hormones. Many organs of the body with other primary functions—such as the heart, stomach, and kidneys—also have endocrine activity.

Interactive Link Questions

Review questions, critical thinking questions.

1. Describe several main differences in the communication methods used by the endocrine system and the nervous system.

2. Compare and contrast endocrine and exocrine glands.

3. True or false: Neurotransmitters are a special class of paracrines. Explain your answer.

Answers for Critical Thinking Questions

• The endocrine system uses chemical signals called hormones to convey information from one part of the body to a distant part of the body. Hormones are released from the endocrine cell into the extracellular environment, but then travel in the bloodstream to target tissues. This communication and response can take seconds to days. In contrast, neurons transmit electrical signals along their axons. At the axon terminal, the electrical signal prompts the release of a chemical signal called a neurotransmitter that carries the message across the synaptic cleft to elicit a response in the neighboring cell. This method of communication is nearly instantaneous, of very brief duration, and is highly specific.
• Endocrine glands are ductless. They release their secretion into the surrounding fluid, from which it enters the bloodstream or lymph to travel to distant cells. Moreover, the secretions of endocrine glands are hormones. Exocrine glands release their secretions through a duct that delivers the secretion to the target location. Moreover, the secretions of exocrine glands are not hormones, but compounds that have an immediate physiologic function. For example, pancreatic juice contains enzymes that help digest food.
• True. Neurotransmitters can be classified as paracrines because, upon their release from a neuron’s axon terminals, they travel across a microscopically small cleft to exert their effect on a nearby neuron or muscle cell.

This work, Anatomy & Physiology, is adapted from Anatomy & Physiology by OpenStax , licensed under CC BY . This edition, with revised content and artwork, is licensed under CC BY-SA except where otherwise noted.

Images, from Anatomy & Physiology by OpenStax , are licensed under CC BY except where otherwise noted.

Access the original for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.