Biological Sciences
Endocrine Signaling
Endocrine signaling is a form of cell communication in which specialized cells release hormones into the bloodstream to target distant cells. These hormones travel through the circulatory system and bind to specific receptors on target cells, triggering a response. This system plays a crucial role in regulating various physiological processes, including metabolism, growth, and reproduction.
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9 Key excerpts on "Endocrine Signaling"
eBook - ePubGeneral and Comparative Endocrinology
An Integrative Approach
- A.M. Schreiber, Alex Schreiber(Authors)
- 2023(Publication Date)
- CRC Press(Publisher)
Despite the somewhat artificial distinctions among these three classes of signaling molecules, the endocrine, immune, and nervous systems communicate with each other to maintain organismal homeostasis. Together these three interacting chemical signaling classes have been referred to as bio-regulators. 3 As such, the scope of modern endocrinology has exploded from its origins as a specialty within the discipline of physiology that focused solely on endocrine glands and their internal secretions to a discipline addressing the entire spectrum of chemical communication in animals ranging from the molecular and cellular to the organismal and population levels. Some important differences between classical and modern endocrine thinking are summarized in Appendix 3. SUMMARY AND SYNTHESIS QUESTIONS Compare and contrast the classical and modern definitions of “hormone” and “endocrinology”. Fundamental Features of Endocrine Signaling LEARNING OBJECTIVE Describe the fundamental features of Endocrine Signaling. KEY CONCEPTS: • Whereas hormones are chemically diverse, ranging from modified amino acids to proteins, lipids, and other chemicals, all of their known receptors are proteins. • Hormones are active at extremely low concentrations and bind to specific receptors located at the surface and inside of target cells. • Many hormones bind to blood transport proteins, which increases their longevity and solubility in circulation. • One hormone can exert distinct effects on different cells and tissues by interacting with different receptors. • Intracellular signaling pathways transduce and amplify hormone signals. • Hormones mediate homeostasis via feedback control. • Hormones can exert “pleiotropic” effects. • In order to adapt to changing conditions, organisms must be able to change the homeostatic set points for a regulated parameter, a concept called “allostasis”. • Hormones are often secreted in rhythmic and pulsatile manners. • Hormones exist in a
No longer available |Learn more- R. Michael Akers, D. Michael Denbow(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
12 Endocrine systemContentsIntroduction and OverviewCell SignalingMechanisms of Cell Surface Hormone Signaling Mechanisms of Internal Hormone Cell Signaling Receptors and Regulation Measuring Circulating Hormone Concentrations Endocrine and Growth Factor SignalingThe Hypophyseal-Pituitary AxisPituitary Overview Negative Feedback Loops Hormones and Cells of the Posterior PituitaryHormones of the Anterior PituitarySomatotropin (GH) The Somatomedin Hypothesis GH Secretion Prolactin Prolactin Secretion Follicle-Stimulating Hormone and Luteinizing Hormone Thyroid-Stimulating Hormone Adrenocortropic HormoneThyroid GlandAdrenal Gland Endocrine Pancreas Other Hormones and Growth Factors IGF Family EGF Family FGF Family TGF-β Family Leptin Chapter SummaryBiosynthesis of Triiodothyronine and Thyroxine Biological Effects of Thyroid Hormones Calcitonin Parathyroid HormoneIntroduction and overview
As we consider regulation of homeostasis , two closely linked interacting physiological systems, the nervous and endocrine system, are critical. As a general rule, actions mediated by the nervous system are typically acute and relatively short-lived, whereas endocrine effects are often slow to develop but frequently generate responses that continue for hours or even weeks. Some simple examples illustrate these points. Consider what happens with overheating. As the core body temperature rises, warmer blood flowing to the hypothalamus and other brain areas initiates nerve impulses relayed by efferent spinal nerve tracts to the smooth muscle sphincters of the arterioles controlling blood flow to the dermis . This produces relaxation and thereby increased blood flow so that heat can be lost. Nerve fibers also stimulate the secretion
eBook - ePubBoron & Boulpaep Concise Medical Physiology E-Book
Boron & Boulpaep Concise Medical Physiology E-Book
- Walter F. Boron, Emile L. Boulpaep(Authors)
- 2020(Publication Date)
- Elsevier(Publisher)
− 12 M) at which many hormones circulate.Once a hormone is recognized by its target tissue or tissues, it can exert its biological action by a process known as signal transduction (see Chapter 3 ). Some hormones elicit responses within seconds (e.g., the increased heart rate provoked by epinephrine or the stimulation of hepatic glycogen breakdown caused by glucagon), whereas others may require many hours or days (e.g., the changes in salt retention elicited by aldosterone or the increases in protein synthesis caused by growth hormone [GH]).Principles of Endocrine Function
Chemical signaling can occur through endocrine, paracrine, or autocrine pathways
As shown in Fig. 3.1A , in classic Endocrine Signaling, a hormone carries a signal from a secretory gland across a large distance to a target tissue. Hormones secreted into the extracellular space can also regulate nearby cells without ever passing through the systemic circulation. This regulation is referred to as paracrine action of a hormone (see Fig. 3.1B ). Finally, chemicals can also bind to receptors on or in the cell that is actually secreting the hormone and thus affect the function of the hormone-secreting cell itself. This action is referred to as autocrine regulation (see Fig. 3.1C ). At the outset, it can be appreciated that summation of the endocrine, paracrine, and autocrine actions of a hormone can provide the framework for a complex regulatory system.Endocrine Glands
The major hormones of the human body are produced by one of seven classic endocrine glands or gland pairs: the pituitary, the thyroid, the parathyroids, the testes, the ovaries, the adrenals (cortex and medulla), and the endocrine pancreas. In addition, other tissues that are not classically recognized as part of the endocrine system produce hormones. These tissues include the central nervous system (CNS), particularly the hypothalamus, as well as the gastrointestinal tract, adipose tissue, liver, heart, and kidney.
eBook - ePub- Richard I. G. Holt, Neil A. Hanley(Authors)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
Part 1 Foundations of Endocrinology CHAPTER 1 Overview of endocrinology Key topics A brief history of endocrinology and diabetes The role of hormones Classification of hormones Control systems regulating hormone production Endocrine disorders Key points Learning objectives To be capable of defining endocrinology To understand what endocrinology means as a basic science and a clinical specialty To appreciate the history of endocrinology To understand the classification of hormones into peptides, steroids and amino acid derivatives To understand the principle of how feedback mechanisms regulate hormone levels in the circulation This chapter introduces endocrinology and diabetes including some of the basic principles that underpin the following chapters Box 1.1 The endocrine and nervous systems are the two main communication systems in the body Monitor internal and external environments Ensure homeostasis Allow appropriate adaptive changes Communicate via chemical messengers Figure 1.1 Chemical signalling in the endocrine and neural systems. (a) In endocrine communication, the producing cell secretes hormone into the blood vessel, where it is carried, potentially over large distances, to its target cell. (b) Sometimes hormones can act on the cell that produces them (autocrine, A) or nearby cells (paracrine, P) without the need for transport via the circulation. For instance, glucagon from α‐cells and somatostatin from δ‐cells can regulate insulin secretion by adjacent β‐cells within the pancreatic islet. (c) In neuroendocrine communication, neurons can secrete hormones into the surrounding blood vessels to reach a more distant target. A good example is hypothalamic regulation of the anterior pituitary. (d) In pure neural communication, neurons activate other neurons via neurotransmitters released from axonic terminals into the synaptic space
eBook - PDF- Bryan H. Derrickson(Author)
- 2019(Publication Date)
- Wiley(Publisher)
The endocrine glands, organs, and tissues of the body collectively form the endocrine system, which is the focus of Chapter 13. Cell signal- ing that is mediated through hormones is referred to as endo- crine signaling. Neurotransmitters Neurotransmitters are extracel- lular chemical messengers that are released from a neuron into a synapse in order to reach a nearby target cell (Figure 6.3b). A synapse is the junction between a neuron and its target cell, which can be another neuron, a muscle cell, or a gland cell. At a synapse, the neuron that releases the neurotransmitter is called the presynaptic neuron, and the cell that receives the neuro- transmitter is called the postsynaptic cell. Although the plasma membranes of a presynaptic neuron and a postsynaptic cell are close, they do not actually touch; instead, they are separated by a narrow synaptic cleft filled with interstitial fluid. The nervous system functions using electrical and chemi- cal signals. For example, when a neuron is excited, an electri- cal signal known as a graded potential is produced in the den- drites or cell body of the neuron (Figure 6.3b). If the graded potential is strong enough, it spreads to the beginning of the neuron’s axon, where it triggers the formation of another type of electrical signal called an action potential. After it is gener- ated, the action potential conducts along the axon in the direction of the synapse, ultimately causing the presynaptic neuron to release neurotransmitters (a chemical signal) into the interstitial fluid of the synaptic cleft (Figure 6.3b). The neurotransmitters then diffuse across the cleft through the fluid and bind to receptors in the plasma membrane of the postsynaptic cell (the target cell) to cause a response. An example of a neurotransmitter is dopamine, which is released at certain synapses in the brain.
eBook - PDF- Stefan Silbernagl, Agamemnon Despopoulos(Authors)
- 2015(Publication Date)
- Thieme(Publisher)
The receptors on the target cells pick out the substances specifically intended for them from a wide variety of different mes-senger substances in their environment. Hormones work closely with the nervous system to regulate digestion, metabolism, growth, physical and mental development, maturation, reproduction, adaptation, and the internal milieu of the body ( homeostasis ) ( A ). Most of these actions are predominately autonomous functions subject to central con-trol by the hypothalamus , which is controlled by higher centers of the brain ( p. 348). Neurotransmitters released at chemical synapses of nerve endings transmit signals to postsynaptic nerve fibers, muscles or glands ( p. 54ff.). Some neuropeptides released by presynaptic neurons also exert their effects in neighboring synapses, resulting in a kind of “paracrine” action. Neurons can also secrete hormones, e.g., epinephrine, oxytocin, and antidiuretic hor-mone. Some transmitter substances of the im-mune system, e.g., thymosin and various cy-tokines, also have endocrine effects. Integrative Systems of the Body 281 11 Hormones and Reproduction Plate 11.1 Integrative Systems of the Body Psychological factors Signals from the environment Messages from within the body (e.g., feedback control) Endocrine system autonomic nervous system somatic nervous system Neurosecretion Hypothalamus Anterior lobe of pituitary Posterior lobe of pituitary Kidneys Thyroid gland Parathyroid glands Ovaries Testes Adrenal cortex Adrenal medulla Pancreas Nutrition Circulation Growth and maturation Metabolism Temperature Water and electrolyte balance Reproduction Immune system Behavior Control and regulation of Peripheral nervous system Motoricity Defense Hormone release Aglandular hormones Sympathetic and parasympathetic nervous systems A. Regulation of autonomic nervous system functions (overview)
eBook - PDF- Mary Ann Clark, Jung Choi, Matthew Douglas(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
The small distance between nerve cells allows the signal to travel quickly; this enables an immediate response, such as, "Take your hand off the stove!" When the neurotransmitter binds the receptor on the surface of the postsynaptic cell, the electrochemical potential of the target cell changes, and the next electrical impulse is launched. The neurotransmitters that are released into the chemical synapse are degraded quickly or get reabsorbed by the presynaptic cell so that the recipient nerve cell can recover quickly and be prepared to respond rapidly to the next synaptic signal. Chapter 9 | Cell Communication 253 Figure 9.3 The distance between the presynaptic cell and the postsynaptic cell—called the synaptic gap—is very small and allows for rapid diffusion of the neurotransmitter. Enzymes in the synapatic gap degrade some types of neurotransmitters to terminate the signal. Endocrine Signaling Signals from distant cells are called endocrine signals, and they originate from endocrine cells. (In the body, many endocrine cells are located in endocrine glands, such as the thyroid gland, the hypothalamus, and the pituitary gland.) These types of signals usually produce a slower response but have a longer-lasting effect. The ligands released in Endocrine Signaling are called hormones, signaling molecules that are produced in one part of the body but affect other body regions some distance away. Hormones travel the large distances between endocrine cells and their target cells via the bloodstream, which is a relatively slow way to move throughout the body. Because of their form of transport, hormones become diluted and are present in low concentrations when they act on their target cells. This is different from paracrine signaling, in which local concentrations of ligands can be very high. Autocrine Signaling Autocrine signals are produced by signaling cells that can also bind to the ligand that is released.
eBook - PDF- Julianne Zedalis, John Eggebrecht(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
Signaling cells secrete ligands that bind to target cells and initiate a chain of events within the target cell. The four categories of signaling in multicellular organisms are paracrine signaling, Endocrine Signaling, autocrine signaling, and direct signaling across gap junctions. Paracrine signaling takes place over short distances. Endocrine signals are carried long distances through the bloodstream by hormones, and autocrine signals are received by the same cell that sent the signal or other nearby cells of the same kind. Gap junctions allow small molecules, including signaling molecules, to flow between neighboring cells. Internal receptors are found in the cell cytoplasm. Here, they bind ligand molecules that cross the plasma membrane; these receptor-ligand complexes move to the nucleus and interact directly with cellular DNA. Cell-surface receptors transmit a signal from outside the cell to the cytoplasm. Ion channel-linked receptors, when bound to their ligands, form a pore through the plasma membrane through which certain ions can pass. G-protein-linked receptors interact with a G-protein on the cytoplasmic side of the plasma membrane, promoting the exchange of bound GDP for GTP and interacting with other enzymes or ion channels to transmit a signal. Enzyme-linked receptors transmit a signal from outside the cell to an intracellular domain of a membrane-bound enzyme. Ligand binding causes activation of the enzyme. Small hydrophobic ligands (like steroids) are able to penetrate the plasma membrane and bind to internal receptors. Water-soluble hydrophilic ligands are unable to pass through the membrane; instead, they bind to cell-surface receptors, which transmit the signal to the inside of the cell. 9.2 Propagation of the Signal Ligand binding to the receptor allows for signal transduction through the cell. The chain of events that conveys the signal through the cell is called a signaling pathway or cascade.
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.
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