Human Anatomy & Physiology - Chapter 16: The Endocrine System Overview

Vocabulary flashcards covering the key terms, organ classifications, signaling pathways, and regulation mechanisms of the endocrine system from Chapter 16.

Hormone

A chemical messenger synthesized and secreted by endocrine cells into the bloodstream that interacts with specific target cells to influence their functions and maintain homeostasis.

Endocrine Gland

A ductless organ consisting of glandular epithelial cells that secrete hormones directly into the extracellular fluid for transport through the bloodstream.

Exocrine Gland

A gland that secretes its products into ducts leading to epithelial surfaces, contrasting with ductless endocrine glands.

Primary Endocrine Organ

An organ that possesses exclusively endocrine functions, including the anterior pituitary, thyroid, parathyroid glands, adrenal cortices, endocrine pancreas, and thymus.

Secondary Endocrine Organ

An organ that has both endocrine capabilities and diverse non-endocrine physiological functions, such as the heart, kidneys, small intestines, testes, and ovaries.

Neuroendocrine Organ

An organ composed of nervous tissue that produces and secretes chemical messengers that act as hormones (neurohormones), which includes the hypothalamus, pineal gland, posterior pituitary gland, and adrenal medulla.

Neurohormone

A chemical messenger released by nervous tissue into the bloodstream to act on distant target cells.

Paracrine

A localized signaling mechanism wherein a chemical is secreted into the extracellular fluid to affect nearby target cells without entering the bloodstream.

Autocrine

A localized chemical signaling process in which a cell secretes a messenger into the extracellular fluid that binds to receptors on and influences the same cell.

Target Cell

A specific cell that contains three-dimensional protein receptors capable of binding a particular hormone and eliciting a cellular response.

Amino-Acid Hormone

A hormone consisting of one or more amino acids ranging from single amines to peptides or proteins; typically hydrophilic, freely circulating in plasma, and binding to plasma membrane receptors.

Steroid Hormone

A lipid-soluble, hydrophobic hormone derived from cholesterol that travels bound to plasma proteins and binds to intracellular receptors in the cytosol or nucleus.

Free Hormone

A hormone that circulates dissolved directly in blood plasma without being bound to carrier proteins, characteristic of most hydrophilic amino-acid hormones.

Bound Hormone

A hormone attached to a plasma protein in the blood, which prevents rapid elimination, balances free hormone levels, and extends its half-life.

Second Messenger System

An intracellular enzyme cascade triggered when a hydrophilic hormone binds to an extracellular plasma membrane receptor, activating proteins to initiate a cellular response.

Hormone-Receptor Complex

A complex formed when a hydrophobic hormone diffuses across the plasma membrane and binds to a specific intracellular receptor located in the cytosol or nucleus.

Up-Regulation

The process where a target cell synthesizes and displays an increased number of receptors, often in response to a temporary drop in blood hormone levels, increasing sensitivity.

Down-Regulation

The process where a target cell decreases its displayed receptor count in response to prolonged exposure to elevated blood hormone concentrations.

Synergists

Hormones that act on the same target cell to produce the same physiological effect, resulting in a more pronounced combined outcome.

Antagonists

Hormones that act on the same target cell but generate opposing physiological actions to regulate physiological balance.

Complementary Actions

A hormonal interaction where different hormones affect different target cells in order to achieve a common physiological goal.

Hormonal Stimulus

The regulation of endocrine secretion in which an endocrine gland increases or decreases hormone release in response to another hormone.

Humoral Stimulus

The regulation of endocrine secretion initiated in response to altered concentrations of specific ions or molecules in blood or extracellular fluid.

Neural Stimulus

The regulation of endocrine secretion caused by direct signals from neurons of the nervous system, such as sympathetic activation of the adrenal medulla.