Chapter 18: The Endocrine System - Vocabulary

Comprehensive vocabulary flashcards generated from Fundamentals of Anatomy & Physiology (11th Edition) Chapter 18 notes on the Endocrine System.

Direct Communication

Intercellular communication occurring through gap junctions that transmits ions, small solutes, and lipid-soluble materials, with effects usually limited to adjacent cells of the same type interconnected by connexons.

Paracrine Communication

Intercellular communication through extracellular fluid using paracrines, where distribution of effects is primarily limited to a local area with high paracrine concentrations and target cells possessing appropriate receptors.

Autocrine Communication

Intercellular communication through extracellular fluid using autocrines, where distribution of effects is limited to the cell that secretes the hormone.

Endocrine Communication

Intercellular communication through the bloodstream using hormones, where target cells are primarily in other tissues and organs and must have appropriate receptors.

Synaptic Communication

Intercellular communication across synapses using neurotransmitters, with effects limited to a very specific area and target cells having appropriate receptors.

Prohormones

Inactive molecules that are converted to active hormones before or after they are secreted.

Eicosanoids

Lipid derivatives derived from arachidonic acid (a 20-carbon fatty acid) that serve as important paracrines coordinating cellular activities and enzymatic processes.

Prostaglandins

A group of eicosanoids involved primarily in coordinating local cellular activities, which in some tissues are converted to thromboxanes and prostacyclins.

Free Hormones

Unattached circulating hormones that remain functional for less than an hour before being inactivated by binding to target cells, absorption by the liver or kidneys, or enzymatic breakdown.

Bound Hormones

Hormones (such as thyroid and steroid hormones) attached to special transport proteins in the blood, allowing more than $99$ percent to remain in circulation long-term as a substantial reserve.

First Messenger

A hormone, catecholamine, or eicosanoid that binds to a membrane receptor on the target cell surface and uses an intracellular intermediary to exert its effects.

Second Messenger

An intracellular intermediary, such as cyclic AMP ($\text{cAMP}$) or calcium ions ($\text{Ca}^{2+}$), whose appearance is triggered by a first messenger to act as an enzyme activator, inhibitor, or cofactor.

G Protein

An enzyme complex coupled to a membrane receptor that serves as a link between the first messenger and the second messenger inside the cell.

Down-Regulation

A cellular process in which the presence of a hormone triggers a decrease in the number of hormone receptors, making the target cells less sensitive to high hormone concentrations.

Up-Regulation

A cellular process in which the absence of a hormone triggers an increase in the number of hormone receptors, making the target cells more sensitive to low hormone concentrations.

Infundibulum

A narrow stalk that connects the pituitary gland to the hypothalamus.

Hypophyseal Portal System

A specialized vascular arrangement where portal vessels deliver blood containing hypothalamic regulatory hormones directly from the primary capillary network in the infundibulum to the capillary network in the anterior pituitary lobe.

Thyroid Follicles

Spherical structures within the thyroid gland lined by simple cuboidal epithelium and filled with colloid storing thyroglobulin.

C Cells

Endocrine cells in the thyroid gland (also called parafollicular cells) located between follicles that secrete calcitonin to decrease blood calcium ion levels.

Calcitriol

The active, hormonal form of vitamin D synthesized by the kidneys that stimulates calcium and phosphate ion absorption along the digestive tract.

Erythropoietin (EPO)

A hormone released by the kidneys in response to reduced renal blood flow and oxygen levels that stimulates red blood cell production in the bone marrow.

Zona Glomerulosa

The outer region of the adrenal cortex that secretes mineralocorticoids, primarily aldosterone, to increase renal reabsorption of $\text{Na}^+$ and water.

Zona Fasciculata

The middle zone of the adrenal cortex stimulated by ACTH to produce glucocorticoids (cortisol, corticosterone, and cortisone) that regulate glucose and lipid metabolism.

Zona Reticularis

The inner zone of the adrenal cortex that produces adrenal androgens under the stimulation of ACTH.

Pancreatic Islets

Endocrine cell clusters in the pancreas (Islets of Langerhans) containing alpha cells that produce glucagon and beta cells that produce insulin.

Type 1 Diabetes

A form of diabetes mellitus characterized by inadequate insulin production by pancreatic beta cells, requiring daily insulin administration.

Type 2 Diabetes

The most common form of diabetes mellitus, where tissues develop insulin resistance and fail to respond properly to produced insulin.

Diabetic Retinopathy

A visual impairment condition caused by capillary proliferation and hemorrhaging at the retina in individuals with diabetes mellitus.

Diabetic Neuropathies

A collection of peripheral nerve and autonomic function disorders caused by abnormal blood flow to neural tissues in diabetic patients.

Diabetic Nephropathy

Degenerative changes in kidney blood vessels resulting from diabetes mellitus that can lead to kidney failure.

A1C Test

A diagnostic blood test that measures the percentage of red blood cells with sugar-coated hemoglobin; normal levels are below $5.7\%$, prediabetes is $5.7\%$ to $6.4\%$, and diabetes is $6.5\%$ or above.

General Adaptation Syndrome (GAS)

The body's general physiological response to stress, divided into the alarm phase, resistance phase, and exhaustion phase.

Alarm Phase

The initial short-term response to crisis in GAS directed by the sympathetic autonomic nervous system and dominated by epinephrine, which mobilizes glucose energy reserves.

Resistance Phase

The phase of GAS entered if stress lasts longer than a few hours, dominated by glucocorticoids that mobilize lipid and amino acid reserves to conserve glucose for neural tissue.

Exhaustion Phase

The final stage of GAS occurring when lipid reserves are depleted and electrolyte imbalances occur, leading to structural damage and vital organ system failure.