Endocrine System Foundations and Mechanisms Flashcards

Flashcards defining key vocabulary related to endocrine structure, hormone classes, mechanisms of action, release stimuli, and hormone interactions from lecture notes.

Exocrine Gland

A gland that has ducts through which non-hormonal substances are secreted to a tissue surface.

Endocrine Gland

A ductless, highly vascularized gland that secretes hormones directly into surrounding interstitial fluid and blood.

Endothelium

The single, thin layer of simple squamous epithelium that forms the structure of capillaries.

Capillaries

Porous, microscopic blood vessels that serve as the on and off ramps to the circulatory system with direct access to cells.

Neuroendocrine Organ

An organ composed of neural tissue that also produces and releases hormones, such as the hypothalamus.

Autocrine

A short-distance chemical messenger that exerts its effects on the exact same cell that secreted it.

Paracrine

A short-distance chemical messenger that acts locally to affect neighboring cells other than the cell that secreted it.

Hormone

A long-distance chemical messenger that travels through the blood or lymph to affect target tissues throughout the body.

Amino Acid-Based Hormones

Water-soluble hormones of varying chain lengths (peptides and proteins) that generally circulate freely in blood and cannot cross plasma membranes.

Steroid-Based Hormones

Lipid-soluble hormones synthesized from cholesterol, produced exclusively by the gonads and adrenal cortex, which require plasma protein carriers in blood.

Thyroxine (T4)

The major metabolic hormone produced by the thyroid gland; an amino acid-based hormone that acts as an exception by entering cells to perform direct gene activation.

Target Cell

A specific cell possessing matching protein receptors for a particular hormone to bind to and exert an effect.

Cyclic AMP (cAMP)

A major intracellular second messenger activated by G proteins inside target cells in response to water-soluble hormone binding.

Direct Gene Activation

The signaling mechanism used by lipid-soluble hormones (steroids and thyroid hormone) where the hormone-receptor complex enters the nucleus and directly binds DNA to initiate transcription.

Upregulation

The process where target cells produce additional receptors in response to persistently low hormone levels to increase sensitivity.

Downregulation

The process where target cells reduce the number of receptors in response to persistently high hormone levels.

Negative Feedback Mechanism

The primary homeostatic mechanism controlling blood hormone concentrations by turning off the release stimulus once normal levels are restored.

Humoral Stimuli

Hormone secretion triggered by direct monitoring of changing levels of critical ions or nutrients in body fluids, such as blood.

Neural Stimuli

Hormone secretion directly triggered by nerve fibers, such as sympathetic nervous activation of the adrenal medulla during stress.

Hormonal Stimuli

Hormone secretion triggered in response to other hormones released by endocrine organs.

Tropic Hormones

Hormones secreted by the anterior pituitary (such as TSH, ACTH, FSH, and LH) that target other endocrine glands to stimulate the release of further hormones.

Adrenal Cortex

The outer three-layered region of the adrenal gland responsible for producing steroid hormones including aldosterone and cortisol.

Adrenal Medulla

The inner region of the adrenal gland made of neural tissue that secretes catecholamines under neural stimulation.

Catecholamines

The stress hormones epinephrine (adrenaline) and norepinephrine released by the adrenal medulla to increase heart rate and dilate airways.

Half-Life

The time required for a hormone's concentration in the blood to decrease by half.

Permissiveness

A hormonal interaction where one hormone requires the presence of another hormone in order to exert its full effects.

Synergism

A hormonal interaction where more than one hormone produces the same effect on a target cell, resulting in an amplified combined output.

Antagonism

A hormonal interaction where one hormone opposes or reverses the functional action of another hormone.

Glucagon

A pancreatic hormone released in response to low blood glucose that stimulates the liver to break down glycogen into glucose.

Atrial Natriuretic Peptide (ANP)

A hormone released by the heart to lower blood pressure, acting as an antagonist to aldosterone.