Chapter 8: Introduction to the Endocrine System

This set of vocabulary flashcards covers the foundational concepts of the endocrine system, including hormone classification, synthesis, transport, feedback mechanisms, and clinical pathologies based on Chapter 8 of the Human Physiology lecture material.

Endocrinology

The scientific study of hormones and their role in regulating body functions.

Hormone

A chemical signal secreted by a cell or group of cells into the blood for transport to a distant target, where it exerts effects at very low concentrations.

Pheromones

Specialized ectohormones that are secreted into the external environment to act on other organisms.

Half-life

A measure used to indicate the duration of a hormone's activity, representing the time it takes for its concentration in the blood to reduce by fifty percent.

Preprohormone

A large, inactive protein precursor that is the initial product of peptide hormone synthesis.

Prohormone

An intermediate molecule produced after the signal sequence is removed from a preprohormone; it is still inactive and requires further processing.

Peptide Hormones

Hormones made of amino acids that are water-soluble, stored in vesicles, and bind to surface membrane receptors because they cannot cross the lipid bilayer.

Steroid Hormones

Lipophilic hormones derived from cholesterol that are synthesized on demand, bound to carrier proteins in the blood, and typically bind to intracellular receptors.

Amine Hormones

Hormones derived from single amino acids, specifically tryptophan (like melatonin) or tyrosine (like catecholamines and thyroid hormones).

Catecholamines

A class of amine hormones, including epinephrine and norepinephrine, that are neurohormones and behave like peptide hormones.

Thyroid Hormones

Amine hormones synthesized from tyrosine and iodine, such as $T_3$ and $T_4$, that behave more like steroid hormones with intracellular receptors.

Trophic Hormone

A hormone that has the primary function of controlling the secretion of another hormone.

Portal System

A specialized blood vessel arrangement, such as the hypothalamic-hypophyseal portal system, where two capillary beds are connected in series by a vein.

Long-loop Negative Feedback

A feedback mechanism where the final hormone in a pathway suppresses the secretion of both its hypothalamic and anterior pituitary trophic hormones.

Short-loop Negative Feedback

A feedback mechanism where a pituitary hormone suppresses the production of the hypothalamic trophic hormone that stimulated it.

Synergism

An interaction where the joint effect of two or more hormones is significantly greater than the simple additive sum of their individual effects.

Permissiveness

A type of hormone interaction where one hormone cannot fully exert its effect unless a second hormone is present.

Antagonism

An interaction where the action of one substance diminishes or opposes the physiological effect of another.

Hypersecretion

The excessive production and secretion of a hormone, which can lead to exaggerated physiological effects.

Hyposecretion

The insufficient production of a hormone, leading to diminished or absent physiological responses.

Down-regulation

A decrease in the number of target cell receptors in response to chronically elevated levels of a hormone to reduce cellular responsiveness.

Primary Pathology

An endocrine disorder that originates in the last endocrine gland of a complex reflex pathway.

Secondary Pathology

An endocrine disorder resulting from a problem in the anterior pituitary gland.

Tertiary Pathology

An endocrine disorder resulting from a problem in the hypothalamus, such as a hypothalamic tumor.