Introduction to the Endocrine System

Vocabulary practice flashcards covering fundamental endocrine terminology, hormone classes, pathway mechanisms, feedback loops, and endocrine disorders.

Endocrinology

The study of hormones and their physiological functions in the body.

Hormone

A chemical signal secreted by a cell or group of cells into the blood, transported to a distant target, and exerting effects at very low concentrations ($10^{-9}\text{ M}$ to $10^{-12}\text{ M}$).

Pheromones

Specialized ectohormones secreted into the extracellular fluid or external environment to act on other individuals.

Copulins

Natural pheromones produced by women prior to ovulation to stimulate sexual attraction and activity in men.

Half-Life

The length of time required to reduce a hormone's concentration in the blood by half, indicating the duration of its activity.

Preprohormone

A large, inactive precursor molecule containing a signal sequence, one or more copies of a hormone, and additional peptide fragments.

Prohormone

An inactive protein precursor created when endoplasmic reticulum enzymes chop the signal sequence off a preprohormone.

C-Peptide

A connecting peptide fragment cleaved from proinsulin alongside active insulin, measured in blood tests to evaluate endogenous insulin production.

Steroid Hormones

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

Hashimoto's Disease

An autoimmune disorder in which antibodies attack the thyroid gland, preventing it from producing sufficient amounts of $T_3$ and $T_4$.

Myxedema

An adult hypothyroid syndrome characterized by a low basal metabolic rate, sluggishness, cold sensitivity, weight gain, and endemic goiter from iodine deficiency.

Endemic Goiter

Enlargement of the thyroid gland resulting from iodine deficiency, causing the gland to store unusable non-iodinated colloid.

Cretinism

Severe congenital hypothyroidism in infants caused by a deficiency of thyroid hormones at birth, leading to physical and mental impairment.

Graves' Disease

An autoimmune form of hyperthyroidism in which antibodies mimic TSH and overstimulate the thyroid gland to produce excess thyroid hormones.

Exophthalmos

Protrusion of the eyes (proptosis) caused by the build-up of water-holding carbohydrates behind the eyes in Graves' disease.

Posterior Pituitary

An extension of neural tissue (neurohypophysis) that stores and releases vasopressin (ADH) and oxytocin synthesized in the hypothalamus.

Anterior Pituitary

A true endocrine gland of epithelial origin (adenohypophysis) that secretes six classic hormones: PRL, TSH, ACTH, GH, FSH, and LH.

Hypothalamic-Hypophyseal Portal System

A modified vascular bed consisting of two capillary beds connected in series by a vein, routing concentrated hypothalamic neurohormones directly to the anterior pituitary.

Long-Loop Negative Feedback

The dominant negative feedback pathway where a hormone secreted by a peripheral endocrine gland suppresses trophic hormone secretion from both the anterior pituitary and hypothalamus.

Short-Loop Negative Feedback

A feedback mechanism in which an anterior pituitary hormone suppresses hypothalamic trophic hormone production.

Synergism

A hormonal interaction where the combined effect of multiple hormones is greater than the additive sum of their individual effects.

Permissive Hormone

A hormone that must be present for another hormone to exert its full physiological effect.

Antagonistic Hormones

Hormones that exert opposing physiological or cellular actions against one another.

Down-Regulation

A decrease in target cell receptor number in response to abnormally high hormone levels to diminish cellular responsiveness.

Type 1 Diabetes Mellitus

An autoimmune disorder characterized by immune destruction of pancreatic beta cells, preventing insulin production and requiring exogenous insulin.

Type 2 Diabetes Mellitus

A metabolic disorder characterized by insulin resistance, missing or abnormal insulin receptors, or insufficient insulin secretion.

Gigantism

A condition in children caused by hypersecretion of growth hormone, resulting in excessive lengthening of long bones and extreme height.

Acromegaly

A condition in adults caused by hypersecretion of growth hormone, leading to bone growth in the face, hands, and feet.

Primary Endocrine Pathology

An endocrine disorder caused by dysfunction or pathology situated within the final endocrine gland of a pathway.

Secondary Endocrine Pathology

An endocrine disorder caused by dysfunction or pathology situated within the pituitary gland.

Tertiary Endocrine Pathology

An endocrine disorder caused by dysfunction or pathology situated within the hypothalamus.

Cushing's Syndrome

A disorder resulting from hypercortisolism (excess cortisol) caused by primary adrenal cortex, secondary pituitary, or tertiary hypothalamic pathology.

Melatonin

An amino acid-derived hormone synthesized from tryptophan in the pineal gland that transmits light-dark cycle information to govern the biological clock.