The Endocrine System Flashcards

Vocabulary practice flashcards covering key terms, hormones, glands, mechanisms, and disorders of the Endocrine System.

Endocrinology

The scientific study of hormones and endocrine organs.

Hormones

Long-distance chemical signals that travel through the blood or lymph and attach to specific receptors to initiate a response in target cells.

Autocrines

Local chemical messengers that exert their effects on the exact same cells that secrete them.

Paracrines

Local chemical messengers that act locally within the same tissue, affecting cells other than those that secreted them.

Exocrine Glands

Glands that produce non-hormonal substances (e.g., sweat, saliva) and carry their secretions to a membrane surface via ducts.

Endocrine Glands

Ductless glands that produce hormones and release them directly into the surrounding blood or lymph.

Amino Acid–Based Hormones

Water-soluble hormones (including amino acid derivatives, peptides, and proteins) that act on extracellular plasma membrane receptors and cannot cross the plasma membrane, with the exception of thyroid hormone.

Steroid Hormones

Lipid-soluble hormones synthesized from cholesterol (including gonadal and adrenocortical hormones) that can cross the plasma membrane and act on intracellular receptors.

Target Cells

Cells that express specific receptors for a particular hormone.

Cyclic AMP (cAMP) Signaling Mechanism

A second-messenger system used by water-soluble hormones where a G protein activates adenylate cyclase to convert ATP to cAMP, which in turn activates protein kinases that phosphorylate target proteins.

PIP2-Calcium Signaling Mechanism

A second-messenger mechanism where a hormone-activated G protein activates phospholipase C to split PIP2 into diacylglycerol (DAG) and inositol trisphosphate (IP3), triggering the release of intracellular $\text{Ca}^{2+}$.

Humoral Stimulus

Endocrine gland stimulation caused directly by changing blood levels of critical ions or nutrients (e.g., declining blood $\text{Ca}^{2+}$ stimulating parathyroid hormone release).

Neural Stimulus

Endocrine gland stimulation caused directly by nerve fiber innervation (e.g., sympathetic fibers stimulating the adrenal medulla to secrete catecholamines).

Hormonal Stimulus

Endocrine gland stimulation caused by other hormones, known as tropic hormones (e.g., hypothalamic hormones stimulating anterior pituitary release).

Up-Regulation

The process by which target cells form additional receptors for a specific hormone in response to persistently low hormone levels.

Down-Regulation

The process by which target cells lose or desensitize receptors in response to persistently high hormone levels to prevent overreaction.

Permissiveness

A hormone interaction where one hormone cannot exert its full physiological effects without another hormone being present (e.g., reproductive hormones requiring thyroid hormone).

Synergism

A hormone interaction in which more than one hormone produces the same effect on a target cell, resulting in amplified combined effects (e.g., glucagon and epinephrine both releasing glucose from the liver).

Antagonism

A hormone interaction where one or more hormones oppose the action of another hormone (e.g., insulin and glucagon).

Infundibulum

The stalk of tissue that physically connects the hypothalamus to the pituitary gland.

Hypothalamic-Hypophyseal Tract

A neural tract running through the infundibulum that connects hypothalamic neurons (paraventricular and supraoptic) directly to the posterior pituitary.

Oxytocin

A neurohormone synthesized by paraventricular neurons of the hypothalamus and released by the posterior pituitary that triggers uterine contractions during labor, milk ejection during breastfeeding, and affectionate behaviors.

Antidiuretic Hormone (ADH / Vasopressin)

A neurohormone synthesized by supraoptic neurons of the hypothalamus and released by the posterior pituitary that acts on kidney tubules to reabsorb water and decrease urine production.

Diabetes Insipidus

A condition caused by an ADH deficiency resulting from damage to the hypothalamus or posterior pituitary, characterized by intense thirst and massive urine output.

Syndrome of Inappropriate ADH Secretion (SIADH)

A clinical condition characterized by excessive ADH secretion leading to abnormal fluid retention, headaches, disorientation, and low blood sodium levels.

Hypophyseal Portal System

A vascular system consisting of a primary capillary plexus, hypophyseal portal veins, and a secondary capillary plexus that transports releasing and inhibiting hormones from the hypothalamus to the anterior pituitary.

Tropic Hormones

Hormones that function primarily to regulate the secretion and activity of other target endocrine glands.

Growth Hormone (GH / Somatotropin)

An anterior pituitary hormone secreted by somatotropic cells that exerts direct anti-insulin metabolic actions and indirect growth-promoting actions via insulin-like growth factors (IGFs).

Insulin-Like Growth Factors (IGFs)

Growth-promoting proteins produced by the liver, skeletal muscle, and bone in response to GH that stimulate cell division, nutrient uptake, protein synthesis, and bone formation.

Gigantism

A clinical condition resulting from hypersecretion of growth hormone in children prior to epiphyseal plate closure, causing excessive linear growth.

Acromegaly

A clinical condition resulting from hypersecretion of growth hormone in adults, characterized by overgrowth of bones in the hands, feet, and face.

Pituitary Dwarfism

A clinical condition resulting from hyposecretion of growth hormone in children, leading to abnormally short stature.

Thyroid-Stimulating Hormone (TSH / Thyrotropin)

A tropic hormone secreted by thyrotropic cells of the anterior pituitary that stimulates normal development and secretion of thyroid hormones by the thyroid gland.

Adrenocorticotropic Hormone (ACTH / Corticotropin)

A tropic hormone secreted by corticotropic cells of the anterior pituitary that stimulates the adrenal cortex to release corticosteroids.

Follicle-Stimulating Hormone (FSH)

A gonadotropin secreted by gonadotropic cells of the anterior pituitary that stimulates gamete production (eggs in females, sperm in males).

Luteinizing Hormone (LH)

A gonadotropin secreted by gonadotropic cells of the anterior pituitary that triggers ovulation and sex hormone production (estrogen/progesterone in females, testosterone in males).

Prolactin (PRL)

An anterior pituitary hormone secreted by prolactin cells that stimulates milk production in female mammary glands.

Colloid

The fluid contained within the lumen of thyroid follicles containing thyroglobulin bound to iodine, acting as the precursor to thyroid hormones.

Parafollicular Cells (C Cells)

Endocrine cells located in the thyroid gland outside the follicles that produce and secrete calcitonin.

Thyroxine ($\text{T}_4$)

The primary form of thyroid hormone secreted by thyroid follicles, consisting of two tyrosine molecules with four bound iodine atoms.

Triiodothyronine ($\text{T}_3$)

The highly active form of thyroid hormone consisting of two tyrosines with three bound iodine atoms, produced in smaller amounts by the thyroid or converted from $\text{T}_4$ in peripheral tissues.

Myxedema

A severe hypothyroid condition in adults characterized by a low metabolic rate, dry skin, puffy eyes, mental sluggishness, lethargy, and edema.

Goiter

An enlargement of the thyroid gland due to iodine deficiency, which prevents proper thyroid hormone synthesis and triggers excess TSH secretion.

Graves' Disease

An autoimmune hyperthyroid disease caused by abnormal antibodies mimicking TSH, leading to an elevated metabolic rate, sweating, rapid heart rate, weight loss, and exophthalmos.

Calcitonin

A hormone produced by parafollicular cells in response to high blood $\text{Ca}^{2+}$ levels that lowers blood calcium at high doses by inhibiting osteoclasts and stimulating calcium uptake into bone.

Parathyroid Hormone (PTH)

The primary hormone regulating calcium homeostasis, secreted by parathyroid glands in response to low blood $\text{Ca}^{2+}$ to stimulate osteoclast activity, renal calcium reabsorption, and intestinal calcium absorption.

Corticosteroids

A group of over 24 steroid hormones produced by the adrenal cortex, including mineralocorticoids, glucocorticoids, and gonadocorticoids.

Zona Glomerulosa

The outermost cortical layer of the adrenal gland responsible for producing mineralocorticoids, primarily aldosterone.

Zona Fasciculata

The middle cortical layer of the adrenal gland responsible for producing glucocorticoids, primarily cortisol.

Zona Reticularis

The innermost cortical layer of the adrenal gland responsible for producing gonadocorticoids (weak adrenal androgens such as DHEA).

Aldosterone

The most potent mineralocorticoid, secreted by the zona glomerulosa, which stimulates sodium retention and potassium elimination in the kidneys to increase blood volume and blood pressure.

Cortisol

The primary glucocorticoid in humans, secreted by the zona fasciculata, which maintains blood glucose levels through gluconeogenesis, manages stress responses, and exerts anti-inflammatory effects.

Catecholamines

Epinephrine (80%) and norepinephrine (20%), amine hormones secreted by the medullary chromaffin cells of the adrenal gland during short-term stress to increase heart rate, blood pressure, and metabolic activity.

Melatonin

An amine hormone secreted by pinealocytes in the pineal gland that follows a diurnal pattern (peaking at night) to regulate sleep-wake cycles and circadian rhythms.

Pancreatic Islets (Islets of Langerhans)

Endocrine cell clusters scattered throughout the exocrine pancreas that contain alpha cells (producing glucagon) and beta cells (producing insulin).

Glucagon

A potent hyperglycemic peptide hormone secreted by pancreatic alpha cells during low blood glucose conditions that stimulates glycogenolysis and gluconeogenesis in the liver.

Insulin

A hypoglycemic peptide hormone secreted by pancreatic beta cells in response to high blood glucose levels that facilitates glucose transport into target cells and inhibits glycogen breakdown.

Glycogenolysis

The metabolic breakdown of liver glycogen into glucose molecules released into the bloodstream.

Gluconeogenesis

The metabolic synthesis of new glucose molecules from noncarbohydrate precursors, such as lactic acid, amino acids, or fats.

Polyuria

A cardinal sign of diabetes mellitus characterized by excessive urine production caused by glucose acting as an osmotic diuretic.

Polydipsia

A cardinal sign of diabetes mellitus characterized by excessive thirst resulting from massive fluid loss via polyuria.

Polyphagia

A cardinal sign of diabetes mellitus characterized by excessive hunger and eating due to cellular starvation caused by the inability to utilize blood glucose.