Chapter 16: Endocrine System

Comprehensive vocabulary flashcards covering the organs, hormones, signal transduction pathways, regulation loops, and clinical pathologies of the endocrine system.

Endocrine Glands

Ductless glands that synthesize and secrete hormones directly into the extracellular fluid.

Exocrine Glands

Glands with ducts that produce nonhormonal substances and release them onto body surfaces or into cavities.

Neuroendocrine Organs

Organs consisting of nervous tissue that synthesize and release hormones, including the hypothalamus, pineal gland, posterior pituitary gland, and adrenal medulla.

Hormones

Chemical messengers that regulate the metabolic and physiologic functions of other cells by binding to specific target cell receptors.

Hydrophilic Hormones

Amino acid–based hormones that cannot cross the phospholipid bilayer and must bind to receptors located on the plasma membrane.

Hydrophobic Hormones

Lipid-soluble chemical messengers, such as steroid and thyroid hormones, that readily diffuse across the plasma membrane to bind intracellular receptors.

Adenylate Cyclase

A membrane-bound enzyme activated by a G-protein subunit that catalyzes the conversion of ATP into cyclic AMP ($\text{cAMP}$).

Protein Kinase A

An enzyme activated by the second messenger $\text{cAMP}$ that phosphorylates specific intracellular proteins to execute cellular responses.

Hormonal Stimuli

The stimulation or inhibition of hormone secretion caused by the action of another hormone, such as GHRH stimulating GH release.

Humoral Stimuli

The stimulation of hormone release in response to changes in extracellular fluid levels of ions or nutrients, such as blood glucose triggering insulin release.

Neural Stimuli

The stimulation of endocrine cells by direct nervous system signals, such as sympathetic neurons triggering catecholamine release from the adrenal medulla.

Infundibulum

The stalk-like structure of connective and nervous tissue that connects the hypothalamus to the pituitary gland.

Hypothalamic-Hypophyseal Tract

A neural tract within the infundibulum along which ADH and oxytocin travel from the hypothalamic nuclei to store in posterior pituitary axon terminals.

Antidiuretic Hormone (ADH)

A hypothalamic hormone stored in the posterior pituitary that causes aquaporins to be inserted into kidney tubules, thereby retaining water and reducing urine output.

Diabetes Insipidus

A pathological condition caused by hyposecretion of ADH, leading to extreme thirst, signs of dehydration, and large volumes of dilute urine.

Oxytocin

A hypothalamic hormone stored in the posterior pituitary that strongly stimulates uterine contractions during labor and triggers milk ejection from mammary glands.

Hypothalamic-Hypophyseal Portal System

A specialized vascular arrangement of capillaries and portal veins in the infundibulum that delivers hypothalamic releasing and inhibiting hormones directly to the anterior pituitary.

Thyroid-Stimulating Hormone (TSH)

An anterior pituitary hormone stimulated by TRH that promotes development and hormone synthesis within the thyroid gland.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary hormone stimulated by CRH that promotes adrenal cortex development and stimulates the synthesis of corticosteroid hormones.

Prolactin (PRL)

An anterior pituitary hormone that stimulates mammary gland development, initiates milk production following childbirth, and maintains lactation.

Luteinizing Hormone (LH)

A gonadotropin secreted by the anterior pituitary that stimulates testosterone synthesis in males, and stimulates estrogen/progesterone synthesis and triggers ovulation in females.

Follicle-Stimulating Hormone (FSH)

A gonadotropin from the anterior pituitary that promotes gamete production in males and ovarian follicle maturation in females.

Growth Hormone (GH)

An anterior pituitary hormone that promotes the growth of target tissues including bone, cartilage, and muscle, while influencing glucose and lipid metabolism.

Insulin-Like Growth Factor (IGF)

A growth-promoting peptide synthesized by the liver, muscle, and bone in response to GH that stimulates cell division, protein synthesis, and tissue growth.

Gigantism

A pathology caused by the hypersecretion of growth hormone that occurs prior to the closure of the epiphyseal plates.

Acromegaly

A condition resulting from hypersecretion of growth hormone after closure of the epiphyseal plates, characterized by enlarged bones in the face, hands, and feet.

Pituitary Dwarfism

A developmental disorder caused by hyposecretion of growth hormone during childhood, leading to short stature with proportionally sized limbs and trunk.

Thyroid Follicles

Spherical structural subunits of the thyroid gland lined with follicle cells that synthesize thyroid hormones and enclose protein-rich colloid.

Colloid

The gelatinous, protein-rich substance stored within the central lumen of thyroid follicles containing precursors to thyroid hormones.

Parafollicular Cells

Endocrine cells situated in the interstitial spaces between thyroid follicles that synthesize and secrete calcitonin.

Triiodothyronine ($\text{T}_3$) and Thyroxine ($\text{T}_4$)

Amino acid–based hormones containing 3 or 4 iodine atoms that set the basal metabolic rate, promote growth and development, and synergize with the sympathetic nervous system.

Graves' Disease

The most common form of hyperthyroidism, leading to weight loss, heat intolerance, elevated metabolic rate, and cardiovascular disruptions.

Goiter

An enlargement of the thyroid gland frequently seen in cases of hypothyroidism due to continuous stimulation by TSH.

Calcitonin

A hormone produced by parafollicular cells of the thyroid gland in response to elevated blood $\text{Ca}^{2+}$ levels.

Parathyroid Hormone (PTH)

A hormone released by chief cells of the parathyroid glands that increases blood $\text{Ca}^{2+}$ concentration by acting on osteoclasts, kidneys, and calcitriol activation.

Calcitriol

The active form of vitamin D activated by the kidneys in response to PTH that increases $\text{Ca}^{2+}$ absorption in the small intestine.

Hyperparathyroidism

An excessive secretion of PTH causing bone demineralization and deformity, nervous system depression, and formation of kidney stones.

Hypoparathyroidism

A deficit in PTH secretion that drops blood $\text{Ca}^{2+}$, causing neuromuscular tetany, respiratory paralysis, and potentially death.

Zona Glomerulosa

The outer layer of the adrenal cortex responsible for synthesizing mineralocorticoid hormones, primarily aldosterone.

Zona Fasciculata

The intermediate and thickest layer of the adrenal cortex that synthesizes glucocorticoid hormones, primarily cortisol.

Zona Reticularis

The deep layer of the adrenal cortex adjacent to the medulla that synthesizes androgenic steroids.

Aldosterone

The primary mineralocorticoid that regulates fluid balance by stimulating $\text{Na}^+$ and $\text{Cl}^-$ retention, water reabsorption, and excretion of $\text{K}^+$ and $\text{H}^+$ in kidney tubules.

Hyperaldosteronism

A condition of aldosterone hypersecretion causing hypokalemia, hypernatremia, and hypertension.

Cortisol

The primary glucocorticoid that mediates stress responses by stimulating gluconeogenesis, mobilizing fatty acids and amino acids, and suppressing inflammatory pathways.

Cushing's Disease

A hypercortisolemic disorder characterized by hyperglycemia, muscle wasting, distinctive fat redistribution, and suppressed immune function.

Addison's Disease

A hyposecretion disorder of the adrenal cortex resulting in reduced cortisol and aldosterone, leading to hypoglycemia, hyponatremia, dehydration, and severe hypotension.

Catecholamines

Epinephrine and norepinephrine, produced by the adrenal medulla, that initiate fight-or-flight responses including increased cardiac output and bronchodilation.

Pancreatic Islets

Endocrine clusters within the pancreas containing alpha cells, beta cells, and delta cells that regulate blood glucose levels.

Glucagon

A hormone produced by pancreatic alpha cells in response to blood glucose falling below $70\text{--}99\,\text{mg/dL}$ that stimulates glycogenolysis and gluconeogenesis in the liver.

Insulin

A hormone secreted by pancreatic beta cells when blood glucose exceeds $70\text{--}99\,\text{mg/dL}$ that stimulates cellular uptake of nutrients and glycogenesis.

Type I Diabetes Mellitus

An autoimmune disorder characterized by the destruction of pancreatic beta cells, resulting in absolute insulin deficiency, glucosuria, ketonuria, and ketoacidosis.

Type II Diabetes Mellitus

A metabolic disease associated with obesity and heredity in which peripheral target tissues become resistant to insulin, leading to chronic hyperglycemia.