endocrine system

Endocrine Gland

Tissue or organ that secretes chemical messages into blood/lymph to reach distant target cells.

Hormone

Chemical messenger secreted into blood or lymph to induce a response in target cells at low concentrations.

Target Cell / Organ

Cells or organs with specific intracellular or surface receptors that bind a specific hormone.

Humoral Stimuli

Hormone secretion triggered by changing blood levels of specific ions or nutrients (e.g., PTH, Insulin).

Neural Stimuli

Hormone release stimulated directly by nerve fibers (e.g., Sympathetic nerves stimulating adrenal medulla).

Hormonal Stimuli

Hormone release stimulated by a hormone produced by another endocrine organ (e.g., TSH, ACTH).

Hydrophilic Hormones

Water-soluble amino acid-based hormones that bind to cell surface receptors (e.g., Insulin, Epinephrine).

Second Messengers

Intracellular signals produced in response to cell surface receptor activation (e.g., cAMP, IP3).

Glycogenolysis

Hydrolysis of stored glycogen to release glucose into the cell/blood.

Adrenergic Receptors

G-protein coupled receptors stimulated by epinephrine and norepinephrine.

Adenylyl Cyclase

Enzyme activated by a G-protein that converts ATP into the second messenger cAMP.

Protein Kinase A (PKA)

Enzyme activated by cAMP that initiates a phosphorylation cascade to activate glycogen breakdown.

Hydrophobic Hormones

Lipid-soluble hormones that cross cell membranes to bind intracellular receptors (e.g., Steroids, T3/T4).

Gluconeogenesis

Metabolic pathway that synthesizes new glucose from non-carbohydrate precursors.

Glucocorticoid Receptors (GR)

Intracellular receptors activated by cortisol that increase PEPCK gene transcription in the liver.

Hypothalamus

Diencephalon region producing releasing hormones (TRH, CRH, GnRH) and posterior pituitary neurohormones.

Pituitary Gland (Hypophysis)

Organ connected to hypothalamus via infundibulum; split into anterior and posterior lobes.

Hypophyseal Portal System

Vascular network allowing hypothalamic releasing hormones to travel directly to the anterior pituitary.

Posterior Pituitary (Neurohypophysis)

Nervous tissue storage/release site for neurohormones synthesized in the hypothalamus.

Oxytocin (OT)

Posterior pituitary neurohormone causing uterine contractions during labor and milk ejection during nursing.

Antidiuretic Hormone (ADH)

Posterior pituitary neurohormone stimulating renal water reabsorption to decrease urine volume.

Anterior Pituitary (Adenohypophysis)

Glandular tissue producing tropic hormones (TSH, ACTH, FSH, LH, GH, PRL).

Tropic Hormones

Hormones that stimulate the growth and secretion of other endocrine glands (e.g., TSH, ACTH).

Thyroid Stimulating Hormone (TSH)

Anterior pituitary hormone that stimulates thyroid gland growth and T3/T4 secretion.

Adrenocorticotropic Hormone (ACTH)

Anterior pituitary hormone that stimulates the adrenal cortex to release glucocorticoids.

Prolactin (PRL)

Anterior pituitary hormone that stimulates mammary gland development and milk production.

Follicle Stimulating Hormone (FSH)

Anterior pituitary hormone regulating gamete production (egg maturation / sperm development).

Luteinizing Hormone (LH)

Anterior pituitary hormone stimulating ovulation/progesterone in females and testosterone in males.

Growth Hormone (GH)

Anterior pituitary hormone promoting cell division in muscle/bone, increasing blood glucose, and generating IGF.

Thyroid Gland

Butterfly-shaped cervical gland producing T3, T4 (metabolic regulation), and calcitonin.

Colloid

Protein-rich gelatinous material within thyroid follicles where T3 and T4 precursors are synthesized.

Thyroglobulin

Tyrosine-rich protein stored in thyroid follicles used to synthesize T3 and T4.

Thyroid Peroxidase

Enzyme that oxidizes iodide ions to iodine for attachment to tyrosine residues on thyroglobulin.

Grave's Disease

Autoimmune hyperthyroidism caused by TRAb autoantibodies stimulating TSH receptors; features exophthalmos and goiter.

Goiter

Enlargement of the thyroid gland resulting from excessive TSH receptor stimulation.

Exophthalmos

Bulging of the eyeballs seen in Grave's disease due to tissue water retention and weakened eye muscles.

Hashimoto's Disease

Autoimmune hypothyroidism caused by destruction of thyroid tissue (TPOAb antibodies); leads to low metabolic rate.

Iodine Deficiency

Lack of dietary iodine preventing T3/T4 synthesis; causes hypothyroidism, goiter, and developmental defects.

Calcitonin

Hormone from thyroid parafollicular cells (C-cells) that lowers blood calcium by inhibiting osteoclasts.

Parathyroid Glands

Four posterior thyroid glands releasing PTH in response to hypocalcemia to elevate blood calcium.

Adrenal Medulla

Inner adrenal region of nervous origin; chromaffin cells release epinephrine and norepinephrine.

Adrenal Cortex

Outer glandular adrenal tissue producing mineralocorticoids, glucocorticoids, and gonadocorticoids.

Zona Glomerulosa

Superficial adrenal cortex layer producing mineralocorticoids like aldosterone (Na+ retention/K+ excretion).

Zona Fasciculata

Middle adrenal cortex layer producing glucocorticoids like cortisol in response to ACTH.

Zona Reticularis

Deep adrenal cortex layer producing weak androgenic gonadocorticoids like DHEA.

Cushing's Syndrome

Condition caused by hypercortisolism or corticosteroid use; features hyperglycemia, moon face, and striae.

Addison's Disease

Adrenal insufficiency caused by autoimmune cortical destruction; features hypoglycemia, hypotension, and hyperpigmentation.

Pancreas

Mixed endocrine/exocrine organ posterior to stomach containing islets of Langerhans.

Glucagon

Hormone from pancreatic alpha cells triggered by hypoglycemia; raises blood glucose via glycogenolysis/gluconeogenesis.

Insulin

Hormone from pancreatic beta cells triggered by hyperglycemia; lowers blood glucose via GLUT 4 insertion and glycogenesis.

GLUT 4 Transporters

Insulin-dependent plasma membrane carriers that facilitate passive glucose entry into muscle and adipose cells.

Diabetes Mellitus (DM)

Inadequate insulin production (Type 1) or target cell sensitivity (Type 2) resulting in chronic hyperglycemia.

Polyuria

Cardinal sign of diabetes mellitus characterized by abnormally increased urine output.

Polydipsia

Cardinal sign of diabetes mellitus characterized by excessive thirst.

Polyphagia

Cardinal sign of diabetes mellitus characterized by excessive hunger and food consumption.

Estrogen (Estradiol)

Ovarian hormone regulating endometrial growth, secondary sex characteristics, and female reproductive development.

Progesterone

Ovarian hormone maintaining endometrial lining for gestation and exerting negative feedback on GnRH/FSH/LH.

Testosterone

Testicular hormone produced by Leydig cells under LH influence; drives spermatogenesis and male secondary sex traits.