Endocrine System – Thyroid, Parathyroid, Adrenal, Pancreas & More

Vocabulary flashcards summarizing key endocrine terms, hormones, organs, feedback loops, and stimuli discussed in the lecture.

Thyroid Gland

Butterfly-shaped gland in the anterior neck that sets the body’s metabolic rate.

Thyroxine (T3/T4)

Collective name for thyroid hormone; raises metabolic rate, heart rate, temperature, etc.

Tri-iodothyronine (T3)

More active form of thyroid hormone containing three iodine atoms.

Thyroxine (T4)

Less active thyroid hormone containing four iodine atoms; converted to T3 in tissues.

Iodine

Mineral required for synthesis of T3 and T4; deficiency leads to hypothyroidism.

Thyroid-Stimulating Hormone (TSH)

Anterior-pituitary hormone that stimulates the thyroid to release T3/T4.

Hyperthyroidism

Excess thyroid hormone; ↑ HR, temperature, anxiety, weight loss.

Hypothyroidism

Deficient thyroid hormone; ↓ metabolism, cold intolerance, constipation.

Calcitonin

Thyroid hormone that lowers blood calcium by stimulating osteoblasts and renal excretion.

Parathyroid Gland

Four small glands on posterior thyroid that secrete parathyroid hormone.

Parathyroid Hormone (PTH)

Raises blood calcium by activating osteoclasts, increasing GI absorption & renal reabsorption.

Osteoblast

Bone cell that builds bone; stimulated by calcitonin.

Osteoclast

Bone-resorbing cell; activated by parathyroid hormone.

Calcitriol (Vitamin D)

Kidney-derived hormone that works with PTH to raise blood calcium.

Adrenal Gland

Endocrine gland atop each kidney; consists of cortex and medulla.

Adrenal Medulla

Inner adrenal region that releases epinephrine and norepinephrine during stress.

Epinephrine (Adrenaline)

Catecholamine causing fight-or-flight responses: ↑ HR, BP, glucose, bronchodilation.

Norepinephrine

Catecholamine similar to epinephrine; also a neurotransmitter.

Adrenal Cortex

Outer adrenal layer producing steroid hormones (aldosterone, cortisol, androgens).

Zona Glomerulosa

Outer cortical zone that secretes aldosterone (mineralocorticoid).

Aldosterone

Mineralocorticoid that conserves Na⁺ & water, excretes K⁺, raising blood pressure.

Zona Fasciculata

Middle cortical zone that secretes glucocorticoids (mainly cortisol).

Cortisol

Glucocorticoid stress hormone; ↑ blood glucose & suppresses immune response.

Zona Reticularis

Inner cortical zone that releases androgens (gonadocorticoids).

Androgens

Steroid precursors converted to testosterone or estrogen in peripheral tissues.

Salt–Sugar–Sex

Mnemonic for adrenal cortex layers: Aldosterone, Cortisol, Androgens.

GFR (Glomerulosa–Fasciculata–Reticularis)

Order of adrenal cortex zones from outer to inner.

Pancreas

Gland with both endocrine (islets) and exocrine (digestive enzyme) functions.

Islets of Langerhans

Endocrine clusters in pancreas containing alpha, beta, delta cells.

Alpha Cells

Pancreatic islet cells that secrete glucagon.

Glucagon

Hormone that raises blood glucose by stimulating glycogen breakdown in liver.

Beta Cells

Pancreatic islet cells that secrete insulin.

Insulin

Hormone that lowers blood glucose by stimulating cellular uptake & glycogen storage.

Delta Cells

Islet cells that release somatostatin (inhibits GI & pancreatic activity).

Acinar Cells

Pancreatic exocrine cells that secrete digestive enzymes and bicarbonate into the duodenum.

Bicarbonate (HCO₃⁻)

Alkaline ion secreted by pancreas to neutralize gastric acid in the small intestine.

Glucose

Primary blood sugar used to generate ATP.

Glycogen

Large storage polymer of glucose in liver & muscle.

Hypoglycemia

Abnormally low blood glucose; triggers glucagon secretion.

Hyperglycemia

Elevated blood glucose; triggers insulin release.

Leydig Cells

Testicular cells that produce testosterone in response to LH.

Sertoli Cells

Testicular ‘nurse’ cells that support spermatogenesis; stimulated by FSH.

Follicle-Stimulating Hormone (FSH)

Anterior-pituitary hormone promoting spermatogenesis or follicular growth.

Luteinizing Hormone (LH)

Pituitary hormone stimulating testosterone production or ovulation.

Testosterone

Primary male sex hormone; develops male genitalia & secondary sex traits.

Ovaries

Female gonads that produce oocytes, estrogen, and progesterone.

Estrogen

Hormone that develops female reproductive organs & secondary sex characteristics.

Progesterone

Hormone that prepares and maintains uterus & breasts for pregnancy.

GnRH (Gonadotropin-Releasing Hormone)

Hypothalamic hormone that stimulates FSH and LH release.

Inhibin

Hormone from Sertoli cells that negatively feeds back to reduce FSH.

Ovulation

Release of a mature egg from the ovary, typically on day 14 of cycle.

Erythropoietin (EPO)

Kidney hormone that increases red blood cell synthesis when O₂ is low.

Renin

Kidney enzyme that starts the renin–angiotensin–aldosterone pathway to raise BP.

Thymus

Immune organ (largest in childhood) that matures T-lymphocytes.

Thymopoietin

Thymic hormone that promotes T cell production.

Thymosin

Thymic hormone that supports maturation & differentiation of T cells.

Pineal Gland

Small brain gland that secretes melatonin.

Melatonin

Hormone regulating circadian sleep–wake cycles; rises in darkness.

Hormonal Stimulus

Hormone release triggered by another hormone (e.g., TSH → T3/T4).

Neural Stimulus

Hormone release triggered by nerve impulses (e.g., sympathetic nerves → epinephrine).

Humoral Stimulus

Hormone release triggered by changes in blood composition (e.g., ↑Ca²⁺ → calcitonin).

Antagonistic Hormones

Hormones with opposite effects on the same target (e.g., insulin vs. glucagon).

Synergistic Hormones

Hormones that produce amplified, similar effects together (e.g., cortisol + glucagon).

Permissive Hormone Action

One hormone must be present for another to act (e.g., thyroid hormone permits epinephrine).

Integrative Hormones

Hormones with different but complementary effects (e.g., prolactin makes milk, oxytocin ejects it).

Fight-or-Flight Response

Acute sympathetic reaction mediated by epinephrine/norepinephrine.

Mineralocorticoid

Adrenal steroid regulating electrolyte balance (main example: aldosterone).

Glucocorticoid

Adrenal steroid affecting metabolism & immunity (main example: cortisol).

Gonadocorticoid

Adrenal cortex androgenic steroid acting as sex-hormone precursor.

Anterior Pituitary

Glandular lobe releasing TSH, ACTH, FSH, LH, GH, prolactin.

Posterior Pituitary

Neurohypophysis storing & releasing oxytocin and antidiuretic hormone (ADH).

Antidiuretic Hormone (ADH/Vasopressin)

Posterior-pituitary hormone that conserves water & raises blood pressure.

Angiotensin II

Potent vasoconstrictor produced in RAA pathway; stimulates aldosterone.

Hypercalcemia

Elevated blood calcium; triggers calcitonin release.

Hypocalcemia

Low blood calcium; triggers parathyroid hormone release.

B-cells (Pancreas)

Another notation for beta cells that secrete insulin.

C-Cells (Thyroid)

Parafollicular thyroid cells that secrete calcitonin.

Ischemic Hypoxia

Reduced tissue oxygen that can stimulate renal EPO release.

Sympathetic Nervous System

Autonomic division that activates adrenal medulla and fight-or-flight physiology.

Negative Feedback

Homeostatic loop where rising hormone levels inhibit their own further release.