Endocrine System: Thyroid, Parathyroid, and Pancreatic Hormones

Vocabulary flashcards covering the anatomy, hormones, functions, and medical conditions related to the thyroid gland, parathyroid glands, and pancreas.

Isthmus

A narrow band of tissue that connects the two large lobes of the thyroid gland.

Thyroid Follicles

Tiny sacs that make up thyroid tissue, each filled with a thick fluid called thyroid colloid.

Thyroid Colloid

A thick fluid filling each thyroid follicle in the thyroid gland.

Triiodothyronine ($T_3$)

A thyroid hormone containing three iodine atoms that increases the body's metabolic rate.

Thyroxine ($T_4$)

A thyroid hormone containing four iodine atoms that increases the body's metabolic rate.

Parafollicular Cells

Cells located between thyroid follicles that secrete calcitonin in response to rising blood calcium levels.

Calcitonin

A hormone secreted by parafollicular cells of the thyroid that promotes bone formation by triggering the deposition of calcium in bone.

Cretinism

A condition resulting from congenital hypothyroidism characterized by retarded growth and sexual development, a low metabolic rate, and mental retardation.

Myxedema

A condition resulting from severe or prolonged hypothyroidism in adults involving swelling and firmness of the skin.

Graves' Disease

An autoimmune disorder caused by hypersecretion of thyroid hormone, characterized by unexplained weight loss, increased heart rate, nervousness, and exophthalmos.

Exophthalmos

A protrusion of the eyeballs resulting from swelling of tissue behind the eye, associated with Graves' disease.

Simple Goiter

An enlarged thyroid gland caused by a dietary deficiency of iodine, leading to hypersecretion of TSH by the anterior pituitary and enlargement of thyroid tissue.

Parathyroid Glands

Four glands embedded on the posterior surface of the thyroid that secrete parathyroid hormone in response to low blood calcium levels.

Parathyroid Hormone (PTH)

The primary hormone used to maintain normal blood calcium levels by stimulating bone breakdown, prompting kidneys to reabsorb calcium, and activating vitamin D.

Hypocalcemia

A calcium deficiency that increases nerve and muscle cell excitability, leading to muscle tremors, spasms, or tetany.

Carpopedal Spasm

A cardinal sign of hypocalcemia involving a tight, sustained contraction of the muscles of the hands and feet.

Hypercalcemia

An excess of calcium in the blood that causes cells to become less responsive, leading to muscle weakness, sluggish reflexes, and potentially cardiac arrest.

Acini

Exocrine cells in the pancreas that secrete digestive enzymes into ducts draining into the small intestine.

Pancreatic Islets

Clusters of endocrine cells interspersed among pancreatic exocrine cells, also known as the islets of Langerhans, constituting about $2\%$ of pancreatic tissue.

Alpha Cells

Endocrine cells in the pancreatic islets that secrete glucagon to raise blood glucose levels when they fall between meals.

Gluconeogenesis

The conversion of fatty acids and amino acids into glucose by liver cells, stimulated by glucagon.

Beta Cells

Endocrine cells in the pancreatic islets that secrete insulin after eating to lower blood glucose levels.

Delta Cells

Endocrine cells in the pancreatic islets that secrete somatostatin to inhibit the release of glucagon, insulin, and growth hormone.