Endocrinology & Metabolism Comprehensive Review

A complete set of vocabulary flashcards covering general endocrinology, the hypothalamus-pituitary axis, thyroid function, adrenal stress response, growth regulation, and metabolic integration.

Endocrinology

The regulation and integration of cells and organ systems by hormones.

Exocrine glands

Glands that release secretions into ducts, where the products are not hormones.

Endocrine glands

Ductless glands that release hormones into the internal environment.

Paracrine signaling

A type of chemical signaling where the messenger acts on nearby cells.

Autocrine signaling

A type of chemical signaling where the messenger acts on the same cell that secreted it.

Amine hormones

Hormones derived from the amino acid tyrosine, including thyroid hormones and catecholamines.

Catecholamines

A group of amine hormones including epinephrine, norepinephrine, and dopamine produced by the adrenal medulla and hypothalamus.

Peptide hormones

A major class of water-soluble hormones synthesized as a preprohormone, then a prohormone, and finally the active hormone.

Steroid hormones

Lipid-soluble hormones synthesized from cholesterol, produced by the adrenal cortex, gonads, and skin.

Up-regulation

An increase in the density of receptors for a hormone, often caused by exposure to low levels of the hormone.

Down-regulation

A decrease in the density of receptors for a hormone, often caused by exposure to high levels of the hormone.

Permissiveness

A situation where one hormone must be present for another hormone to have its full effect (e.g., thyroid hormone's effect on epinephrine).

Infundibulum

The structure that connects the pituitary gland to the hypothalamus.

Adenohypophysis

The anterior pituitary gland, which is composed of glandular tissue.

Neurohypophysis

The posterior pituitary gland, which is composed of neural tissue.

Oxytocin

A posterior pituitary hormone that stimulates milk ejection and uterine smooth muscle contraction during labor.

Vasopressin (ADH)

A posterior pituitary hormone that stimulates contraction of blood vessels and decreases water loss through the kidneys.

Hypophysiotropic hormones

Hormones released by the hypothalamus that stimulate or inhibit the release of anterior pituitary hormones.

Long-loop negative feedback

A feedback mechanism where the third hormone in a sequence acts back on the hypothalamus or anterior pituitary to inhibit further secretion.

Short-loop negative feedback

A feedback mechanism where the second hormone in a sequence (from the anterior pituitary) acts back on the hypothalamus.

Hyporesponsiveness

A condition where the endocrine gland produces normal hormone levels, but target cells fail to respond properly; also known as hormone resistance.

Triiodothyronine ($T_3$)

The major active thyroid hormone produced by the thyroid gland or through the conversion of $T_4$ in target cells.

Thyroxine ($T_4$)

The major form of thyroid hormone circulating in the blood, which acts primarily as a prohormone.

Iodide trapping

The first step in thyroid hormone synthesis where iodide is carried into follicular cells by a unidirectional $Na^+ / I^-$ symporter.

Iodine organification

The step where thyroid peroxidase oxidizes iodide to an iodine free radical and binds it to tyrosine residues on thyroglobulin.

Calorigenic effect

The increase in whole-body heat production induced by thyroid hormone.

Congenital hypothyroidism

A condition (formerly called cretinism) caused by a lack of thyroid hormone during fetal development, resulting in mental retardation.

Hashimoto’s disease

An autoimmune destruction of the thyroid gland and the most common form of primary hypothyroidism in the U.S.

Grave’s disease

An autoimmune disorder where antibodies activate the TSH receptor, leading to primary hyperthyroidism and goiter.

Exophthalmos

The bulging of the eyes often observed in patients with Graves’ disease due to immune attack behind the eyes.

Cortisol

The primary glucocorticoid hormone released by the adrenal cortex in response to stress.

Cytokines

Chemical signaling agents secreted by immune cells that can stimulate $ACTH$ secretion and link the endocrine stress response to the immune system.

Gluconeogenesis

The synthesis of glucose from non-carbohydrate sources such as amino acids, glycerol, and lactate.

Addison’s disease

Primary adrenal insufficiency caused by the destruction of adrenal gland tissue, often resulting in hypotension.

Cushing’s Syndrome

A condition caused by chronically elevated cortisol levels, characterized by moon face, obesity, and hypertension.

Epiphyses

The ends of an immature long bone.

Diaphysis

The shaft of an immature long bone.

Epiphyseal growth plate

The cartilage junction between the ends and shaft of a growing bone where active proliferation occurs.

Osteoblasts

Cells that convert cartilage into bone during the process of bone growth.

Chondrocytes

Cells that put down new cartilage in the interior of the epiphyseal growth plate.

Mitogen

Any chemical that stimulates cell division and growth.

Insulin-like growth factor 1 (IGF-1)

A mitogen stimulated by growth hormone that directly causes chondrocytes and osteoblasts to become active.

Gigantism

Abnormally tall height caused by excessive levels of $IGF-1$ while epiphyseal growth plates are still open.

Acromegaly

The enlargement and broadening of bones caused by excessive levels of $IGF-1$ after the epiphyseal growth plates have closed.

Compensatory growth

A rapid growth spurt (catch-up growth) that occurs after normal growth was temporarily inhibited due to malnutrition or illness.

Absorptive State

The metabolic period during eating and up to $4$ hours after a meal where nutrients enter the blood from the GI tract.

Postabsorptive State

The metabolic state where nutrients are provided from body stores to maintain blood glucose, specifically for the CNS.

Glycogenolysis

The breakdown of glycogen stored in the liver to release glucose into the blood.

Glucose sparing

The process where non-neural cells switch to using fats for fuel, reserving plasma glucose for the brain.

Islets of Langerhans

Clusters of endocrine cells in the pancreas containing beta cells (which produce insulin) and alpha cells (which produce glucagon).

Type 1 Diabetes Mellitus

A disease resulting from the autoimmune destruction of pancreatic beta cells, causing a total lack of insulin.

Type 2 Diabetes Mellitus

A disease characterized by insulin resistance, often associated with obesity.

Low density lipoproteins (LDL)

Lipoproteins that deliver cholesterol to cells, often referred to as 'bad' cholesterol.

High density lipoproteins (HDL)

Lipoproteins that remove cholesterol from cells and plaques, often referred to as 'good' cholesterol.