Lecture 14: Endocrine System

Comprehensive vocabulary flashcards covering the organs, hormones, control pathways, feedback mechanisms, and clinical conditions of the human endocrine system.

Endocrine System

An organ system that controls the activities of other organ systems by secreting hormones into the bloodstream to regulate homeostasis, reproduction, growth, development, and metabolism.

Hormone

A chemical messenger produced by endocrine glands that travels via the bloodstream to bind specific receptors on target cells, inducing a physiological change.

Target Cell (Effector)

A cell equipped with specific receptors that bind a circulating hormone, triggering a change in cellular function.

Exocrine Gland

A gland that secretes products into a duct leading to a specific epithelial surface, such as sweat glands and salivary glands.

Endocrine Gland

A ductless gland that releases hormones directly into the bloodstream to reach tissues throughout the entire body.

Protein Hormone

A class of hormones composed of chains of amino acids; smaller chains are termed peptide hormones (e.g., Growth Hormone).

Biogenic Amine

A class of hormones synthesized from an altered single amino acid (e.g., Thyroid hormone).

Steroid Hormone

A class of lipid-soluble hormones derived chemically from cholesterol (e.g., Testosterone).

Negative Feedback

A homeostatic control mechanism in which the hormone itself or its metabolic product shuts down further secretion once a set point is reached.

Positive Feedback

A regulatory mechanism in which a process is accelerated and amplified once started until a defined end goal is achieved (e.g., oxytocin release during suckling or childbirth).

Hypothalamus

The master regulator of the endocrine system that monitors the body, produces regulatory hormones for the anterior pituitary, produces ADH and oxytocin, and stimulates the adrenal medulla via the sympathetic division of the ANS.

Regulatory Hormones

Chemical signals produced by the hypothalamus—classified as releasing hormones (RH) and inhibitory hormones (IH)—that stimulate or inhibit secretion from the anterior pituitary.

Pituitary Gland

An endocrine gland located inferior to the hypothalamus consisting of an anterior epithelial lobe and a posterior nervous lobe.

Anterior Pituitary

The anterior lobe of the pituitary gland composed of epithelial tissue that synthesizes and secretes hormones in response to hypothalamic regulatory hormones.

Posterior Pituitary

The posterior lobe of the pituitary gland composed of nervous tissue that stores and releases antidiuretic hormone (ADH) and oxytocin synthesized in the hypothalamus.

Hypothalamo-Hypophyseal Portal System

A specialized vascular pathway connecting two capillary beds between the hypothalamus and the anterior pituitary, serving as a shortcut for hypothalamic regulatory hormones.

Hypothalamo-Hypophyseal Tract

The bundle of neurosecretory axons along which ADH and oxytocin travel from the hypothalamus to the posterior pituitary.

Tropic Hormone

A hormone that targets and regulates other endocrine glands or cells to stimulate the secretion of further hormones (e.g., FSH, LH, ACTH, and TSH).

Thyroid-Stimulating Hormone (TSH)

An anterior pituitary tropic hormone that stimulates the thyroid gland to produce thyroid hormone.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary tropic hormone that stimulates the adrenal cortex to produce corticosteroids.

Follicle-Stimulating Hormone (FSH)

An anterior pituitary tropic gonadotropin that regulates reproductive cell development and hormone release in the testes or ovaries.

Luteinizing Hormone (LH)

An anterior pituitary tropic gonadotropin that stimulates the testes or ovaries.

Prolactin (PRL)

An anterior pituitary hormone that acts directly on the mammary glands to stimulate milk production.

Growth Hormone (GH)

An anterior pituitary hormone that stimulates somatic tissue growth by acting directly on bones and muscles.

Antidiuretic Hormone (ADH)

A hormone produced in the hypothalamus and stored in the posterior pituitary that prevents water loss at the kidneys.

Oxytocin

A hormone synthesized in the hypothalamus and released from the posterior pituitary that stimulates milk ejection from the breast and uterine contractions during labor.

Thyroid Gland

A vascular endocrine gland located anterior to the trachea consisting of two lobes connected by an isthmus; it regulates metabolism and lowers elevated blood calcium.

Thyroid Hormone (Thyroxine / T4)

An iodine-containing biogenic amine synthesized by thyroid follicular cells that increases cellular metabolism, elevates body temperature, and increases ATP production.

Follicular Cells

Simple cuboidal epithelial cells within the thyroid gland that require iodine to synthesize thyroid hormone (thyroxine).

Parafollicular Cells

Cells located between thyroid follicles that synthesize and secrete calcitonin in response to high blood calcium levels.

Calcitonin

A thyroid hormone made by parafollicular cells that reduces osteoclast activity to lower elevated blood calcium levels.

Parathyroid Glands

Four small endocrine glands embedded on the posterior surface of the thyroid gland that secrete parathyroid hormone to elevate blood calcium levels.

Parathyroid Hormone (PTH)

A hormone secreted when blood calcium is low; it increases osteoclast bone resorption, inhibits calcium loss in urine, and stimulates renal calcitriol synthesis.

Calcitriol

The active hormonal form of vitamin D produced by the kidneys in response to PTH to increase calcium absorption in the small intestine.

Adrenal Gland (Suprarenal Gland)

A paired gland superior to each kidney consisting of an outer cortex that secretes corticosteroids and an inner medulla that secretes catecholamines.

Adrenal Cortex

The three-layered outer region of the adrenal gland that produces corticosteroids (mineralocorticoids, glucocorticoids, and sex hormones) in response to ACTH.

Adrenal Medulla

The inner core of the adrenal gland that secretes epinephrine under sympathetic nervous system stimulation to increase heart rate, respiration, bronchodilation, and blood pressure.

Mineralocorticoids

Steroid hormones produced by the outer layer of the adrenal cortex that regulate electrolyte balance in body fluids (e.g., aldosterone).

Aldosterone

A mineralocorticoid synthesized by the outer adrenal cortex that promotes sodium retention in the kidneys and increases blood volume.

Glucocorticoids

Steroid hormones produced in the middle layer of the adrenal cortex that elevate blood glucose, provide energy during stress, and suppress the immune system (e.g., cortisol).

Cortisol

The primary glucocorticoid of the middle adrenal cortex that elevates blood glucose levels and exerts anti-inflammatory/immunosuppressive effects.

Pancreas

A dual exocrine and endocrine gland situated posterior to the stomach; its acini secrete digestive enzymes into ducts and its islets secrete glucose-regulating hormones.

Pancreatic Islets (Islets of Langerhans)

Clusters of endocrine cells dispersed throughout the pancreas containing alpha cells (glucagon) and beta cells (insulin).

Alpha Cells

Endocrine cells in pancreatic islets that produce and secrete glucagon to elevate blood glucose levels.

Beta Cells

Endocrine cells in pancreatic islets that produce and secrete insulin to facilitate cellular glucose uptake and lower blood glucose levels.

Insulin

A hormone released by pancreatic beta cells that decreases blood sugar by facilitating cellular glucose uptake and stimulating the liver to store glucose as glycogen.

Glucagon

A hormone released by pancreatic alpha cells that increases blood sugar by stimulating the liver to release stored glucose.

Type 1 Diabetes

An endocrine disorder resulting from the autoimmune destruction of pancreatic beta cells, preventing insulin synthesis and causing elevated blood glucose.

Type 2 Diabetes

A metabolic disorder caused by target cell insulin resistance or diminished insulin secretion, resulting in elevated blood glucose levels.

Pineal Gland

An endocrine structure located in the epithalamus of the brain that secretes melatonin to regulate sleep-wake patterns.

Melatonin

A biogenic amine hormone produced by the pineal gland that signals sleep to the body.

Gonads

The primary reproductive organs—testes in males producing androgens (testosterone) and ovaries in females producing estrogen and progesterone.

Thymus

An endocrine and lymphatic organ deep to the sternum and superior to the heart that secretes thymopoietin and thymosin to stimulate the maturation of T-lymphocytes.

Atrial Natriuretic Peptide (ANP)

A cardiac hormone released when the heart wall is excessively stretched that promotes sodium and water excretion in the urine.

Erythropoietin (EPO)

A hormone produced by the kidneys in response to low blood oxygen that stimulates red blood cell (erythrocyte) production in the bone marrow.

Acromegaly

An endocrine disorder characterized by abnormal somatic overgrowth caused by hypersecretion of Growth Hormone (GH).