Endocrine System Overview

This set of flashcards covers key terms and definitions related to the endocrine system, glands, hormones, and related physiological processes.

Endocrine System

A messenger system that influences metabolic activity by means of hormones.

Hormones

Chemicals secreted by glands that travel through the circulatory system to regulate target organs.

Endocrine Glands

Glands that are ductless and secrete hormones directly into the bloodstream.

Exocrine Glands

Glands that have ducts and secrete substances onto an epithelial surface.

Pituitary Gland

A small gland located at the base of the brain, often called the 'master gland' because it regulates many bodily functions.

Growth Hormone (GH)

A hormone produced by the anterior pituitary that stimulates growth and cell reproduction.

Thyroid Stimulating Hormone (TSH)

A hormone that stimulates the thyroid gland to produce thyroid hormones.

Luteinizing Hormone (LH)

A hormone that triggers ovulation and stimulates the production of testosterone.

Oxytocin

A hormone produced by the posterior pituitary that stimulates uterine contractions and milk ejection.

Thyroglobulin

A protein produced by the follicular cells of the thyroid gland that is a precursor to thyroid hormones.

Calcitonin

A hormone secreted by parafollicular cells of the thyroid that helps lower blood calcium levels.

Parathyroid Hormone (PTH)

A hormone secreted by the parathyroid glands that regulates calcium levels in the blood.

Glucagon

A hormone produced by alpha cells of the pancreas that increases blood glucose levels.

Insulin

A hormone produced by beta cells of the pancreas that decreases blood glucose levels.

Adrenal Glands

Paired glands located on top of the kidneys that produce hormones related to stress response.

Epinephrine

Also known as adrenaline, a hormone secreted by the adrenal medulla during stress responses.

Glucose Tolerance Test

A test that measures the body's response to sugar; used to diagnose diabetes.

Hyperglycemia

An abnormally high level of glucose in the blood.

Hypoglycemia

An abnormally low level of glucose in the blood.

Islets of Langerhans

Clusters of cells in the pancreas that secrete hormones such as insulin and glucagon.

Pineal Gland

A small endocrine gland in the brain that produces melatonin, which helps regulate the body's sleep-wake cycles (circadian rhythms).

Melatonin

A hormone secreted by the pineal gland that peaks at night and is involved in the regulation of biological rhythms.

Antidiuretic Hormone (ADH)

A hormone produced by the hypothalamus and released by the posterior pituitary that signals the kidneys to reabsorb more water, reducing urine volume.

Adrenocorticotropic Hormone (ACTH)

A hormone secreted by the anterior pituitary that stimulates the adrenal cortex to produce and release corticosteroids, especially cortisol.

Cortisol

A steroid hormone produced by the adrenal cortex that helps the body manage stress, increases blood sugar, and suppresses the immune system.

Aldosterone

A mineralocorticoid produced by the adrenal cortex that helps regulate blood pressure by managing sodium and potassium levels in the blood.

Negative Feedback Mechanism

A physiological control system in which the body's response to a stimulus opposes the initial change to maintain homeostasis (e.g., the regulation of blood sugar levels).

Diabetes Mellitus

A metabolic disorder characterized by persistent hyperglycemia due to either inadequate insulin production (Type 1) or the body's inability to use insulin effectively (Type 2).

Prolactin (PRL)

A hormone produced by the anterior pituitary that stimulates milk production in mammary glands after childbirth.

Follicle-Stimulating Hormone (FSH)

A gonadotropin that stimulates the production of gametes (eggs in females and sperm in males).

Hypothalamus

A region of the forebrain that coordinates both the autonomic nervous system and the activity of the pituitary gland, serving as the main link between the nervous and endocrine systems.

Triiodothyronine (T_3)

A potent thyroid hormone that regulates metabolism, body temperature, and heart rate; it is often converted from T_4 in target tissues.

Thyroxine (T_4)

The primary hormone secreted by the thyroid gland into the bloodstream; it acts as a precursor to the more active T_3.

Target Cells

Specific cells equipped with receptors that bind to particular hormones, allowing them to respond to endocrine signals.

Thymus

An endocrine gland located in the upper thorax that secretes thymosin, which is essential for the development of T lymphocytes and immune system function.

Estrogen

A class of steroid hormones, primarily produced by the ovaries, responsible for the development of female secondary sexual characteristics and regulation of the reproductive system.

Testosterone

An androgenic steroid hormone produced primarily in the testes that stimulates the development of male secondary sexual characteristics and sperm production.

Progesterone

A steroid hormone produced by the corpus luteum in the ovaries that helps prepare the uterine lining for pregnancy.

Humoral Stimuli

Hormone release triggered by changing blood levels of certain ions or nutrients, such as the release of parathyroid hormone in response to low calcium levels.

Hormonal Stimuli

A type of stimulus where endocrine glands are activated by hormones produced by other endocrine organs, such as the anterior pituitary stimulating the thyroid gland.

Neural Stimuli

Hormone release stimulated by nerve fibers, such as the sympathetic nervous system triggering the release of epinephrine from the adrenal medulla.

Steroid Hormones

Lipid-soluble hormones derived from cholesterol, such as cortisol and testosterone, which can cross the plasma membrane to bind to intracellular receptors.

Amino Acid-Based Hormones

Water-soluble hormones, including amines, peptides, and proteins, that generally circulate freely in the blood and act on receptors in the plasma membrane.

Second Messenger System

A mechanism used by water-soluble hormones (like epinephrine) where the hormone binds to a surface receptor and triggers an internal cascade, often involving cyclic AMP (cAMP).

Direct Gene Activation

The mechanism used by lipid-soluble hormones to enter a cell, bind to an intracellular receptor, and directly interact with the DNA to trigger protein synthesis.

Anterior Pituitary (Adenohypophysis)

The glandular part of the pituitary gland that synthesizes and secretes hormones like GH, TSH, and ACTH under the control of the hypothalamus.

Posterior Pituitary (Neurohypophysis)

The neural part of the pituitary gland that stores and releases hormones (ADH and oxytocin) produced by the hypothalamus; it does not synthesize its own hormones.

Up-regulation

A process where target cells form more receptors in response to low levels of a hormone to increase sensitivity.

Down-regulation

A process where target cells lose receptors in response to high levels of a hormone, desensitizing the target cell to prevent overreaction.

Synergism

A situation where more than one hormone produces the same effects at the target cell and their combined effects are amplified (e.g., glucagon and epinephrine both causing the release of glucose).

Permissiveness

A hormonal interaction where one hormone is required to be present for another hormone to exert its full effect on a target cell.

Antagonism

A type of hormonal interaction where one hormone opposes or reverses the effect of another hormone, such as insulin and glucagon.

Gigantism

A clinical condition caused by the hypersecretion of Growth Hormone (GH) during childhood, leading to excessive long bone growth and height.

Acromegaly

A condition resulting from the hypersecretion of Growth Hormone (GH) in adults, characterized by thickening of bones in the face, hands, and feet.

Pituitary Dwarfism

A condition caused by an insufficient production of Growth Hormone (GH) during childhood, resulting in a significantly shorter stature.

Diabetes Insipidus

A condition characterized by excessive thirst and large volumes of dilute urine, typically caused by a deficiency of Antidiuretic Hormone (ADH).

Graves' Disease

An autoimmune disorder and the most common cause of hyperthyroidism, often characterized by an enlarged thyroid and exophthalmos.

Goiter

An abnormal enlargement of the thyroid gland, which can occur due to iodine deficiency or overactivity of the gland.

Cushing's Syndrome

A hormonal disorder caused by prolonged exposure to high levels of the hormone cortisol, characterized by a "moon face" and "buffalo hump."

Addison's Disease

A chronic disorder where the adrenal glands do not produce enough cortisol and aldosterone, leading to fatigue and low blood pressure.

Growth Hormone Releasing Hormone (GHRH)

A hypothalamic hormone that triggers the secretion of growth hormone (GH) from the anterior pituitary.

Somatostatin (GHIH)

Also known as growth hormone-inhibiting hormone, it inhibits the release of GH and several other hormones from the pituitary gland.

Thyrotropin-Releasing Hormone (TRH)

A hypothalamic hormone that stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH).

Corticotropin-Releasing Hormone (CRH)

A hormone from the hypothalamus that regulates the release of adrenocorticotropic hormone (ACTH) by the pituitary gland.

Gonadotropin-Releasing Hormone (GnRH)

A hypothalamic hormone that stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Hypophyseal Portal System

A specialized system of blood vessels that connects the hypothalamus with the anterior pituitary, facilitating the rapid transport of regulatory hormones.

Exophthalmos

The bulging or protrusion of the eyeballs, which is a common clinical sign of hyperthyroidism, particularly in Graves' disease.

Myxedema

A severe form of hypothyroidism in adults characterized by low metabolic rate, lethargy, and swelling of the skin and underlying tissues.

Cretinism

A condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones during development.

Norepinephrine

A chemical released by the adrenal medulla and sympathetic nervous system that acts as both a hormone and a neurotransmitter to increase blood pressure.

Target Cell Specificity

The concept that hormones only affect cells with specific receptors, despite circulating throughout the entire body.

Infundibulum

The stalk-like structure that connects the hypothalamus to the pituitary gland.

Colloid

The amber-colored, sticky material within the thyroid follicles that stores thyroglobulin and iodine.

Leptin

A hormone secreted by adipose tissue that serves as a signal to the brain to suppress appetite and increase energy expenditure.

Erythropoietin (EPO)

A hormone produced mainly by the kidneys that stimulates the production of red blood cells in the bone marrow.

Atrial Natriuretic Peptide (ANP)

A hormone secreted by the heart in response to high blood pressure that promotes sodium and water excretion to lower blood volume.

Positive Feedback Mechanism

A control system in which the initial stimulus produces a response that reinforces the stimulus, such as the release of oxytocin during labor.

Half-life

The time required for a hormone's blood level to decrease by 50, reflecting how quickly the hormone is cleared from the circulatory system.

Alpha Cells

Endocrine cells in the pancreatic islets that synthesize and secrete the hormone glucagon.

Beta Cells

Endocrine cells in the pancreatic islets that synthesize and secrete the hormone insulin.

Tropic Hormones

Hormones that regulate the secretory action of other endocrine glands, such as TSH, ACTH, FSH, and LH.

Mineralocorticoids

A class of steroid hormones, including aldosterone, produced by the adrenal cortex that regulate electrolyte and water balance.

Glucocorticoids

Steroid hormones, such as cortisol, that help the body manage long-term stress by increasing blood glucose levels and reducing inflammation.

Type 1 Diabetes Mellitus

An autoimmune disorder characterized by the destruction of pancreatic beta cells, leading to a total deficiency of insulin.

Type 2 Diabetes Mellitus

A condition where the body's cells fail to respond properly to insulin, or the pancreas does not produce enough insulin to maintain normal glucose levels.

Polyuria

A classic sign of diabetes mellitus involving the excretion of excessive amounts of urine due to the osmotic effect of high glucose levels.

Polydipsia

A sign of diabetes mellitus characterized by excessive thirst resulting from the dehydration caused by high urine output.

Polyphagia

A symptom of diabetes mellitus described as extreme hunger because the body cannot effectively transport glucose into cells for energy.

Catecholamines

A group of hormones (epinephrine and norepinephrine) produced by the adrenal medulla that facilitate the "fight-or-flight" response.

Gonadotropins

Hormones released by the anterior pituitary, specifically FSH and LH, that stimulate the function of the ovaries and testes.