The Endocrine System

These flashcards cover key vocabulary terms and definitions related to the endocrine system and hormonal regulation.

Endocrine System

Glands, tissues, and cells that secrete hormones.

Hormone

Chemical messengers transported by the bloodstream that stimulate physiological responses in target cells.

Hypothalamus

A region of the brain that controls endocrine organs and releases regulatory hormones.

Pituitary Gland

Known as the 'master gland', it directs other glands to function properly by releasing hormones.

Negative Feedback

Mechanism that regulates hormone secretion, where the output reduces the input.

Adrenal Glands

Glands located on top of the kidneys that secrete hormones like cortisol and aldosterone.

Thyroid Gland

Gland that regulates metabolism by producing hormones such as T3 and T4.

Diabetes Mellitus

An endocrine disorder defined by excessively high blood glucose and insulin issues.

Insulin

A hormone produced by the pancreas that lowers blood glucose levels.

Glucagon

A hormone secreted by the pancreas that raises blood glucose levels.

Hypophyseal Portal System

Capillary system that allows hypothalamic hormones to reach the anterior pituitary directly.

Tropic Hormones

Hormones that stimulate other endocrine glands to secrete hormones.

Parathyroid Hormone (PTH)

Hormone that regulates calcium levels in the blood.

Epinephrine

Also known as adrenaline, a hormone that prepares the body for 'fight or flight' responses.

Cortisol

A glucocorticoid hormone that increases blood sugar levels in response to stress.

Thyroid Hormones

Hormones produced by the thyroid responsible for regulating metabolism.

Melatonin

Hormone produced by the pineal gland that regulates circadian rhythms.

Sympathetic Nervous System

Part of the nervous system that prepares the body for stressful or emergency situations.

Releasing Hormones

Hormones released by the hypothalamus that stimulate the anterior pituitary to produce tropic hormones.

Growth Hormone

Hormone from the pituitary gland that stimulates growth and cell reproduction.

Adrenocorticotropic Hormone (ACTH)

Stimulates the adrenal cortex to release glucocorticoids.

Luteinizing Hormone (LH)

Hormone that stimulates ovulation and the secretion of sex hormones.

Follicle-Stimulating Hormone (FSH)

Stimulates the development of ovarian follicles in females and sperm production in males.

Ovaries

Female reproductive organs that produce hormones such as estrogen and progesterone.

Testes

Male reproductive organs that produce testosterone.

Thymus

Gland involved in immune response, especially during childhood and adolescence.

Stress Response

A complex physiological reaction to stressors that involves hormonal changes.

General Adaptation Syndrome (GAS)

Three-phase response to stress: alarm, resistance, and exhaustion.

Homeostasis

A state of balance or equilibrium in physiological systems.

Endocrinology

The study of the endocrine system and its hormonal functions.

Hormone receptor

A protein on target cells that binds hormones and initiates a physiological response.

Antidiuretic Hormone (ADH)

Produced by the hypothalamus and stored in the posterior pituitary; it increases water retention by the kidneys.

Oxytocin

A hormone involved in labor contractions, milk ejection, and emotional bonding.

Neurohypophysis

The posterior lobe of the pituitary gland, which stores and releases ADH and OT.

Adenohypophysis

The anterior lobe of the pituitary gland, which synthesizes and secretes various tropic and direct hormones.

Prolactin (PRL)

Hormone that stimulates mammary glands to produce milk.

Calcitonin

Hormone produced by the thyroid gland that lowers blood calcium levels by inhibiting osteoclasts.

Aldosterone

A mineralocorticoid that promotes sodium and water retention and potassium excretion.

Pineal Gland

A small gland in the brain that secretes melatonin and helps regulate sleep cycles.

Islets of Langerhans

Clusters of endocrine cells in the pancreas that contain alpha, beta, and delta cells.

Alpha Cells

Pancreatic cells that secrete glucagon.

Beta Cells

Pancreatic cells that secrete insulin.

Delta Cells

Pancreatic cells that secrete somatostatin, which inhibits insulin and glucagon release.

Zona Glomerulosa

The outer layer of the adrenal cortex that produces mineralocorticoids.

Zona Fasciculata

The middle layer of the adrenal cortex that produces glucocorticoids like cortisol.

Zona Reticularis

The inner layer of the adrenal cortex that produces sex steroids (androgens).

Steroid Hormones

Hormones derived from cholesterol, such as estrogen and testosterone.

Peptide Hormones

Hormones composed of short chains of amino acids, such as insulin.

Monoamines

Hormones derived from single amino acids (e.g., Epinephrine, Thyroxine).

Second Messenger System

A cascade of molecular events inside a cell (like cAMP) triggered by a hormone binding to a surface receptor.

Cyclic AMP (cAMP)

A common intracellular second messenger that activates protein kinases.

Up-regulation

The process by which a cell increases the number of receptors to become more sensitive to a hormone.

Down-regulation

The process by which a cell decreases the number of receptors in response to long-term high hormone concentrations.

Permissive Effect

When one hormone enhances the target organ's response to a second hormone.

Antagonistic Effect

When one hormone opposes the action of another hormone (e.g., insulin vs. glucagon).

Synergistic Effect

When two or more hormones act together to produce an effect greater than the sum of their separate effects.

Exocrine Glands

Glands that secrete substances into ducts rather than directly into the bloodstream.

Humoral Stimulus

Hormone release triggered by changes in blood levels of certain ions or nutrients (e.g., calcium).

Neural Stimulus

Hormone release triggered by nerve fiber stimulation (e.g., adrenal medulla during stress).

Hormonal Stimulus

Hormone release triggered by another hormone (e.g., TSH stimulating the thyroid).

Acromegaly

Hypersecretion of growth hormone in adults, causing thickening of bones and soft tissues.

Gigantism

Hypersecretion of growth hormone during childhood/adolescence, causing excessive height.

Cushing Syndrome

Condition caused by hypersecretion of cortisol, often resulting in a 'moon face' or 'buffalo hump'.

Addison Disease

Adrenal insufficiency characterized by hyposecretion of glucocorticoids and mineralocorticoids.

Diabetes Insipidus

A disorder caused by ADH deficiency, leading to chronic polyuria and extreme thirst.

Goiter

Enlargement of the thyroid gland, often caused by iodine deficiency.

Grave's Disease

An autoimmune disorder causing hyperthyroidism and possibly bulging eyes (exophthalmos).

Polyuria

Excessive production and passage of urine.

Polydipsia

Excessive thirst, often a symptom of diabetes.

Polyphagia

Excessive hunger or increased appetite.

Type 1 Diabetes

Autoimmune destruction of pancreatic beta cells, requiring external insulin.

Type 2 Diabetes

Condition of insulin resistance where target cells fail to respond to insulin effectively.

Follicular Cells

Cells in the thyroid that synthesize thyroxine (T4) and triiodothyronine (T3).

Parafollicular (C) Cells

Cells in the thyroid that produce calcitonin.

Paracrine

Chemical messengers that diffuse to nearby cells in the same tissue.

Autocrine

Chemical messengers that stimulate the same cell that secreted them.

Eicosanoids

A family of paracrine secretions derived from fatty acids (e.g., prostaglandins).

Norepinephrine

Neurotransmitter/hormone from the adrenal medulla that contributes to the 'fight or flight' response.

G Proteins

Proteins that couple membrane receptors to effector enzymes like adenylate cyclase.

Thyroid-Stimulating Hormone (TSH)

Pituitary hormone that stimulates the thyroid to release its hormones.

Hydrophilic Hormones

Water-soluble hormones (like peptides) that cannot cross the cell membrane and bind to surface receptors.

Hydrophobic Hormones

Lipid-soluble hormones (like steroids) that cross the cell membrane to bind to internal receptors.

Transport Proteins

Proteins in the blood that carry hydrophobic hormones.

Half-life

The time required for 50% of a hormone to be cleared from the blood.

Metabolic Clearance Rate (MCR)

The rate of hormone removal from the blood.

Erythropoietin

A hormone produced by the kidneys that stimulates red blood cell production.

Calcitriol

The active form of Vitamin D produced by the kidneys to increase blood calcium.

Atrial Natriuretic Peptide

A hormone from the heart that lowers blood pressure by increasing sodium excretion.

Ghrelin

A hormone secreted by the stomach that stimulates hunger.

Leptin

A hormone produced by adipose tissue that signals satiety and controls fat storage.

Angiotensin II

A potent vasoconstrictor that also stimulates aldosterone secretion.

Inhibin

A hormone from the gonads that inhibits FSH secretion.

Prostaglandins

Diverse eicosanoids that mediate pain, inflammation, and various smooth muscle functions.

Pheochromocytoma

A tumor of the adrenal medulla that secretes excessive amounts of epinephrine.

Hypogonadism

A condition in which the gonads produce little or no hormones.

Ketosis

A metabolic state wherein the body uses ketones (from fat) for fuel, often associated with diabetes.

Alarm Reaction

The first stage of GAS, characterized by the release of epinephrine and sympathetic activity.

Stage of Resistance

The second stage of GAS, where cortisol dominates to maintain energy levels.

Stage of Exhaustion

The third stage of GAS, where fat stores are depleted and organ failure may occur.

Gastrin

A hormone secreted by the stomach that stimulates acid production.