Chapter 16: The Endocrine System Flashcards

Vocabulary flashcards covering key terms, structures, hormones, and clinical conditions discussed in Chapter 16 of Human Anatomy and Physiology.

Target Cells

Specific cells containing receptors that bind hormones, resulting in changes in cellular function.

Paracrine Signals

Chemical signals secreted by cells into the extracellular fluid to influence nearby cells without entering the bloodstream.

Autocrine Signals

Chemical signals secreted by a cell into the extracellular fluid to elicit effects from the same cell that secreted them.

Endocrine Glands

Ductless organs consisting of glandular epithelial cells that secrete hormones into the interstitial fluid for transport by the bloodstream.

Paraneoplastic Syndrome

Signs and symptoms accompanying hormone secretion from cancer cells, most commonly arising from lung and gastrointestinal cancers.

Free Hormones

Generally small, hydrophilic amino acid-based or peptide hormones that circulate freely in the water-based plasma of the blood.

Bound Hormones

Hydrophobic hormones that form complexes with binding proteins in plasma to enable transport in blood and extend their half-life.

Upregulation

The process where target cells produce more receptors for a hormone when blood levels of that hormone decline, increasing sensitivity.

Downregulation

The process where target cells decrease the number of receptors specific for a hormone, typically following prolonged exposure to high hormone levels.

Second-Messenger System

A signaling cascade initiated when a hydrophilic hormone binds to a cell surface receptor, producing intracellular signaling compounds like cAMP, IP3, or DAG.

Phosphorylation

An enzyme-catalyzed reaction in which a protein kinase transfers a phosphate group from ATP to another substance, altering its shape and activity.

Hormone-Response Elements

Specific regions of DNA in the nucleus to which hydrophobic hormone-receptor complexes bind to initiate cellular changes.

Synergists

Hormones that act on the same target cell to exert the same biological effect.

Antagonists

Hormones that act on the same target cell to exert opposite biological effects.

Half-Life

The amount of time required for the plasma concentration of a hormone to be reduced by half.

Humoral Stimuli

Hormone secretion initiated in response to changes in the concentration of an ion or compound in the blood or extracellular fluid.

Hypothalamic-Hypophyseal Portal System

A specialized network of capillaries and portal veins in the infundibulum that transports hypothalamic hormones directly to the anterior pituitary.

Antidiuretic Hormone (ADH)

A posterior pituitary neurohormone synthesized in the supraoptic and paraventricular nuclei that causes the insertion of aquaporins in kidney tubules to retain water.

Diabetes Insipidus

A condition caused by an abnormal lack of ADH secretion or activity, resulting in extreme thirst, dehydration, and elevated blood solute concentration.

Oxytocin

A posterior pituitary neurohormone that triggers uterine smooth muscle contractions and milk ejection from mammary glands via a positive feedback system.

Thyroid-Stimulating Hormone (TSH)

An anterior pituitary hormone secreted by thyrotrophs that stimulates thyroid gland development and its secretion of thyroid hormones.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary hormone secreted by corticotrophs that stimulates development of the adrenal glands and release of their steroid hormones.

Prolactin

An anterior pituitary hormone produced by lactotrophs that stimulates mammary gland growth and milk production.

Growth Hormone (GH)

An anterior pituitary hormone produced by somatotrophs that exerts short-term metabolic effects and long-term growth effects via insulin-like growth factor.

Gigantism

A growth hormone disorder caused by hypersecretion of GH prior to the closure of the epiphyseal plates, resulting in extreme height and enlarged organs.

Acromegaly

A growth hormone disorder caused by hypersecretion of GH after epiphyseal plate closure, causing increased girth of bones and tissues in the face, hands, and feet.

Pituitary Dwarfism

A disorder caused by hyposecretion of GH prior to epiphyseal plate closure, leading to short stature with proportional limbs and trunk.

Triiodothyronine ($T_3$)

A highly active thyroid hormone containing three iodine atoms that diffuses into target cells to bind intracellular nuclear receptors.

Thyroxine ($T_4$)

A thyroid hormone containing four iodine atoms that circulates in blood and is converted into active $T_3$ within peripheral target cells.

Basal Metabolic Rate (BMR)

The amount of energy required by the body to carry out all of its chemical reactions when at rest.

Graves Disease

An autoimmune cause of hyperthyroidism in which abnormal proteins mimic TSH, leading to an elevated metabolic rate, heat intolerance, exophthalmos, and goiter.

Exophthalmos

Bulging eyeballs resulting from weakened extrinsic eye muscles and water retention, commonly seen in Graves disease.

Goiter

Enlargement of the thyroid gland resulting from abnormal TSH-like proteins or accumulated thyroglobulin due to iodine deficiency.

Parathyroid Hormone (PTH)

A peptide hormone produced by chief cells of the parathyroid glands in response to hypocalcemia that acts on bones, kidneys, and intestines to increase blood calcium.

Calcitriol

The active form of vitamin D ($D_3$) produced by the kidneys under PTH stimulation, which increases calcium ion absorption in the small intestine.

Calcitonin

A hormone produced by thyroid parafollicular cells in response to hypercalcemia that acts to inhibit osteoclast activity when secreted at high levels.

Aldosterone

The primary mineralocorticoid produced by the zona glomerulosa of the adrenal cortex that maintains extracellular sodium, potassium, fluid volume, and blood pressure.

Cortisol

The chief glucocorticoid produced by the zona fasciculata of the adrenal cortex that mediates the stress response, stimulates gluconeogenesis, and acts as an anti-inflammatory agent.

Iatrogenic Cushing's Syndrome

A condition resulting from long-term clinical use of synthetic corticosteroids, producing moon facies, buffalo hump, hyperglycemia, and muscle wasting.

Adrenal Crisis

A life-threatening complication arising when a patient with HPA axis suppression faces severe stress without sufficient cortisol, causing low blood pressure, hypoglycemia, and potential death.

Addison Disease

Adrenal insufficiency caused by hyposecretion of cortisol and aldosterone, placing patients at risk for fluid, electrolyte, and acid-base imbalances.

Chromaffin Cells

Neuroendocrine cells in the adrenal medulla derived from nervous tissue that secrete catecholamines (epinephrine and norepinephrine) into the blood.

Glucagon

A peptide hormone secreted by pancreatic alpha cells in response to low blood glucose that stimulates glycogenolysis, gluconeogenesis, and ketone body synthesis.

Insulin

A peptide hormone secreted by pancreatic beta cells in response to high blood glucose that promotes cellular nutrient uptake, glycogenesis, and lipogenesis.

Ketoacidosis

A dangerous lowering of blood pH caused by accumulation of ketone bodies during prolonged starvation or uncontrolled diabetes mellitus.

Type 1 Diabetes Mellitus

An autoimmune disease characterized by destruction of pancreatic beta cells, resulting in lack of insulin production, severe hyperglycemia, glucosuria, polyuria, and polydipsia.

Type 2 Diabetes Mellitus

A disease characterized by insulin resistance in target cells and reduced beta cell responsiveness, strongly associated with heredity and obesity.

Leptin

A protein hormone produced by adipocytes that acts on hypothalamic neurons to promote satiety and suppress appetite.

Atrial Natriuretic Peptide (ANP)

A hormone produced by cardiac muscle cells in response to atrial stretch that promotes vasodilation and kidney natriuresis to reduce blood volume and blood pressure.

Erythropoietin (EPO)

A hormone secreted by kidney cells in response to low blood oxygen levels that stimulates red blood cell production in red bone marrow.