Key Terms

acromegaly

disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet

adenylyl cyclase

membrane-bound enzyme that converts ATP to cyclic AMP, creating cAMP, as a result of G-protein activation

adrenal cortex

outer region of the adrenal glands consisting of multiple layers of epithelial cells and capillary networks that produces mineralocorticoids and glucocorticoids

adrenal glands

endocrine glands located at the top of each kidney that are important for the regulation of the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels

adrenal medulla

inner layer of the adrenal glands that plays an important role in the stress response by producing epinephrine and norepinephrine

adrenocorticotropic hormone (ACTH)

anterior pituitary hormone that stimulates the adrenal cortex to secrete corticosteroid hormones (also called corticotropin)

alarm reaction

the short-term stress, or the fight-or-flight response, of stage one of the general adaptation syndrome mediated by the hormones epinephrine and norepinephrine

aldosterone

hormone produced and secreted by the adrenal cortex that stimulates sodium and fluid retention and increases blood volume and blood pressure

alpha cell

pancreatic islet cell type that produces the hormone glucagon

angiotensin-converting enzyme

the enzyme that converts angiotensin I to angiotensin II

antidiuretic hormone (ADH)

hypothalamic hormone that is stored by the posterior pituitary and that signals the kidneys to reabsorb water

atrial natriuretic peptide (ANP)

peptide hormone produced by the walls of the atria in response to high blood pressure, blood volume, or blood sodium that reduces the reabsorption of sodium and water in the kidneys and promotes vasodilation

autocrine

chemical signal that elicits a response in the same cell that secreted it

beta cell

pancreatic islet cell type that produces the hormone insulin

calcitonin

peptide hormone produced and secreted by the parafollicular cells (C cells) of the thyroid gland that functions to decrease blood calcium levels

chromaffin

neuroendocrine cells of the adrenal medulla

colloid

viscous fluid in the central cavity of thyroid follicles, containing the glycoprotein thyroglobulin

cortisol

glucocorticoid important in gluconeogenesis, the catabolism of glycogen, and downregulation of the immune system

cyclic adenosine monophosphate (cAMP)

second messenger that, in response to adenylyl cyclase activation, triggers a phosphorylation cascade

delta cell

minor cell type in the pancreas that secretes the hormone somatostatin

diabetes mellitus

condition caused by destruction or dysfunction of the beta cells of the pancreas or cellular resistance to insulin that results in abnormally high blood glucose levels

diacylglycerol (DAG)

molecule that, like cAMP, activates protein kinases, thereby initiating a phosphorylation cascade

downregulation

decrease in the number of hormone receptors, typically in response to chronically excessive levels of a hormone

endocrine gland

tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion

endocrine system

cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes

epinephrine

primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called adrenaline

erythropoietin (EPO)

protein hormone secreted in response to low oxygen levels that triggers the bone marrow to produce red blood cells

estrogens

class of predominantly female sex hormones important for the development and growth of the female reproductive tract, secondary sex characteristics, the female reproductive cycle, and the maintenance of pregnancy

exocrine system

cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts

first messenger

hormone that binds to a cell membrane hormone receptor and triggers activation of a second messenger system

follicle-stimulating hormone (FSH)

anterior pituitary hormone that stimulates the production and maturation of sex cells

G protein

protein associated with a cell membrane hormone receptor that initiates the next step in a second messenger system upon activation by hormone–receptor binding

general adaptation syndrome (GAS)

the human body’s three-stage response pattern to short- and long-term stress

gigantism

disorder in children caused when abnormally high levels of GH prompt excessive growth

glucagon

pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels

glucocorticoids

hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism

goiter

enlargement of the thyroid gland either as a result of iodine deficiency or hyperthyroidism

gonadotropins

hormones that regulate the function of the gonads

growth hormone (GH)

anterior pituitary hormone that promotes tissue building and influences nutrient metabolism (also called somatotropin)

hormone

secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body

hormone receptor

protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response

hyperglycemia

abnormally high blood glucose levels

hyperparathyroidism

disorder caused by overproduction of PTH that results in abnormally elevated blood calcium

hyperthyroidism

clinically abnormal, elevated level of thyroid hormone in the blood; characterized by an increased metabolic rate, excess body heat, sweating, diarrhea, weight loss, and increased heart rate

hypoparathyroidism

disorder caused by underproduction of PTH that results in abnormally low blood calcium

hypophyseal portal system

network of blood vessels that enables hypothalamic hormones to travel into the anterior lobe of the pituitary without entering the systemic circulation

hypothalamus

region of the diencephalon inferior to the thalamus that functions in neural and endocrine signaling

hypothyroidism

clinically abnormal, low level of thyroid hormone in the blood; characterized by low metabolic rate, weight gain, cold extremities, constipation, and reduced mental activity

infundibulum

stalk containing vasculature and neural tissue that connects the pituitary gland to the hypothalamus (also called the pituitary stalk)

inhibin

hormone secreted by the male and female gonads that inhibits FSH production by the anterior pituitary

inositol triphosphate (IP₃)

molecule that initiates the release of calcium ions from intracellular stores

insulin

pancreatic hormone that enhances the cellular uptake and utilization of glucose, thereby decreasing blood glucose levels

insulin-like growth factors (IGF)

protein that enhances cellular proliferation, inhibits apoptosis, and stimulates the cellular uptake of amino acids for protein synthesis

leptin

protein hormone secreted by adipose tissues in response to food consumption that promotes satiety

luteinizing hormone (LH)

anterior pituitary hormone that triggers ovulation and the production of ovarian hormones, and the production of testosterone

melatonin

amino acid–derived hormone that is secreted in response to low light and causes drowsiness

mineralocorticoids

hormones produced by the zona glomerulosa cells of the adrenal cortex that influence fluid and electrolyte balance

neonatal hypothyroidism

condition characterized by cognitive deficits, short stature, and other signs and symptoms in people born to people who were iodine-deficient during pregnancy

norepinephrine

secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called noradrenaline

osmoreceptor

hypothalamic sensory receptor that is stimulated by changes in solute concentration (osmotic pressure) in the blood

oxytocin

hypothalamic hormone stored in the posterior pituitary gland and important in stimulating uterine contractions in labor, milk ejection during breastfeeding, and feelings of attachment (produced by males and females)

pancreas

organ with both exocrine and endocrine functions located posterior to the stomach that is important for digestion and the regulation of blood glucose

pancreatic islets

specialized clusters of pancreatic cells that have endocrine functions; also called islets of Langerhans

paracrine

chemical signal that elicits a response in neighboring cells; also called paracrine factor

parathyroid glands

small, round glands embedded in the posterior thyroid gland that produce parathyroid hormone (PTH)

parathyroid hormone (PTH)

peptide hormone produced and secreted by the parathyroid glands in response to low blood calcium levels

phosphodiesterase (PDE)

cytosolic enzyme that deactivates and degrades cAMP

phosphorylation cascade

signaling event in which multiple protein kinases phosphorylate the next protein substrate by transferring a phosphate group from ATP to the protein

pineal gland

endocrine gland that secretes melatonin, which is important in regulating the sleep-wake cycle

pinealocyte

cell of the pineal gland that produces and secretes the hormone melatonin

pituitary dwarfism

disorder in children caused when abnormally low levels of GH result in growth retardation

pituitary gland

bean-sized organ suspended from the hypothalamus that produces, stores, and secretes hormones in response to hypothalamic stimulation (also called hypophysis)

PP cell

minor cell type in the pancreas that secretes the hormone pancreatic polypeptide

progesterone

predominantly female sex hormone important in regulating the female reproductive cycle and the maintenance of pregnancy

prolactin (PRL)

anterior pituitary hormone that promotes development of the mammary glands and the production of breast milk

protein kinase

enzyme that initiates a phosphorylation cascade upon activation

second messenger

molecule that initiates a signaling cascade in response to hormone binding on a cell membrane receptor and activation of a G protein

stage of exhaustion

stage three of the general adaptation syndrome; the body’s long-term response to stress mediated by the hormones of the adrenal cortex

stage of resistance

stage two of the general adaptation syndrome; the body’s continued response to stress after stage one diminishes

testosterone

steroid hormone secreted by the testes and important in the maturation of sperm cells, growth and development of the reproductive system, and the development of secondary sex characteristics

thymosins

hormones produced and secreted by the thymus that play an important role in the development and differentiation of T cells

thymus

organ that is involved in the development and maturation of T-cells and is particularly active during infancy and childhood

thyroid gland

large endocrine gland responsible for the synthesis of thyroid hormones

thyroid-stimulating hormone (TSH)

anterior pituitary hormone that triggers secretion of thyroid hormones by the thyroid gland (also called thyrotropin)

thyroxine

(also, tetraiodothyronine, T₄) amino acid–derived thyroid hormone that is more abundant but less potent than T₃ and often converted to T₃ by target cells

triiodothyronine

(also, T₃) amino acid–derived thyroid hormone that is less abundant but more potent than T₄

upregulation

increase in the number of hormone receptors, typically in response to chronically reduced levels of a hormone

zona fasciculata

intermediate region of the adrenal cortex that produce hormones called glucocorticoids

zona glomerulosa

most superficial region of the adrenal cortex, which produces the hormones collectively referred to as mineralocorticoids

zona reticularis

deepest region of the adrenal cortex, which produces the steroid sex hormones called androgens