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adrenal gland

One of two endocrine glands located adjacent to the kidneys in mammals. Endocrine cells in the outer portion (cortex) respond to ACTH by secreting steroid hormones that help maintain homeostasis during long-term stress. Neurosecretory cells in the central portion (medulla) secrete epinephrine and norepinephrine in response to nervous inputs triggered by short-term stress.

adrenocorticotropic hormone (ACTH)

A tropic hormone that is produced and secreted by the anterior pituitary and that stimulates the production and secretion of steroid hormones by the adrenal cortex.

androgen

Any steroid hormone, such as testosterone, that stimulates the development and maintenance of the male reproductive system and secondary sex characteristics.

anterior pituitary

Also called the adenohypophysis; portion of the pituitary that develops from nonneural tissue; consists of endocrine cells that synthesize and secrete several tropic and nontropic hormones.

antidiuretic hormone (ADH)

A peptide hormone, also known as vasopressin, that promotes water retention by the kidneys. Produced in the hypothalamus and released from the posterior pituitary, ADH also has activities in the brain.

autocrine

Referring to a secreted molecule that acts on the cell that secreted it.

biological clock

An internal timekeeper that controls an organism's biological rhythms. The biological clock marks time with or without environmental cues but often requires signals from the environment to remain tuned to an appropriate period. See also circadian rhythm.

calcitonin

A hormone secreted by the thyroid gland that lowers blood calcium levels by promoting calcium deposition in bone and calcium excretion from the kidneys; nonessential in adult humans.

catecholamine

Any of a class of neurotransmitters and hormones, including the hormones epinephrine and norepinephrine, that are synthesized from the amino acid tyrosine.

circadian rhythm

A physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues.

corticosteroid

Any steroid hormone produced and secreted by the adrenal cortex.

cytokine

Any of a group of proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of lymphocytes and other cells of the immune system.

ecdysone

A steroid hormone, secreted by the prothoracic glands, that triggers molting in arthropods.

endocrine gland

A ductless gland that secretes hormones directly into the interstitial fluid, from which they diffuse into the bloodstream.

endocrine system

The internal system of communication involving hormones, the ductless glands that secrete hormones, and the molecular receptors on or in target cells that respond to hormones; functions in concert with the nervous system to effect internal regulation and maintain homeostasis.

epinephrine

A catecholamine that, when secreted as a hormone by the adrenal medulla, mediates "fight-or-flight" responses to short-term stresses; also released by some neurons as a neurotransmitter; also known as adrenaline.

estradiol

A steroid hormone that stimulates the development and maintenance of the female reproductive system and secondary sex characteristics; the major estrogen in mammals.

estrogen

Any steroid hormone, such as estradiol, that stimulates the development and maintenance of the female reproductive system and secondary sex characteristics.

follicle-stimulating hormone (FSH)

A tropic hormone that is produced and secreted by the anterior pituitary and that stimulates the production of eggs by the ovaries and sperm by the testes.

G protein-coupled receptor

A signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein. Also called a G protein-linked receptor.

glucagon

A hormone secreted by pancreatic alpha cells that raises blood glucose levels. It promotes glycogen breakdown and release of glucose by the liver.

glucocorticoid

A steroid hormone that is secreted by the adrenal cortex and that influences glucose metabolism and immune function.

growth hormone (GH)

A hormone that is produced and secreted by the anterior pituitary and that has both direct (nontropic) and tropic effects on a wide variety of tissues.

hormone

In multicellular organisms, one of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the body to change their functioning.

hypothalamus

The ventral part of the vertebrate forebrain; functions in maintaining homeostasis, especially in coordinating the endocrine and nervous systems; secretes hormones of the posterior pituitary and releasing factors that regulate the anterior pituitary.

insulin

A hormone secreted by pancreatic beta cells that lowers blood glucose levels. It promotes the uptake of glucose by most body cells and the synthesis and storage of glycogen in the liver and also stimulates protein and fat synthesis.

islets of Langerhans

Clusters of endocrine cells within the pancreas that produce and secrete the hormones glucagon (from alpha cells) and insulin (from beta cells).

juvenile hormone

A hormone in arthropods, secreted by the corpora allata (a pair of glands), that promotes the retention of larval characteristics.

local regulator

A secreted molecule that influences cells near where it is secreted.

melanocyte-stimulating hormone (MSH)

A hormone produced and secreted by the anterior pituitary that regulates the activity of pigment-containing cells in the skin of some vertebrates.

melatonin

A hormone secreted by the pineal gland that regulates body functions related to seasonal day length.

mineralocorticoid

A steroid hormone secreted by the adrenal cortex that regulates salt and water homeostasis.

negative feedback

A primary mechanism of homeostasis, whereby a change in a physiological variable triggers a response that counteracts the initial change.

nervous system

The fast-acting internal system of communication involving sensory receptors, networks of nerve cells, and connections to muscles and glands that respond to nerve signals; functions in concert with the endocrine system to effect internal regulation and maintain homeostasis.

neurohormone

A molecule that is secreted by a neuron, travels in body fluids, and acts on specific target cells to change their functioning.

neurotransmitter

A molecule that is released from the synaptic terminal of a neuron at a chemical synapse, diffuses across the synaptic cleft, and binds to the postsynaptic cell, triggering a response.

nitric oxide (NO)

A gas produced by many types of cells that functions as a local regulator and as a neurotransmitter.

norepinephrine

A catecholamine that is chemically and functionally similar to epinephrine and acts as a hormone or neurotransmitter; also known as noradrenaline.

oxytocin

A hormone produced by the hypothalamus and released from the posterior pituitary. It induces contractions of the uterine muscles during labor and causes the mammary glands to eject milk during nursing.

pancreas

A gland with the following dual functions: The nonendocrine portion functions in digestion, secreting enzymes and an alkaline solution into the small intestine via a duct; the ductless endocrine portion functions in homeostasis, secreting the hormones insulin and glucagon into the blood.

paracrine

Referring to a secreted molecule that acts on a neighboring cell.

parathyroid gland

Any of four small endocrine glands, embedded in the surface of the thyroid gland, that secrete parathyroid hormone.

parathyroid hormone (PTH)

A hormone secreted by the parathyroid glands that raises blood calcium level by promoting calcium release from bone and calcium retention by the kidneys.

pheromone

In animals and fungi, a small molecule released into the environment that functions in communication between members of the same species. In animals, it acts much like a hormone in influencing physiology and behavior.

pineal gland

A small gland on the dorsal surface of the vertebrate forebrain that secretes the hormone melatonin.

pituitary gland

An endocrine gland at the base of the hypothalamus; consists of a posterior lobe (neurohypophysis), which stores and releases two hormones produced by the hypothalamus, and an anterior lobe (adenohypophysis), which produces and secretes many hormones that regulate diverse body functions.

positive feedback

A physiological control mechanism in which a change in a variable triggers mechanisms that amplify the change.

posterior pituitary

Also called the neurohypophysis; an extension of the hypothalamus composed of nervous tissue that secretes oxytocin and antidiuretic hormone made in the hypothalamus; a temporary storage site for these hormones.

progesterone

A steroid hormone that prepares the uterus for pregnancy; the major progestin in mammals.

prolactin (PRL)

A hormone produced and secreted by the anterior pituitary with a great diversity of effects in different vertebrate species. In mammals, it stimulates growth of and milk production by the mammary glands

prostaglandin (PG)

One of a group of modified fatty acids secreted by virtually all tissues and performing a wide variety of functions as local regulators.

prostate gland

A gland in human males that secretes an acid-neutralizing component of semen.

second messenger

A small, nonprotein, water-soluble molecule or ion, such as a calcium ion (Ca2+) or cyclic AMP, that relays a signal to a cell's interior in response to a signaling molecule bound by a signal receptor protein.

semen

The fluid that is ejaculated by the male during orgasm; contains sperm and secretions from several glands of the male reproductive tract.

signal transduction

The linkage of a mechanical, chemical, or electromagnetic stimulus to a specific cellular response.

testosterone

A steroid hormone required for development of the male reproductive system, spermatogenesis, and male secondary sex characteristics; the major androgen in mammals.

thyroid gland

An endocrine gland, located on the ventral surface of the trachea, that secretes two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4), as well as calcitonin.

thyroxine (T4)

One of two iodine-containing hormones that are secreted by the thyroid gland and that help regulate metabolism, development, and maturation in vertebrates.

triiodothyrodine (T3)

One of two iodine-containing hormones that are secreted by the thyroid gland and that help regulate metabolism, development, and maturation in vertebrates.

tropic hormone

A hormone that has another endocrine gland as a target.

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