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Endocrine System

A system composed of ductless glands that synthesize and secrete hormones.

Hormones

Chemical messengers released into the blood, transported throughout the body, and bind to target cells with specific receptors to elicit a response.

Ligands

Chemical messengers released by both the endocrine and nervous systems that bind to cellular receptors on target cells.

Endocrine Reflexes

Reflexes that regulate hormone release.

Hormonal Stimulation

A method of hormone release where a gland cell releases its hormone when another hormone binds to it.

Humoral Stimulation

A method of hormone release where a gland cell releases its hormone when there is a change in nutrient or ion levels in the blood.

Nervous System Stimulation

A method of hormone release where a gland cell releases its hormone when a neuron stimulates it.

Steroids

Lipid-soluble molecules synthesized from cholesterol, including gonadal steroids and those synthesized by the adrenal cortex.

Biogenic Amines (Monoamines)

Modified amino acids, including catecholamines, thyroid hormone, and melatonin.

Local Hormones

Signaling molecules that don’t circulate in the blood but bind to the cells that release them or neighboring cells.

Eicosanoids

A type of local hormone formed from fatty acids within the phospholipid bilayer of the membrane.

Prostaglandins

Eicosanoids that stimulate pain and inflammatory responses.

Bound Hormone

Hormone that is attached to a carrier protein.

Free Hormone

Hormone that is unattached to a carrier protein and able to exit the blood and bind to target cell receptors.

Half-Life

The time required to reduce a hormone's concentration to half of its original level.

Hormone-Receptor Complex

The structure formed when a hormone binds to its receptor.

Hormone-Response Element (HRE)

A region of DNA to which a hormone-receptor complex can bind.

First Messenger

A hormone that initiates events by binding to a receptor.

G-Protein

An internal membrane protein activated by a hormone binding to a receptor.

Second Messenger

A molecule that modifies cellular activity after the activation of a membrane enzyme.

Up-Regulation

An increase in the number of receptors, increasing sensitivity to a hormone.

Down-Regulation

A decrease in the number of receptors, decreasing sensitivity to a hormone.

Synergistic Interaction

When one hormone reinforces the activity of another hormone.

Permissive Interaction

When one hormone requires the activity of another hormone.

Antagonistic Interaction

When one hormone opposes the activity of another hormone.

Pituitary Gland (Hypophysis)

A pea-sized gland connected to the hypothalamus by the infundibulum, partitioned into anterior and posterior sections.

Posterior Pituitary (Neurohypophysis)

The section of the pituitary gland that stores and releases antidiuretic hormone (ADH) and oxytocin (OT).

Oxytocin (OT)

A hormone that causes uterine contraction, milk ejection, and emotional bonding.

Prolactin (PRL)

A hormone that causes milk production and mammary gland growth in females.

Glycogenolysis

The breakdown of glycogen into glucose.

Gluconeogenesis

The conversion of nutrients into glucose.