The Endocrine System Overview

This set covers the basic definitions, types, actions, and stimulus mechanisms of the endocrine system as described in the lecture notes.

Hormones

Chemical substances, secreted by endocrine cells into extracellular fluids, that regulate the activity of other cells.

Amino acid based

A variety of hormone that is protein based.

Steroids

A variety of hormone that is cholesterol based.

Prostaglandins

Nonsteroidal lipid molecules that act as a variety of hormone.

Target Cells

Specific cells or organs that respond to a particular hormone because they possess the correct receptor.

Direct gene activation

A mechanism of action where the hormone receptor is in the nucleus and transcription factors are directly affected.

Second messenger systems

A mechanism of action where the signal is transmitted through the membrane by a molecule other than the hormone because the hormone cannot enter the cell.

Hormonal stimulus

A mechanism where one hormone causes the release of another hormone; it is very common and tends to be rhythmic in nature.

Humoral stimulus

A mechanism where changes in blood levels of ions or nutrients, such as a low concentration of $Ca^{2+}$, stimulate the release of a hormone.

Neural stimulus

A rare mechanism where nerve fibers directly stimulate endocrine cells to release hormones, usually in the sympathetic nervous system.

Parathyroid hormone (PTH)

A hormone secreted by the parathyroid glands in response to a humoral stimulus of low $Ca^{2+}$ in the blood.

Catecholamines

Hormones, specifically epinephrine and norepinephrine, secreted by the medulla of the adrenal gland in response to a neural stimulus.