Glossary of Physiology Terms

Anoxia

Describes a condition in which there is an absence of oxygen supply to tissues.

Anoxemia
Hypoxia
Hypoxemia

Deiodinase

The enzyme found in target tissues of the thyroid hormones that converts thyroxine (also known as tetraiodothyronine or T₄) to triiodothyronine (T₃).

Specifically, 5'-deiodinase converts T₄ to the active form of the thyroid hormone, T₃.

5-Deiodinase converts T₄ to the inactive form of the thyroid hormone, reverse T₃ (rT₃).

Electrophysiology

Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an action potential. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).

Hormone

A chemical messenger molecule secreted (i.e., released) by endocrine cells within endocrine glands.

By definition, a hormone molecule is released into the bloodstream and travels throughout the body to find its target cells. Teget cells may be within the intravascular compartment (i.e., within blood vessels), but most hormones have target cells in tissues outside of the blood vessels.

Endocrine cell
Endocrine gland

Hypoxia

Describes a condition in which there is a decrease in oxygen supply to tissues. It may be generalized (whole body) or local (e.g., brain).

Anoxia
Anoxemia
Hypoxemia