Outermost embryonic germ layer; it gives rise to the skin and nervous system.

An organ, muscle, or gland used by an organism to respond to a stimulus.

A neuron that transmits nervous impulses from the spinal cord to an effector.

The chain of cytochromes in mitochondria that transfers electrons from NADH to oxygen with the release of energy, which is then used to synthesize ATP via oxidative phosphorylation.

The early developmental stage of an organism. In humans it refers to the first two months after fertilization.

Refers to the ductless glands that produce or secrete hormones.

The innermost embryonic germ layer; it later gives rise to the linings of the alimentary canal and of the digestive and respiratory organs.

The membrane network in cytoplasm that is composed of tubules or cisternae. Some membranes carry ribosomes on their surfaces while others are smooth.

Maintaining a relatively constant and warm body temperature independent of environmental temperature; homeothermic. Also known as warm bloodedness.

A protein that catalyzes chemical reactions of other substances without itself being destroyed or altered upon completion of the reactions. Enzymes are divided into six main groups: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

The outermost and nonvascular layer of the skin, derived from the embryonic ectoderM

An elongated cordlike structure along the posterior border of the testis; its coiled duct provides for storage, transit, and maturation of spermatozoa and is continuous with the ductus deferens.