The Endocrine System

The body control system composed of a group of glands that maintain a stable internal environment by producing chemical regulatory substances called hormones. The endocrine system includes the pituitary gland, thyroid gland, parathyroid glands, adrenal gland, pancreas, ovaries, and testes (see testis). The thymus gland, pineal gland, and kidney (see urinary system) are also sometimes considered endocrine organs.

The Respiratory System

The integrated system of organs involved in the intake and exchange of oxygen and carbon dioxide between an organism and the environment.

The Muscular System

The bodily system that is composed of skeletal, smooth, and cardiac muscle tissue and functions in movement of the body or of materials through the body, maintenance of posture, and heat production.

The Urinary System

The bodily system consisting of the organs that produce, collect, and eliminate urine and including the kidneys, ureters, urinary bladder, and urethra.

The urinary system consists of the kidneys, urinary ducts, and bladder. Similarities are not particularly evident among the many and varied types of excretory organs found among vertebrates. The variations that are encountered are undoubtedly related to problems with which vertebrates have had to cope in adapting to different environmental conditions.

The Skeletal System

The supporting tissues of animals which often serve to protect the body, or parts of it, and play an important role in the animal's physiology.