Reproductive systems Consists of gonads and accessory tissues and organs that are necessary for producing the gametes and delivering the sperm to the oocytes. Organs are also present for nurturing the young, if internal fertilization and development are utilized. In mammals, mammary glands are present to provide nutrients for the infant. Sex organs also secrete hormones that are important in sexual development, behavior, and reproduction. Digestive system Provides internal systems with nutrients and expels some solid wastes.
Respiratory system Provides internal systems with oxygen and removes carbon dioxide.
Circulatory system Transports blood cells, nutrients, gases, hormones, wastes, heat, and other substances to and from the tissues. Involved in immunity. Transports excess fluids and proteins from interstitial fluids back to the blood. Involved in immunity. Excretory system Eliminates nitrogenous wastes and maintains salt and water balance.