"Physiologies" redirects here. For other uses, see Physiology. The study of the human body involves anatomy and physiology. The human body can show anatomical non-pathological anomalies known as variations which need to be able to be recognised. Physiology focuses on the systems and their organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis. Structure The human body has several body cavities the largest of which is the abdominopelvic cavity. Composition The main elements that compose the human body are shown from most abundant to least abundant. The average adult body contains between 5 and 5½ litres of blood and approximately 10 litres of interstitial fluid. The composition of the human body can be referred to in terms of its water content, elements content, tissue types or material types. The proportions of the elements of the body can be referred to in terms of the main elements, minor ones and trace elements.