"Physiologies" redirects here. For other uses, see Physiology.

The human body includes the entire structure of a human being and comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet. Every part of the body is composed of various types of cells, the fundamental unit of life.[1]

At maturity, the estimated average number of cells in the body is given as 37.2 trillion. This number is stated to be of partial data and to be used as a starting point for further calculations. The number given is arrived at by totalling the cell numbers of all the organs of the body and cell types.[2] The composition of the human body is made up of a number of certain elements including carbon, calcium and phosphorus.

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.

Skeletal structure frames the overall shape of the body and does not alter much over a lifetime. General body shape (and female body shape) is influenced by the distribution of muscle and fat tissue and is also affected by various hormones. The average height of an adult male human (in developed countries) is about 1.71.8m (5'7" to 5'11") and the adult female is about 1.61.7m (5'2" to 5'7"). Height is largely determined by genes and diet. Body type and composition are influenced by factors such as genetics, diet, and exercise.

The human body has several body cavities the largest of which is the abdominopelvic cavity. These cavities house the various body organs including the spinal cord which also accommodates the production and flow of cerebrospinal fluid in the ventricular system of the brain.

Many other smaller cavities exist throughout the body called sinuses, which have varied functions. Sinuses in general usage refers to the paranasal sinuses which are involved in the condition sinusitis. The paranasal sinuses are four pairs of vital air-cavities in the cranial bones. These air-filled spaces are paired between the eyes, above the eyes, deeper behind the eyes and around the nasal cavity.

The average adult body contains between 5 and 5 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 adult human body contains approximately 60% water, and so makes up a significant proportion of the body, both in terms of weight and volume. Water content can vary from a high 75% in a newborn infant to a lower 45% in an obese person. (These figures are necessarily statistical averages).

The vast majority of cells in the human body are not human at all; rather they are of bacteria, archaea, and methanogens such as Methanobrevibacter smithii. The largest proportion of these form the gut flora. The whole population of microbiota include microorganisms of the skin and other body parts and this altogether is termed as the human microbiome.

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