Human body Human body The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet. The study of the human body involves anatomy, physiology, histology and embryology. The body varies anatomically in known ways. Physiology focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis,
Effect of spaceflight on the human body lymphocytes. As these cells are central to the immune system, any damage weakens the immune system, which means that in addition to increased vulnerability to new exposures, viruses already present in the body—which would normally be suppressed—become active. In space, T-cells (a form of lymphocyte) are less able to reproduce properly, and the T-cells that do reproduce are less able to fight off infection. Over time immunodeficiency results in the rapid spread of infection among crew members, especially in the confined areas of space flight systems. On 31 May 2013, The NASA scientists reported that a possible manned mission to