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 changes included a flattening of the eyeball and changes to the retina. Space traveler's eye-sight can become blurry after too much time in space. Another effect is known as Cosmic ray visual phenomena Because weightlessness increases the amount of fluid in the upper part of the body, astronauts experience increased intracranial pressure. This appears to increase pressure on the backs of the eyeballs, affecting their shape and slightly crushing the optic nerve. This effect was noticed in 2012 in a study using MRI scans of astronauts who had returned to Earth following at least one month in space. Such eyesight