Any element that accounts for more than 0.1% of the total body mass in the human body is called a macro element. Approximately 98% of the human body is made up of just five macro elements: oxygen, carbon, hydrogen, nitrogen and calcium. The proportion of the oxygen contained in the human body is extremely high (about 65% of the total body mass). The main reason for this is that most of the body consists of water, and oxygen can also be found in numerous organic and inorganic substances in the body. Another important component of organic compounds is carbon. It accounts for about 18% of the total body mass. The third most abundant macro element in the body is hydrogen. Nitrogen is the fourth most abundant element in the human body. It is primarily a component of amino acids (and thus of proteins) and nucleic acids (DNA and RNA). The fifth most abundant element in the body is calcium. It is indispensable in cellular processes and an important component of bones and teeth.
Molecules are particles consisting of two or more atoms bonded by chemical bonds. Molecules are electrically neutral. The water molecule is the most indispensable molecule for the human body. Water is constantly being eliminated from the body and therefore it needs to be replenished. Water accounts for about two-thirds of the total body mass. The rest comprises protein, lipid and nucleic acid molecules. Proteins play a vital role in the body: they participate in all the biological processes of the cells. Proteins may also have a stabilising, structural function by providing shape for the cells. Lipids are essential for most living organisms, they play a vital role both in the structure and metabolism of the body. RNA molecules are required for the protein synthesis taking place within the cells.
Cells are the smallest structural and functional units of the body. The single cell formed by the fertilisation of an egg cell develops into about 3 x 10¹³ cells in a series of cell divisions during the development of the body. The human body has a symbiotic relationship with numerous bacteria that contribute to its development and health. Such bacteria can be found in the gastrointestinal tract and on the skin surface. The number of these bacteria exceeds the number of the body's own cells. According to estimations, there are about 3.8 x 10¹³ bacteria in the body.
Bones provide attachment sites for the muscles, participating in movement passively, they also provide physical protection for certain organs and play an important role in hematopoiesis (the production of blood). Newborn babies have approx. 270 bones. As the body matures, some bones fuse and therefore, by the time we reach adulthood, we have just over 200 bones. In humans, like in other vertebrates, the mass of the skeleton is only a fraction of the total body mass. In an adult, the mass of the skeleton is only about 5 kg.
Approx. 30% of the female body mass is muscle.
Approx. 40% of the male body mass is muscle.
The active organs of movement are the skeletal muscles. Humans have approximately 350 skeletal muscles, which account for around 30-40% of total body mass. Based on their shape, muscles can be grouped as long, short, flat and circular muscles. Based on their location, we differentiate between the muscles of the trunk, the neck, the head, the upper and lower limbs. Muscles are connected to bones by tendons.
We have 4.5–5.7 L of blood on average.
The cardiovascular system provides the cells of the body with oxygen, hormones and nutrients, and removes substances unnecessary for them. The nearly 100,000 km long vascular system reaches all the cells in the body. In the human body, there is approximately 4.5–5.7 litres of blood, half a litre which is reserved, mobilised only when necessary.