1.1 THE HUMAN BODY 1 Scientists have discovered that every second our body produces 25 million new cells. Can you name five vital organs of the human body? Our biggest organ is our skin. On average, it covers around 2m2 and weighs about 5 kilograms. Other systems are the integumentary and lymphatic. blood vessel: vaso sanguigno naked: nudo tissue: tessuto THE HUMAN BODY, AN INTRODUCTION The structure and working of the human body have always been fascinating for man, who, for various reasons, has tried to understand its complex structure and mechanisms. This is why different sciences have been created to analyse this perfect machine. Anatomy The word anatomy comes from the Greek word , which means to cut apart . This science studies the structures of the body and can be divided into: Gross anatomy, which is the study of the structures visible to the naked eye without the help of a microscope. It can be further divided into: Systemic anatomy, which is the study of the structures that work together to perform a unique body function (e.g. a systemic anatomical study of the skeletal system would consider all of the bones of the body); Regional anatomy, which is the study of the interrelationships of all of the structures in a specific body region (e.g. a regional anatomical study of the head would consider all the muscles, nerves, blood vessels, and other structures that serve it); Microscopic anatomy, which requires the use of a microscope. ORGANISATION IN ORGANISM 14 Physiology The word physiology comes from the Greek and means the study of nature . Whereas anatomy is about structure, physiology is about function and therefore studies the chemistry and physics of the structures of the body and the ways in which they work together to support the functions of life. In other words, physiology focuses on the body s tendency towards homeostasis, that state of steady, balanced internal conditions maintained by living things. Structural organisation of the human body The human body has different structural levels of organisation, starting from atoms and molecules, and increasing in size and complexity to cells , tissues, organs, and the systems which make up the complete organism. A cell is the smallest independent unit of living things. A tissue is made up of many similar cells that perform a specific function. An organ is an integrated collection of two or more kinds of tissues that work together to perform a function, e.g. the heart. A system is a group of organs that work together to perform major functions, e.g. the digestive system. The main systems of the human body are: the skeletal system, the muscular system, the nervous system, the endocrine system, the cardiovascular system, the respiratory system, the digestive system, the urinary system, the reproductive system, the sensory system.