What is our body made of?

• We have learned that all living things are made of of tiny estructures of living material called cells.

Cells :

• The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing (except virus, which consists only from DNA/RNA covered by protein and lipids), and is often called the building block of life. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). Humans contain about 100 trillion (1014) cells .Most plant and animal cells are between 1 and 100 µm and therefore are visible only under the microscope.

Cells

Tissues

• Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of similar cells from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.

• The study of tissue is known as histology or, in connection with disease, histopathology. The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope.

Tissues

Organs • In biology, an organ is a collection of tissues joined in a structural unit

to serve a common function.[1]

• There is a "main" tissue, parenchyma, and "sporadic" tissues, stroma. The main tissue is the one that is unique for the specific organ. For example, the main tissue in the heart is the myocardium, while sporadic tissues include the nerves, blood and connective tissues. Functionally related organs often cooperate to form whole organ systems. Organs exist in all higher biological organisms, in particular they are not restricted to animals, but can also be identified in plants. In single-cell organisms like bacteria, the functional analogues of organs are called organelles.

• A hollow organ is a visceral organ that is a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity, like the heart or urinary bladder.[2

Organs

Systems

• The human body is made up of several organ systems that work together as one unit. Ten major organ systems of the body are listed below, along with several organs that are associated with each system.