Introduction to Anatomy
 A cell is the smallest living unit in each organism, fundamentally specialized in carrying out one or few functions and, in the majority of cases, it is able to produce new life. In multicellular organisms it joins other adjacent cells by means of support structures, in order to form tissues. In their turn, the tissues three-dimensionally penetrate each other, creating organs, specialized work units in living organisms.
The dimensions of a cell in human beings can vary from 5 to about 150 microns and the life of each cell can oscillate between a few days to the entire life of the individual hosting it.1
The synergies that are established among the different organs can form systems or apparatuses. The first is composed of organs characterized by structural and functional similarities (skeletal; muscular, etc.); the second by different organs that cooperate in order to obtain a common function (circulatory; respiratory, etc.).
Structurally speaking, we distinguish between empty organs and full organs.
Empty organs are made up of different tonaca joined together to make a wall. The wall of empty organs is three-dimensionally structured creating a cavity inside the organ, which can have variable shapes and dimensions from organ to organ.
The tonaca that make up the wall of organs also has a precise function, apart from a name in order to identify it.
Starting from the most internal wall we can identify the tonaca mucosa, called tonaca intima if referring to blood and lymphatic vessels.
Moving towards the external part, adherent to the tonaca mucosa, we can recognize the tonaca muscolare, defined once again tonaca media with reference to blood and lymphatic vessels.
Finally, the last covering is the tonaca avventizia.
Full organs have a considerably more complex structure, with singular common constitutive elements: the capsular and stromal device and the parenchyma.
The capsular device is formed by a cover sheet, which exists in all full organs, represented mainly by dense connective tissue. This tissue penetrates the organ, becoming less thick in the process, in this way defining the septa in which the parenchyma of the organ is housed.
It is precisely the capsular device that represents the support structure of the organ, which is defined stroma.
The parenchima, as previously mentioned, is housed in the cavity defined by the stroma. It has different structural and functional characteristics from organ to organ, therefore it is the element that is able to give its own characteristics to full organs.
(1)From “A scuola di fitness” by Pierluigi De Pascalis, Ed. Calzetti Mariucci.
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