The word epithelial is of Greek origin (epi = upon; thele = nipple).The epithelium covers or lines surfaces: the outer skin (epidermis), mucous membranes, gastrointestinal tract, urinary tracts, and inner linings of the blood vessels.
In a multicellular living being, work is divided among uniquely differentiated cells. Each of the 60 billion cells in the human body exhibits a typical form, which is determined by the function of the particular complex of cells where the cell is located. This indicates a universal characteristic of living cells, namely to react flexibly to particular functional requirements. In the human body, a large number of different cells with differing functions can be identified.
The reproduction of cells involves the division of existing cells. This process of cell division is known as mitosis. This means the equal distribution of the genetic information stored in the cell nucleus and division of the cytoplasm. This process of cell division takes between 20 minutes and 4 hours and can be broken down into five different phases, each of which smoothly transitions into the next (Fig 2-3):
The cell nucleus is separated from the hyaloplasm by a nuclear membrane. It is the cell's control center and contains the chromosomes, which carry the genetic information. The cell nucleus is part of each and every cell. The most important exceptions are the red blood cells, which only live for about 100 days because they lack a nucleus.
Cytoplasm
The cytoplasm can be divided into four structural units: hyaloplasm, cell organelles, metaplasm, and paraplasm.
Sound knowledge of the structure and functions of the human body starts from the very smallest components, moves through increasingly larger units, and ends with the whole organism.The smallest independent functional unit of any organism is the cell.The structure and function of the cell are described in general cytology (cytos = cell, cellula = small chamber).
In their close collaboration, dentists and dental technicians need to be able to refer to specific teeth clearly. The term mandibular left second molar is correct and clear as it stands, but it is far too long-winded. Based on the dental formula, various notations have been developed to allow clear communication when referring to the teeth within each dental arch.
In dentitions that are only shed and replaced once (diphyodontia), the rather smaller teeth of the first dentition are replaced by the larger teeth of the second dentition. In humans, the primary dentition appears first with 20 teeth (dentes decidui). It is replaced and supplemented by the complete, secondary dentition of 32 permanent teeth (dentes permanentes). The primary dentition is also known as the temporary dentition.
The roots of teeth are located in sockets (alveolus dentalis) of the jawbone, where they are firmly and flexibly anchored with collagenous fibers and a connective tissue periodontium. In addition, there is a special ligamentous apparatus at the
gingival margin. Teeth are slightly mobile within the alveolar sockets, rather like a joint. Anatomically, the attachment apparatus includes the gingiva, the root cement (cementum), and the bony alveoli.The tooth is supplied via the blood vessels and nerves that enter the periodontium and the tooth itself.
In Latin, the word teeth is dentes (dens = tooth; dentis = of the tooth). Dental means relating to the tooth. In Greek, tooth is odous (odontes = teeth).