Cell Specialisation
In multicellular organisms, functions are typically divided between specialised cell types. Cells of similar origin working together are organised into tissues. Despite having the same genetic material, the cells of an organism acquire distinct structural and molecular characteristics that enable them to perform their specific role. This process is known as cellular differentiation. During differentiation, different genes are selectively switched on and off, leading to the development of specialised cell types.
To illustrate the structural diversity that cells can achieve through differentiation, let us take a look at several examples from hundreds of specialised cell types of the human organism.
The respiratory epithelium is a specialised tissue which lines the lung airways preventing the entry of pathogens and dust particles into the organism. Its predominant cell type is the ciliated cells. Ciliated cells are adapted to move mucus, a viscous fluid that traps pathogens and foreign particles, towards the pharynx. These elongated cells are characterised by the presence of numerous hair-like structures called cilia, which extend from their surface. The coordinated beating of cilia propels the mucus along the airways, clearing it from the lungs.
Another example of highly specialised cells is macrophages. Macrophages, a subtype of white blood cells, engulf and digest pathogens, such as bacteria, as well as dying cells. Macrophages are capable of moving towards their targets by extending long flexible processes called pseudopodia. Upon encountering a pathogen, a macrophage initiates phagocytosis, ingesting the invader into a vesicle for subsequent digestion.
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