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Cilia are microscopic, hair like structures that are found on the surface of most cells. These organelles are divided into two groups: Motile (moving) cilia and non-motile or primary cilia. They were recently discovered about a century ago and initially their purpose was unknown. At first primary cilium were thought to be vestigial organs, but now they prove to be an important part of our bodies (Hoey, Downs & Jacobs, 2012, pg 17-26). Some detect signals from other cells or fluids nearby and are present in organs such as the kidney and eye (Dvorak et al., 2011). Motile cilia have a waving motion and are found in the lungs and respiratory tract to keep the airways clear. Each group of cilia are different in structure and this allows for unique functions. Cilia also has a role in respiratory diseases such as primary ciliary dyskinesia, where cilia contains a defective structure and as a result mucociliary clearance is impaired. There are two groups of cilia, primary and motile cilia which differ in structure and function. The primary cilia is a complex structure with various components such as the ciliary and sub-ciliary compartments. The ciliary compartment consists of a core called an axoneme with nine microtubule doublets that sit around a central core without two central microtubules, commonly known as the ‘9 + 0’ arrangement (Hoey, Downs & Jacobs, 2012, pg 17-26). The core is projected from the basal body and this basal body stems from the mother centriole (Dvorak et al., 2011). The doublets consist of two tubules, one comprising 13 protofilaments known as a complete tubule A, and the other comprising 10 protofilaments known as an incomplete tubule B (Hoey, Downs & Jacobs, 2012, pg 17-26). The microtubule doublets have it... ... middle of paper ... ...primary cilia and motile cilia have varying structures, the most obvious one being that motile cilia have a ‘9+2’ arrangement whilst primary cilia are missing the central pair of microtubules a ‘9+0’ arrangement. Radial spoke proteins and nexin proteins restrict sliding but promote bending in motile cilia, whilst primary cilia are stiff due to the mass of the microtubules being distributed on the circumference. Determining the structure of each type of cilia aids in understanding the role of cilia in respiratory diseases such as PCD. Cilia as discussed is extremely important in our bodies, especially in the respiratory regions as it regulates mucociliary clearance and thus denies pathogens and irritants access to our bodies. However when cilia becomes dysfunctional in various ways, it becomes immotile, and this can cause diseases such as primary ciliary dyskinesia.

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