Meaning of Cilios

What are Cilios:

Cilia are a series of short and numerous mobile processes of the plasma membrane that line the cell surface of some eukaryotic organisms.

Cilia have an internal structure made up of proteins and microtubules that allow the movement of the cell and the transport of materials over the epithelia, as well as the movement of fluids both in the respiratory tract and in the reproductive system.

The movements of the cilia are rhythmic and coordinated, they can be illustrated as the movement of wheat fields when they are shaken by the wind. This movement is possible because the cilia receive energy from proteins in the form of ATP, and allow the transport of single-celled cells and particles.

The cilia perform several important functions thanks to their rhythmic movements, such as protection against the attack of microorganisms in the respiratory tract by allowing the expulsion of particles accumulated in the mucosa, such as dust.

Also, in the reproductive system, the cilia allow the ovum to move from the fallopian tubes to the uterus. They also move water around the gills, among others.

On the other hand, cilia share some characteristics with flagella, which are few structures (1 or 2) in the cells of eukaryotic organisms, which allow their movement, however, they are structure with different functions.

Cilia function

Cilia are structures that can move and allow the movement of various fluids and particles, hence they can perform the following functions:

  • Generate small streams of movement near the plasma membrane that attract food.
  • Regulate the nervous system.
  • Allow the movement of fluids.
  • Allow the displacement of particles located on its surface.
  • Allow the propulsion of protist unicellular organisms.
  • Allow the displacement of mucous membranes in the respiratory tract.
  • Allow the movement of gametes in the reproductive system.
  • Regulate the water balance of the excretory organs.
  • Filter the particles that pass through the gills.

Structure of the cilia

The cilia have a diameter of approximately 0.25 μm and a length between 5 and 50 μm. Here is how the cilia are structured:

Axoneme or stem: they are composed of two simple central microtubules that are surrounded by 9 doublets of outer microtubules, this arrangement is known as (9 + 2). Microtubules allow the movement of cilia and are associated with proteins called molecular motors (kinesin and dynein).

The central microtubule doublets contain nexin. On the other hand, in the 9 outer microtubule doublets, two microtubules can be distinguished:

  • Microtubule A: contains 13 protofilaments and is complete. From this microtubule, two arms with protein dynein are attached to microtubule B. This union allows the movement of the cilia.
  • Microtubule B: contains 10 protofilaments, of which it shares three with microtubule A.

Transition zone: there is a change in the structure of the axoneme of (9 + 2) with the structure of the basal corpuscle (9 + 0). In this process, the central microtubules disappear, so that the external doublets become triplets.

Basal corpuscle or centriole: it is located below the cytoplasmic membrane. It contains nine triplets and lacks the central microtubule pair, that is (9 + 0). It is a cylinder that is located at the base of the cilium and allows the union of the axoneme with the cell, as well as the organization of the microtubules.

In general, the microtubules are anchored to the basal corpuscle by the ciliary roots that extend into the cell, which gives greater stability to the beating movements of the cilia.

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