Cillia

Cillia is a term that refers to cilia, which are short, hair-like appendages found on the surface of many eukaryotic cells. These structures are composed of microtubules and are responsible for various cellular functions, including locomotion, sensing the environment, and moving substances. Cilia are typically found in multicellular organisms, but are also present in some unicellular eukaryotes.

The structure of a cilium is highly organized, featuring a core arrangement of nine doublets of microtubules surrounding two single microtubules, known as the 9+2 arrangement. This arrangement is crucial for the ciliary beating motion, which can propel cells through liquid environments or move fluids along the cell surface. For instance, in the respiratory tract, cilia work in coordination to sweep mucus and trapped particles away from the lungs. In the fallopian tubes, cilia help to move the egg towards the uterus.

In some organisms, cilia also play a sensory role, detecting external stimuli such as light, chemicals, or mechanical forces. These sensory cilia are often modified in structure compared to motile cilia. Defects in cilia can lead to a range of human diseases, collectively known as ciliopathies, which can affect multiple organ systems and manifest with diverse symptoms. Research into cilia continues to expand our understanding of their fundamental roles in cell biology and disease.