Cilium

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Eukaryotic cilium diagram en

Blausen 0766 RespiratoryEpithelium

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Bronchiolar epithelium 4 - SEM

Nodal cilia

Cilium (plural: cilia) is a microscopic, hair-like structure found on the surface of eukaryotic cells. Cilia are known for their role in cellular locomotion and are also important in various other cellular processes including sensory reception, signal transduction, and fluid movement across the cell surface. There are two main types of cilia: motile cilia and primary cilia, which differ in structure, number per cell, and function.

Structure and Function

Cilia are composed of a core structure called the axoneme, which usually contains nine pairs of microtubules arranged in a ring around a central pair (known as the "9+2" structure). This arrangement is typical of motile cilia. In contrast, primary cilia, which are non-motile, typically lack the central pair of microtubules, resulting in a "9+0" structure. The axoneme is anchored to the cell by a structure called the basal body.

Motile Cilia

Motile cilia are primarily involved in moving fluids across the cell surface or in locomotion of the cell itself. In humans, motile cilia are found in the respiratory tract, where they help to move mucus and trapped particles out of the lungs, and in the fallopian tubes, where they facilitate the movement of the egg from the ovary to the uterus. Motile cilia beat in a coordinated, wave-like pattern that is driven by the motor protein dynein, which causes the microtubules to slide against each other.

Primary Cilia

Primary cilia are typically found as a single cilium per cell and play a key role in cell signaling pathways, including those involved in development and maintenance of tissue. They act as sensory organelles that can detect changes in the cell's environment and relay signals to the nucleus to elicit a response. Defects in primary cilia function can lead to a variety of human diseases, collectively known as ciliopathies, which include conditions such as polycystic kidney disease and Bardet-Biedl syndrome.

Ciliopathies

Ciliopathies are a group of disorders caused by dysfunctional cilia. These diseases can affect multiple organ systems, including the kidneys, liver, pancreas, brain, and eyes. Symptoms and severity of ciliopathies can vary widely, even among individuals with the same condition. The study of ciliopathies has been crucial in understanding the diverse functions of cilia in human health and disease.

Research and Applications

Research on cilia has expanded our understanding of their roles in cell biology and human disease. This has led to the development of diagnostic and therapeutic strategies for ciliopathies. Additionally, understanding the mechanism of cilia movement has potential applications in the design of microscopic robotic devices for medical and industrial applications.