cilia

Cilia are hair-like structures that protrude from the surface of eukaryotic cells. They are microscopic and play an essential role in various biological processes. Cilia can be divided into two main types: motile cilia and immobile (primary or sensory) cilia.

Motile cilia

Motile cilia are found on the surface of many cell types and are responsible for movement. Their wave-like movements can transport fluids across the surface of cells or tissues. A classic example of their function is the movement of mucus and foreign particles from the respiratory tract. Another example is the movement of egg cells through the fallopian tubes of the female reproductive organs.

Immobile (primary) cilia

Immobile or primary cilia are found on almost every human cell and have a variety of sensory and signaling functions. They act as antennas for the cell, receiving signals from the environment and relaying them to the cell interior. This function is crucial for a multitude of signaling pathways that regulate cell growth, development, and homeostasis.

Structure of the cilia

The structure of cilia is complex. They consist of a microtubule network, the axoneme, which is surrounded by a cell membrane. The axoneme of most motile cilia has a "9+2" structure, consisting of nine microtubule doublets forming a ring and a central pair of microtubules. Immotile cilia often have a "9+0" structure without the central pair.

Functions and meaning

Transport : Motile cilia help to transport fluids and particles across cell surfaces, such as in the respiratory epithelium of the lungs.
Signal transduction : Immobile cilia are involved in important signal transduction pathways that control cell growth, specialization, and development.
Sensory Functions : Primary cilia are involved in the perception of mechanical stimuli (mechanosensation) and light (in the photoreceptors of the retina).

Diseases related to cilia

Disruptions in the function or structure of cilia can lead to a number of genetic disorders known as ciliopathies. These include:

Primary Ciliary Dyskinesia (PCD) : A condition that affects the mobility of the cilia and leads to respiratory problems, infertility, and other issues.
Polycystic Kidney Disease (PKD) : A disease in which the function of the primary cilia is impaired, leading to the formation of cysts in the kidneys.
Bardet-Biedl syndrome and Joubert syndrome : diseases caused by defects in the primary cilia and exhibiting a variety of symptoms, including kidney dysfunction, retinal degeneration, and neurological problems.

Research into cilia and their functions has broadened our understanding of a wide range of biological processes and diseases, and offers potential approaches for new therapies.