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 (motile) cilia and immotile (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 eggs 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 serve as antennas for the cell by picking up signals from the environment and transmitting them to the inside of the cell. This function is crucial for a variety of signaling pathways that regulate cell growth, development and homeostasis.

Structure of the cilia

The structure of the cilia is complex. They consist of a microtubule framework, 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. Immobile cilia often have a “9+0” structure without the central pair.

Functions and meaning

Transport : Motile cilia help 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

Disturbances in the function or structure of cilia can lead to a number of genetic diseases known as ciliopathies. This includes:

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

Research into cilia and their functions has expanded our understanding of a variety of biological processes and diseases and offers potential approaches for new therapies.