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Cilia are freely moving cell extensions. There are primary and secondary cilia. They differ in terms of the number of microtubules they contain and their ability to move. Cilia are included with the flagella under the collective term undulipodium because both have similar anatomical structures.
Definition
Secondary cilia are cell extensions that are able to move freely. They are found in the ciliated epithelium of the lungs . In contrast to the primary cells, they contain central microtubules. The movements of these cell processes enable the transport of mucus and fluids.
Diseases such as cystic fibrosis or asthma are due to paralysis of the cilia, which impedes the evacuation of fluids and mucus, which can lead to breathing difficulties, bronchitis and lung disease.
Anatomy
Cilia are free-moving cell extensions formed as fine hairs on the cell surface. It is five to ten microns long plasma membrane protuberances with cytoplasm that are 0.25 microns slim. Their skeleton is enriched with an axoneme equipped with microtubules. The cytoplasm is pointed and surrounded by basal bodies in which all cilia are firmly anchored. They are also found in the testicles , fallopian tubes , and respiratory tract.
Primary and secondary cilia differ in terms of their ability to move and the number of their microtubules. Cilia are not to be confused with microvilli, which are found in the gut and do not have microtubule properties. They work like a ship’s propeller, are smaller than cilia and are not surrounded by a membrane.
The outstanding feature of the cilia is that they are enclosed by the plasma membrane. Axonemes are axial threads made up of contractile proteins and kinesin. Proteins are the prerequisite for the mobility of the cilia. Microfibers are fine hollow fibers that dock to the axoneme. They have the form of molecular compounds, are electrically charged and have a negative and a positive tubule.
Each microtubule doublet is divided into an A-tubule and a B-tubule. The A-tubule has arm-like structures that are always aligned with the B-tubule of the adjacent cilia. Each cilia has double microtubules. This form is referred to in technical jargon as doublets. They are arranged in a circle and form the tubular skeleton of the cilia.
In the circular center, some cilia have two additional microtubules in the form of secondary cilia. Cilia without central microtubules form the primary cilia. Its interior contains cytoplasm, which forms the cytoskeleton and in this way generates the axoneme. The individual microtubule doublets are connected to each other by nexin connectors. The decentralized doublets of the secondary cilia are connected to the central doublets by radial spokes.
Function
Cilia are 3D hairy locomotion devices, so to speak, that move cells, process signals and ensure that organs are arranged correctly. However, they can only fulfill these tasks if the transport system also supplies them with all vital substances.
Secondary cilia can actively flap and row to move. Strained microtubules allow them to bend and stretch. This alternating movement creates a sliding mechanism. The arm of the A-tubule makes contact with the B-tubule of the adjacent cilia. In the next step, he moves the tubules of the tubulin doublets against each other.
The task of the flexible protein nexin is to keep the neighboring doublets together during this shift. When the cilia protrude, they are stretched, when they retract, they are flexed.
Secondary cilia are predominantly arranged in large groups and move in a coordinated manner according to the principle of extension and flexion. The opposite rows of a row of cilia beat back and forth with a minimal time lag. This coordinated movement principle is called metachrone in technical jargon.
The surfaces of the cilia groups record a uniform ciliated current running in waves. The beat rate is about twenty per second. The coordinated movements serve to remove mucus and liquids. Primary cells function as a sensory antenna, are mostly immobile, and are found in the olfactory and visual apparatus.
Diseases
- [[Lung infection]
- They have dyskinesia
- Kartagener Syndrome
- Bardet-Bidl-Syndrome
Molecules are transported along a fiber bundle inside the cilia. If this intraflagellar transport (IFT) is disturbed, errors in the construction of the cilia can occur, which can lead to various diseases such as bronchitis, coughing or pneumonia.
The most common ciliary disease is primary ciliary dyskinesia, a genetic disorder of the ciliary cells that causes respiratory infections, sinusitis, or rhinitis.
This congenital respiratory disease is also known as Kartagener Syndrome, which is a disorder of the movement of the cilia. This movement-related loss of function of the cilia is also known as ciliopathy, which can be responsible for the formation of cysts .
The rather rare Bardet-Bidl syndrome can also occur due to a disruption in cilia function. This disease leads to multiple malformations that vary in their combination and severity, such as diabetes mellitus , obesity , mental disabilities, motor disorders or short stature.
Hello and welcome to my Health Guide & Encyclopedia! My name is Dorothy Farrar, and I'm the founder and main author of this platform.
My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.