Cilia

Cilia are tiny, slender, hair-like structures present overs the surface of all mammalian cells. They are primitive in nature and could be single or many more.

Cilia plays a significant role in locomotion. they’re additionally concerned in mechanoreception. The organisms that possess cilia square measure are referred to as ciliates. They use their cilia for feeding and maneuvering.

Types of Cilia

Following squares the measure of the 2 differing types of cilia:

Motile Cilia

These square measures are found in massive numbers on the surface of the cell. In humans, these square measures are found within the metastasis epithelial tissue of the tract. Here, they perform by clearing the secretion and dirt out of the lungs.

Non-motile Cilia

Primary Cilia square measures non-motile cilia that were initially discovered in 1898. These structures were long believed to be rudimentary organelles. However, recent researches bestowed the biological roles of primary cilia that they perform as a sensory cellular antenna that coordinates an oversized variety of cellular signalling pathways. excluding these, they additionally facilitate in:

• Proper excretory product flows by signalling the urinary organ cells.

• They act as mechanoreceptors and also sensory receptors.

• The cilia perform by allowing the transfer of vital particles from one facet of the sensitive cells to a different within the tissue layer.

Cilia Structure

Cilia are made up of microtubules coated by the plasma membrane. Each cilium comprises nine pairs of microtubules that form the outside ring and two central microtubules. This structure is called an axoneme. The nine outer pairs are made up of motor proteins called dynein. These are large and flexible that allows the cilia to move.

Cilia are attached to the cell at the basal body that is made up of microtubules arranged in nine triplets. They are very minute structures ranging from 0.25μm in diameter to 20μm in length.

Cilia Function

The important functions performed by cilia involve locomotion and sensory functions. They play a major role in cell cycle and replication and also in the development of humans and animals.

Multiple cilia move in a rhythmic motion that keeps the internal passageways free from mucus or any foreign agent.

A few non-motile cilia act as an antenna that receives sensory information for the cells and processes these signals from the surrounding fluids. E.g. The cilia present in the kidney bend forcefully as the urine passes.  This sends signals to the cells that the urine is flowing.

The non-motile cilia found in the photoreceptors of the retina help in the transport of molecules from one end to the other.

Cilia Disorders

Ciliopathies: It is a genetic disorder of the cilia structures – the basal bodies or of cilia function. Dysfunction or defects in primary and motile cilia are known to cause numerous distressing genetic disorders known as ciliopathies. 

Primary Ciliary Dyskinesia: It is an autosomal recessive disorder in which the cilia do not function normally. This condition prevents the clearing of mucus from the lungs, ears and sinuses.

Flagella Overview  

Flagella are microscopic hair-like structures that are involved in the locomotion of the cells. The word ‘flagellum’ itself means ‘whip.’ Flagella are known to have a whip-like appearance, and they help a cell to propel through the liquid around it. There are a few organisms in which flagella act as sensory organs to assist in the change of pH and temperature. They are usually found in bacteria, archaea, and eukaryotes. There are four different types of flagella: monotrichous, lophotrichous, peritrichous, and amphitrichous. Monotrichous is a single flagellum that is present at one end or the other. These have the ability to rotate clockwise and anti-clockwise. The lophotrichous are the several flagellums that are attached at one end or the other. They can rotate clockwise and anti-clockwise. Peritrichous are the several flagellums that are attached all over the organism. They are non-polar, and they can rotate anti-clockwise. Amphitrichous are the single flagellum that is attached to both ends of the organism. They are polar and can rotate clockwise and anti-clockwise.

Structure of Flagella

The flagella are a helical-like structure that is composed of flagellin protein. The flagella structure can be divided into three parts, namely hook, basal body, and filament. The basal body is attached to the cell membrane and the cytoplasmic membrane. The hook is a broader area that is present at the base of the filament. It connects the filament to the motor protein in the base, and the hook length is a gram +ve bacteria. The filament is the hair-like structure that arises from the hook. 

Function of Flagella

Flagella helps an organism in movement, and they act as sensory organs to detect the pH and temperature changes. A few eukaryotes also use flagellum to increase reproduction rates. It has been found recently that the flagella are also used as a secretory organelle.

Conclusion

The organelle cilia are found in eukaryotic cells. They can be of two types – motile cilia and non-motile cilia. The non-motile cilia are known as primary cilia and act as sensory organelles. Cilia are structurally identical to flagella. Microorganisms such as paramecium contain cilia for locomotion.