What is Cilia?

Cilia is an organelle that is present on the membrane of most of the eukaryotic cells and it is also known as cilium (singular). It is absent in bacterial and archaeal cells. The shape of the cilia is slender, and it is a thread-like structure that arises from the surface of the cell membrane. Cilia is like flagella, which is a locomotive organ present in bacterial cells.

The function of Cilia is to provide locomotion and propelling of cell and food particles, respectively. There are two types of Cilia, including motile and non-motile. They are also present in humans as well. In this article, we will study the cilia, its structure, types, and Functions.

Definition of Cilia

Cilia are microscopic, hair-like structures that protrude from the surface of eukaryotic cells.

What is Cilia?

Cilia are hair-like structures, which are protruding from the cell membrane of the eukaryotic cell. There are various functions in which Cilia helps including locomotion, signal transmission, sensing of signals and propelling of food particles, etc. There are two types of Cilia, and they are known as motile and non-motile Cilia. Cilia assist in a number of tasks, including as signal transmission, food particle propulsion, motility, and signal perception. Cilia are classified as either motile or non-motile depending on their kind.

Structure of Cilia

Cilia is composed of basal body, ciliary rootlet, transition zone and axoneme.

Basal Body

• The first of cilium structure is basal body which is considered to be the foundation of Cilia.
• Mammalian cell Cilia consists of subdistal appendages, nine triplet microtubule and distal appendages.
• Distal appendages attaches the basal body of Cilia to the base of Cilia.

Ciliary Rootlet

• It is a cytoskeleton type of structure and have diameter of 80 – 100nm, which protruding from the basal body of Cilia at the proximal end.
• Ciliary rootley is made up of protein known as rootlet protein, which is encoded by CROCC gene.

Transition Zone

• Transition zone is also known as ciliary gate which is responsible of entry and exit of protein from Cilia.
• Ciliary gate consists of Y shaped structure which connects it to the axoneme. Ciliary gate only allow selected protein entry.

Axoneme

• Core of Cilia is made up of microtubule known as axoneme.
• In a motile cilium, the axoneme serves as a framework for the inner and outer dynein arms that propel the cilium and as a pathway for the kinesin and dynein microtubule motor proteins.

Types of Cilia

There are basically four types of Cilia which includes

1. Non-motile Cilia
2. Modified non-motile Cilia
3. Motile Cilia
4. Modified motile Cilia

Non-motile Cilia

• These are also known as primary Cilia and are discovered in 1898.
• These type of Cilia found on every animal cell except blood cells.
• These are present on olfactory neurons, retinal photoreceptor cells.
• Function of non-motile Cilia are chemosensation, control of cell growth and signal transduction.

Modified non-motile Cilia

• Modified non-motile Cilia are also known as Kinocilia.
• Modified non-motile Cilia are present in the inner ear hair cells.
• They have 9+2 axoneme of motile Cilia but these Cilia do not have dynein arm that provide motility to the Cilia.

Motile Cilia

• They are found in tracheal respiratory tract.
• These type of Cilia is also present in mammalians respiratory tract.
• In respiratory tract about 200 Cilia are present on every repiratory epithilium cells.
• They help in cleaning and sweeping of mucus.
• These also aid in motion of egg cells from ovaries to uterus.
• In brain ventricle ciliated cell aid in proper circulation of CSF.

Modified motile Cilia

• When motile Cilia do not have central apparatus are known as modified motile Cilia.
• They are present on nodel cells as nodel Cilia.
• Modified motile Cilia have dynein arm which allows it to move.
• These are present on choroid plexus epithelial cells.

Nodel Cilia

• These are also known as monocilium due to having only single cilium.
• They are present on early development stage of embryo.

Functions of Cilia

There are so many functions of Cilia that depends upon the type of Cilia. Some of the functions are listed below

1. Movement of body fluids: This function is performed by motile Cilia. Motile Cilia is present of various of cells. For an instance respiratory cell, Cilia help in sweeping and movement of mucous.
2. Sensory transduction: This function is performed by non-motile cell. These type of Cilia recieves signals from outer environment and transduce that signal to the cell. These Cilia are present in olfactory route and visual route.
3. Embryonic development: This function is processed by non-motile Cilia and help in development of embryonic development by a hedgehog signaling. These Cilia help in tissue seperation of developing embryo.
4. Movement of female eggs: This function is performed by motile Cilia. These aid in transportation of female egg from ovaries to uteurs.
5. Cell movement: In single cell organism Cilia helps in movement of cell.

Disorders of Cilia

Malfunction and abnormalties in Cilia formation causes disorders known as ciliopathies. Below are the some listed disorders related to Cilia.

1. Primary Ciliary Dyskinesia: Disorder of respiratory cilia.
2. Polycystic kidney disease: This leads to formation of fluid filled cyst in kidney.
3. Bardet Biedl syndrome: Mutation in Cilia sysnthesis gene reults in obesity, retinal disorders.
4. Joubert syndrome: This brain disorder result in malformation known as molar tooth sign.
5. Nephronophthisis: Development of fibrous tissue in kidney results in kidney failure.
6. Altrom syndrome: This a rare genetic syndrome which consists of cardia problem, hearing issue and obesity.

Example of Cilia

Some example of different type of cilia are:

1. Respiratory Cilia: These are found in respiratory tract trachea and bronchi and aid in sweeping of mucus.
2. Fallopian tube Cilia: These help in transportation of eggs from fallopian tube to uteurs.
3. Brain ventricular system Cilia: These Cilia helps in proper circulation of CSF around brain.
4. Kidney tubule Cilia: These Cilia aid proper filteration of fluid from the kidney.
5. Olfactory Cilia: These Cilia helps in detection of smell or odour.
6. Intestinal Cilia: These helps in movement of particles and absorption of nutrients.

Importance of Cilia

Cilia are important for so many physiological processes and some of the importance in which Cilia aids are listed below.

1. Locomotion: Cilia helps in motility of single cell organisms.
2. Respiratory functions: Cilia facilitate the removal of mucus through trachea and bronchi
3. Reproduction: Cilia aid in movement or transportation of eggs from fallopian tubes to uteurs.
4. Sensory functions: Cilia aid in detection of external signal such as smell.
5. Embryo development: In embryonic development, hedgehog pathways signaling aided by Cilia.
6. Transduction of signal: Recieving of signal from outside to pass it into the inside of cell.
7. Environment sensing: Cilia responds to slighlty change in the external environment such as mechanical stimuli.

Conclusion

1. Several human body cells as well as those of several other cells have minute, hair-like projections called Cilia on their surface.
2. Cilia are adaptable structures that serve a variety of purposes.
3. They affect the way cells move physically as well as how signals are received and sent.
4. They are essential to a number of physiological functions, and their dysregulation can have a big impact on both health and illness.

FAQ’s – Cilia

1. What is Cilia?

Cilia, slender and hair-like structures ubiquitous on the surface of all mammalian cells, exhibit both singularity and multiplicity in their primitive nature. They aid in cellular locomotion and engage actively in mechanoreception processes.

2. What are the Function of Cilia?

Cilia function by orchestrating a rhythmic movement that propels water in relation to the cell. This dynamic process can either propel the entire cell through the water or facilitate the movement of water and its contents across the cell’s surface.

3. Is Flagella a Cilia?

Cilia are prevalent in organisms like paramecia, whereas flagella are observed in bacteria and sperm cells. Cilia, being shorter and more abundant than flagella, serve as common organelles for locomotion in many unicellular organisms.

4. What is the difference between cilia and flagella?

Cilia and flagella are cellular appendages responsible for movement. Cilia are short, numerous hair-like structures that cover the cell surface. On the other hand, flagella are longer, typically one or a few tail-like structures that propel the entire cell.

5. Does Cilia Help in Locomotion?

Yes, cilia can play a role in locomotion. While cilia are often shorter than flagella, they are still capable of generating coordinated, rhythmic movements that can contribute to the movement of cells or particles.