Microvilli
Microvilli are very small microscopic projections that are present everywhere in and around the cells.
Microvilli are finger-like plasma membrane projections that are present at the top of a wide variety of cells but are most abundant and elaborated on epithelial cell, for instance, intestinal lining and the outer surface of the kidney proximal tubule.
Microvilli are primarily a bunch of inter-connected actin fibers. Even though they are cellular extensions, there are few or no cellular organelles present in the microvilli.
Structure
Microvilli are encased in the cell membrane, which surrounds Cytoplasm and microfilaments. They are often almost 0.1 µm in diameter and vary in length from a few micrometres to approximately 2 µm. Every microvillus has a tightly packed pile of inter-connected actin filaments, which represents its structural core.
Location
They are present at the surface of many cell types but are in the plentiful amount on the small intestine, on the exterior of egg cells and also on leukocytes (WBCs).
Function
- The tiny microvilli efficiently enlarge the surface area of the cell and play role in absorption, cellular adhesion, secretion mechano-transduction functions.
- They contribute towards easier fertilization as they help the sperm to reach the egg easily.
- Inside the intestine, they work together with villi to take in a large number of nutrients and various materials because they increase the surface area of the intestine.
Comparison chart between microvilli and cilia
Even though microvilli and cilia may seem to be similar at first sight, they are very dissimilar. Let’s have a look at differences between them.
| Sr. No | Basis of comparison | Cilia | Microvilli |
| 1 | Description | Cilia are confined and long hair-like projections from the apical membranes of many cells. | Microvilli are folds of the plasma membrane that prolong in an outward direction from the surface of numerous cells. |
| 2 | Function | Cilia are not involved in absorption. | Microvilli functions in process of absorption. |
| 3 | Location | They are present in cells of the respiratory and reproductive tract. | They are observed in the intestine; where they facilitate in absorption and secretion. |
| 4 | Presence of granules | Cilia usually came from basal granules. | Microvilli lack basal granules. |
| 5 | Composition | Cilia are built from larger vacant tubes called microtubules. | Microvilli hold little fibres called as actin filaments. |
| 6 | Size | Cilia have a larger diameter and thin. | They have a narrow diameter and are thick as compared to cilia. |
Cilia
Cilia are tiny, thin, short eyelash shaped filament that is very abundant on tissue cells of many animals which and usually present on the top of all mammalian cells. They are ancient in nature and could be one or many.
Ciliates belong to protozoans that have cilia.
Structure
A cilium is built from a central core which comprises of two microtubules covered in the plasma membrane. The microtubules are compact vacant rods made of the protein tubulin that is bordered by an exterior ring of nine pairs of microtubules. This arrangement is known as an axoneme. The nine exterior pairs are manufactured from a motor protein called dynein. The two middle microtubules end before entering the basal body.
Function
- They play important role in locomotion of protozoans of the phylum Ciliophora.
- Cilia are involved in discarding impurities from organs or tissue by providing help to the fluids to move over the cell.
- They take part in mechanoreception.
Location
Some motile cilia are present on the epithelial cells of many inner organs for example lungs, trachea, digestive system, etc. They are observed on the protozoans too like paramecium and aids them in locomotion. Whereas, the non-motile cilia are present on in the dendritic protrusion of the olfactory neuron.
Types of Cilia
Motile Cilia
Many eukaryotes, e.g. mammals possess motile cilia. Motile cilia are very small, lash-like organelles whose beating bring about an oriented fluid flow. Motile cilia are essentially needed in several physiologic activities.
Non-motile Cilia
The non-motile cilia are also named as primary cilia and serve as sensory organelles. They protrude from the apical membrane of numerous cells. Formerly, these structures were considered to be vestigial organelles. But current findings demonstrate the biological position of non-motile cilia that they work as a sensory cellular antenna that synchronize a great number of cellular signalling passageways.
