Cilia are tail like outgrowths of cytoplasm found only in eukaryotic cells which help in locomotion while microvilli are cellular membrane protrusions that increase the surface area of eukaryotic cells for absorption.
What are Cilia?
The surface of mostly cells have extensions which are used in movement, absorption, phagocytosis, etc. Cilia and microvilli are two protoplasmic extensions of cells. Cilia is the plural of the cilium. These structures are either motile or nonmotile. Motile cilia can beat towards one direction so that organism can move the entangle particles from the surface. Celia is also present in some other specialized cells which are called sensory cells of a vertebrate ear. For example, normal cilia are surrounded by actin based stereocilia which are responsible for providing initial sensory input for hearing. These projections are also part of other organelles along with flagella, which is called undulipodia. The core of this structure is made up of microtubules that are arranged uniformly in a longitudinal orientation which is known as (9+2) orientation. 9+2 means that the core of each cilium contains nine microtubules doubly present in the periphery and two single microtubules in the center. Each cilium originates from a unique structure which is called a basal body. Basal body has different arrangements of microtubules. Basal body has nine microtubules which are present in triplets with no central tubules instead of the peripheral arrangement of nine tubules in a cilium core.
What are Microvilli?
Microvilli are the plural of microvillus. Microvilli are present on three types of cells which are specialized in absorption. The first site is the striated border of the intestinal epithelium; the second site is brushed border of proximal tubule of the kidney while the third site is gall bladder epithelium. Microvilli possess tiny fibers which are called actin filaments that extend parallel to each other down the length of microvillus. The filaments are attached to each other and to the cell membrane by proteins. These proteins run perpendicular across the actin filaments. Microvilli are held together to form bundles by cross linking proteins which are known as villin and fimbrin. The chief function of the microvilli is the absorption of substances. Cells produce these microfilaments to enhance the surface area of absorption in the intestinal surface, to participate in carbohydrate digestion and to transport materials which are absorbed. Microvilli are packed in large numbers which make its appearance brush like. These brush boarders are present on the luminal surfaces of the epithelium of intestine, for absorption.
- Both cilia and microvilli contain protein fibers which extend outward to provide shape for the structure.
- Cilia are larger in length and diameter than microvilli.
- Cilia are made up of microtubules which contain (9+2) ultrastructure. Microvilli are made of microfilament which lacks (9+2) ultrastructure.
- Cilia are not surrounded by glycocalyx layer. Microvilli are surrounded by glycocalyx layer.
- Cilia are taper distally. Microvilli are extremely thin and short.
- Cilia are used in the movement of cell or objects over the surface of the cells; microvilli enhance the surface area of the cell and increase the rate of diffusion of materials into the cell.
- Cilia are located on the surfaces of the columnar epithelia cells of the uterine tube or respiratory tract while microvilli are present on the surface of the columnar cells of the kidney tubules and small intestine.