what is epithelial tissue? mention different types of epithelial tissue. write their location and function
Answers
Answer:
Explanation:
Structure
Epithelial cells are the building blocks of epithelial tissue. Like every other cell, they are surrounded by cellular membranes. Epithelial cell membranes have three regions (domains) different in structure and function; apical, lateral and basal. This feature is called membrane polarity.
Polarity
Plasma membrane; Image: Paul Kim
Plasma membrane
Each membrane pole exhibits various features. These can include receptors and channels for transportation of substances that the epithelial cell needs to internalize or expel, or membrane specializations.
Apical poles project towards the external surface or the lumen of an organ which epithelia cover, which is why they’re also called free surfaces or free domains. This pole may also show apical membrane specializations which alter the shape of this surface. Lateral surfaces are the sites where adjacent cells interconnect, forming tightly packed contiguous cells. Basal surfaces are in contact with the underlying basement membrane. As both lateral and basal surfaces are adjusted to interact with surrounding structures, they’re often mentioned together as a basolateral surface.
Apical specializations
Apical specializations are different types of fingerlike cytoplasmic extensions of the apical surface. They differ in their length, motility and function. There are three types of specializations;
Microvilli; Image:
Microvilli
Microvilli - motile specializations. They are found everywhere where great absorptive surface and continuous passage of material is required (e.g. lower digestive tract and the kidneys)
Stereocilia - a type of microvilli, but these are immotile and longer than microvilli. Their functions are absorption (epididymis and ductus deferens) and mechano-sensory reception (inner ear)
Cilia - fingerlike structures present on almost every epithelial cell. There are three types of cilia; motile, primary and nodal. Their respective functions are; removing foreign particles from the epithelial surface, transportation of signals from the ECM to the intracellular space, and fetal development.
Junctions
Intercellular junctions are protein complexes on the basolateral cell membranes of epithelial cells. Their functions are to establish membrane polarity, connect adjacent cells and anchor the epithelial tissue to the connective tissue underneath it. There are five main types of junctions:
Tight junctions (occluding junctions) – a complex intercellular junction that blocks the intercellular space between adjacent cells making it impassable.
Adhering junctions and desmosomes – connect the cytoskeletons of adjacent cells.
Communicating (gap) junctions – passageways between adjacent cells that allow the transfer of small molecules between adjacent cells.
Anchoring junctions (hemidesmosomes) – a cell matrix junction that anchors the cell to the basement membrane.
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Answer:
Epithelial tissue is the outer most layer of Plant or animals
Skin of animals and plant