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In biology, tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. [1] [2] Tissues occupy a biological organizational level between cells and a complete organ. Accordingly, organs are formed by the functional grouping together of multiple tissues. [3]
There are four basic types of animal tissues: muscle tissue, nervous tissue, connective tissue, and epithelial tissue. [5] [9] All animal tissues are considered to be subtypes of these four principal tissue types (for example, blood is classified as connective tissue, since the blood cells are suspended in an extracellular matrix, the plasma). [9]
This tissue is thus the initial site where pathogenic agents, such as bacteria that have breached an epithelial surface, are challenged and destroyed by cells of the immune system. [1] In the past, the designations areolar tissue, adipose tissue, and reticular tissue have been listed as subsets of loose connective tissue. However, they are no ...
Dense connective tissue also known as fibrous tissue [8] is subdivided into dense regular and dense irregular connective tissue. [9] Dense regular connective tissue, found in structures such as tendons and ligaments, is characterized by collagen fibers arranged in an orderly parallel fashion, giving it tensile strength in one direction. Dense ...
Reticular connective tissue is a type of connective tissue [1] with a network of reticular fibers, made of type III collagen [2] (reticulum = net or network). Reticular fibers are not unique to reticular connective tissue, but only in this tissue type are they dominant. [3] Reticular fibers are synthesized by special fibroblasts called ...
In all vertebrates, these progenitor cells differentiate into all adult tissues and organs. [5] In the human embryo, after about three days, the zygote forms a solid mass of cells by mitotic division, called a morula. This then changes to a blastocyst, consisting of an outer layer called a trophoblast, and an inner cell mass called the embryoblast.
Granulation tissue is composed of tissue matrix supporting a variety of cell types, [3] most of which can be associated with one of the following functions: formation of extracellular matrix; operation of the immune system; vascularisation; An excess of granulation tissue (caro luxurians) is informally referred to as hypergranulation or "proud ...
This type of connective tissue is found mostly in the reticular layer (or deep layer) of the dermis. [3] It is also in the sclera and in the deeper skin layers. Due to high portions of collagenous fibers, dense irregular connective tissue provides strength, making the skin resistant to tearing by stretching forces from different directions.