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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).
In animals, the plasma membrane is the outer boundary of the cell, while in plants and prokaryotes it is usually covered by a cell wall. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids , which are amphiphilic (partly hydrophobic and partly hydrophilic ).
Cells in animal tissues were observed later than those in plants because their tissues are fragile and difficult to study. Biologists believed that there was a fundamental unit to life, but until Henri Dutrochet were unclear what it was. Besides stating “the cell is the fundamental element of organization”, Dutrochet claimed that cells were ...
Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. [1] It develops mostly from the mesenchyme , derived from the mesoderm , the middle embryonic germ layer . [ 2 ]
Cell junctions [1] or junctional complexes are a class of cellular structures consisting of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals. [2] They also maintain the paracellular barrier of epithelia and control paracellular transport. Cell junctions ...
The birth rate in America has long been on a decline, with the fertility rate reaching historic lows in 2023. More women between ages 25 to 44 aren’t having children, for a number of reasons.
Some animals, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Other animals such as bilaterians produce a third layer (the mesoderm) between these two layers, making them triploblastic. Germ layers eventually give rise to all of an animal's tissues and organs through the process of organogenesis.