by Trianna Mitchel

Created on: May 21, 2008   Last Updated: October 13, 2008

Tissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.

The study of tissue is known as histology or, in connection with disease,

histopathology.

The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

Contents[hide

1 Animal tissues

1.1 Epithelium
1.2 Connective tissue
1.3 Muscle tissue
1.4 Neural tissue
2 Plant tissues

2.1 Meristimatic tissues

2.1.1 Characteristics of meristematic tissues
2.2 Permanent tissue

2.2.1 Simple permanent tissues

2.2.1.1 Parenchyma
2.2.1.2 Collenchyma
2.2.1.3 Sclerenchyma
2.2.2 Complex permanent tissue

2.2.2.1 Xylem
2.2.2.2 Phloem
3 See also
4 References

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[edit Animal tissues
Based on morphology, animal tissues can be grouped into four basic types. Multiple tissue types comprise organs and body structures. While all animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals. The epithelium in all animals is derived from the ectoderm and endoderm with a small contribution from the mesoderm which forms the endothelium. By contrast, a true connective tissue is present only in triploblastic animals; diploblastic animals such as sponges, jellyfish and coral in effect do not have connective tissue but rather an acellular gel known as the mesoglea separates different tissues types in these animals. The mesoglea serves the function of a connective tissue but is derived from ectoderm.

[edit Epithelium
Epithelium is single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier. This tissue covers all organismal surfaces that come in contact with the external environment such

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