Tissue (biology)
A tissue or cell tissue is a collection of differentiated cells including their extracellular matrix . The cells of a tissue have similar functions and together perform the tasks of the tissue. All the proportions of most multicellular cells can be assigned to a tissue, or they have been produced by a tissue type.
Histology deals with the structure of tissue , and histopathology with pathological changes . The formation of tissue is called histogenesis . After removal, some tissues can be kept extracorporeally in tissue culture for a limited time under suitable conditions (e.g. plant tissue culture ).
Animal tissues
In all tissues animals (including, not fabric-free multicellular animals such as sponges ) can be distinguished four basic types of tissue:
- Epithelial tissue: layers of cells that cover all internal and external surfaces. It is roughly divided into surface and glandular epithelia.
- Connective and supporting tissue : Tissue that provides structural cohesion and fills spaces (this also includes bones , cartilage and adipose tissue ) and, in the broadest sense , produces other specialized tissues ( blood , free cells).
- Muscle tissue: cells that are specialized for active movement by contractile filaments.
- Nerve tissue : cells that make up the brain, spinal cord, and peripheral nerves.
Some authors also count tissue fluid or liquid tissue such as blood and lymph under the basic tissue types, others consider them to be a special type of tissue. Organs often consist of the actual functional tissue ( parenchyma ) and the intermediate tissue ( interstitium ).
Vegetable tissues
Basically, two types of tissue can be distinguished in plants: Formative tissue consists of embryonic cells capable of dividing (see meristem ). If the cells are no longer able to divide, it is permanent tissue .
The permanent tissues of plants can be divided into:
- Base fabric
- Parenchyma : As a rule, the cells that make up the tissue do not show any particular anatomical differentiation. Parenchymal cells are thin-walled cells of the basic tissue that make up the majority of non-woody (herbaceous) plant structures (although in some cases their cell walls can be lignified) and serve, for example, to store nutrients.
- Strengthening fabric
- Collenchyma : Consists of living cells with non-lignified, expandable cell walls.
- Sklerenchyma : Consists of mostly dead cells with secondary thickened, mostly lignified ( lignified ) cell walls.
- Finishing fabric
- Conductive tissue
histology
Marie François Xavier Bichat is considered the founder of histology , who discovered a variety of tissue types in the human body.
Examining fixed and stained tissue sections under the light microscope is the classic method of histology. Electron microscopy , fluorescence microscopy , freeze fracture techniques and advances in molecular biology have decisively influenced and advanced knowledge of the structure and function of tissues.
Legal relevance
Risk assessment
The risk of using components from animal tissues is based on the “vulnerability of the human body”. It is derived from the fact that dead tissue can also contain potentially pathogenic agents such as germs, viruses or prions , regardless of whether such pathogens are known.
drug
Medicines whose raw materials ( active ingredients or auxiliary substances ) come from animal tissue require an EDQM certificate ( European Directorate for the Quality of Medicinal Products ) or a consultation process with the competent authority about the risk-benefit assessment of the use of such a raw material.
Medical devices
With the risk classification of medical devices in the 4 risk classes I, IIa, IIb or III, it is important whether the biological material originates from dead animal tissue. This is stipulated in Directive 93/42 / EEC on medical devices and in the medical device laws of Germany and Austria.
"All products that have been manufactured using killed animal tissues or derived products are assigned to class III, unless these products are intended to come into contact only with intact skin."
In this sense, honey , wool and milk are not considered animal tissues, but for example leather , catgut or blood .
The standards " DIN EN ISO 22442-1, Animal tissues and their derivatives, which are used for the manufacture of medical devices - Part 1: Application of risk management", "DIN EN ISO 22442-2, Animal tissues and their derivatives, which are used for the manufacture of Medical devices are used - Part 2: Controls of procurement, material extraction and handling "and" DIN EN ISO 22442-3, Animal tissues and their derivatives, which are used for the manufacture of medical devices - Part 3: Validation of the elimination and / or inactivation of viruses and pathogens of transmissible cancellous encephalopathy (TSE) ”provide information on how to deal with specific risks.
literature
- M. Gremse, A. Chang et al. a .: The BRENDA Tissue Ontology (BTO): the first all-integrating ontology of all organisms for enzyme sources. In: Nucleic acids research . Volume 39, Database issue January 2011, pp. D507-D513, ISSN 1362-4962 . doi : 10.1093 / nar / gkq968 . PMID 21030441 . PMC 3013802 (free full text).
