A cell type is a classification used to identify

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

that share morphological or

phenotypical In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...

features. A

multicellular organism A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially ...

may contain cells of a number of widely differing and specialized cell types, such as

muscle cell A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a mus ...

s and

skin cell Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...

s, that differ both in appearance and function yet have identical genomic sequences. Cells may have the same

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

, but belong to different cell types due to the differential

regulation Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. Fo ...

of the

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ...

s they contain.

Classification Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood. Classification is the grouping of related facts into classes. It may also refer to: Business, organizat ...

of a specific cell type is often done through the use of

microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of mic ...

(such as those from the

cluster of differentiation The cluster of differentiation (also known as cluster of designation or classification determinant and often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules providing targets for immunophe ...

family that are commonly used for this purpose in

immunology Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see ther ...

). Recent developments in single cell RNA sequencing facilitated classification of cell types based on shared gene expression patterns. This has led to the discovery of many new cell types in e.g. mouse cortex,

hippocampus The hippocampus (via Latin from Greek , ' seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system ...

dorsal root ganglion A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dorsa ...

and

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

. Animals have evolved a greater diversity of cell types in a

multicellular A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni ...

body (100–150 different cell types), compared with 10–20 in plants, fungi, and protists. The exact number of cell types is, however, undefined, and the

Cell Ontology The Cell Ontology is an ontology that aims at capturing the diversity of cell types in animals. It is part of the Open Biomedical and Biological Ontologies (OBO) Foundry. The Cell Ontology identifiers and organizational structure are used to annot ...

, as of 2021, lists over 2,300 different cell types.

Multicellular organisms

All higher

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

s contain cells specialised for different functions. Most distinct cell types arise from a single

totipotent Pluripotency: These are the cells that can generate into any of the three Germ layers which imply Endodermal, Mesodermal, and Ectodermal cells except tissues like the placenta. According to Latin terms, Pluripotentia means the ability for many thin ...

cell that differentiates into hundreds of different cell types during the course of development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

s during

division Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplication *Division algorithm, a method for computing the result of mathematical division Military *Division (military), a formation typically consisting ...

Multicellular organisms A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially un ...

are composed of cells that fall into two fundamental types:

germ cell Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during embr ...

s and

somatic cell A somatic cell (from Ancient Greek σῶμα ''sôma'', meaning "body"), or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. Such cells comp ...

s. During development, somatic cells will become more specialized and form the three primary

germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three pr ...

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from th ...

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical Embr ...

, and

endoderm Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastru ...

. After formation of the three

s, cells will continue to specialize until they reach a terminally differentiated state that is much more resistant to changes in cell type than its progenitors.

Conceptual definition

Even though the concept of cell type is widely used, specialists still discuss the exact definition of what constitutes a cell type.

Humans

A list of cell types in the human body may include several hundred distinct types depending on the source.

References

External links

*{{Commons category-inline, Cell types Developmental biology

Multicellular organisms

Conceptual definition

Humans

See also

References

Further reading

External links