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The list of human cell types provides an enumeration and description of the various specialized cells found within the human body, highlighting their distinct functions, characteristics, and contributions to overall physiological processes. Cells may be classified [1] by their physiological function, histology (microscopic anatomy), [2] lineage, or gene expression.
The adult human body is estimated to contain about 30 trillion (3×1013) human cells, with the number varying between 20 and 100 trillion depending on factors such as sex, age, and weight. Additionally, there are approximately an equal number of bacterial cells. The exact count of human cells has not yet been empirically measured in its entirety and is estimated using different approaches based on smaller samples of empirical observation. [3] [4] [5] [6] [7] [8] [9] It is generally assumed that these cells share features with each other and thus may be organized as belonging to a smaller number of types. [10] [11]
As a definition of "cell type" is yet to be agreed, it is not possible yet to arrive at a precise number of human cell types. [12] There is, for example, significant variation in these cell types depending on the specific surface proteins they possess.
An extensive listing of human cell types was published by Vickaryous and Hall in 2006, collecting 411 different types of human cells (with 145 types of neuron among those). [11]
The Human Cell Atlas project, which started in 2016, had as one of its goals to "catalog all cell types (for example, immune cells or brain cells) and sub-types in the human body". [13] By 2018, the Human Cell Atlas description based the project on the assumption that "our characterization of the hundreds of types and subtypes of cells in the human body is limited", but the word hundreds was removed in later versions. [14] [13]
On 2021, Stephen Quake guessed that the upper limit of the number of human cell types would be around 6000, based on a reasoning that "if biologists had discovered only 5% of cell types in the human body, then the upper limit of cell types to discover is somewhere around 6000 (i.e., 300/0.05)." [10]
Other different efforts have used different numbers. A count of cells in the human body published in 2023 divided the cells in about 400 types to perform the calculation. [4]
 | Cell type | % cell count |
| Erythrocytes (red blood cells) | 84.0 | |
| Platelets | 4.9 | |
| Bone marrow cells | 2.5 | |
| Vascular endothelial cells | 2.1 | |
| Lymphocytes | 1.5 | |
| Hepatocytes | 0.8 | |
| Neurons and glia | 0.6 | |
| Bronchial endothelial cells | 0.5 | |
| Epidermal cells | 0.5 | |
| Respiratory interstitial cells | 0.5 | |
| Adipocytes (fat cells) | 0.2 | |
| Dermal fibroblasts | 0.1 | |
| Muscle cells | 0.001 | |
| Other cells | 2.0 |
In 1996, scientists revealed a 'map' of 16,000 human genes. [15] This led to estimates that humans likely had around 100 000 genes [16] (or regions that code for human proteins). However, actual sequencing did not start before around 1999, and it was not until 2003 [17] that the first complete draft of a human genome revealed that there was roughly 20000-25000 protein-coding genes, as most DNA does not code for any protein. It is difficult to say that there have not been similar mistakes when estimating how many cells humans have as there are still substantial gaps in understanding human cells.[ citation needed ]
Several efforts have been made to make a list or a map of all human cells. [18] [19] [20] One of the largest and most recent is the HuBMAP (Human BioMolecular Atlas Program). [21]
The HuBMAP project has organized 1551 different samples in 17 collections, each dedicated to a different system. However, this project still only mapped about 31 of the human bodies' 70 organs. Their datasets and visualisations place great emphasis on biomarkers and location in the body, but less on cell development and how cells can change over time. Usually specific surface proteins are used to identify cells, and based on this they are put into different categories.
Another major effort to make an overview of these proteins that allows us to observe cell types is the Human Protein Atlas. [22]
A similar project, the Human Brain Project has also attempted to map the human brain, although much of the publicly accessible model does not have cellular resolution. [23] [24]
So far not all cells which can be found in the human body have been documented. There is no good way to make the experiment where one checks if all cell types identified so far could be taken from and measured in a single donor, proving that the cell types are universal to all humans. This is partly due to a lack of standards, as scientists are still not entirely sure what is needed to measure, in order to capture every cell type which can be found.[ citation needed ]
Some attempts have been made – and some are still in progress– for creating standards for identifying cells consistently. [25] [26] [27] The Cell Ontology provides arguably the most comprehensive metadata standard to date, cataloging over 2500 cell classes and being used actively by the Human Cell Atlas community. [28]
There is still no standard which is used industry wide, nor any definitions which have been accepted by the wider scientific community. Often making it difficult to say whether some collected and observed cells are really one or multiple types of cells. This lack of standards makes it difficult to estimate how many cell types and how many of each cell types can be found in the human body, as well as difficult to predict which young cells one would need to develop with mature cells. The list on this Wikipedia article also suffers to some inconsistencies due to multiple sources using different conventions.[ citation needed ]
 | This section needs expansion. You can help by adding to it. (April 2024) |
| Name | Provider | Sources of revenue/sponsors | Scope | Amount of cells identified so far |
|---|---|---|---|---|
| HubMap [30] | A series of US based universities | Unknown | ~1200 | |
| Human Cell Atlas | Columbia University Medical Center at Columbia University | Chan Zuckerberg Initiative | 37 trillion cells | |
| CellXgene [31] | Chan Zuckerberg Initiative [32] |
The endodermal cells primarily generate the lining and glands of the digestive tube. [33]
There are nerve cells, also known as neurons, present in the human body. They are branched out. These cells make up nervous tissue. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. [ citation needed ]
A neuron, neurone, or nerve cell is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. They are located in the brain and spinal cord and help to receive and conduct impulses. Neurons communicate with other cells via synapses, which are specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.
Neuroscience is the scientific study of the nervous system, its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, developmental biology, cytology, psychology, physics, computer science, chemistry, medicine, statistics, and mathematical modeling to understand the fundamental and emergent properties of neurons, glia and neural circuits. The understanding of the biological basis of learning, memory, behavior, perception, and consciousness has been described by Eric Kandel as the "epic challenge" of the biological sciences.
Computational biology refers to the use of techniques in computer science, data analysis, mathematical modeling and computational simulations to understand biological systems and relationships. An intersection of computer science, biology, and data science, the field also has foundations in applied mathematics, molecular biology, cell biology, chemistry, and genetics.
A cell type is a classification used to identify cells that share morphological or phenotypical features. A multicellular organism may contain cells of a number of widely differing and specialized cell types, such as muscle cells and skin cells, that differ both in appearance and function yet have identical genomic sequences. Cells may have the same genotype, but belong to different cell types due to the differential regulation of the genes they contain. Classification of a specific cell type is often done through the use of microscopy. 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, dorsal root ganglion and spinal cord.
L1, also known as L1CAM, is a transmembrane protein member of the L1 protein family, encoded by the L1CAM gene. This protein, of 200 to 220 kDa, is a neuronal cell adhesion molecule with a strong implication in cell migration, adhesion, neurite outgrowth, myelination and neuronal differentiation. It also plays a key role in treatment-resistant cancers due to its function. It was first identified in 1984 by M. Schachner who found the protein in post-mitotic mice neurons.
The Rat Genome Database (RGD) is a database of rat genomics, genetics, physiology and functional data, as well as data for comparative genomics between rat, human and mouse. RGD is responsible for attaching biological information to the rat genome via structured vocabulary, or ontology, annotations assigned to genes and quantitative trait loci (QTL), and for consolidating rat strain data and making it available to the research community. They are also developing a suite of tools for mining and analyzing genomic, physiologic and functional data for the rat, and comparative data for rat, mouse, human, and five other species.
A neurodegenerative disease is caused by the progressive loss of neurons, in the process known as neurodegeneration. Neuronal damage may also ultimately result in their death. Neurodegenerative diseases include amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, multiple system atrophy, tauopathies, and prion diseases. Neurodegeneration can be found in the brain at many different levels of neuronal circuitry, ranging from molecular to systemic. Because there is no known way to reverse the progressive degeneration of neurons, these diseases are considered to be incurable; however research has shown that the two major contributing factors to neurodegeneration are oxidative stress and inflammation. Biomedical research has revealed many similarities between these diseases at the subcellular level, including atypical protein assemblies and induced cell death. These similarities suggest that therapeutic advances against one neurodegenerative disease might ameliorate other diseases as well.
Glucose transporter 3, also known as solute carrier family 2, facilitated glucose transporter member 3 (SLC2A3) is a protein that in humans is encoded by the SLC2A3 gene. GLUT3 facilitates the transport of glucose across the plasma membranes of mammalian cells. GLUT3 is most known for its specific expression in neurons and has originally been designated as the neuronal GLUT. GLUT3 has been studied in other cell types with specific glucose requirements, including sperm, preimplantation embryos, circulating white blood cells and carcinoma cell lines.
Neuronal migration protein doublecortin, also known as doublin or lissencephalin-X is a protein that in humans is encoded by the DCX gene.
Neuron navigator 2 is a protein that in humans is encoded by the NAV2 gene. The vitamin A metabolite, all-trans retinoic acid (atRA), plays an important role in neuronal development, including neurite outgrowth. NAV2 is an atRA-responsive gene.
Brevican core protein is a protein that in humans is encoded by the BCAN gene. Brevican is a member of the lectican protein family.
Brain mitochondrial carrier protein 1 is a protein that in humans is encoded by the SLC25A14 gene.
Transgelin-3 or neuron protein NP25 is a protein that is in the nerve cells of humans, rats, mice, and chickens. It is encoded by the TAGLN3 gene.
Cholinergic receptor, nicotinic, alpha 6, also known as nAChRα6, is a protein that in humans is encoded by the CHRNA6 gene. The CHRNA6 gene codes for the α6 nicotinic receptor subunit that is found in certain types of nicotinic acetylcholine receptors found primarily in the brain. Neural nicotinic acetylcholine receptors containing α6 subunits are expressed on dopamine-releasing neurons in the midbrain, and dopamine release following activation of these neurons is thought to be involved in the addictive properties of nicotine. Due to their selective localisation on dopaminergic neurons, α6-containing nACh receptors have also been suggested as a possible therapeutic target for the treatment of Parkinson's disease. In addition to nicotine, research in animals has implicated alpha-6-containing nAChRs in the abusive and addictive properties of ethanol, with mecamylamine demonstrating a potent ability to block these properties.
Neurogenetics studies the role of genetics in the development and function of the nervous system. It considers neural characteristics as phenotypes, and is mainly based on the observation that the nervous systems of individuals, even of those belonging to the same species, may not be identical. As the name implies, it draws aspects from both the studies of neuroscience and genetics, focusing in particular how the genetic code an organism carries affects its expressed traits. Mutations in this genetic sequence can have a wide range of effects on the quality of life of the individual. Neurological diseases, behavior and personality are all studied in the context of neurogenetics. The field of neurogenetics emerged in the mid to late 20th century with advances closely following advancements made in available technology. Currently, neurogenetics is the center of much research utilizing cutting edge techniques.
The sense of smell, or olfaction, is the special sense through which smells are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.
The Human Protein Atlas (HPA) is a Swedish-based program started in 2003 with the aim to map all the human proteins in cells, tissues and organs using integration of various omics technologies, including antibody-based imaging, mass spectrometry-based proteomics, transcriptomics and systems biology. All the data in the knowledge resource is open access to allow scientists both in academia and industry to freely access the data for exploration of the human proteome. In June 2023, version 23 was launched where a new Interaction section was introduced containing human protein-protein interaction networks for more than 11,000 genes that will add new aspects in terms of protein function.
The mouse brain refers to the brain of Mus musculus. Various brain atlases exist.
Netrin-5 (NTN5), also known as netrin-1-like protein, is a protein that in humans is encoded by the NTN5 gene. Netrin-5 is included in the family of secreted laminin-related proteins.
The Human Biomolecular Atlas Program (HuBMAP) is a program funded by the US National Institutes of Health to characterize the human body at single cell resolution, integrated to other efforts such as the Human Cell Atlas. Among the products of the program is the Azimuth reference datasets for single-cell RNA seq data and the ASCT+B Reporter, a visualization tool for anatomical structures, cell types and biomarkers.
