List of distinct cell types in the adult human body

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The adult human body is estimated to contain about 30 trillion (3×10¹³) human cells, with the number varying between 20 to 40 trillion depending on factors such as sex, age, and weight. Additionally, there are approximately an equal number of bacterial cells. The exact count has not yet been empirically measured in its entirety and is based on smaller samples of empirical observation.^{[1][2][3][4][5][6]}

Human cells have been categorized into over 500 cell types based on their location and function within the body.^[2] There is usually a significant variation in these cell types depending on the specific surface proteins they possess. Approximately 1,000 cells have been assigned unique names, most of which are documented in the HubMap database.

The main cellular components of the human body by count^[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 16000 human genes.^[7] This lead to estimates that humans likely had around 100 000 genes^[8] (or regions that code for human proteins). However, actual sequencing did not start before around 1999, and it was not until 2003^[9] that the first complete draft of a human genome revealed that there was roughly 20000-25000, as most DNA does not code for any protein but rather serve other more administrative functions or leftovers from the past. 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]}

Major efforts to map all human cells

Several efforts have been made to make a list or a map of all human cells.^[10][11][12] One of the largest and most recent is the HuBMAP (Human BioMolecular Atlas Program).^[13] They managed to organize 1551 samples across 17 collections. 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 Swedish Protein Atlas.^[14]

The Human Brain Project has attempted to map the human brain,^[15][16] although much of the publicly accessible model does not have cellular resolution.

Standards and naming conventions

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 celltypes identified so far could be taken from an measured in a single donor, proving that the cells 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]}

A good few attempts have been made and is being made, for creating standards for identifying cells consistently,^[17] as well as for how to work with especially STEM cells.^[18] However there is still no standard which are used industry wide, nor any definitions which have been accepted by the wider scientific community. Often making it difficult to say weather 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]}

Complete lists of human cells known so far