Cell Types

Adrenergic neurons are nerve cells that release norepinephrine (noradrenaline) as their primary neurotransmitter. They are key components of the sympathetic nervous system, orchestrating the "fight-or-flight" response by increasing heart rate, blood pressure, and alertness. Found in brainstem nuclei like the locus coeruleus and sympathetic ganglia, they regulate arousal, attention, and stress responses. Dysfunction is linked to anxiety, depression, and hypertension.

Neurons are electrically excitable cells that transmit information through electrochemical signals across synapses. As the principal functional units of the nervous system, they integrate synaptic inputs and relay outputs via axons to other neurons, muscles, or glands. Neuronal subtypes differ widely in morphology, neurotransmitter identity, connectivity, and firing properties.

Astrocytes are star-shaped glial cells, the most abundant in the central nervous system (CNS). They are vital for homeostasis: they form part of the blood-brain barrier, regulate blood flow, control extracellular ion/neurotransmitter balance (e.g., glutamate uptake), and provide metabolic support to neurons. Through the "tripartite synapse," they modulate synaptic strength and plasticity. They also respond to injury via reactive astrogliosis, playing dual roles in scar formation and neuroprotection.

Enteric glial cells (EGCs) are the resident glia of the enteric nervous system (ENS), the "gut brain." They resemble CNS astrocytes and are integral to gastrointestinal homeostasis. EGCs support enteric neurons, regulate intestinal barrier integrity, modulate immune responses within the gut wall, and influence motility. Their dysfunction is implicated in inflammatory bowel diseases (IBD), infections, and functional GI disorders, highlighting their role beyond mere structural support.

Enteric neurons are the functional units of the enteric nervous system (ENS), a complex network embedded in the gastrointestinal wall. They autonomously control gut functions including motility, secretion, blood flow, and immune responses. Comprising sensory neurons, interneurons, and motor neurons, they use diverse neurotransmitters (ACh, serotonin, NO, etc.). This "second brain" operates independently but communicates bidirectionally with the central nervous system.

Granule cells are small, numerous excitatory neurons with a characteristic granular appearance. Key populations exist in the cerebellum (input neurons of the cortical layer), dentate gyrus of the hippocampus (forming new memories), and olfactory bulb. They typically receive multiple inputs, process information in a dense network, and project to larger principal cells (e.g., Purkinje cells, pyramidal cells), playing crucial roles in motor coordination, learning, and sensory processing.

Inhibitory neurons reduce the probability of their postsynaptic target neuron firing an action potential. They primarily release the neurotransmitters GABA (in the brain) or glycine (in the spinal cord/brainstem). They are crucial for balancing neural circuit activity, preventing runaway excitation, generating rhythmic outputs (e.g., in pacemaker circuits), and shaping the temporal and spatial precision of neural computations. Types include interneurons like basket cells and Purkinje cells.

Oligodendrocyte progenitor cells (OPCs), also called NG2-glia, are a population of glial cells found throughout the CNS. They are proliferative and maintain the capacity to differentiate into mature, myelinating oligodendrocytes. OPCs are critical for developmental myelination and remain in the adult CNS, where they contribute to remyelination after demyelinating injuries (e.g., in Multiple Sclerosis) and may have additional roles in monitoring neural circuits.

Oligodendrocytes are the myelinating glial cells of the central nervous system (CNS). Each oligodendrocyte extends multiple processes to wrap and insulate segments of several different axons with concentric layers of myelin membrane. This myelin sheath greatly increases the speed of action potential propagation (saltatory conduction). They also provide metabolic support to the axons they enwrap. Loss of oligodendrocytes or myelin disrupts nerve signaling.

Purkinje cells are large, GABAergic inhibitory neurons that form a single layer in the cerebellar cortex. They are the sole output neurons of the cerebellar cortex, projecting to the deep cerebellar nuclei. They receive massive excitatory input from parallel fibers (granule cell axons) and powerful, instructive input from a single climbing fiber. Their complex dendritic tree integrates these signals to fine-tune motor coordination, balance, and motor learning.

Schwann cells are the principal glial cells of the peripheral nervous system (PNS). Myelinating Schwann cells wrap around single axons to form the myelin sheath, enabling fast saltatory conduction. Non-myelinating Schwann cells ensheath multiple small-diameter axons. Schwann cells are crucial for supporting axon health and guiding regeneration after PNS injury, forming regeneration tubes (Bands of Büngner) that direct axonal regrowth.

Microglia are the resident macrophages and primary immune cells of the central nervous system (CNS). In their resting state, they constantly survey the parenchyma. Upon detecting injury, infection, or pathological signals, they activate, becoming phagocytic to clear debris, dead cells, and pathogens. They also play essential roles in synaptic pruning during development, modulating neuroinflammation, and can contribute to both repair and neurodegeneration in diseases.

Melanocytes are neural crest-derived cells located in the basal layer of the epidermis and in hair follicles. Their primary function is the production of melanin, a pigment that provides color to skin and hair and protects underlying cells from UV radiation damage. Melanin is synthesized in organelles called melanosomes, which are then transferred to neighboring keratinocytes via dendritic processes.

Neuronal cells (Neural cells) in species SP451. Single-cell UMAP atlas.

Olfactory Receptor Neurons (Neural cells) in species SP451. Single-cell UMAP atlas.

Sensory neurons (Neural cells) in species SP451. Single-cell UMAP atlas.

Neuronal/Neural Cells (Neural cells) in species SP451. Single-cell UMAP atlas.

Neuronal/Glial Cells (Neural cells) in species SP451. Single-cell UMAP atlas.

Olfactory sensory neurons (Neural cells) in species SP451. Single-cell UMAP atlas.

Olfactory Sensory Neurons (Neural cells) in species SP451. Single-cell UMAP atlas.

B cells are lymphocytes responsible for the humoral arm of the adaptive immune response. They develop in the bone marrow and, upon maturation, circulate in blood and lymph. When activated by antigen (often with T cell help), they proliferate and differentiate into antibody-secreting plasma cells or long-lived memory B cells. Their antibodies neutralize pathogens, opsonize them for phagocytosis, and activate the complement system.

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that act as sentinels linking innate and adaptive immunity. Immature DCs in tissues capture antigens, then mature and migrate to lymph nodes. There, they present processed antigens on MHC molecules to naive T cells, providing the critical "signal 1" and costimulatory "signal 2" required for T cell activation and differentiation, thereby initiating antigen-specific immune responses.

Kupffer cells are specialized tissue-resident macrophages located within the sinusoids of the liver. They are the largest population of fixed macrophages in the body. They phagocytose pathogens, toxins, cellular debris, and aged red blood cells from the portal blood flow. They play crucial roles in liver immunity, iron recycling, lipid metabolism, and maintaining overall hepatic homeostasis. Their activation can contribute to liver inflammation and fibrosis.

Macrophages are large, phagocytic cells of the innate immune system present in all tissues (where they have specific names like Kupffer cells, microglia). They derive from blood monocytes or local progenitors. They engulf and destroy pathogens and dead cells, secrete cytokines and chemokines to regulate inflammation, present antigens, and are key players in tissue repair, remodeling, and homeostasis. They exhibit remarkable functional plasticity (M1/M2 spectra).

Mast cells are tissue-resident granulocytes found near blood vessels and nerves, particularly in skin, lungs, and gut mucosa. They store pre-formed inflammatory mediators (histamine, tryptase, heparin) in their granules. They are central effectors in IgE-mediated allergic reactions (anaphylaxis, hay fever) and defense against parasites. Upon activation, they rapidly degranulate and also synthesize cytokines/chemokines, influencing inflammation, immunity, and even tissue remodeling.

Monocytes are circulating white blood cells (agranulocytes) that serve as precursors for macrophages and dendritic cells. Produced in the bone marrow, they patrol the bloodstream for several days before migrating into tissues in response to inflammatory signals. In tissues, they differentiate into macrophages or dendritic cells. In blood, they can phagocytose pathogens and present antigens, acting as a bridge between innate and adaptive immunity.

Natural Killer (NK) cells are cytotoxic lymphocytes of the innate immune system. They provide rapid responses to virus-infected cells and tumor cells without prior sensitization. They use a balance of activating and inhibitory receptors to detect "missing self" (loss of MHC I) or "induced self" (stress ligands). They kill targets by releasing perforin and granzymes (cytotoxic granules) and through death receptor ligands like FasL.

Natural Killer T (NKT) cells are a unique subset of T lymphocytes that bridge innate and adaptive immunity. They express an invariant T cell receptor (TCR) that recognizes lipid antigens presented by the non-classical MHC molecule CD1d. Upon activation, they rapidly produce large quantities of cytokines (e.g., IFN-γ, IL-4), influencing the activity of many other immune cells and shaping immune responses to infection, cancer, and autoimmunity.

Neutrophils are the most abundant white blood cell and the first responders to sites of bacterial or fungal infection. They are highly motile phagocytic cells that engulf and destroy pathogens using antimicrobial granules (containing myeloperoxidase, defensins) and reactive oxygen species. They form neutrophil extracellular traps (NETs) to ensnare microbes. Their short lifespan and potent effector functions make them crucial for acute inflammation.

Plasma B cells (or plasma cells) are the terminal, fully differentiated effector state of activated B lymphocytes. They are antibody factories, specializing in the massive secretion of antibodies of a single specificity. They possess extensive endoplasmic reticulum and a prominent Golgi apparatus to support high-rate protein synthesis. Most are short-lived, but some become long-lived plasma cells that reside in the bone marrow, providing sustained antibody levels.

T cells (T lymphocytes) are central players in cell-mediated adaptive immunity. They develop in the thymus and express T cell receptors (TCRs) that recognize peptide antigens presented by MHC molecules. Major subsets include: Helper T cells (CD4+, which secrete cytokines to help B cells and macrophages), Cytotoxic T cells (CD8+, which kill infected/cancerous cells), and Regulatory T cells (Tregs, which suppress immune responses to prevent autoimmunity).

T/NKT cells encompass T lymphocyte populations together with natural killer T (NKT) cells, which recognize lipid antigens presented by the non-polymorphic CD1d molecule. NKT cells bridge innate and adaptive immunity by rapidly releasing large amounts of cytokines upon activation. They are implicated in tumor surveillance, autoimmunity, and antimicrobial responses.

Club cells (formerly Clara cells) are non-ciliated secretory cells found in the bronchiolar epithelium of the lungs. They secrete surfactant proteins and components of the airway lining fluid. They possess cytochrome P450 enzymes for detoxification. Importantly, they function as progenitor cells for both themselves and ciliated cells in the bronchioles, contributing to the repair and maintenance of the distal airway epithelium.

Pancreatic islet (islets of Langerhans) cells are the endocrine cells of the pancreas, organized into clusters scattered throughout the exocrine tissue. Major types include: Alpha cells (secrete glucagon, raises blood sugar), Beta cells (secrete insulin, lowers blood sugar), Delta cells (secrete somatostatin, inhibits other islet cells), and PP cells (secrete pancreatic polypeptide). They precisely regulate glucose homeostasis.

T cells and Natural killer cells (Immune cells) in species SP451. Single-cell UMAP atlas.

B cells/Plasma B cells (Immune cells) in species SP451. Single-cell UMAP atlas.

Immune cells (Immune cells) in species SP451. Single-cell UMAP atlas.

Acinar cells are the exocrine secretory cells of glands like the salivary glands and pancreas. In the pancreas, they are organized into acini and synthesize, store, and secrete digestive pro-enzymes (zymogens) into a ductal network. They have a highly developed rough ER and abundant secretory (zymogen) granules. When stimulated (e.g., by cholecystokinin), they release their contents into the pancreatic duct, which empties into the duodenum.

Alveolar type 1 (AT1) cells are thin, squamous epithelial cells that cover approximately 95% of the gas exchange surface in the lung alveoli. Their extremely flattened morphology (extending over large areas) is ideal for the passive diffusion of oxygen and carbon dioxide between the airspace and the underlying pulmonary capillaries. They are terminally differentiated and crucial for maintaining the delicate blood-air barrier.

Alveolar type 2 (AT2) cells are cuboidal epithelial cells found in the alveolar corners. They have three critical functions: (1) They synthesize and secrete pulmonary surfactant, a phospholipid-protein mixture that reduces surface tension and prevents alveolar collapse. (2) They serve as progenitor cells for both AT1 and AT2 cells, repairing the alveolar epithelium after injury. (3) They contribute to innate immune defense in the alveoli.

Cells of the thick ascending limb (TAL) of the loop of Henle in the kidney nephron. They are impermeable to water but actively reabsorb sodium, potassium, and chloride via the Na-K-2Cl cotransporter (NKCC2) on their apical membrane. This transport is critical for generating the hypertonic medullary interstitium necessary for water reabsorption in the collecting duct. They also contribute to magnesium and calcium reabsorption.

Basal cells are a layer of mitotically active epithelial progenitor/stem cells found attached to the basement membrane in stratified and pseudostratified epithelia (e.g., skin, airways, prostate). They divide to give rise to cells that differentiate and move upward to replenish the superficial layers. In the airway, they are major stem cells capable of regenerating both ciliated and secretory cells after injury.

Cholangiocytes are the epithelial cells that line the intrahepatic and extrahepatic bile ducts. They modify the composition of bile (through secretion and absorption of water, ions, and bicarbonate), form a protective barrier, and respond to hormonal signals. They express receptors and channels (e.g., CFTR) critical for bile flow. Their proliferation and dysfunction are central to cholangiopathies like primary sclerosing cholangitis (PSC).

Ciliated cells are epithelial cells characterized by the presence of motile cilia (hair-like projections) on their apical surface. They are found in the respiratory tract, oviducts, and ventricles of the brain (ependymal cells). Coordinated, rhythmic beating of cilia moves fluid or mucus over the epithelial surface. In the airways, this "mucociliary escalator" traps and propels inhaled particles and pathogens out of the lungs, a key defense mechanism.

Enterocytes are the principal absorptive columnar epithelial cells lining the small intestine villi. Their apical surface is covered with microvilli, forming a "brush border" that dramatically increases surface area for nutrient absorption. They digest and absorb carbohydrates, peptides, amino acids, and lipids. They also secrete water and ions and form a crucial barrier between the gut lumen and the internal environment.

These are the columnar epithelial cells lining the epididymis, a coiled tube where sperm mature and are stored. They create a unique luminal microenvironment by secreting and absorbing fluids, ions, and proteins. They are involved in sperm concentration, protection, and acquisition of motility and fertilizing capacity. The epithelium includes principal cells (for absorption/secretion) and basal cells (stem/progenitor cells).

Glandular cells are specialized epithelial cells that constitute the secretory units of exocrine and endocrine glands. They synthesize and release specific products. Exocrine glandular cells (e.g., in salivary, sweat glands) secrete via ducts. Endocrine glandular cells (e.g., in thyroid, pituitary) secrete hormones directly into the bloodstream. Their morphology is adapted for secretion, with abundant rough ER and secretory granules.

Hepatocytes are the principal parenchymal cells of the liver, making up about 80% of its mass. They are metabolic powerhouses with functions including: protein synthesis (albumin, clotting factors), bile production, detoxification and metabolism of drugs/toxins, glycogen storage and glucose homeostasis, lipid metabolism, and cholesterol synthesis. They are arranged in plates radiating from central veins, with polarized faces facing sinusoids and bile canaliculi.

Keratinocytes are the predominant cell type in the epidermis (the outermost skin layer). They originate from basal layer stem cells and undergo a process of terminal differentiation as they move outward, producing keratin intermediate filaments. In the stratum corneum, they become anucleate corneocytes, forming a tough, waterproof barrier that protects against mechanical injury, water loss, and microbial invasion.

Lactotropes (or mammotropes) are endocrine cells in the anterior pituitary gland that produce and secrete prolactin (PRL). Prolactin's primary role is to stimulate milk production (lactation) in the mammary glands after childbirth. Its secretion is primarily under inhibitory control by dopamine from the hypothalamus. Lactotropes can increase in number during pregnancy and lactation.

These are the epithelial cells that directly face the lumen (hollow cavity) of a duct or gland. In tissues like the mammary gland or prostate, they form the inner secretory layer and are often hormonally responsive. They are typically more differentiated than basal cells and carry out the tissue-specific secretory functions (e.g., producing milk proteins or prostatic fluid).

Pancreatic ductal cells form the lining of the ductal network that transports digestive enzymes from the acini and bicarbonate-rich fluid from the centroacinar cells to the duodenum. They modify the pancreatic juice by secreting bicarbonate ions (HCO3-) to neutralize gastric acid. They express CFTR, and mutations here cause cystic fibrosis-related pancreatic disease. They can also act as progenitor cells in certain contexts.

Podocytes are highly specialized epithelial cells in the Bowman's capsule of the kidney glomerulus. They wrap around capillaries with primary and secondary foot processes. The slits between these foot processes, covered by the slit diaphragm, form the final filtration barrier preventing proteins from entering the urine. Podocyte injury or loss leads to proteinuria and glomerular diseases like focal segmental glomerulosclerosis (FSGS).

In the kidney's collecting duct, principal cells are the most abundant cell type. They are responsible for the final regulation of water, sodium, and potassium balance. They express aquaporin-2 channels on their apical membrane (inserted in response to vasopressin/ADH) for water reabsorption. They also reabsorb sodium via ENaC channels and secrete potassium, processes regulated by aldosterone.

These cells line the proximal convoluted tubule (PCT) of the nephron, the first and longest segment. They are responsible for the bulk reabsorption of filtered nutrients (glucose, amino acids), ions (sodium, chloride, bicarbonate), and water (~65%). Their apical surface has a dense brush border of microvilli to increase surface area. They also actively secrete organic acids and bases into the filtrate.

Somatotropes are endocrine cells in the anterior pituitary gland that produce and secrete growth hormone (GH or somatotropin). GH secretion is stimulated by growth hormone-releasing hormone (GHRH) and inhibited by somatostatin from the hypothalamus. GH promotes growth in children by stimulating liver production of insulin-like growth factor 1 (IGF-1) and has metabolic effects in adults (e.g., lipolysis).

This term often refers to cells bearing stereocilia, which are long, non-motile microvillus-like projections that increase surface area. True stereocilia are found on sensory hair cells in the inner ear for mechanotransduction. Cells in the epididymis and ductus deferens also have long, immotile structures called stereocilia (though structurally more like giant microvilli) involved in absorption and secretion.

Peritubular myoid cells are smooth muscle-like cells that surround the seminiferous tubules in the testes. They contract rhythmically to help move sperm and testicular fluid through the tubules. They also secrete extracellular matrix components and growth factors, providing structural support and contributing to the microenvironment necessary for spermatogenesis within the tubules.

Sertoli cells are the "nurse" or sustentacular cells within the seminiferous tubules of the testes. They create the blood-testis barrier, provide structural and nutritional support to developing sperm cells (spermatogenesis), phagocytose residual bodies, and secrete fluid, androgen-binding protein (ABP), and hormones like inhibin and anti-Müllerian hormone (AMH). They are essential for male fertility.

Fibroblasts are the most common cells of connective tissue. They synthesize and secrete the extracellular matrix (ECM) components, including collagen, elastin, and fibronectin, providing structural and biochemical support to surrounding cells. They are key players in wound healing, where they proliferate, migrate to the injury site, and differentiate into contractile myofibroblasts to close wounds. They also communicate with immune and epithelial cells.

Pericytes are contractile mesenchymal cells that wrap around the endothelial cells of capillaries and venules. They are embedded in the basement membrane and are crucial for vascular stability, regulating blood flow, promoting endothelial survival, and participating in the formation and maintenance of the blood-brain barrier. They also have stem cell properties and can differentiate into other mesenchymal cells during tissue repair.

In the liver, hepatic stellate cells (HSCs) reside in the space of Disse. In their quiescent state, they store vitamin A. Upon liver injury, they activate, proliferate, and transform into myofibroblast-like cells that produce large amounts of extracellular matrix, driving liver fibrosis and cirrhosis. Pancreatic stellate cells play a similar fibrogenic role in pancreatitis and pancreatic cancer.

Stromal cells in human. 101,901 cells across 16 tissues.

Satellite cells are the resident stem cells of skeletal muscle, located between the basal lamina and the sarcolemma of muscle fibers. They are normally quiescent but activate, proliferate, and differentiate into myoblasts in response to injury or exercise. They fuse with existing fibers or with each other to form new myofibers, enabling muscle growth and repair.

Skeletal myonuclei are the multiple nuclei contained within a single, multinucleated skeletal muscle fiber (myofiber). They are post-mitotic and are responsible for gene expression to maintain the massive cytoplasmic volume of the myofiber. They are evenly distributed, but in some muscle types, they may be clustered near the neuromuscular junction or myotendinous junction.

Smooth muscle cells (SMCs) are involuntary, non-striated muscle cells found in the walls of hollow organs (e.g., blood vessels, gut, bladder, uterus). They are spindle-shaped with a single central nucleus. They contract slowly and can maintain tension for long periods (tonus). Contraction is regulated by the autonomic nervous system, hormones, and local factors (e.g., nitric oxide, endothelin).

Endothelial cells form a single layer (the endothelium) lining the interior surface of all blood and lymphatic vessels. They are more than a passive barrier; they actively regulate vascular tone, blood clotting (hemostasis), inflammation, immune cell trafficking, and angiogenesis. They produce key molecules like nitric oxide (vasodilation), endothelin-1 (vasoconstriction), and von Willebrand factor. Dysfunction is central to cardiovascular diseases.

Spermatogonia are the undifferentiated germ stem cells located on the basement membrane of the seminiferous tubules. They undergo mitotic divisions to self-renew and produce a population of cells committed to differentiation (primary spermatocytes). Type A spermatogonia are the stem cell reservoir, while Type B spermatogonia are committed progenitors. They are the foundation of lifelong sperm production.

Germ cells (Germ cells) in species SP451. Single-cell UMAP atlas.

Proliferating cells (Other) in species SP451. Single-cell UMAP atlas.

Ribosomal protein-enriched cells in human. 2,198 cells across 1 tissues.

Unknown/Non-specific cell type (Other) in species SP451. Single-cell UMAP atlas.