Cell Types

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.

Bipolar cells are retinal neurons that relay visual information directly from photoreceptors (rods and cones) to ganglion cells. They have a characteristic morphology with one dendrite connecting to photoreceptors and one axon synapsing in the inner plexiform layer. They are functionally divided into ON and OFF types, responding to light increments and decrements, respectively. This segregation initiates the parallel pathways essential for contrast perception and visual processing.

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.

Excitatory neurons are nerve cells that, when activated, increase the likelihood of their target neuron firing an action potential. They primarily release the neurotransmitter glutamate at their synapses. They form the primary driving force in neural circuits throughout the brain (e.g., cortical pyramidal neurons) and are fundamental for information propagation, synaptic plasticity (like LTP), and processes such as learning, memory, and cognition.

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.

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.

Enteric glial cells in human. 1,233 cells across 2 tissues.

Muller cells are specialized radial glial cells that span the entire thickness of the retina, from the inner to the outer limiting membrane. They are the principal support cells of the retina, maintaining its structural integrity and homeostasis. They regulate extracellular ion and water balance, recycle neurotransmitters (especially glutamate), store glycogen for energy, and guide light to photoreceptors. Their dysfunction is involved in many retinal diseases.

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.

Rod cells are photoreceptors specialized for low-light (scotopic) vision. They are extremely light-sensitive, containing the pigment rhodopsin, and are responsible for night vision and peripheral vision. Rods do not mediate color perception, providing monochromatic (black-and-white) vision. Their signals converge heavily onto bipolar cells, maximizing sensitivity at the expense of fine detail. They are more numerous than cones and are absent from the central fovea.

Schwann cells in human. 10,349 cells across 6 tissues.

Cycling B cells refer to B lymphocytes that are actively proliferating, progressing through the cell cycle (G1, S, G2, M phases). This occurs during immune activation following antigen encounter and T cell help, leading to clonal expansion within germinal centers of lymph nodes or in extrafollicular sites. This proliferation is essential to generate a large population of antigen-specific B cell clones for antibody production and memory formation.

Cycling T cells are T lymphocytes undergoing active cell division. This is a hallmark of T cell activation following antigen recognition via the TCR and costimulation. Massive clonal expansion occurs, transforming a few naive antigen-specific T cells into thousands of effector T cells to combat infection. It is a fundamental step in mounting an effective adaptive immune response and generating long-lived memory T cells.

Hematopoietic stem and progenitor cells (HSPCs) reside in the bone marrow and are responsible for lifelong blood cell production (hematopoiesis). Hematopoietic stem cells (HSCs) have long-term self-renewal and multipotent differentiation capacity. Progenitor cells (like CMPs, CLPs) are more restricted in potential but highly proliferative. Together, they give rise to all lineages of blood and immune cells.

Megakaryocyte erythrocyte progenitors (MEPs) are bipotent hematopoietic progenitor cells derived from the Common Myeloid Progenitor (CMP). MEPs are committed to producing two critical blood cell types: megakaryocytes (which fragment into platelets for clotting) and erythrocytes (red blood cells for oxygen transport). The MEP stage represents the final branch point before lineage-specific commitment to platelet or red cell production.

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.

Basophils in human. 1,735 cells across 3 tissues.

Common myeloid progenitors (CMPs) are bone marrow progenitors committed to the myeloid lineage. They are derived from hematopoietic stem cells and can generate all myeloid blood cells: erythrocytes (red blood cells), megakaryocytes (platelets), mast cells, and the granulocyte-monocyte lineage (neutrophils, eosinophils, basophils, monocytes, macrophages, and some dendritic cells). The CMP is a key intermediate in myeloid cell production.

Dendritic cells in human. 4,097 cells across 8 tissues.

Erythroid cells in human. 15,325 cells across 13 tissues.

Granulocytes are a category of white blood cells characterized by prominent cytoplasmic granules and a multi-lobed nucleus. The three main types are neutrophils (phagocytic first responders to bacterial/fungal infection), eosinophils (combat parasites and modulate allergic responses), and basophils (mediate allergic reactions). They are key components of the innate immune system, providing rapid defense through phagocytosis, degranulation, and cytokine release.

Kupffer cells in human. 2,547 cells across 1 tissues.

Macrophages in human. 71,193 cells across 24 tissues.

Mast cells in human. 5,568 cells across 16 tissues.

Monocytes in human. 49,964 cells across 13 tissues.

Natural killer cells in human. 13,552 cells across 9 tissues.

Natural killer T cells in human. 3,861 cells across 4 tissues.

Neutrophils in human. 53,763 cells across 14 tissues.

Plasma B cells in human. 26,014 cells across 20 tissues.

Platelets (thrombocytes) are small, anucleate cell fragments derived from megakaryocytes in the bone marrow. They circulate in blood and are essential for hemostasis: upon vascular injury, they adhere, activate, aggregate to form a plug, and provide a surface for coagulation factors. They also secrete growth factors and cytokines, playing roles in inflammation, immunity, and tissue repair.

T cells in human. 87,030 cells across 21 tissues.

Thymocytes in human. 10,038 cells across 1 tissues.

The choroid plexus is a specialized structure in the brain's ventricles composed of a network of capillaries surrounded by a monolayer of modified epithelial cells (choroid plexus epithelial cells). Its primary function is to produce cerebrospinal fluid (CSF) by filtering blood plasma and actively secreting ions and water. It also forms the blood-CSF barrier and secretes growth factors and signaling molecules into the CSF.

Connecting tubule (CNT) cells are specialized cells in the nephron that link the distal convoluted tubule to the collecting duct. They play a significant role in fine-tuning sodium, potassium, and acid-base balance. They are sensitive to aldosterone and reabsorb sodium while secreting potassium and protons. They express the calcium channel TRPV5 and are important for the final regulation of calcium reabsorption.

Cycling gastric epithelial cell (Epithelial cells) in species SP024. Single-cell UMAP atlas.

Ependymal cells are ciliated epithelial-like glial cells that line the ventricles of the brain and the central canal of the spinal cord. Their coordinated ciliary beating helps circulate cerebrospinal fluid (CSF). They contribute to the blood-CSF barrier, secrete factors into the CSF, and in certain niches (like the lateral ventricles), some can act as neural stem cells (radial glia-like cells).

In the thyroid gland, follicular cells (thyrocytes) are the principal epithelial cells that form spherical follicles. They synthesize thyroglobulin and, upon stimulation by TSH, take up iodine to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are stored in the colloid-filled follicle lumen and released into the blood to regulate metabolism, growth, and development.

This describes epithelial cells that exhibit molecular signatures of progenitor or stem cells but are not the most primitive stem cell. They are often in an intermediate state, possessing the capacity to proliferate and give rise to differentiated cells, but may have some lineage restriction. They are crucial for steady-state tissue maintenance and repair after injury.

Taste cells are specialized sensory epithelial cells grouped into taste buds on the tongue and palate. They are not neurons but are chemosensory receptors that synapse with afferent nerve fibers. Different types detect sweet, salty, sour, bitter, and umami (savory) stimuli. When activated, they depolarize and release neurotransmitters to stimulate gustatory nerves, sending signals to the brain.

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 cells in human. 1,894 cells across 1 tissues.

Alveolar type 2 cells in human. 6,020 cells across 1 tissues.

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 in human. 21,697 cells across 6 tissues.

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.

Club cells in human. 1,975 cells across 1 tissues.

Cycling epithelial cells in human. 16,895 cells across 1 tissues.

Enterocytes in human. 9,066 cells across 2 tissues.

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.

Goblet cells in human. 1,734 cells across 2 tissues.

Hepatocytes in human. 2,715 cells across 1 tissues.

Intercalated cells are specialized cells found in the collecting ducts of the kidney nephron. They are critical for regulating systemic acid-base balance. There are two main types: Type A (alpha) cells secrete protons (H+) via H+-ATPase pumps and reabsorb bicarbonate, correcting acidosis. Type B (beta) cells secrete bicarbonate and reabsorb protons, correcting alkalosis. They also play a role in potassium balance.

Keratinocytes in human. 7,295 cells across 2 tissues.

Luminal epithelial cells in human. 21,145 cells across 3 tissues.

Medullary thymic epithelial cells (mTECs) are a specialized stromal cell population in the thymus medulla. They play a crucial role in central tolerance by expressing a wide array of tissue-specific antigens (promiscuous gene expression) under the control of the AIRE transcription factor. They present these self-antigens to developing thymocytes, enabling the deletion of self-reactive T cells (negative selection) to prevent autoimmunity.

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.

Mesothelial cells form a monolayer (the mesothelium) that lines the body's serous cavities (pleural, pericardial, peritoneal) and covers the outer surface of internal organs. They produce a lubricating serous fluid that allows organs to move smoothly. They also provide a protective barrier, participate in immune surveillance and inflammation, and can undergo transition to a fibroblast-like phenotype (mesothelial-to-mesenchymal transition) in pathology.

Mucous cells in human. 2,026 cells across 1 tissues.

Pancreas ductal cells in human. 1,280 cells across 1 tissues.

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.

Parietal cells (or oxyntic cells) are found in the gastric glands of the stomach lining. They secrete hydrochloric acid (HCl) into the stomach lumen, creating the highly acidic environment necessary for protein digestion and killing ingested microbes. They also secrete intrinsic factor, a glycoprotein essential for vitamin B12 absorption in the ileum. They have a distinctive intracellular canaliculus system for acid secretion.

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).

Principal cells in human. 1,571 cells across 1 tissues.

Proximal tubule cells in human. 6,414 cells across 1 tissues.

Retinal pigmentary epithelial cells in human. 2,496 cells across 1 tissues.

Serous cells in human. 7,067 cells across 1 tissues.

Squamous cells are thin, flat, scale-like epithelial cells. Simple squamous epithelium (e.g., endothelium, alveolar lining) facilitates diffusion and filtration. Stratified squamous epithelium (e.g., skin epidermis, oral mucosa, esophagus) provides protection against abrasion and pathogens. The outermost cells may be keratinized (skin) or non-keratinized (esophagus). Their shape minimizes friction and allows for easy sloughing and replacement.

These are non-sensory epithelial cells in the vestibular sensory patches (e.g., maculae of utricle/saccule, cristae of semicircular canals) of the inner ear. They surround and provide structural and metabolic support to the hair cells. They help maintain the ionic composition of the endolymph and may participate in repair processes, though their regenerative capacity in mammals is limited.

This is a general term for the epithelial cells that form the outermost layer of a tissue, directly facing a lumen or the external environment. Their specific function depends on location (e.g., protection in skin, absorption in intestine, secretion in stomach). They are the first line of interaction with the external world and are often specialized accordingly.

Urothelial cells in human. 13,117 cells across 1 tissues.

Vestibular dark cells are specialized ion-transporting epithelial cells located in the vestibular apparatus of the inner ear, near the sensory epithelia. They are responsible for secreting potassium ions (K+) into the endolymph, thereby generating and maintaining the unique high-potassium, low-sodium composition of this fluid, which is essential for the proper function of vestibular hair cells in detecting balance and head movement.

Adipocyte progenitor cells (APCs), also known as preadipocytes, are mesenchymal stem cells committed to the adipocyte lineage. They reside in adipose tissue depots and have the capacity to proliferate and differentiate into mature lipid-filled adipocytes. They play key roles in adipose tissue expansion, both in normal growth and in obesity. They also secrete various factors (adipokines) and contribute to tissue remodeling.

Chondrocytes found in fibrocartilage, a tough tissue in intervertebral discs, menisci, and tendon-bone junctions. These cells produce an extracellular matrix rich in type I collagen (in addition to type II) and proteoglycans, giving the tissue great tensile strength and resistance to compression and shear forces. Their phenotype is distinct from that of hyaline cartilage chondrocytes.

Stromal cells are a heterogeneous group of connective tissue cells that provide structural support and create the microenvironment ("stroma") for parenchymal cells within an organ. They include fibroblasts, adipocytes, pericytes, and various types of mesenchymal stem/stromal cells. They produce ECM, secrete growth factors and cytokines, and play critical roles in tissue architecture, homeostasis, repair, and disease progression (e.g., in cancer).

A chondrocyte state that may precede full-blown inflammatory activation. These cells might be experiencing early stress signals (biomechanical, metabolic) that prime them to respond more aggressively to subsequent inflammatory triggers, or they may be initiating a low-level catabolic program before progressing to a clear "inflammatory" phenotype.

A proposed state where chondrocytes may act to suppress inflammation or catabolism within the cartilage, perhaps by secreting anti-inflammatory cytokines (e.g., IL-4, IL-10, IL-1Ra) or tissue inhibitors of metalloproteinases (TIMPs). This concept is less defined but highlights the potential functional heterogeneity among chondrocytes in maintaining tissue homeostasis.

Chondrocytes attempting to repair damaged cartilage matrix. They may increase anabolic activity, upregulating synthesis of collagen and proteoglycans in response to injury or mild degradation signals. However, in adult articular cartilage, this reparative capacity is very limited and often insufficient to counteract the catabolic processes in degenerative joint disease.

Adipocytes (fat cells) are the primary cells of adipose tissue, specialized in storing energy as triglycerides within a large, single lipid droplet (white adipocytes) or in dissipating energy as heat via uncoupling protein 1 (UCP1) in numerous smaller droplets (brown/beige adipocytes). White adipocytes also secrete hormones (leptin, adiponectin) and cytokines, making adipose tissue an important endocrine organ involved in metabolism and inflammation.

Effector chondrocytes in human. 1,143 cells across 1 tissues.

Endoneurial cells in human. 4,673 cells across 1 tissues.

Epineurial cells in human. 2,803 cells across 1 tissues.

Fibroblasts in human. 44,389 cells across 7 tissues.

Homeostatic chondrocytes in human. 5,839 cells across 1 tissues.

The final stage of chondrocyte differentiation in the growth plate during endochondral ossification. These cells enlarge (hypertrophy), dramatically alter their matrix to promote calcification (secrete type X collagen), and express factors like VEGF that attract blood vessels and osteoclasts. Ultimately, they undergo apoptosis or transdifferentiation, leaving behind a calcified scaffold that is replaced by bone.

Inflammatory chondrocytes in human. 4,861 cells across 1 tissues.

Mesenchymal cells in human. 21,485 cells across 1 tissues.

Pericytes in human. 9,926 cells across 5 tissues.

Perineurial cells in human. 6,967 cells across 1 tissues.

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.

Precursor fibrocartilage chondrocytes in human. 1,258 cells across 1 tissues.

Pre-hypertrophic chondrocytes in human. 1,849 cells across 1 tissues.

Chondrocytes in the growth plate that are actively dividing, forming characteristic stacked columns. This rapid proliferation is responsible for the longitudinal growth of bones via endochondral ossification. They produce a matrix rich in type II collagen and aggrecan. In articular cartilage, adult chondrocytes are normally non-proliferative, but limited proliferation may occur in response to injury.

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.

Tendon cells are the resident cells of tendons, primarily tenocytes. Tenocytes are specialized fibroblasts that are elongated and aligned with the collagen fibers. They synthesize, maintain, and remodel the dense, regularly arranged collagenous extracellular matrix that gives tendons their high tensile strength, allowing them to transmit forces from muscle to bone.

Theca cells in human. 1,333 cells across 1 tissues.

Spermatocytes are developing male germ cells that undergo meiosis. Primary spermatocytes (diploid, 4N DNA) result from spermatogonial mitosis. They undergo Meiosis I to form two secondary spermatocytes (haploid, 2N DNA). Secondary spermatocytes rapidly undergo Meiosis II to produce four spermatids (haploid, 1N DNA). This process occurs within the seminiferous tubules, supported by Sertoli cells.

Spermatocytes in human. 5,433 cells across 1 tissues.

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.

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.

Cardiomyocytes are the striated muscle cells that constitute the cardiac muscle of the heart. They are responsible for generating the contractile force that pumps blood. They are connected end-to-end by intercalated discs containing gap junctions for electrical coupling and desmosomes for mechanical attachment. Unlike skeletal muscle, they are mononucleated or binucleated and have intrinsic automaticity (pacemaker cells).

Satellite cells in human. 7,790 cells across 2 tissues.

Smooth muscle cells in human. 30,038 cells across 17 tissues.

In skeletal muscle, myonuclei within slow-twitch (Type I) muscle fibers. These fibers are oxidative, fatigue-resistant, and suited for endurance. Their myonuclei govern the expression of genes for mitochondrial proteins, myosin heavy chain I, and other components defining the slow, aerobic metabolic phenotype of the fiber.

In skeletal muscle, myonuclei within fast-twitch (Type II) muscle fibers. These fibers are glycolytic, generate more force but fatigue quickly. Type II myonuclei (subtypes IIa, IIx/d) govern the expression of genes for glycolytic enzymes, fast myosin heavy chains, and other components defining the fast, anaerobic metabolic phenotype of the fiber.