Club cell

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Club cell
Latin exocrinocytus bronchiolaris
TH H3.
Anatomical terms of microanatomy

Club cells, also known as bronchiolar exocrine cells, [1] and originally known as Clara cells, are dome-shaped cells with short microvilli, found in the small airways (bronchioles) of the lungs. [2]

Cell (biology) the basic structural and functional unit of all organisms. Includes the plasma membrane and any external encapsulating structures such as the cell wall and cell envelope.

The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life. Cells are often called the "building blocks of life". The study of cells is called cell biology or cellular biology.

Lung essential respiration organ in many air-breathing animals

The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their different muscles to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians. In humans, the main muscle of respiration that drives breathing is the diaphragm. The lungs also provide airflow that makes vocal sounds including human speech possible.


Club cells are found in the ciliated simple epithelium. These cells may secrete glycosaminoglycans to protect the bronchiole lining. Bronchiolar cells gradually increase in number as the number of goblet cells decrease.

Glycosaminoglycan long unbranched polysaccharides consisting of a repeating disaccharide unit

Glycosaminoglycans (GAGs) or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of an amino sugar along with a uronic sugar or galactose. Glycosaminoglycans are highly polar and attract water. They are therefore useful to the body as a lubricant or as a shock absorber.

Goblet cell Goblet cell

Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin MUC5AC. The goblet cells mainly use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secretions, when under stress. The term goblet refers to the cell's goblet-like shape. The apical portion is shaped like a cup, as it is distended by abundant mucus laden granules; its basal portion lacks these granules and is shaped like a stem.

One of the main functions of club cells is to protect the bronchiolar epithelium. They do this by secreting a small variety of products, including club cell secretory protein uteroglobin, and a solution similar in composition to pulmonary surfactant. They are also responsible for detoxifying harmful substances inhaled into the lungs. Club cells accomplish this with cytochrome P450 enzymes found in their smooth endoplasmic reticulum. Club cells also act as a stem cell, multiplying and differentiating into ciliated cells to regenerate the bronchiolar epithelium. [3]

Epithelium type of animal tissue and human

Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin.

Uteroglobin protein-coding gene in the species Homo sapiens

Uteroglobin, also known as secretoglobin family 1A member 1 (SCGB1A1), is a protein that in humans is encoded by the SCGB1A1 gene.

Pulmonary surfactant

Pulmonary surfactant is a surface-active lipoprotein complex (phospholipoprotein) formed by type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorbing to the air-water interface of alveoli, with hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main lipid component of surfactant, dipalmitoylphosphatidylcholine (DPPC), reduces surface tension.


The respiratory bronchioles represent the transition from the conducting portion to the respiratory portion of the respiratory system. The narrow channels are usually less than 2 mm in diameter and they are lined by a simple cuboidal epithelium, consisting of ciliated cells and non-ciliated club cells, which are unique to bronchioles. In addition to being structurally diverse, club cells are also functionally variable. One major function they carry out is the synthesis and secretion of the material lining the bronchiolar lumen. This material includes glycosaminoglycans, proteins such as lysozymes, and conjugation of the secretory portion of IgA antibodies. These play an important defensive role, and they also contribute to the degradation of the mucus produced by the upper airways. The heterogeneous nature of the dense granules within the club cell's cytoplasm suggests that they may not all have a secretory function. Some of them may contain lysosomal enzymes, which carry out a digestive role, either in defense: Club cells engulf airborne toxins and break them down via their cytochrome P-450 enzymes (particularly CYP4B1, which is only present in the club cells) present in their smooth endoplasmic reticulum; or in the recycling of secretory products. Club cells are mitotically active. They divide and differentiate to form both ciliated and non-ciliated epithelial cells.

Lumen (anatomy) cavity within an organ

In biology, a lumen is the inside space of a tubular structure, such as an artery or intestine. It comes from Latin lumen, meaning 'an opening'.

Lysozyme protein-coding gene in the species Homo sapiens

Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase is an antimicrobial enzyme produced by animals that forms part of the innate immune system. Lysozyme is a glycoside hydrolase that catalyzes the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan, which is the major component of gram-positive bacterial cell wall. This hydrolysis in turn compromises the integrity of bacterial cell walls causing lysis of the bacteria.

Clinical significance

Club cells contain tryptase, which is believed to be responsible for cleaving the hemagglutinin surface protein of influenza A virus, thereby activating it and causing the symptoms of flu. [4] When the l7Rn6 protein is disrupted in mice, these mice display severe emphysema at birth as a result of disorganization of the Golgi apparatus and formation of aberrant vesicular structures within club cells. [5] Malignant club cells are also seen in bronchioalveolar carcinoma of the lung. Serum club cell proteins are used as a biomarker of lung permeability. Exposure to particulate air pollution may compromise the integrity of the lung epithelium and lead to rapid increase in epithelial barrier permeability, as reflected by increased serum club cell concentrations. [6]

Tryptase enzyme

Tryptase is the most abundant secretory granule-derived serine proteinase contained in mast cells and has been used as a marker for mast cell activation. Club cells contain tryptase, which is believed to be responsible for cleaving the hemagglutinin surface protein of influenza A virus, thereby activating it and causing the symptoms of flu.

Hemagglutinin substance that causes red blood cells to agglutinate

Hemagglutinin or haemagglutinin[p] refers to glycoproteins which cause red blood cells (RBCs) to agglutinate. This process is called hemagglutination or haemagglutination.

Golgi apparatus A compound membranous cytoplasmic organelle of eukaryotic cells, consisting of flattened, ribosome-free vesicles arranged in a more or less regular stack. The Golgi apparatus differs from the endoplasmic reticulum in often having slightly thicker mem

The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian scientist Camillo Golgi and named after him in 1898.


Club cells were previously called Clara cells, as they were first described by Max Clara (1899–1966), in 1937. Clara was an active member of the Nazi Party and used tissue taken from executed victims of the Third Reich for his research—including the work that led to his discovery of Clara cells. [7] In May 2012, the editorial boards of most of the major respiratory journals (including the journals of the American Thoracic Society, the European Respiratory Society and the American College of Chest Physicians) concluded that the continued use of Clara's eponym would be equivalent to honoring him; they therefore introduced a name-change policy, which went into effect beginning January 1, 2013. [8] The term "Clara" was used parenthetically after "club cell" for a 2-year period, after which "Clara cell" and "Clara cell secretory protein" were conclusively replaced with "club cell" and "club cell secretory protein", respectively. [9]

Max Clara Austrian scientist

Max Clara was a German anatomist. He was appointed as Chair of Anatomy at Leipzig University in 1935. Clara is known for having close ties with the Nazi Party, controversially basing much of his work on his studies of the bodies of executed prisoners, without the consent of the prisoners' families. His main work, "Das Nervensystem des Menschen" was written in 1942 in Leipzig during the Third Reich's dictatorship.

Nazi Party Fascist political party in Germany (1920-1945)

The National Socialist German Workers' Party, commonly referred to in English as the Nazi Party, was a far-right political party in Germany that was active between 1920 and 1945, that created and supported the ideology of Nazism. Its precursor, the German Workers' Party, existed from 1919 to 1920.

The American Thoracic Society (ATS) is a nonprofit organization focused on improving care for pulmonary diseases, critical illnesses and sleep-related breathing disorders. It was established in 1905 as the American Sanatorium Association, and changed its name in 1938 to the American Trudeau Society. In 1960, it changed its name again to the American Thoracic Society. Originally the medical section of the American Lung Association, the Society became independently incorporated in 2000 as a 501 (c) (3) organization.

See also

Related Research Articles

Pulmonary alveolus

A pulmonary alveolus is a hollow cavity found in the lung parenchyma, and is the basic unit of ventilation. Lung alveoli are the ends of the respiratory tree, branching from either alveolar sacs or alveolar ducts, which like alveoli are both sites of gas exchange with the blood as well. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates. The alveolar membrane is the gas exchange surface. Carbon dioxide rich blood is pumped from the rest of the body into the capillaries that surround the alveoli where, through diffusion, carbon dioxide is released and oxygen is absorbed.

Respiratory tract Organs involved in transmission of air to and from the point where gases diffuse into tissue

In humans, the respiratory tract is the part of the anatomy of the respiratory system involved with the process of respiration. Air is breathed in through the nose or the mouth. In the nasal cavity, a layer of mucous membrane acts as a filter and traps pollutants and other harmful substances found in the air. Next, air moves into the pharynx, a passage that contains the intersection between the esophagus and the larynx. The opening of the larynx has a special flap of cartilage, the epiglottis, that opens to allow air to pass through but closes to prevent food from moving into the airway.

Bronchus airway in the respiratory tracti

A bronchus is a passage of airway in the respiratory system that conducts air into the lungs. The first bronchi to branch from the trachea are the right main bronchus and the left main bronchus. These are the widest and enter the lungs at each hilum, where they branch into narrower secondary bronchi known as lobar bronchi, and these branch into narrower tertiary bronchi known as segmental bronchi. Further divisions of the segmental bronchi are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. The bronchi when too narrow to be supported by cartilage are known as bronchioles. No gas exchange takes place in the bronchi.

Bronchiole passageways by which air passes through the nose or mouth to the alveoli of the lungs

The bronchioles or bronchioli are the passageways by which air passes through the nose or mouth to the alveoli of the lungs, in which branches no longer contain cartilage or glands in their submucosa. They are branches of the bronchi, and are part of the conducting zone of the respiratory system. The bronchioles divide further into smaller terminal bronchioles which are still in the conducting zone and these then divide into the smaller respiratory bronchioles which mark the beginning of the respiratory region.

Immunoglobulin A antibody that plays a critical role in mucosal immunity

Immunoglobulin A is an antibody that plays a crucial role in the immune function of mucous membranes. The amount of IgA produced in association with mucosal membranes is greater than all other types of antibody combined. In absolute terms, between three and five grams are secreted into the intestinal lumen each day. This represents up to 15% of total immunoglobulins produced throughout the body.

Amelogenesis is the formation of enamel on teeth and begins when the crown is forming during the advanced bell stage of tooth development after dentinogenesis, forms a first layer of dentine. Although dentin must be present for enamel to be formed, ameloblasts must also be for dentinogenesis to continue. A message is sent from the newly differentiated odontoblasts to the inner enamel epithelium (IEE), causing the epithelial cells to further differentiate into active secretory ameloblasts. Dentinogenesis is in turn dependent on signals from the differentiating IEE in order for the process to continue. This prerequisite is an example of the biological concept known as reciprocal induction, in this instance between mesenchymal and epithelial cells.

Respiratory epithelium

Respiratory epithelium is a type of ciliated columnar epithelium found lining most of the respiratory tract, where it serves to moisten and protect the airways. It is not present in the larynx and pharynx. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by the action of mucociliary clearance.

Simple cuboidal epithelium

Simple cuboidal epithelium is a type of epithelium that consists of a single layer of cuboidal (cube-like) cells. These cuboidal cells have large, spherical and central nuclei.

Idiopathic interstitial pneumonia pneumonia located in the lung parenchyma of unknown cause

Idiopathic interstitial pneumonia (IIP), or noninfectious pneumonia are a class of diffuse lung diseases. These diseases typically affect the pulmonary interstitium, although some also have a component affecting the airways. There are seven recognized distinct subtypes of IIP.

Diffuse panbronchiolitis

Diffuse panbronchiolitis (DPB) is an inflammatory lung disease of unknown cause. It is a severe, progressive form of bronchiolitis, an inflammatory condition of the bronchioles. The term diffuse signifies that lesions appear throughout both lungs, while panbronchiolitis refers to inflammation found in all layers of the respiratory bronchioles. DPB causes severe inflammation and nodule-like lesions of terminal bronchioles, chronic sinusitis, and intense coughing with large amounts of sputum production.

A peg cell is a non-ciliated epithelial cell within the uterine tube. These cells are also known as an intercalated or intercalary cell. These cells represent one of 3 epithelial cell types found within the normal fallopian tube epithelium and are the most infrequent. The other two cell types include ciliated columnar and non-ciliated secretory cells. The ratio of these remaining cells is dictated by an individual's hormone status. Peg cells are thought to represent a quiescent maturational stage of the background non-ciliated secretory cells. Unlike secretory cells, these cells lack apical granules reflecting their non-functional nature.

Salivary gland–like carcinomas of the lung generally refers a class of rare cancers that arise from the uncontrolled cell division (mitosis) of mutated cancer stem cells in lung tissue. They take their name partly from the appearance of their abnormal cells, whose structure and features closely resemble those of cancers that form in the major salivary glands of the head and neck. Carcinoma is a term for malignant neoplasms derived from cells of epithelial lineage, and/or that exhibit cytological or tissue architectural features characteristically found in epithelial cells.

FOXJ1 protein-coding gene in the species Homo sapiens

Forkhead box protein J1 is a protein that in humans is encoded by the FOXJ1 gene. It is a member of the Forkhead/winged helix (FOX) family of transcription factors that is involved in ciliogenesis. FOXJ1 is expressed in ciliated cells of the lung, choroid plexus, reproductive track, embryonic kidney and pre-somite embryo stage.

Chronic Mycoplasma pneumonia and Chlamydia pneumonia infections are associated with the onset and exacerbation of asthma. These microbial infections result in chronic lower airway inflammation, impaired mucociliary clearance, an increase in mucous production and eventually asthma. Furthermore, children who experience severe viral respiratory infections early in life have a high possibility of having asthma later in their childhood. These viral respiratory infections are mostly caused by respiratory syncytial virus (RSV) and human rhinovirus (HRV). Although RSV infections increase the risk of asthma in early childhood, the association between asthma and RSV decreases with increasing age. HRV on the other hand is an important cause of bronchiolitis and is strongly associated with asthma development. In children and adults with established asthma, viral upper respiratory tract infections (URIs), especially HRVs infections, can produce acute exacerbations of asthma. Thus, Chlamydia pneumoniae, Mycoplasma pneumoniae and human rhinoviruses are microbes that play a major role in non-atopic asthma.


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