Type II pneumocyte
Encyclopedia
Type II pneumocytes also called great alveolar cells or septal cells are granular
and roughly cuboidal in shape. Type II pneumocytes are typically found at the alveolar-septal junction
. Although they comprise 60% of the alveolar lining cells, because of their shape they cover a much smaller surface area than type I cells (<5%).
, secreting small amounts of surfactant. However, adequate amounts of surfactant are not secreted until about 35 weeks of gestation - this is the main reason for increased incidence rates of Infant respiratory distress syndrome
, which drastically reduces at ages above 35 weeks gestation.
(the majority of which are dipalmitoylphosphatidylcholine
), a group of phospholipids
that reduce the alveolar surface tension. Surfactant phospholipids are stored in Type II pneumocytes in lamellar bodies, which are specialized vesicles. Release of surfactant in lamellar bodies occurs from an infant's first breath onwards.
Type II pneumocytes can replicate in the alveoli and will replicate to replace damaged Type I pneumocyte
s.
MUC1
, a human gene associated with type II pneumocytes, has been identified as a marker in lung cancer
.
Granularity
Granularity is the extent to which a system is broken down into small parts, either the system itself or its description or observation. It is the "extent to which a larger entity is subdivided...
and roughly cuboidal in shape. Type II pneumocytes are typically found at the alveolar-septal junction
Alveolar-capillary barrier
The alveolar-capillary barrier exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood, and from blood entering the alveoli. It is formed by the type 1 pneumocytes of the alveolar wall, the endothelial cells of the capillaries and the basement...
. Although they comprise 60% of the alveolar lining cells, because of their shape they cover a much smaller surface area than type I cells (<5%).
Development
Type II cells start to develop at about 24 weeks of gestationGestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
, secreting small amounts of surfactant. However, adequate amounts of surfactant are not secreted until about 35 weeks of gestation - this is the main reason for increased incidence rates of Infant respiratory distress syndrome
Infant respiratory distress syndrome
Infant respiratory distress syndrome , also called neonatal respiratory distress syndrome or respiratory distress syndrome of newborn, previously called hyaline membrane disease, is a syndrome in premature infants caused by developmental insufficiency of surfactant production and structural...
, which drastically reduces at ages above 35 weeks gestation.
Function
Type II cells are responsible for the production and secretion of surfactantSurfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
(the majority of which are dipalmitoylphosphatidylcholine
Dipalmitoylphosphatidylcholine
Dipalmitoylphosphatidylcholine is a phospholipid consisting of two palmitic acids and is the major constituent of pulmonary surfactant. It is also the only surface active component of lung surfactant capable of lowering surface tension to near zero levels. DpPC is synthesized mainly through...
), a group of phospholipids
Phospholipid
Phospholipids are a class of lipids that are a major component of all cell membranes as they can form lipid bilayers. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from...
that reduce the alveolar surface tension. Surfactant phospholipids are stored in Type II pneumocytes in lamellar bodies, which are specialized vesicles. Release of surfactant in lamellar bodies occurs from an infant's first breath onwards.
Type II pneumocytes can replicate in the alveoli and will replicate to replace damaged Type I pneumocyte
Type I pneumocyte
Type I pneumocytes are responsible for gas exchange in the alveoli and cover a majority of the alveolar surface area . While type I pneumocytes account for most of the surface area, they are approximately half as numerous as type II cells, due to differences in size...
s.
MUC1
MUC1
Mucin 1, cell surface associated or polymorphic epithelial mucin is a mucin encoded by the MUC1 gene in humans. MUC1 is a proteoglycan with extensive O-linked glycosylation of its extracellular domain. Mucins line the apical surface of epithelial cells in the lungs, stomach, intestines, eyes and...
, a human gene associated with type II pneumocytes, has been identified as a marker in lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
.