Alveolar type II cells
secrete a lipoprotein material called surfactant, whose primary function is to reduce the surface tension in the alveoli.
What cells secrete surfactant?
Surfactant is synthesized and secreted by
Type II alveolar epithelial cells, also called pneumocytes
, which differentiate between 24 and 34 weeks of gestation in the human.
What do Type 1 alveolar cells secrete?
Type I alveolar cells are squamous extremely thin cells involved in the process of gas exchange between the alveoli and blood. Type II alveolar cells are involved in the secretion of surfactant
proteins
.
What is the difference between Type 1 and 2 alveolar cells?
The type I cell is a complex branched cell with multiple cytoplasmic plates that are greatly attenuated and relatively devoid of organelles; these plates represent the gas exchange surface in the alveolus. On the other hand, the type II cell acts as the “
caretaker”
of the alveolar compartment.
What do type II alveolar cells produce?
Type II cells produce and secrete
pulmonary surfactant
and for that purpose they need to synthesize the lipids of surfactant. One of the regulators of lipogenesis is the transcription factor sterol regulatory element binding protein-1c (SREBP-1c). This is a key transcription factor regulating fatty acid synthesis.
What age is surfactant?
A baby normally begins producing surfactant sometime
between weeks 24 and 28 of pregnancy
. Most babies produce enough to breathe normally by week 34.
What is the main role of surfactant?
The main functions of surfactant are as follows: (1)
lowering surface tension at the air–liquid interface
and thus preventing alveolar collapse at end-expiration, (2) interacting with and subsequent killing of pathogens or preventing their dissemination, and (3) modulating immune responses.
What are the 3 types of alveolar cells?
- Type 1 pneumocytes.
- Type 2 pneumocytes.
- Alveolar macrophages.
What are the two types of alveolar cells?
The pulmonary alveolar epithelium is mainly composed of two types of epithelial cells:
alveolar type I (AT1) and type II (AT2) cells
. AT2 cells are smaller, cuboidal cells that are best known for their functions in synthesizing and secreting pulmonary surfactant.
What are Type 3 cells?
The type III cell has two distinctive features that are not present in other lung epithelial cells: a
microvillous brush border and bundles of fine filaments
. Regarding its topography, the cell appears to have a preferential although variable localization in different species.
Which type of pneumocytes secrete surfactant?
Surfactant is a macroaggregate molecule secreted by
type 2 pneumocytes
as the infant approaches term gestation. Surfactant is made up of 90% phospholipid and 10% proteins (surfactant protein [SP] A, B, C, and D). The primary function of surfactant is to reduce surface tension in the lung.
Where are type 2 alveolar cells found?
Two types are pneumocytes or pneumonocytes known as type I and type II cells found
in the alveolar wall
, and a large phagocytic cell known as an alveolar macrophage that moves about in the lumens of the alveoli, and in the connective tissue between them.
What do type 1 pneumocytes produce?
Type 1 pneumocyte: The cell responsible for
the gas (oxygen and carbon dioxide)
exchange that takes place in the alveoli. It is a very large thin cell stretched over a very large area.
What is the main function of the type II alveolar cells?
Four major functions have been attributed to alveolar type II cells: (1)
synthesis and secretion of surfactant
; (2) xenobiotic metabolism; (3) transepithelial movement of water; and (4) regeneration of the alveolar epithelium following lung injury.
What are type II pneumocytes?
Type II pneumocytes are identified as
the synthesizing cells of the alveolar surfactant
, which has important properties in maintaining alveolar and airway stability. Lung surfactant can reduce the surface tension and prevent alveolar collapse and the airway walls collapse.
Are Clara cells type II pneumocytes?
These cells were first recognized as a distinct cell type based on morphology and histochemistry in 1881 by Kölliker (1). … In 1967, Niden suggested that Clara cells secrete pulmonary surfactant and that the lamellar bodies seen in alveolar type II pneumocytes represented phagocytized surfactant (4).
