alveolar lamellar body

Definition

Target type: cellularcomponent

A specialized secretory organelle found in type II pneumocytes and involved in the synthesis, secretion, and reutilization of pulmonary surfactant. [GOC:cjm, Wikipedia:Lamellar_granule]

Alveolar lamellar bodies (also known as lamellar bodies or surfactant bodies) are complex, multilamellar organelles found within type II alveolar epithelial cells in the lungs. They are the primary source of pulmonary surfactant, a complex mixture of phospholipids, proteins, and carbohydrates essential for normal lung function.

**Cellular Component Description:**

* **Phospholipid Bilayers:** The core of a lamellar body consists of multiple concentric layers of phospholipid bilayers. These bilayers are stacked upon each other, forming a characteristic lamellar structure. The major phospholipids present are dipalmitoylphosphatidylcholine (DPPC), phosphatidylglycerol (PG), and phosphatidylinositol (PI).
* **Surfactant Proteins:** Embedded within the phospholipid bilayers are various surfactant proteins, including SP-A, SP-B, SP-C, and SP-D. These proteins play critical roles in the function of surfactant, including reducing surface tension, regulating surfactant synthesis and secretion, and immune defense.
* **Lipid Droplets:** In addition to the lamellar structures, lamellar bodies contain lipid droplets. These droplets store neutral lipids, which can be incorporated into the lamellar structure as needed.
* **Other Components:** Lamellar bodies may also contain small amounts of other components, such as enzymes involved in lipid metabolism and transport, as well as cholesterol and other minor lipids.

**Function:**

The primary function of lamellar bodies is to store and release pulmonary surfactant. Surfactant is crucial for maintaining lung function by reducing surface tension at the air-liquid interface within the alveoli. This prevents the alveoli from collapsing during exhalation and facilitates gas exchange.

**Formation and Secretion:**

Lamellar bodies are formed within type II alveolar epithelial cells through a process of biogenesis. The phospholipids and surfactant proteins are synthesized and transported to the Golgi apparatus, where they are packaged into lamellar bodies. These bodies then migrate to the cell surface and fuse with the plasma membrane, releasing their contents into the alveolar space.

**Clinical Significance:**

Defects in lamellar body formation or surfactant production can lead to respiratory distress syndrome (RDS), especially in premature infants. RDS is characterized by difficulty breathing due to collapsed alveoli. Surfactant replacement therapy is a crucial treatment for RDS.'
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Proteins (2)

Compounds (13)