Interalveolar septum

The interalveolar septum is the wall between adjacent alveoli. It is lined by a simple squamous epithelium of Type I cells and cuboidal Type II cells (septal cells). The connective tissue core of the septum possesses connective tissue cells and reticular and elastic fibers. Numerous capillaries protrude from the septa into alveolar spaces to facilitate gas exchange. The alveolus is coated by a thin film of surfactant that prevents the alveolus from collapsing.

The interalveolar septum is the wall between adjacent alveoli. It is lined by a simple squamous epithelium of Type I cells and cuboidal Type II cells (septal cells). The connective tissue core of the septum possesses connective tissue cells and reticular and elastic fibers. Numerous capillaries protrude from the septa into alveolar spaces to facilitate gas exchange. The alveolus is coated by a thin film of surfactant that prevents the alveolus from collapsing.

The interalveolar septum is the wall between adjacent alveoli. It is lined by a simple squamous epithelium of Type I cells and cuboidal Type II cells (septal cells). The connective tissue core of the septum possesses connective tissue cells and reticular and elastic fibers. Numerous capillaries protrude from the septa into alveolar spaces to facilitate gas exchange. The alveolus is coated by a thin film of surfactant that prevents the alveolus from collapsing.

The interalveolar septum is the wall between adjacent alveoli. It is lined by a simple squamous epithelium of Type I cells and cuboidal Type II cells (septal cells). The connective tissue core of the septum possesses connective tissue cells and reticular and elastic fibers. Numerous capillaries protrude from the septa into alveolar spaces to facilitate gas exchange. The alveolus is coated by a thin film of surfactant that prevents the alveolus from collapsing.

The interalveolar septum is the wall between adjacent alveoli. It is lined by a simple squamous epithelium of Type I cells and cuboidal Type II cells (septal cells). The connective tissue core of the septum possesses connective tissue cells and reticular and elastic fibers. Numerous capillaries protrude from the septa into alveolar spaces to facilitate gas exchange. The alveolus is coated by a thin film of surfactant that prevents the alveolus from collapsing.

A very thin simple squamous epithelium composed of Type I cells (pulmonary epithelial or Type I pneumocytes) lines most of the alveolar space, thus providing a minimal barrier for gas exchange.

Type II cells (septal cells or Type II pneumocytes) also line the alveolar space although they cover far less surface area than do the Type I cells. These cuboidal cells can be identified by their frothy cytoplasm, indicative of the phospholipid surfactant they secrete. The thin surfactant layer reduces surface tension, thus aiding inflation of the alveoli during inspiration and preventing collapse.

Type II cells (septal cells or Type II pneumocytes) also line the alveolar space although they cover far less surface area than do the Type I cells. These cuboidal cells can be identified by their frothy cytoplasm, indicative of the phospholipid surfactant they secrete. The thin surfactant layer reduces surface tension, thus aiding inflation of the alveoli during inspiration and preventing collapse.

The air-blood barrier is composed of the simple squamous epithelium of type I cells lining the alveolus, the simple squamous endothelium lining the capillary, and their fused basal laminae. This barrier may be as thin as 0.5 microns.

Alveolar macrophages, derived from blood monocytes, are present in the interalveolar septum and in the alveolar lumen. They migrate into the air space where they phagocytose air-borne particles, thus giving them their name, dust cells. These macrophages also phagocytose red blood cells present in alveoli during congestive heart failure, thus giving them their name, heart failure cells.