On alveoli walls, the squamous epithelial cells are well suited for rapid diffusion of gases between the alveoli and the blood.
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport and detection of sensation. In Greek "ἐπί" ("epi") means "on" or "upon", and "θηλή" ("thēlē") means "nipple". Epithelial layers are avascular, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane. Epithelia can also be organized into clusters of cells that function as exocrine and endocrine glands.
Squamous epithelial cell
An alveolus (plural: alveoli, from Latin alveolus, "little cavity") is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the terminal ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which 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 alveolar blood vessels where, through diffusion, it releases its carbon dioxide and absorbs oxygen.
In anatomy, squamous epithelium (from Latin squama, "scale") is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells called squamous epithelial cells. Epithelium may be composed of one layer of these cells, in which case it is referred to as simple squamous epithelium, or it may possess multiple layers, referred to then as stratified squamous epithelium. Both types perform differing functions, ranging from nutrient exchange to protection.]citation needed[
Cancers of the squamous epithelium include squamous cell carcinoma, basal cell carcinoma, and other adnexal tumors.]citation needed[
The respiratory system (or ventilatory system) is the biological system that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs. Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.
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An alveolar macrophage (or dust cell) is a type of macrophage found in the pulmonary alveolus, near the pneumocytes, but separated from the wall.
Activity of the alveolar macrophage is relatively high, because they are located at one of the major boundaries between the body and the outside world.