Why does simple squamous line the alveoli

These are simple columnar epithelial cells whose nuclei appear at different heights, giving the misleading hence pseudo impression that the epithelium is stratified when the cells are viewed in cross section.

Pseudostratified epithelium can also possess fine hair-like extensions of their apical luminal membrane called cilia. In this case, the epithelium is described as ciliated pseudostratified epithelium. Ciliated epithelium is found in the airways nose, bronchi , but is also found in the uterus and fallopian tubes of females, where the cilia propel the ovum to the uterus. Stratified epithelium differs from simple epithelium by being multilayered. It is therefore found where body linings have to withstand mechanical or chemical insults.

Stratified epithelia are more durable and protection is one their major functions. Since stratified epithelium consists of two or more layers, the basal cells divide and push towards the apex, and in the process flatten the apical cells.

Stratified epithelia can be columnar, cuboidal, or squamous type. However, it can also have the following specializations:. In keratinized epithelia, the most apical layers exterior of cells are dead and lose their nucleus and cytoplasm. They contain a tough, resistant protein called keratin. This specialization makes the epithelium waterproof, and it is abundant in mammalian skin. The lining of the esophagus is an example of a non-keratinized or moist stratified epithelium.

Transitional epithelia are found in tissues that stretch and it can appear to be stratified cuboidal when the tissue is not stretched, or stratified squamous when the organ is distended and the tissue stretches.

It is sometimes called the urothelium since it is almost exclusively found in the bladder, ureters, and urethra. Privacy Policy. Skip to main content. Organization at the Tissue Level. Search for:. Epithelial Tissue. Characteristics of Epithelial Tissue The human body consists of four types of tissue: epithelial, connective, muscular, and nervous. Learning Objectives Describe the primary functions and characteristics of epithelial tissue.

Key Takeaways Key Points Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another. Epithelial layers are avascular, but innervated. Epithelial cells have two surfaces that differ in both structure and function. Glands, such as exocrine and endocrine, are composed of epithelial tissue and classified based on how their secretions are released. Key Terms epithelium : A membranous tissue composed of one or more layers of cells that form the covering of most internal and external surfaces of the body and its organs.

Types of Epithelial Tissue Epithelial tissue is classified by cell shape and the number of cell layers. Learning Objectives Classify epithelial tissue by cell shape and layers. Key Takeaways Key Points There are three principal cell shapes associated with epithelial cells: squamous epithelium, cuboidal epithelium, and columnar epithelium.

In addition, simple squamous epithelium lines the cavities, which arise from the coelom of the mesoderm i. Figure 4: Endothelial tissue of a blood vessel.

Ackerley, S. Epithelial Tissue. Alberts B. The Molecular Biology of The Cell 4th ed. Finazzo, S. King, D. Epithelium Study Guide. The process of cleansing the air inhaled through the bronchi. Correct answer: Exchange of carbon dioxide and oxygen between the blood vessels and the alveoli.

Explanation : Diffusion is the spontaneous process by which substances move from areas of high to low concentration. Example Question 7 : Respiratory System. Possible Answers: A thin layer of epithelial cells separated from endothelial cells in capillaries by interstitial fluid.

A thin layer of epithelial cells directly connected to endothelial cells in capillaries. Tiny sacks that fill up with blood to facilitate the exchange of oxygen and nutrients. A thick layer of epithelial cells directly connected to endothelial cells in capillaries. Correct answer: A thin layer of epithelial cells directly connected to endothelial cells in capillaries. Explanation : The alveoli's structure maximizes the efficient transfer of gas from air to the capillaries and vice versa.

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