Understanding Epithelial and Endothelial Cells - AP Biology

Transitional epithelial cells are able to expand and contract based on the degree of tension. This transition to a different morphology depends on the cell layer in which the transitional cells are located.

Pseudostratified epithelial cells are single layers of cells—simple epithelium—that may be easily confused as a stratified epithelium. This confusion arises from the cross section, which shows nuclei located at different heights. As a result, it appears as if pseudostratified epithelial cells are multiple cell layers.

Simple epithelia are epithelial tissue that is only one cell layer thick; therefore, each cell has direct contact with the basement membrane. All epithelial cell morphologies can be found in simple epithelia.

Stratified epithelia consist of two or more layers of epithelial cells. They plan an important role in protection from chemical and mechanical forces. Stratified epithelia are specialized into keratinized and transitional layers.

The basement membrane is a matrix of cells that separates the outer tissue from the connective tissue. It functions as a barrier to prevent deep penetration and also anchors down the outer tissues (e.g. the epithelium).

Keratinized epithelia are specialized stratified epithelia. They consist of a layer of dead exterior cells that contain the protein keratin. Keratin “waterproofs” the cells, offering protection. As a result, keratinized epithelia are commonly found in mammalian skin.

Transitional epithelia are specialized stratified epithelial cell layers that are present in tissues that need to stretch; therefore, transitional epithelia are located in the urethra, ureter, and bladder.

Epithelial tissue is one of the major types of tissues in the human body. Epithelial cells function in secretion, absorption, protection, and transport. As a result, epithelial tissue is located at the interface of structures and tissues including the lining of body cavities, the surface of blood vessels, and the surface of organs.

Cell junctions are common in epithelial tissue because they allow for communication and contact between neighboring cells.

During embryological development, epithelial tissue develops from all three germ layers (endoderm, mesoderm, and ectoderm).

The infolding of epithelial tissue forms glands that function in the exocrine and endocrine systems. Glands secrete products that are taken up by the circulatory system for delivery.

Epithelial tissue has a sensory detection function that utilizes cilia to sense signals from the external environment. Once the signal is recognized and transduced, epithelial cells secrete messenger proteins that transmit the signal downstream.

The endothelium is a specialized type of epithelium that lines the lymphatic and circulatory system. The endothelium originates from the mesoderm during embryogenesis and develops into squamous cells. Within the lymphatic and circulatory systems, endothelial cells function as barriers, in blood clotting, and in inflammation.

The main storage form of lipids is in the form of triglycerides. Phospholipids are found in the cell membrane.

Epithelial cells have three distinct morphologies: squamous, cuboidal, and columnar. Squamous cells are wider than they are tall. In other words, they are flat.

Simple epithelia are layers of epithelial cells that are one cell thick. Simple epithelia are only composed of a monolayer of cells; therefore, their main functions are absorption and filtration.

Stratified epithelia are composed of two or more layers of epithelial cells. The increased number of cells associated with stratified epithelia creates a more complex function; stratified epithelia are involved in protection from mechanical and chemical forces.

Epithelial cells can be categorized by morphology, or shape. Epithelial cells exist in the following morphologies: squamous, columnar, or cuboidal.

Endothelial cells line the insides of blood vessels and lymphatic vessels and have many important functions, including but not limited to those described in the question. One additional function of endothelial cells is involvement in blood clotting.

Endothelium generally lines fully internal pathways (such as the vascular system), while epithelium generally lines pathways that are open to the external environment (such as the respiratory and digestive systems). Nerve cells are specialized for signaling, and red blood cells are specialized for oxygen transport.