Membranes are a vital component in protecting the body from its surrounding environment. In the human body, membranes are composed of Epithelial and Connective tissue. Each one of these membranes will consist of a sheet of epithelial cells and an underlying connective tissue layer. Membranes can be divided into four main categories:
- Mucous Membranes
- Serous Membranes
- Cutaneous Membranes
- Synovial Membranes
Mucous membranes can be found in the digestive, urinary, respiratory, and reproductive tracts due to their ability to secrete a barrier of protection. This barrier of protection is responsible for resisting pathogen entry into the body and deeper tissues. The layer of secretion is created by mucous glands and it also helps maintain the moisture of epithelial cell surfaces.
In mucous membranes, the tissue that connects the epithelium to the underlying tissue is called the lamina propria. This is an areolar tissue that allows the epithelium to move free when compared to the deeper tissue.
Serous membranes are located in the lining of body cavities. Within these membranes, there are two major layers, the visceral and parietal layers. The visceral layer is responsible for covering the organ of the cavity. The parietal layer can be found lining the walls of the cavity the organ is located in. It is also important to know that within serous membranes there is a fluid called transudate. This serous fluid is responsible for reducing friction between layers. There are three types of serous membranes:
Pleura serous membranes are responsible for lining the lungs. The parietal layer of this membrane is attached to the chest wall while the visceral layer is attached to the lungs. The fluid between these two layers is called the pleural fluid.
Peritoneum serous membranes can be found lining the peritoneal cavity (abdominal cavity). In this membrane, the visceral layer attaches itself to the organs of the peritoneal cavity such as the intestines, and helps hold it in place. This membrane helps reduce friction and maintain the organization of the organs during bodily processes and mechanical movements.
The pericardium serous membranes are found lining the heart. The main function of this membrane is to hold the heart in place and help it function properly.
The cutaneous membrane is one of the largest membranes in your body and the most recognizable. This layer of epithelial cells and connective tissue in your skin consists of keratinized stratified squamous epithelium. The keratinization of the epithelium results in a waterproof and thick characteristic. The deeper cells are connected to areolar tissue and dense irregular tissue that helps maintain and secure the epithelial cells.
Synovial membranes can be found lining the joint cavities of bones. These membranes are different from the other ones because it has no basal lamina or reticular lamina, the cells are created from fibroblasts and macrophages, and there are gaps between the cells.
Within this membrane, there is a fluid produced called synovial fluid. This functions to reduce friction between the joints to reduce damage to the bones and cartilage.