Mucous membrane
A mucosa is a layer made up of epithelium and underlying loose connective tissue (lamina propria) that lines the internal walls of organs that are in contact with the outside of the body. It is usually associated with numerous mucus-secreting glands. In general, they have protective, secretory, and absorptive functions, and harbor highly developed and specialized immune subsystems.
They are soft and moist organic tissues (such as the inside of the mouth) that line the inside of the digestive organs (oral cavity, pharynx, esophagus, stomach, small intestine, colon and rectum), the respiratory organs (nasal mucosa, trachea and bronchi), urological (urethra, bladder, ureters) and female genitalia (part of the vulva and vagina).
This fabric has three layers:
- An epithelium coating that has direct contact with organ light.
- An underlying layer of areolar connective tissue, along with a layer of connective tissue of greater fibers, called Lamina Propia.
- In some cases, such as the digestive tract, there is a thin terminal layer of smooth muscle, called mucosae muscularis, which in turn consists of an internal layer of transverse fibers and an external longitudinal layer. In this case, the connective tissue of the corion receives the name of its own sheet.
Epithelium
Variable type, depending on its function and location.
1. Alimentary canal: The epithelium of the mouth and external pharynx is non-keratinized stratified squamous type and its main function is protective.
Simple columnar epithelium, which is involved in secretion and absorption, lines the stomach and intestines. The cells of this second type of epithelium are tightly bound to one another in a tight manner. These tight junctions prevent the passage of digestive material between cells, from the lumen of the intestine (external environment) to the blood (internal environment).
2. Urinary system: The most characteristic epithelium of this system is the transitional epithelium or urothelium, which can be seen from the renal minor calyces to the bladder. It is a pseudostratified epithelium with a variable degree of stratification depending on the state of distension of the organ. When the organ contracts and its epithelial surface area decreases, the cells "clump up" each other, giving the impression that the number of layers has increased.
Lamina propria
The lamina propria is areolar connective tissue that contains numerous blood and lymphatic vessels, through which nutrients are absorbed in the case of the digestive tract, and which generally provides support to the epithelium and joins it with the muscularis mucosa, if it exists This layer of the mucosa includes the Mucosa Associated Lymphoid Tissue (MALT). In MALT we can find diffuse lymphoid tissue and prominent lymphoid follicles, which contain immune system cells with a protective function. MALT lymphocytes and macrophages recognize and produce immune responses against microbes and other antigens, such as bacteria that penetrate the epithelium.
Muscularis mucosae
A thin layer of smooth muscle fibers, the lamina muscularis mucosa, forms the mucosa of the stomach and small intestine into numerous small folds, which increase the surface area for digestion and absorption. The movements of the muscularis cause all the absorptive cells to be exposed to the contents of the digestive tract.