Single layer squamous epithelium (single layer squamous epithelium/egg-shaped/oval nuclei)

Single-layer cuboidal epithelium (mainly distributed in certain ducts, renal tubules, thyroid follicles, etc., with absorptive and secretory functions)

Single layer columnar epithelium (the cell nucleus is oval, close to the base/mainly distributed in the luminal surface of the stomach, intestine, gallbladder, uterus and fallopian tube, its main function is absorption and secretion)

Pseudostratified ciliated columnar epithelium (composed of columns, cones, spindles, and goblet cells/with swinging cilia on the free surface/mainly distributed in the luminal surface of the respiratory tract, and goblet cells can secrete)

Stratified squamous epithelium (stratified squamous epithelium/new cells gradually differentiate from the base to the surface/located in the skin, oral cavity, esophagus, vagina, anus, cornea, etc./the junction between this epithelium and deep connective tissue is uneven, increasing the contact area , conducive to nutrient supply, fixed/stratified squamous epithelium has mechanical protective effects such as resistance to friction and preventing foreign body invasion, and has strong regeneration and repair capabilities after injury)

Stratified columnar epithelium (mainly found in the conjunctiva, male urethra and large ducts of some glands)

Migrant epithelium (mainly distributed in the renal pelvis, renal calyces, ureters, bladder and other luminal surfaces/cover cells/cells with variable shape and size)

Microvilli (tiny finger-like protrusions/containing longitudinal microfilaments, which play a supporting role, extend downward from the top, and are connected to the terminal network arranged parallel to the top of the cytoplasm/columnar cells of the small intestinal epithelium and the epithelial cells of the proximal tubule of the kidney) Microvilli are numerous and long, each cell can have thousands of them and are neatly arranged. Under the light microscope, they appear as striated borders or brush borders/microvilli increase the cell surface area and improve the cell's absorption function)

Cilia (thick and long protrusions/ciliated epithelium mainly found in the respiratory tract, each cell has about 300 cilia/rhythmic directional swings)

Among the above four types of connections, if 2 or more of them exist immediately adjacent to each other, they are called connection complexes. The connections and changes of cells often change with the different developmental stages and functional states of organs and pathological changes.

Tight link (closed junction/near the top/viewed from the top of the cell, surrounds the cell in a hoop shape/under an electron microscope, the outer layers of two adjacent cell membranes are simply fused together, tightly adhered by the mosaic proteins of the two membranes) Together, they form a network of ridges/This connection can prevent macromolecular substances from entering the tissue from outside the cell through the intercellular space. It is the basis of various barriers in the body and can limit the diffusion of substances)

Adhesive zonules (middle connections/beneath the tight links, are strips of varying lengths that surround the top of epithelial cells, adhering adjacent cells together/maintaining cell shape/transmitting cell contractility)

Desmosomes (focal adhesions/are located deep in the middle connection, are spot-shaped or button-shaped, and vary in size/desmosomes are a strong connection that connects target cells like rivets, in areas such as the skin and esophagus that are susceptible to friction. Especially developed in stratified squamous epithelium)

Gap junctions (communication connections/widely distributed in various tissues/deep in the sides of epithelial cells, in the form of spots of varying sizes)

Basement membrane (a thin film between the basal surface of epithelial cells and deep connective tissue/basement membrane = basal plate + reticular plate, basal plate = transparent layer + dense layer / The basal plate is formed by epithelial cells, and the reticular plate is composed of reticular fibers and Matrix composition, produced by fibroblasts/supports, connects and fixes/semi-permeable membrane/facilitates material exchange between epithelial cells and deep connective tissue/guides the movement of epithelial cells and affects cell proliferation and differentiation)

The infoldings of the plasma membrane (the thin film on the basal surface of epithelial cells, are many folds formed by indentations into the cell). There are a large number of mitochondria arranged in longitudinal rows in the cytoplasm between the infoldings. The cytoplasm is eosinophilic and can be seen under a light microscope. There are longitudinal striations at the base. The infoldings of the plasma membrane expand the surface area of ​​the cell base, which is beneficial to the transport of water and electrolytes, and is mainly distributed in the proximal tubule of the kidney)

Hemidesmosomes (half of the desmosome structure/there is also an attachment plate in the plasma membrane, keratin filaments are attached to it, folded into loops and returned to the cytoplasm/strengthen the connection between the cell and the basement membrane/mainly found in the basal layer of complex squamous epithelial cells)