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Mindmap-Galerie epithelial tissue
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epithelial tissue
Epithelial tissue plays an important role in the human body. It is the first line of defense between the human body and the external environment and has the function of protecting the body from harmful substances in the outside world.
Bearbeitet um 2024-04-08 10:51:06
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epithelial tissue
composition
A large number of regular, densely arranged epithelial cells and a small amount of extracellular matrix
Have polarity
Polarity: Different surfaces of a cell have distinct differences in structure and function
free surface
its surface facing the body or the side of an organ with a cavity
basal surface
The side facing the deep connective tissue opposite the free side
side
junction between epithelial cells
Classification
Covering epithelium
1. Single layer squamous epithelium
Also known as single layer squamous epithelium
Composition: A layer of flat cells
Viewed from the epithelial surface
Cells are irregular or polygonal
The nucleus is oval and located in the center of the cell
The edges of cells are jagged or wavy, and they are chimeric with each other.
Viewed from vertical section
Cells are flat and thin
Less cytoplasm
The core-containing part is slightly thicker
endothelium
The surface is smooth, which is conducive to the flow of blood and lymph, and is conducive to the exchange of substances by endothelial cells.
Lining the lumen of the heart, blood vessels, and lymphatic vessels
Mesothelium
The surface is moist and smooth, which can reduce friction in organ activities.
Distributed on the surface of pleura, peritoneum and pericardium
2. Single layer cuboidal epithelium
Composition: A layer of approximately cubic cells
Viewed from the epithelial surface
Cells are hexagonal or polygonal
Viewed from vertical section
Cells are cuboidal in shape with round nuclei in the center.
3. Single layer columnar epithelium
Composition: A layer of prismatic cells
Observed from the surface
Cells are hexagonal or polygonal
Viewed from vertical section
The cells are columnar, the nucleus is oval, and its long axis is consistent with the long axis of the cell.
Distribution: gastrointestinal, gallbladder and uterus, etc.
Function: Absorption or secretion
goblet cells
Shaped like a goblet, the bottom is narrow and contains darkly stained cores, and the top is enlarged and filled with particles
Mucin granules: contain PAS-positive mucin
After secretion, mucin combines with water to form mucus, which lubricates and protects the epithelium.
4. Pseudostratified ciliated columnar epithelium (single layer)
Distribution: respiratory tract lumen surface
Composition: columnar cells (most), spindle cells, cone cells, goblet cells, with a large number of cilia on the surface
The cells have different shapes, different heights, and the nuclear positions are not at the same level.
The base is attached to the basement membrane
5. Stratified squamous epithelium (stratified squamous epithelium)
Composition: Multiple layers of cells
Epithelial vertical section observation
cells of different shapes
6. Stratified columnar epithelium
Composition: Several layers of cells
Deep: one or more layers of polygonal cells
Superficial part: a layer of neatly arranged short columnar cells
Distribution: conjunctiva, male urethra, large ducts of some glands
7. Changing epithelium (stratified)
Distribution: urinary tract
Classification
1. Surface cells (cover cells)
2. Middle layer cells
3. Basal cells
Features: Cell shape and number of layers can change according to the empty and expanded state of the organ
Empty bladder: the epithelium thickens, the number of cell layers increases, and the cover cells become large cuboids.
Full bladder: the epithelium becomes thinner, the number of cell layers decreases, and the cover cells become flat.
glandular epithelium and glands
Glandular epithelium: an epithelium composed of glandular cells with mainly secretory function
Glandular cells secrete enzymes, mucus, hormones, etc.
Gland: An organ or structure whose main component is glandular epithelium.
Exocrine glands: Some gland secretions are discharged through ducts to the body surface or into organ cavities (for example: sweat glands, salivary glands, etc.)
1. Secretory Department
Shape: tubular, vesicular, tubular vesicular
Acini: Alveolar and tubulo-alveolar secretory parts
Composition: Single layer of glandular cells with central cavity
Glandular cells: mostly cone-shaped, with different shapes due to different secretions
Classification
serous cells
nuclear oval
cell base
Strong basophilic staining of the basal cytoplasm
The top cytoplasm contains more eosinophilic secretory granules (zymogen granules)
Under electron microscope
dense rough endoplasmic reticulum
A relatively developed Golgi complex and varying numbers of secretory granules can be seen in the supranuclear area (ultrastructural characteristics of protein secretion cell membranes)
mucus cells
nuclear oval
Located at the base of the cell
Except for a small amount of perinuclear cytoplasm that is basophilic, most of the cytoplasm is almost unstained.
Under electron microscope
There is a certain amount of rough endoplasmic reticulum in the basal cytoplasm
The supranuclear region has a well-developed Golgi complex and extremely abundant coarse clay particles.
Goblet cells are also scattered mucus cells
The functions of all gland cells are finely regulated by autonomic nerves and hormones (regulatory secretory cells)
Glandular cells that secrete proteins, glycoproteins, and peptides are in the non-secretory phase, and a large number of secretory granules can be stored in the cytoplasm.
Serous gland: a gland whose secretory part is composed entirely of serous acini (e.g. parotid gland)
Mucinous gland: A gland composed entirely of mucinous acini (e.g., duodenal glands)
Mixed gland: a gland composed of three types of acini (for example: submandibular gland, sublingual gland)
Mixed acini: acini composed of both serous and mucinous cells
Most mixed acini are composed primarily of mucinous cells, with a small number of serous cells located at the base of the acini, appearing as a half-moon structure in section (called a serous lunula)
The spaces between mucous cells are partially enlarged to form secretory tubules, and the secretions of the plasma half moon can be released into the acinar cavity through the secretory tubules.
Outside the gland cells, there can also be flat, multi-projected membrane myoepithelial cells with actin in the cytoplasm, whose contraction helps discharge secretions.
2.Catheter
Directly connected to the secretory part and composed of single or stratified epithelium
discharge secretions to the body surface or into organ cavities
Some ductal epithelial cells can also secrete or absorb water and electrolytes
Endocrine glands: Some glands have no ducts and generally release endocrine (hormones) into the blood (eg: thyroid, adrenal glands, etc.)
The specialized structure of epithelial cells (except for cilia and a few thick basement membranes, all can only be observed under an electron microscope)
free surface
1. Microvilli: tiny finger-like protrusions
Function: Significantly increases the cell surface area, which is beneficial to the cell's absorption function
2. Cilia: Thick and long protrusions
Function: Ability to swing rhythmically and directionally
side
1. Tight junction (closed junction)
Best method: Freeze etching replica method
lipid bilayer that splits the cell membrane
Exposing granular proteins embedded within membranes
Observe with transmission electron microscope
Function: Block substances from passing through the intercellular space, acting as a barrier
2. Adhesive zonules
Function: Adhesion, maintaining cell shape and transmitting cell contraction force
3. Desmosomes (focal adhesions)
Function: Firm mechanical connection allows epithelium to withstand friction (skin, esophagus)
4. Gap connection (communication connection)
Connecting bodies: There are many regularly distributed columnar particles in the cell membrane at gap junctions.
The connectosome is surrounded by 6 rod-shaped connexin molecules and has a central lumen with a diameter of 2 nm.
Function: Generally, substances with a molecular weight less than 1500D, including ions, information molecules such as cAMP, amino acids, glucose, vitamins, etc., can circulate between adjacent cells, making extracellular nutrition metabolism, proliferation, differentiation, and functions unified (synchronized). change)
basal surface
1. Basement membrane
A thin film formed between the basal surface of epithelial cells and deep connective tissue
It is very thin and does not show color with HE staining, but the basement membrane in pseudostratified ciliated columnar epithelium and stratified squamous epithelium is thicker and appears pink, and appears black with silver-plated staining.
Close to the epithelium is the basal plate
The thin layer close to the basal surface of epithelial cells is the stratum lucidum
The lower electron density is high, and the thicker layer is the dense layer.
Main ingredients: laminin, type IV collagen, heparin sulfate proteoglycan, etc.
Laminin function: It plays a mediating role in the connection between cells and extracellular matrix, and can promote cells to adhere to the basement membrane and spread out.
Connected to connective tissue to form a mesh
Reticular plate: secreted by fibroblasts of connective tissue, mainly composed of reticular fibers and matrix, with a few collagen fibers
Function
1. Support, connection, fixation
2. Semi-permeable membrane facilitates material exchange between epithelial cells and deep connective tissue
3. Guide epithelial cells to move and influence cell proliferation and differentiation
2. Plasma membrane infoldings
Mainly found in renal tubules
Function: Expands the surface area of the cell base, which is conducive to the rapid transport of water and electrolytes
3. Hemidesmosome
is half of the desmosome structure
Function: Fix epithelial cells to the basement membrane
Regeneration and metaplasia of epithelial tissue
Epithelial cells continue to age, die and shed, and are constantly replenished by the proliferation of undifferentiated cells (stem cells) in the epithelium. This process is called the renewal or physiological regeneration of epithelial tissue.
Under certain physiological or pathological conditions, the epithelial cells of differentiated and mature epithelial tissue can adapt to the changed conditions and undergo transformation in shape, arrangement and function, which is called epithelial tissue metaplasia.