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epithelial tissue

23 years of clinical medicine "Histology and Embryology" mind map of the content of epithelial tissue. Epithelial tissue is referred to as epithelium. It is composed of a large number of regular, densely arranged epithelial cells and a very small amount of extracellular matrix.

Edited at 2023-10-14 13:16:56

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Outline

Epithelial Tissue Classification
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epithelial tissue
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Biology - Epithelial Tissue
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connective tissue
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Epithelial tissue (epithelium)

definition:

Referred to as epithelium, it is composed of a large number of regular and densely arranged epithelial cells and a very small amount of extracellular matrix.

Distribution: Covering the surface of the body and the cavity surface of cavity organs

Structural features

Many cells, tightly arranged, little extracellular matrix

There is polarity

Free surface: toward the surface of the body or the cavity surface with cavities

side

Basal surface: the side opposite the free surface, attached to the basement membrane

Avascular

Rich in nerve endings

Classification

Covering epithelium

single layer

single layer squamous epithelium

Also known as single layer squamous epithelium

observe

surface view

Cells are irregular or polygonal

The nucleus is oval and located in the center of the cell

The edges of the cells are jagged or wavy, and they are chimeric with each other.

cross-sectional view

flat cells

The core-containing part is slightly thicker

Distribution and functionality

endothelium

Heart, blood vessels and lymphatic lumen

Function: Facilitates the flow of substances through blood and lymph

Mesothelium

Pleura, peritoneum, pericardium surface

Function: Conducive to visceral movement

other

Kidney cyst wall, alveoli, etc.

Features:

Smooth, reduces friction, facilitates material exchange, and has strong permeability

single layer cuboidal epithelium

observe

surface view

Cells are hexagonal or polygonal

cross-sectional view

Cells are cuboidal

The nuclear circle is centered

Distribution and functionality

Thyroid follicles, renal tubules, etc.

Function: secretion and absorption

Features:

A layer of approximately cubic cells

simple columnar epithelium

observe

surface view

Cells are hexagonal or polygonal

cross-sectional view

Cells are columnar

Nuclear ellipse, close to the base

Distribution and functionality

Gastrointestinal, gallbladder and uterus, etc.

Function: secretion and absorption

goblet cells

top

enlarge

filled with clay particles

Contains mucin, which combines with water to form mucus after secretion

Lubricates and protects the epithelium

bottom

narrow

The nucleus is deeply stained and appears as an inverted triangle.

Function: secretion and lubrication

Features: A layer of prismatic cells

pseudostratified ciliated columnar epithelium

observe

cross-sectional view

Looks like a multi-layer but is actually a single layer

Distribution and functionality

respiratory tract mucosa

Function: secretion, protection

composition

columnar cells:

At most, there are a large number of cilia on the free surface

spindle cells

cone cells

goblet cells

Features

The nuclei are not at the same level, but the bases are all attached to the basement membrane

basement membrane thickness

Multilayer

Stratified squamous epithelium

stratified squamous epithelium

distributed

Keratinized stratified squamous epithelium

skin epidermis

The nuclei of superficial cells disappear, the cytoplasm is filled with keratin, and the cells become hard and fall off.

Unkeratinized stratified squamous epithelium

Mouth, esophagus and anus

Superficial cells have nuclei and contain little keratin

Function

Friction-resistant; prevents the intrusion of foreign matter (protective effect); strong regeneration and repair ability

composition

surface layer

flat scaly

multilayered flat cells

basal layer

Basal cells:

One layer, short columnar shape, with the ability to proliferate

middle layer

polygon cells

spindle cells

Flat cells:

Superficial layer, exfoliated and keratinized

Features:

Rough basal surface

The basal surface and the free surface are not parallel

Stratified columnar epithelium

distributed:

Conjunctiva, male urethra and large ducts of some glands

Features:

Made up of several layers of cells

The deep part is one or several layers of polygonal cells

The shallow part is a layer of neatly arranged short columnar cells.

metastatic epithelium

distributed:

urinary tract

composition

Basal cells (layer 1):

cubic or dwarf columnar

Middle layer cells:

polygon, inverted pear shape

Surface cells (1 layer of cover cells):

large cube

Cover cells: one surface cell can cover several middle cells

Function:

protective

Features:

Epithelial thickness changes with physiological conditions

When the bladder is empty, the epithelium becomes thicker, the number of cell layers increases, and the cover cells become large cuboids.

When the bladder is full and expanded, the epithelium becomes thinner, the number of cell layers decreases, and the cover cells become flat.

The basal surface and the free surface are parallel

glandular epithelium

definition

Glandular epithelium:

Epithelium composed of glandular cells with mainly secretory function

Glands:

Organs mainly composed of glandular epithelium

Classification

endocrine glands

Secretions (hormones) released directly into the blood

No ducts, such as: thyroid gland, adrenal gland, pituitary gland, etc.

exocrine glands

Single cell gland:

Microstructures, such as goblet cells

multicellular gland

secretory department

shape

tubular glands

alveolar gland

tubuloalveolar glands

secretory part called acinus

composition

serous gonads

composed of serous acini

(Serous acini are composed of serous cells)

serous cells

Features

Generally cone-shaped or columnar

The nucleus is round, close to the base of the cell

Strong basophilic staining of the basal cytoplasm

The top cytoplasm contains more eosinophilic secretory granules, called zymogen granules.

Electron microscopy

Dense rough endoplasmic reticulum at the base

There are well-developed Golgi complex and secretory granules above the nucleus.

Function

Secretion of serous fluid, thin

Distribution: Parotid gland

mucous gonads

Made of mucinous acini

(Mucinous acini are composed of mucinous cells)

mucous cells

Features

Generally cone-shaped

The nucleus is flat and oval, located at the base

A small amount of perinuclear cytoplasm showed basophilic staining

Most of the cytoplasm is almost colorless and appears as foam or vacuoles.

(Light cytoplasmic staining)

The top cytoplasm is filled with a large number of mucin granules

Electron microscopy

There is a certain amount of rough endoplasmic reticulum in the basal cytoplasm

There is a well-developed Golgi complex and extremely abundant coarse clay particles above the nucleus.

Function

secretion of mucus, thick

Distribution: duodenal glands

mixed gonads

Composed of three types of acini

mixed acini

Composed of serous cells and mucinous cells

The common form is: the acinus is mainly composed of mucinous cells, and the serous cells are located at the bottom or end of the acinus. They are arranged in a half-moon shape on the section, so it is called serous half-moon.

Distribution: sublingual gland, submandibular gland

Catheter Department

Directly connected to the secretory part and surrounded by single or stratified epithelium

Function:

Discharge secretions, some of which secrete or absorb water and electrolytes

With or without branching into simple complex glands

Secretions are discharged through ducts to the body surface or into organ cavities

Acinar ducts, such as sweat glands, salivary glands, gastric glands, etc.

The acini are alveolar or tubular, composed of a single layer of cuboidal or cone-shaped cells, with epimyoblasts

special structure

free surface

microvilli

About 0.1 μm in diameter, tiny finger-like protrusions extending from the free surface of epithelial cells;

Cytoplasm inside, cell membrane outside

Electron Microscope (EM)

Surface: cell membrane

Central axis (in the cytoplasm): longitudinal microfilaments

(Microfilaments are actin filaments, and microfilament contraction can make microvilli elongate or shorten)

Light microscope (LM)

A large number of microvilli are densely arranged to form

Striatal border (the surface of the columnar epithelial cells of the small intestinal mucosa) or brush border (the renal tubular epithelium)

Function:

Increase surface area for better absorption

cilia

Thick and long protrusions extending from the free surface of epithelial cells,

5~10μm long, 0.3~0.5μm diameter;

Cytoplasm inside, cell membrane outside

Electron Microscope (EM)

Surface: cell membrane

Center axis: Visible 9 2 structure

There are 2 single microtubules in the center and 9 groups of doublet microtubules around them.

Light microscope (LM)

visible

Function:

Rhythmic directional swing

matrix

The base of the cilium has basically the same structure as the centriole

Its microtubules are connected to the microtubules of cilia

side

(cell connection)

The intercellular space is very narrow, strengthening the mechanical connection between cells,

Maintain the integrity and coordination of the organizational structure

The formation and maintenance of cell junctions are dependent on calcium ions

It is composed of local cell membrane, cytoplasm and intercellular space between adjacent cells.

When two or more connections exist at the same time, it is called a connection complex

Tight junction/closed junction (occlusive zonules)

located at the top of the side of the cell

Electron microscopy

Adjacent cell membranes form approximately 2 to 4 point-like fusions

The intercellular space disappears at the fusion point

There is a very narrow gap at the non-fusion point

Function:

Block substances from passing through intercellular spaces

(barrier effect)

Intermediate connection/adhesive tape (adhesive tape)

Located beneath tight junctions and surrounding the top of the cell

Electron microscopy

transmembrane cadherin

The gap between adjacent cells is 15~20nm and contains dense filaments.

The cytoplasmic inner surface of the membrane contains a thin layer of dense material and microfilaments.

Microfilaments form a terminal network in the cytoplasm

Function:

intercellular adhesion,

Maintain cell shape and transmit cell contractility

Desmosomes (focal adhesions)

Spot-like or button-like, varying in size, located deep in the adhesive zonules

In areas prone to friction such as skin and esophagus

Especially developed in stratified squamous epithelium

Electron microscopy

wide intercellular space

There is a middle line, made of interwoven filaments

Cytoplasmic surface: thicker dense material forming the attachment plate

Attachment plate: There are intermediate filaments (keratin filaments) attached in the form of loops

Function:

Strong mechanical connection, supporting and fixing

Gap junction/communication connection (communication connection)

Widespread, deep surface of columnar cells

Electron microscopy:

Adjacent cell membranes are highly parallel,

The intercellular space is about 3 nm, and there are many junctions at approximately equal intervals.

There are many regularly distributed connectosomes in the cell membrane

Columnar particles, aggregated into spots of varying sizes

There are many roughly equally spaced connection points within the

Diameter 7~9nm,

Surrounded by 6 rod-shaped connexins, with a small tube with a diameter of 2 nm in the center

Adjacent cells are connected through small tubes, which serve as communication channels between cells.

Function:

Transmit chemical information and electrical impulses

basal surface

basement membrane

A thin film formed between the basal surface of epithelial cells and deep connective tissue

The basement membrane of pseudostratified ciliated columnar epithelium and stratified squamous epithelium is thicker and pink.

Generally cannot be distinguished in HE stained sections

Silver-plated dyeing, the base film is black

Under the capillary endothelium, around muscle cells and some glial cells,

The base film consists only of the substrate

Electron microscopy

substrate

close to epithelium

Produced by epithelial cells,

Thick 50~100nm

two floors

transparent layer

A thin layer with low electron density close to the basal surface of epithelial cells

Dense layer

High electron density and thicker

composition

Laminin, fibronectin and type IV collagen, etc.

stencil

Connected to connective tissue

Produced by fibroblasts of connective tissue

Mainly composed of reticular fibers and matrix, sometimes with a few collagen fibers

Function:

Support, connect, and fixate; semipermeable membrane, conducive to material exchange;

Also guides epithelial cell movement, affecting proliferation and differentiation

plasma membrane infolding

structure

Electron Microscope (EM)

Infolding of the basal cell membrane into the cytoplasm

Perpendicular to the basal surface of the cell

The inner folds contain many parallel long rod-shaped mitochondria.

(Longitudinal mitochondria)

Light microscope (LM)

Vertical lines

Distribution: Mainly in renal tubules

Function:

Expand the basal area of cells to facilitate the movement of water and electrolytes

hemidesmosome

Located on the basal surface of epithelial cells

half of the desmosome structure

There are also attachment plates on the inside of the cell membrane.

Tension filaments attach to it, fold into loops and return to the cytoplasm

Function:

anchor epithelial cells to the basement membrane