Epithelial Tissue Flashcards
What are the principal functions of epithelial tissues?
- Covering, lining, and protecting surfaces (eg, skin)
- Absorption (eg, the intestines)
- Secretion (eg, the parenchymal cells of glands)
- Contractility (eg, myoepithelial cells).
What are the functions of epithelial cells?
- Protection – epidermis of the skin
- Absorption – epithelium of the small intestine
- Excretion – epithelium of the kidney
- Secretion – glandular epithelium
- Sensory reception - neuro-epithelium
- Lubrication – goblet cells and sebaceous glands
- Reproduction – lining epithelium of the seminiferous
tubules and germinal epithelium of the ovary - A few specialized epithelial cells are contractile
(myoepithelial cells).
CHARACTERISTICS OF EPITHELIAL CELL
- LAMINA PROPRIA
- PAPILLAE
- Basal pole
- Apical pole
- Lateral surfaces
serves to support the
epithelium
LAMINA PROPRIA
it provides nutrition and binds epithelia to underlying structures
LAMINA PROPRIA
a type of loose connective tissue that are found beneath the epithelium
LAMINA PROPRIA
small invagination’s or irregularities in the connective tissue surface that increases area of contact between the connective tissue and the epithelial tissue
PAPILLAE
region of the cell contacting the connective tissue
Basal pole
facing a space
Apical pole
regions that adjoin the adjacent cells
Lateral surfaces
a felt-like sheet of extracellular material in
the basal surface of epithelial cells
Basement membrane
Two structures of basement membrane
- BASAL LAMINA
- RETICULAR LAMINA
2 components of basal lamina
- Lamina Lucida
- Lamina Densa
network of fine fibrils
BASAL LAMINA
connected with the epithelium (appear light under EM)
LAMINA LUCIDA
nearer to the
underlying connective tissue
LAMINA DENSA
a more diffuse and fibrous layer
RETICULAR LAMINA
The macromolecular components of basal laminae
- LAMININ
- TYPE IV COLLAGEN
These are large glycoprotein molecules that self-assemble to form a lace-like sheet immediately below the cells’ basal poles where they are held in place by the transmembrane integrins.
Found in Lamina lucida
LAMININ
Monomers of _____ contain three polypeptide chains and self-assemble further to form a felt-like sheet associated with the laminin layer.
Found in Lamina densa
TYPE IV COLLAGEN
laminin and type IV collagen network are held
together by adhesive glycoprotein
________ and by ____ a
proteoglycan
ENTACTIN/NIDOGEN
PERLECAN
Diffuse meshwork of reticular laminae contains
Type III collagen
Type VII collagen
Functions of the basement membrane
- anchors the epithelium
- serves as a mechanical barrier (prevents malignant
cells from invading the deeper tissues - simple structural and filtering functions
- influence cell polarity
- regulate cell proliferation and differentiation by binding and concentrating growth factors
- influence cell metabolism and survival
- organize the proteins in the adjacent plasma
- membrane (affecting signal transduction)
- serve as pathways for cell migration
- the basal lamina seems to contain the information
necessary for many cell-to-cell interactions
is used to denote the lamina densa and its
adjacent layers and structures seen with the TEM.
“BASAL LAMINA
is used to denote the structures seen with the light microscope.
“BASEMENT MEMBRANE”
(INTERCELLULAR ADHESION AND OTHER JUNCTIONS)
Various junctions serve to function as:
- Seals to prevent the flow of materials between the
cells (occluding junctions)
- upper most part - Sites of adhesion (adhesive or anchoring junctions)
- interact with actin and intermediate
filaments
- function to provide mechanical stability - Channels for communication between adjacent
cells (gap junctions)
- diffusion of molecules
upper most part
Seals to prevent the flow of materials between the
cells (occluding junctions)
- interact with actin and intermediate
filaments - function to provide mechanical stability
Sites of adhesion (adhesive or anchoring junctions)
- diffusion of molecules
Channels for communication between adjacent
Four distinct zone
- ZONULA OCCLUDENS
- ZONULA ADHERENS (intermediate junction)
- MACULA ADHERENS (desmosomes)
- NEXUS (gap junction)
- important in transporting epithelium
- maintaining the structural integrity of
epithelium
ZONULA OCCLUDENS
- “terminal web”
- Serves as a site of insertion for the
contractile microfilaments that form the
core of the microvilli. - Aid in contraction of microvilli
ZONULA ADHERENS (intermediate junction)
- Appears as dense dots or fusiform
thickening of the cells - Site of attachment of the cytoskeleton to
the cell surface
MACULA ADHERENS (desmosomes)
- Sites of cell to cell adhesion
- In LM; entire structure is called “terminal
Bar”
MACULA ADHERENS (desmosomes)
- Concerned with cell to cell communication
- “communicating junction”
NEXUS (gap junction)
- Each membrane is studded with polygonal
projections (connexions) - Adhesive function; area of low electrical
resistance, important in cell-to-cell communication for coordination of cellular
activities.
NEXUS (gap junction)
- Present in: between osteocytes, smooth
and cardiac muscles, neurons - Absent in: skeletal muscle, blood
NEXUS (gap junction)
– Delicate vertical striations in a refractile border of columnar epithelium
– Prominent in cells whose principal function is absorption
Microvili
- Striated or Brush border– intestinal epithelium, epithelial tissues of the kidney
- Small finger-like processes
- Increase the efficiency of absorption
Microvili
– Long pyriform tuft of slender processes projecting into the lumen from each cell
– Found in lining epithelium of the epididymis and the proximal part of the ductus deferens
Stereocilia
– Promote absorption by amplifying cell surface like the microvilli
– Longer than microvilli and much less motile
– Basal infoldings- increases the surface area at the base of a cell promoting absorption like the microvilli
Stereocilia
– Larger than microvilli
– Function to propel fluid or coating of mucus towards the exterior
Cilia
non motile but enriched with receptors and signal transduction complexes
Primary cilium
found only in epithelia, abundant on the
apical surface of cuboidal or columnar cells
Motile cilia
Main Groups of Epithelia
- Covering (lining) epithelia
- Secretory (glandular) epithelia
Classification of Covering Epithelia
* number of cell layers
– Simple
– Pseudostratified
– Stratified
Classification of Covering Epithelia
* cell morphology
– Squamous
– Cuboidal
– Columnar
– transitional
- Very thin, flat cells
- Mosaic pattern
- Attenuated cytoplasm with central bulging nucleus
Simple Squamous Epithelium
-lining of blood vessel, lymph vessels, cavities of the heart
Endothelium
lining serous cavities like pleura, pericardium, peritoneum, tunica vaginalis testis
Mesothelium
-lines the interior chamber of the eye, perilymph spaces of the internal ear, subdural and subarachnoid spaces.
Mesenchymal
–lining the pulmonary alveoli, bowman’s capsule
Flattened cells
- Main Functions of Simple Squamous Epithelium
– Facilitates the movement of the viscera
(mesothelium)
– Active transport by pinocytosis
(mesothelium and endothelium)
– Secretion of biologically active molecules
- Row of square or rectangular profile
- Nuclei tend to aligned at the same level in all of the cells, “box-like”, “cube-like”
Simple Cuboidal Epithelium
Simple Cuboidal Epithelium
*Example of Distribution
– Covering the ovary
– Thyroid follicles
– choroid plexus
– pigmented epithelium of the retina
- Main Function of Simple Cuboidal Epithelium
– Covering
– secretion
- A membrane composed of cylindrical cells possessing an appreciable height aside from length and width.
- Nuclei are at the same level and situated nearer to the basal surface than the apical surface.
- Associated with secretion or absorption
Simple Columnar Epithelium
Simple Columnar Epithelium
* Example of Distribution
– Simple plain tall columnar – mucosa of the stomach, small and large intestine, gallbladder, bigger ducts of glands
– Simple plain low columnar – smaller ducts of glands, some excretory tubules of kidney
Simple Columnar Epithelium
* Main Function
– Protection
– Lubrication
– absorption
– secretion
Stratified Epithelia
I. Stratified Squamous
II. Stratified Cuboidal
III. Stratified Columnar
- Cells become more irregular in shape and flatten as they accumulate keratin
- they become hardened, cornified and removed progressively closer to the skin surface
- Thin, metabolically inactive packets of keratin-lacking nuclei
Stratified Squamous Epithelia
(Keratinized)
Stratified Squamous Epithelia
(Keratinized)
Example of Distribution
epidermis
Stratified Squamous Epithelia
(Keratinized)
Main Function
Protection
Prevents water lost
- Lines wet cavities where loss of water is not a problem
- Inner most surface of the body
- Flattened cell of the surface layer contain
much less keratin, retaining their nuclei and metabolic function - Non-keratinized stratified squamous epithelium
Stratified Squamous Epithelia (Non-Keratinized)
Stratified Squamous Epithelia
(Non-Keratinized)
Ex of Distribution
– Mouth
– Esophagus
– Larynx
– Vagina
– Anal canal
Stratified Squamous Epithelia
(Non-Keratinized)
Main Function
– Protection
– Secretion
– Prevents water loss
II. Stratified Cuboidal Epithelia
* Example of Distribution
– Excretory ducts of salivary and sweat glands
– Developing ovarian follicles
II. Stratified Cuboidal Epithelia
* Main Function
– Protection
– Secretion
III. Stratified Columnar Epithelia
Distribution and Function
- Example of Distribution
– Conjunctiva - Main Function
– Protection
– secretion
- Thin basal lamina
- Appear very thin when organ is distended and thicker when the organ is collapsed
Transitional (Urothelium) Epithelia
- Consists of many layers (contracted stage)
– Deepest layer- one or two rows
– Pyriform/pear shaped cells-1-3 rows
– Superficial layer- flattened/umbrella shaped cells - Two layers (stretched)
– Superficial layer- large flattened/squamous cells
– Layer of cuboidal cells
Transitional (Urothelium) Epithelia
Transitional (Urothelium) Epithelia
- Example of Distribution
– Bladder
– Ureter
– Rena calyces - Main Function
– Protection
– Distensibility
- Appears to be composed of several layers of cell when in reality, there is only one layer
- All cells rest upon the basement membrane
Pseudostratified Epithelia
- Not all of the cells reach the surface
- Cells vary in shape
– Tall columnar
– Fusiform/spheroidal
Pseudostratified Epithelia
Pseudostratified Epithelia
Distribution
– Lining of trachea
– Bronchi
– Nasal cavity
Pseudostratified Epithelia
Main Function
– Protection
– Secretion
– Cilia-mediated transport of particles trapped in mucus out the air passages
- Epithelial cells specialized for secretion
- Epithelial structures are called “gland”
Glandular Epithelium
- The molecules to be secreted are generally stored in the cells in small membrane-bound vesicles called secretory granules.
- Secretory products is passed into a system of tubes/ducts which transport it to the surface.
Glandular Epithelium
Two major categories of Glandular Epithelium
Exocrine and Endocrine
deliver their product into a system of ducts
opening on an external or internal surface
Exocrine
release their product into the blood or lymph
for transport to another part of the body.
Endocrine
secretion is not discharged from the cells
producing it.
Acrine glands
produce enzyme not released but utilized within the cells for phagocytosis
Granular leukocytes and phagocytes
EXOCRINE GLANDS Secretory products
– Serous – acinar cells of pancreas and parotid (trypsin,
amylase, pepsin)
– Mucous – gastric glands and respiratory secretions
– Others secreted by:
* Sebaceous gland cells –secrete sebum
* Mammary gland cells –secretes milk
* Gastric gland parietal cells- secrete HCL
- General structure
– Multicellular – arranged in
cords, bundles, or islet
– Connective tissue stroma - supports the cells
containing numerous
fenestrated blood vessels
– Arrangement- thyroid-follicular
Others- scattered randomly
ENDOCRINE GLANDS
Secrete hormones directly into the neighboring blood capillaries
Endocrine Glands
– Four Major Categories of Endocrine Glands
- Endocrine cells secreting polypeptide/pure proteins hormones
- Endocrine cells secreting glycoprotein hormones
- Endocrine cells secreting steroid hormone
- Endocrine cells secreting biochemical amines
– Distinct nucleolus
– Abundant GER
– Membrane bound secretory granules
- Endocrine cells secreting glycoprotein hormones
– Numerous mitochondria with tubular cristae
– Abundant SER
– Absence of secretory granules
– Liposomes and lipofuscin pigments are frequentlyseen
- Endocrine cells secreting steroid hormone
– Located within the cytoplasm or within the
secondary granules
– Dense-cored vesicles with EM
– Content are released by exocytosis
- Endocrine cells secreting biochemical amines
Classification of Glands
I. According to Number of Component Cells
– Unicellular
* One celled, (goblet cell)
* Secretes mucin
– Multicellular
* Many cells
* Forms the parenchyma of pancreas or liver
Classification of Exocrine Glands
According to Shape
- Simple- ducts not branched
a. Simple tubular
b. Branched tubular
c. Coiled tubular
d. Acinar (alveolar)
e. Branched acinar - Compound- ducts from several secretory units converge into larger ducts
a. Tubular
b. Acinar
c. tubuloacinar
*Secretory portions (Exocrine Glands Shape)
– Acinar- rounded and sac-like
– Tubular- either short or long and coiled
– Either type of secretory portions may be branched even if duct is not branch
Features (SIMPLE)
* Elongated secretory portion
* Duct usually short or absent
Simple Tubular
Example of Simple Tubular
- mucous glands of the colon
- Intestinal glands or crypts (of Lieberkuhn)
Features (SIMPLE)
* Several long secretory parts joining to drain 1 duct
Branched Tubular
Example of Branched Tubular
- glands in the uterus and stomach
Features (SIMPLE)
* Secretory portion is very long and coiled
Coiled Tubular
Example of Coiled Tubular
sweat glands
Features (SIMPLE)
* Rounded, saclike secretory portion
Acinar (alveolar)
Example of Acinar (alveolar)
- small mucous glands along the urethra
Features (SIMPLE)
* Multiple saclike secretory parts entering the same duct
Branched Acinar (alveolar)
Example of Branched Acinar (alveolar)
- Sebaceous glands of the skin
Features (COMPOUND)
* Several elongated, coiled secretory units and their ducts converge to form larger ducts
Tubular
Features (COMPOUND)
* Several saclike secretory units with small ducts converge at a larger duct
Acinar (alveolar)
Examples of Tubular (COMPOUND)
- Submucosal mucous glands (of Brunner) in the duodenum
- Kidneys, testis, liver
Features (COMPOUND)
* Ducts of both tubular and acinar secretory units converge at larger ducts
Tubuloacinar
Classification of Exocrine Glands According to the Way the Secretory Products Leave the Cell
Merocrine Secretion
Holocrine Secretion
Apocrine Secretion
Examples of Tubuloacinar
- Salivary glands
- glands of respiratory passages and
pancreas
Example of Acinar (alveolar)
- Exocrine pancreas, mammary gland
- Also called eccrine, typical exocytosis of proteins or glycoproteins. This is the most common mode of secretion.
- Maintain the integrity of their constituent cells throughout the process of secretion
- Sweat and salivary gland
Merocrine Secretion
- involves the cell filling with secretory product and then the whole cell being disrupted and shed. This is best seen in the sebaceous glands of skin
- Cells suffer more or less complete destruction in the process of secretion, being transformed into the secretion itself.
- Seminiferous epithelium (testis) – release of spermatozoa
Holocrine Secretion
- In an intermediate type
- the secretory product is typically a large lipid droplet and is discharged together with some of the apical cytoplasm and plasmalemma
- Cells suffer a partial destruction of their distal borders in the process of secretion
- Mammary gland, some axillary sweat glands
Apocrine Secretion
Classification According to Nature of
Secretory Products
Serous glands
Mucous glands
Mixed glands
Cytogenic or Cellular Glands
- Acidophilic granular cytoplasm with a round nucleus
- basal ends of serous cells have well-developed RER and Golgi complexes
Serous Glands
- cells are filled apically with secretory granules in different stages of maturation
- stain intensely with any basophilic or acidophilic stain.
- Parotid and pancreas
Serous Glands
- are typically larger than serous cells,
- Basophilic non-granular, reticulated cytoplasm and flattened nucleus t the basement membrane
Mucous gland
- The apical region and most of the other cytoplasm of each mucous cell is filled with secretory granules containing mucin like that of goblet cells.
- The basal region contains the RER, nucleus, and a welldeveloped Golgi apparatus.
- Sublingual gland, in the stomach, the various salivary glands, the respiratory tract, and the genital tract.
Mucous gland
- Both serous and mucous
- Clumps of serous cells at the ends of some mucous tubules appear as crescent-shaped structures called serous demilunes
- Submaxillary glands and submandibular salivary glands have both mucous and serous secretory units, typically shaped as acini and tubules respectively
Mixed Glands
- Glands that produce cells
- Testis, ovary
- Cytocrine –melanocytes-melanin
Cytogenic or Cellular Glands
