Epithelial tissue Flashcards
Tissue
System of similar cellular and non-cellular structures with same origin and same specific functions
Non-cellular structures:
ECM (fibers + Ground substance)
Symplast (formed by Fusion of myoblasts in striated msucle)
Syncytium (dividing cells that remain connected by cytoplasmic bridges
The four Basic types of tissue
- Epithelial tissue (covers surfaces, lines cavities and forms Glands)
- Connective tissue
- Muscle tissue
- Nervous tissue
Epithelial tissue origin and function
From all three germ layers
Protection, Absorption, Transport, secretion, sensory
Structural characteristics of epithelium
cells are connected by intercellular junctions
rest on Basement membrane
is AVASCULAR
Classification of epithelium
Simple: squamous, cuboidal, columnar, pseudostratified
Stratified: Squamous keratinized/ non-keratinized, cuboidal, columnar, transitional
Simple squamous epithelium
flattened nuclei
Location: Endothelium (blood vessels), Mesothelium (Body cavities), Epithelium (lung alveoli)
Function: Transport of gases or fluids
Embryological origin: Mesoderm and endoderm
Simple cuboidal epithelium
round nucleus in Center
Location: ducts and tubules
Function: excretory, secretory or absoptive
Embryological origin: ectoderm, Mesoderm, endoderm
Simple columnar epithelium
elongated nuclei at base
microvilli or cilia on apical Surface
Location: gastrointestinal, female reproductive
Function: Absorption, secretion, Transport
Embryological origin: Mesoderm and endoderm
Pseudostratified epithelium
nuclei are disposed on different Levels
Location: respiratory System, male reproductive
Function: protection, Transport
Embryological origin: Endoderm and mesoderm
Stratified cuboidal /columnar
Location: large excretory ducts
Function: protection
Embryological origin: ectoderm
Stratified squamuos non-keratinized
Location: cavities which are mechincally affected –> oral cavity, Pharynx, esophagus, anal canal, vagina
Function: protection
Emrbyological origin: ectoderm, endoderm
Stratified squamous keratinized
Location: Skin
Function: protection
Embryological origin: ectoderm
Layers of stratified squamous keratinized Epithelium (thin and thick Skin)
Thin Skin: basal, spinous, granular, corneal
Thick Skin: basal, spinous, granular, clear, corneal layer
Transitional Epithelium /urothelium
Basal cells–> cuboidal
Intermediate cells –> polygonal
Apical cells –> umbrella/dome cells
Location: Urinary tract
Function: for streching, withstands toxicity of Urine
Embryological origin: Mesoderm and endoderm
Surface specializations on basal, apical and lateral surfaces
Basal Surface: Plasma membrane interdigitations, Basement membrane, hemidesmosomes
Apical Surface: Microvilli, cilia, stereocilia
Lateral Surface: intercellular junctions
Plasma membrane interdigitations
Infoldings of Plasma membrane
in kidney tubules and striated ducts
Function: increasing the Surface for fluid transport
Basement membrane
- attachment site for overlying epithelial cells and Underlying CT
- 3 regions:
1. Lamina lucida
2. Lamina densa
3. Lamina fibroreticularis
Lamina lucida
Electron lucent
ARTIFACT
Lamina densa
Electron dense
Type IV Collagen, glycoproteins
Lamina fibroreticularis
Electron lucent
type III, IV, VII Collagen, elastic fibers
Functions of the Basement membrane (5)
structural support metabolic support selective permeability barrier cell Migration Control of epithelial growth and differentiation
Microvilli
Finger-like
Have core of actin micofilaments –> stability
Actin microfilaments are Held together by actin binding protein (VILLIN)
Actin microfilaments are connected to Plasma membrane by MYOSIN I
All microvilli in equal size: striated border
Mocrovilli in unequal size: brush border
Cilia
Long, hair-like
two types: motile and non-motile
Motile cilia:
Core (AXONEME): 2 microtubules
–> surrounded by 9 peripheral doublets
doublets are linked by NEXIN, connected to core by RADIAL SPOKES
DYNEIN ARMS: motor protein that moves along the Surface of the adjacent microtubule
Location: respiratory and female reproductive
Function: fluid flow and move of oocyte
Non-motile cilium
called: Primary cilium, monocilium, sensory cilium
Function: sensor for mechanical and chemical Signals
Central doublet is absent!!
Dynein, nexin and radial spokes are absent!!
Stereocilia
Immotile!!!
in Male reproductive and inner ear
internal bundle of actin Filaments
increase Surface for absoption in epidydimis and exitation in inner ear
Functional types of intercellular junctions
- occluding (tight) junctions: barrier, for Regulation of permeability
- Adhering (anchoring) junctions: glue cells together, mechanical stability
- Communicating junctions: passage of small molecules
Occluding junctions –> Zona occludens
- Most apical Junction
- blocks passage of laminar Contents
- sealing Strands: transmembrane proteins of two cells link and acclude
Pathways for Transport of substances across epithelia
TRANSCELLULAR: across Plasma membrane, active, required Energy dependent channels and proteins
PARACELLULAR: across zonula occludens, dependend on tightness of zonula occludens
Types of adhering (anchoring) junctions
Zonula adhernes
Macula adherens (desmosomes)
Hemidesmosomes
Zonula adherens
belt - like and near apical Surface
links cells by transmembrane proteins –> CADHERINS
binds to actin Filament of cell
electron dense Plaque can be seen on the cytoplasmic side of the membrane
Macula adherens (desmosomes)
spot-like scattered over intercellular surfaces
overlapping Segments of CADHERINS
Hemidesmosomes
- on basal Surface of cell
- connects Plasma membrane to Basement membrane - via INTEGRINS
- Integrins bind to LAMININS in b.m.
LAMININS bind to intermediate filaments
Communicating Junction (gap or Nexus Junction)
patch-like
Accumulation of transmembrane channels or pores
Each channel is formed by two half channels –> CONNEXONS
connexon made of 6 CONNEXIN subunits
Exocrine vs Endocrine glands
Exocrine: connected to the Surface Epithelium by ducts
Endocrine: lost Connection to Epithelium, NO DUCTS; release secretions (Hormones) into blood
Glands by their number of cells
- Unicellular Glands: goblet cells and cells of DNES
2. Mulitcellular glands
Goblet cell
Modified columnar cells
in simple Epithelium of intestine and respiratory tract
Aggregation of mucigen granules in apical Region
Nucleus in basal part
Has microvilli
Multicellular exocrine gland
Secretory comonent (end piece) and duct (cennects secretory component to Surface)
Classification of Glands according to shape of secretroy component
Tubule - like: TUBULAR
Spherical: ACINAR ( ALVEOLAR)
Branched: BRANCHED (TUBULAR or ACINAR or TUBULE-ACINAR)
Classification of Glands according to shape of the duct
Unbranched –> SIMPLE GLAND
Branched –> COMPOUND GLAND
Classification of Glands according to chemical composition of secretory products
Serous (Proteins)
Mucous (rich in carbs)
Mixed (serous and mucous)
Sebaceous (sebum –> oily material)
Classification of Glands accrding to the way of secretion
Merocrine (eccrine)
Apocrine
Holocrine
Merocrine (eccrine) secretion
most common
secretory product is delivered in membrane Bound vesicles to apical Surface –> exocytosis
Apocrine secretion
- found in lacting mammary Gland
- product is released in apical Portion of cell
- apical Portion of the cell is pinched off
Holocrine secretion
- in sebaceous Glands of Skin
- Product accumulates within maturing which then undergoes programmed cell death
- Product and debris are discharged Tino lumen of gland
Epithelial cell renewal
- rate of cell death = rate of cell replacement
- replacement cells are produced by mitosis of adult stem cells
- stem cells are located in niches:
- -> in simple epith: between differentiated cells
- -> in stratified epith: on b.m.
