5 epithelium sp
TRANSCRIPT
EPITHELIUMDR. SWATI PATIL
INTRODUCTIONEpi= upon; Thelia= nipple
DEVELOPMENTEctoderm- skin, mouth, nose and anal canal.
Endoderm- GIT, glands, resp tract Mesoderm-body cavities
(Mesothelium), endothelium.
Function of Epithelial Tissue
• Protection
• Absorption
• Filtration
• Secretion
Characteristics of Epithelial Tissue• Form continuous sheets
(fit like tiles)
• Apical Surface– All epithelial cells
have a top surface that borders an open space (lumen)
• Basement Membrane – anchors
epithelial cells to underlying connective tissue
BASEMENT MEMBRANE
- visible under LM- PAS +- comprises of basal lamina & reticular lamina
BASAL LAMINA- visible in EM- 20-100 nm thick- consists of dense and clear layers- composed of macromolecules
1. Laminin2. Type IV collagen3. Entactin (Nidogen)4. Proteoglycans
• Avascularity – Lacks blood
vessels– Nourished by
connective tissue• Regenerate & repair
quickly
Classification of Epithelial Tissue
Classification of Epithelial Tissue - Criteria
• Cell Shape– Squamous – flattened– Cuboidal - cubes– Columnar - columns
• Cell Layers– Simple (one layer)– Stratified (many layers)
• Named after type of cell at apical surface
Simple Squamous Epithelium• Structure
– Single Layer of flattened cells
• Function– Absorption, and filtration– Not effective protection –
single layer of cells.• Location
– Walls of capillaries, air sacs in lungs
– Form serous membranes in body cavity
Simple Cuboidal Epithelium
• Structure– Single layer of cube
shaped cells• Function
– Secretion and transportation in glands, filtration in kidneys
• Location– Glands and ducts
(pancreas & salivary), kidney tubules, covers ovaries
Simple Columnar Epithelium• Structure
– Elongated layer of cells with nuclei at same level
• Function– Absorption, Protection
& Secretion– When open to body
cavities – called mucous membranes
• Special Features– Microvilli, bumpy
extension of apical surface, increase surface area and absorption rate.
– Goblet cells, single cell glands, produce protective mucus.
• Location– Linings of entire digestive
tract
Simple Columnar Epithelium
Features of Apical Surface of Epithelium
Finger-like extensions of plasma membrane of apical epithelial cell
Increase surface area for absorption
Temporary or permanent 1 µm : height, 0.8 µm : width BRUSH/STRIATED BORDER:
seen in LM Terminal web : supports
microvilli composed of actin filaments w/
fimbrin & villin(eg.) in small intestine
Microvilli
Features of Apical Surface of Epithelium
Cilia: (eg.) respiratory tubes Whip-like, motile extensions Moves mucus, etc. over epithelial surface 1-way 5-10 µm : length 0.2 µm : diameter
* Flagella: (eg.) spermatozoa Extra long cilia Moves cell
Stereocilia (eg.) epididymis & ductus deferens Longer but non motile, compared to microvilli Branched
Pseudostratified Epithelium• Structure
– Irregularly shaped cells with nuclei at different levels – appear stratified, but aren’t.
– All cells reach basement membrane
• Function– Absorption and Secretion– Goblet cells produce mucus– Cilia (larger than microvilli)
sweep mucus • Location
– Respiratory Linings & Reproductive tract
Myoepithelial cells
Stratified Squamous Epithelium• Structure
Many layers (usually cubodial/columnar at bottom and squamous at top)
Function– Protection– Keratin (protein) accumulates in older cells near
the surface • waterproofs and toughens skin.
• Location Nonkeratinised
Keratinised
Stratified squmous keratinised
Stratified squamous non-keratinised
Stratified cuboidal epithelium
Stratified columnar epithelium
Transitional Epithelium • Structure
– Many layers– Very specialized
• cells at base are cuboidal or columnar, at surface will vary.
– Change between stratified & simple as tissue is stretched out.
• Function– Allows stretching (change size)
• Location– Urinary bladder, ureters &
urethra
GLANDS• One or more cells that make and secrete a product.• Secretion = protein in aqueous solution: hormones, acids, oils.• Endocrine glands
– No duct, release secretion into blood vessels – Often hormones– Thyroid, adrenal and pituitary glands
• Exocrine glands– Contain ducts, empty onto epithelial surface– Sweat, Oil glands, Salivary glands, Mammary glands.
Modes of Secretion
• (How the gland’s product is released)
• Merocrine - secretory products are released by
exocytosis– Ex: Sweat glands and salivary glands
• Apocrine-apical part is shed off to discharge –
secretion- Ex:mammary glands
Modes of Secretion
• Holocrine– Entire cell disintegrates
while discharging its secretion
– Sebaceous (oil glands on the face) only example
Classification of Exocrine glands
Branching
Simple – single, unbranched duct
Compound – branched.
• Shape:– tubular or alveolar– Tubular – shaped like a tube– Alveolar – shaped like flasks or sacs– Tubuloalveolar – has both tubes and sacs in
gland
Cell Junctions & Cell-Cell Adhesion
Classification of cell contacts
• Unspecialised contacts -cell adhesion molecule -intermediate protein
Cell-cell adherence junctions
1. Calcium-dependent
Cadherins
Selectins
Integrins
2. Calcium-independent
Neural cell adhesion molecule
Intercellular adhesion molecule
Actin cytoskeleton dependent cell-cell and cell-ECM adhesions
• Specialized contacts -Anchoring junctions 1.Adhesive spots or desmosomes or macula
adherens 2.Adhesive belts or zona adherens 3.Adhesive strips or fascia adherens - Occluding junction or zonula occludens or tight
junction -Communicating junctions or gap junctions
Desmosomes
Zonula adherens
Fascia adherens
Desmosomes
&
hemidesmosomes
Focal adhesion plaques
Tight Junctions
Types of Cell Junctions
Summary of cell junctions
Thank you