18 epithelium poonam
TRANSCRIPT
EPITHELIUM
CAPT DR POONAM SINGHDEPT OF ANATOMY
SEQUENCE OF PPT
1. INTRODUCTION2. DEVELOPMENT3. CLASSIFICATION4. HISTOLOGICAL APPEARANCE5. APICAL DOMAIN & ITS MODIFICATIONS6. LATERAL DOMAIN & ITS SPECIALIZATIONS7. BASAL DOMAIN8. GLANDS & ITS TYPES
TISSUES4 Basic types
DEVELOPMENT
5 – 6 DAY
Implantation of the Blastocyst6th DAY
9TH DAY
DEVELOPMENT
DEVELOPMENT OF EPITHELIUM
1. Ectoderm:- skin, hair follicles, mammary glands, cornea, conjunctiva, some parts of mouth & anal canal.
2. Endoderm:- GIT ( except part of mouth &anal canal), resp tract, glands.
3. Mesoderm:-body cavities (Mesothelium), endothelium.
EPITHELIUM
• Avascular tissue composed of cells,1. Covers the exterior of body surfaces2. Lines internal body cavities & body tubes3. Forms parenchyma of glands their ducts4. Specialized epi cells fxn as receptors for the
special senses.
• Nourished by connective tissue• Regenerate & repair quickly
FUNCTIONS
1. Protection2. Absorption3. Secretion4. lubrication5. Transportation6. Receptor fxn ( sensory)
Characteristics
1. Cell junctions:- specific cell-to-cell adhesion molecules.
2. Exhibit functional & morphological polarity a) Apical domain
b) lateral domainc) basal domain
3. Rest on basement membrane- anchors epithelial cells to underlying connective tissue
CLASSIFICATION
• Based on 2 factors:-
1. Simple / Unilaminar
2. Compound / Stratified / Multilaminar
Based on the shape of surface cells:-
W > H
W = H H>W
EPITHELIUM
UNILAMINAR/ SIMPLE MULTILAMINAR/ SRTATIFIED
STRATIFIED SQUAMOUS
KERATINIZED
NON-KERATINIZED
STRATIFIED CUBOIDAL
STRATIFIED COLUMNAR
TRANSITIONAL
SQUAMOUS
CUBOIDAL
COLUMNAR WITHOUT SPECIALIZATION
WITH SPECIALIZATIONS
MICROVILLI CILIA
GLANDULAR CELLSPSEUDOSTRATIFIED
MYOEPITHELIAL CILIA
SENSORY CELLS
NONCILIATED CILIATED STEREOCILIA
Classification of Epithelial Tissue
Simple Squamous Epithelium• Structure
– Single Layer of flattened cells• Function
– Diffusion and filtration– Not effective protection – single
layer of cells.• Location
– Endothelium– Mesothelium– Lung alveolus
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, germinal layer ofovaries
Simple Columnar Epithelium• Structure
– Elongated layer of cells with nuclei at same level
• Function-- Absorption, Protection
& Secretion
• Location-- GIT
Simple Columnar Epithelium with specializations
1. Ciliated columnar epithelium:--cell surface bears cilia.-lines the resp tract, uterus, uterine tubes.
2. Simple columnar epithelium with microvilli:--visible only under EM.-striated border:- small intestine- brush border:- GB- increase surface area & absorption rate
Simple Columnar Epithelium with specializations
3. With secretory function: Goblet cells- scattered in the mucosa of stomach & small intestines- single cell glands, produce protective mucus.
Stratified Squamous Epithelium
• StructureMany layers (usually Cuboidal/columnar at base & squamous at
surface) Found in those surfaces subject to friction.
• Function– Protection– Keratin (protein) accumulates in older cells near the surface
• waterproofs and toughens skin
• Keratinized/ Non-keratinized
Stratified squamous keratinized • Loc:- skin
• Superficial cell die & lose their nuclei
• Keratin (+)
Stratified squamous non-keratinised• Loc:-
Mouth, tongue, pharynx, esophagus, vagina & cornea.
Stratified squamous epithelium
• Eg..vagina
Stratified Cuboidal epithelium
• Loc:-large ducts of sweat glands, salivary glands, pancreas.
Stratified columnar epithelium
• Loc:- palpebral conjunctiva
Special classification of epithelium1. 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
2. TRANSITIONAL EPITHELIUM
• Structure– Many layers / Stratified epithelium– 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)– Impermeable to salts
• Location– Urinary bladder, ureters & urethra
URINARY BLADDER
-exhibits special structural surface modifications to carry out specific fxns.
Apical domain and its modifications
1. Microvilli- fingerlike cytoplasmic projections- increase surface area for absorption- length= 5 µm - varya) short, irregular, bleb-like (transepithelial transport is less).b) tall, closely-packed, uniform ( transport fluid & absorb metabolites).
2. STEREOCILIA
• Extremely long, immotile microvilli.
• length= 5-10 µmLimited to:-• Epididymis• Proximal part of ductus
deferens• Sensory cells of the
inner earIn EM:- hairs of a paint
brush
3. Cilia- hair like extensions of apical plasma membrane containing anoxeme.- motile extensions Moves mucus, etc. over epithelial surface 5-10 µm : length 0.2 µm : diameter
3 Types of cilia1. Motile:- large no. (+)nt on the apical domain of many epithelial cells.
2. Primary / Monocilia:- - solitary projections, Immotile- single cilium per cell (+)ntfxn:- Chemosensors mediate light sensation Osmosensors Odorant Mechanosensors sound perception in multiple organs in the body
3. Nodal cilia:- -Found in the embryo on the bilaminar germ disc -Concentrated in the area that surrounds the primitive node.
Lateral domain & its specializations
• Characterized by the presence of CAMs
Classification of cell contacts
• Unspecialized contacts
-Cell adhesion molecule - Each CAM is in contact with
intermediate protein.-Force is transmitted from
cytoskeleton of one cell to another.
-TEM:- bead-like
Specialized junctional structures• Forms the barrier & attachment device junctional complex
responsible for joining cell together.• Three types:-1. Anchoring jxns 2. Occluding jxns/ tight cell to cell contact: jxns / Zonula occludens(a). Macula adherens
(Desmosomes)(b). Zonula adherens 3. communicating jxns/ Gap
(Adhesive belts) jxns
Cell to extracellular matrix :(a) Focal adhesions / Adhesive strips(b) Hemidesmosomes / Focal spots
Desmosomes
Zonula adherens
ANCHORING JUNCTIONS
DESMOSOME ZONULA ADHERENS
Fascia adherens
Hemidesmosomes
Occluding junctions
Gap junctions
TYPES OF CELL JUNCTIONS
TYPES OF CELL JUNCTIONS
Basal domainBASEMENT MEMBRANE• Amorphous, dense layer of
variable thickness at the basal surfaces of epithelia.
• Consists of:1. Basal lamina
a). Lamina densa b). Lamina Lucida2. Reticular lamina• Visible under LM
BASEMENT MEMBRANE
• Functions:1. Adhesion 2. Act as barriers3. Cell organization4. Regeneration of
peripheral nerves after injury
GLANDS
EXOCRINE GLANDS ENDOCRINE GLANDS-Consists of duct - Lacks duct system-Secretes their product into the surface directly / thru the duct
- Secrete their product into the CT enter bloodstream reach target cells
-Secretion: Unaltered, concentrated -product called as HORMONES
- Sweat, Oil glands, Salivary glands, Mammary glands.
- Thyroid, adrenal and pituitary glands
Classification of Exocrine glands
1. Unicellular- simplest, single cell- Unbranched duct
2. Multicellular / compound- > one cell- Branched duct
1. Tubular:- tube like2. Alveolar/ Acinar:- flask shaped3. Tubuloalveolar:- tube ends in sac like dilation
** Tubular secretory portions:- straight, branched, coiled
** Alveolar portions:- single / branched
Modes of Secretion
1. Merocrine Glands:-• secretory products
del in membrane bounded vesicles apical surface of cells extrude by exocytosis
• Eg.. Pancreatic acinar cells, sweat gland, salivary glands
Modes of Secretion
2. Apocrine Glands:-• Secretory product
released in apical portion of cell surrounded by a thin layer of cytoplasm within an envelope of plasma membrane.
• Eg.. Mammary gland, ceruminous gland of ext auditory meatus
Modes of Secretion
3. Holocrine Glands:-• Secretory product
accumulates within the cell programmed cell death
• Sec products & cell debris discharged into lumen
• Eg.. Sebaceous gland of skin, meibomian glands
PARACRINE GLANDS
• Secretory material reaches the target cells by diffusion through the extracellular space / subjacent CT.
ENDOCRINE GLANDS• Eg… Pituitary gland, ovaries, testes, pancreas
Thyroid gland, Adrenal gland
DISCUSSION