Epithelial Tissue Flashcards
General Overview
- Line some internal cavities and body
surface. - Form boundaries.
- Often against external environment.
- Form glands.
Where are epithelial cells situated
1) Covering and Lining Epithelium
* Epidermis of skin
* Lining the respiratory, reproductive, urinary & GI tracts.
2) Glandular Epithelium
* Secreting portion of glands; thyroid, adrenal, and sweat glands
Roles of Epithelial Tissues
-FILTRATION
-SECRETION
-ABSORPTION
-EXCRETION
-FORMS BOUNDARIES FOR PROTECTION
Introduction to epithelial
tissues
- Tightly packed sheets of cells
- Single or multiple layers
- Avascular
Simple epithelium in general
- Single layer
- Diffusion, osmosis, filtration, secretion and
absorption
Simple squamous epithelium
Like thin floor tiles
* Central nucleus
* Found at filtration and
diffusion sites
* Lines alveoli,
Bowman’s capsules of
kidneys
Simple cuboidal epithelium
- Shaped like cubes/hexagons
- May have microvilli
- Secretion and absorption
- Central nucleus
- Secretion & absorption
- Thyroid gland, kidney tubules, glandular
ducts
Simple columnar epithelium
- Protection
- Secretion
- Absorption
-Apical Surface may have microvilli /cillia
-Cell nuclei towards basal surface
-NON-CILIATED IN GI TRACT
-CILLIATED IN RESPIRATORY TRACT AND GENITOURINARY TRACT
Stratified epithelium
- 2 or more layers
- Protection
Transitional Epithelium
- Change from cuboidal to flat as organs stretch (e.g. bladder)
Pseudostratified epithelium
Pseudostratified epithelium is a type of epithelial tissue that appears to have multiple layers of cells due to the varying positions of nuclei, but all cells actually rest on the basement membrane.
Simple non-ciliated columnar
epithelium
- Microvilli increase SA & goblet cells secrete mucus
- Lines GI tract, glandular ducts and gallbladder
- Secretion and absorption
Ciliated simple columnar epithelium
- Cilia at apical surface ‘waft’ substances
- Goblet cells in some regions (e.g. respiratory tract)
- Upper respiratory tract, fallopian tubes, brain ventricles
- Secretion and aid movement
Pseudostratified columnar
epithelium
- Nuclei at different levels
- Ciliated lines airways
- Secretion and aid movement
Stratified squamous epithelium
(keratinized)
- Apical layer squamous cells
- Deep cell layers variable in shape
- Dead cells sloughed off at apical
surface - Keratinized- apical layer and
several layers deep to it contain
keratin (fibrous protein) - Protection
- Superficial layer of the skin
Stratified squamous epithelium
(non-keratinized)
- Lines ‘wet’ surfaces, mouth , vagina, oesophagus
- Protection
Stratified cuboidal epithelium
- Rare- oesophageal glands
- Protection, limited secretion/absorption Rare- oesophageal glands
Stratified columnar epithelia
- Also rare
- Part of urethra, ducts of oesophageal glands
- Protection and secretion
Transitional epithelium
- Permits distension
- Lines urinary bladder, ureter and urethra
Clinical significance - COPD
Clinical significance – smear
tests
- Papanicolaou Smear (Pap smear)
- Collect sloughed off cells from wall of cervix
- Detect cellular changes (pre-cancerous cells)
- Recommended for women over 25
Glandular epithelia
- Collection of epithelial cells specialised for
secretion. - Scattered cells or complete organs
ENDOCRINE glands – secrete into interstitial fluid
EXOCRINE glands secrete into ducts
Endocrine glands
- Secretions enter interstitial fluid then diffuse into blood.
- HORMONES (regulate numerous physiological
processes to maintain homeostasis). - Examples Pituitary, Islets of Langerhans (pancreas) &
adrenal glands.
Exocrine glands
- Secretions EXIT into a DUCT.
- Duct empties onto surface epithelium or into the
lumen of an internal passageway. - Secretions include mucus, earwax, sweat, saliva,
digestive enzymes and oil. - Exocrine glands include sweat and salivary
glands.
Functional classification- how
secretions released
- MEROCRINE GLANDS (Salivary, pancreas)
- Secretions released from secretory vesicles by exocytosis
- APOCRINE GLANDS (Mammary gland)
- Accumulate secretion at apical cell surface
- Cell ‘pinches’ off releasing secretion
- HOLOCRINE GLANDS (sebaceous gland)
- Secretory cell matures and ruptures releasing product
Structural classification of exocrine
glands
- Shape of secretory portion:
- Tubes: tubular
- Blind pockets: Alveolar
- Both: Tubuloalveolar - The structure of the duct:
- Simple: Single duct that does not
divide
- Compound: If duct divides
