Epithelia Flashcards
Epithelial covers________, lines ________ and forms__________
covers body surface
• lines hollow organs, cavities and ducts
• forms the glands of the body
The cells of an epithelium are arranged in….
continuous sheets as single or multiple layers
Epithelium cells are held together by a variety of cell junctions including
Tight junctions Adherens junctions Gap junctions Desmosomes Hemidesmosomes
Key Functions of Epithelial tissues
- Selective Barriers (limit or aid transfer)
- Secretory (onto a free surface)
- Protective (especially from abrasion)
Three surfaces of epithelial cells are
apical, lateral, basal
Epithelia contain _____ but not ______. They are ______
nerves but not blood vessels. Avascular
Two types of epithelial tissue are
Covering and lining, Glandular
Cytoskeleton microfilaments
(brown) – e.g. ACTIN
-bundles beneath cell membrane and
cytoplasm; strength, alter cell shape; link
cytoplasm to membrane; tie cells
together; muscle contraction
Cytoskeleton
intermediate filaments
(purple)-e.g. KERATIN
-Cytoskeleton strength; may move some
materials through cytoplasm
TIGHT JUNCTIONS
electrically tight, ions cannot travel
proteins : claudins and
occludins
ADHERENS JUNCTIONS
“Belt desmosome”
• Cadherins (span the gap)
• Catenins link the Cadherins to Actin (cytoplasmic skeleton)
DESMOSOME JUNCTIONS
Lateral wall
• Resist shearing forces eg.they bind muscle cells
• Cadherin spans the gap
• Join cell surface to Keratin
GAP JUNCTIONS
Direct connection between cells
• 6 connexin protein molecules form
connexon/ hemichannel (donut)
• 2 hemichannels make up gap junction
What are the names of the lateral Junctions?
Tight, Adherens, Gap, Demosome
Hemidesmosome
Connect epithelia to basement membrane • Links Keratin to basement membrane • Hemidesmosome (e.g. Integrin instead of cadherin binds to Laminin in the BM and Keratin in cytoplasm
What are the names of the Basal Junctions?
Hemidesmosome
What is a junctional complex?
The combination of: tight junction, adherens junction
and desmosome
ALL epithelia overlay a basement
membrane composed of two
parts:
i. BASAL LAMINA (secreted by the epithelial cells) containing collagen, laminin, other proteoglycans, glycoproteins ii. RETICULAR LAMINA (produced by cells of the underlying connective tissue known as fibroblasts) containing fibrous proteins such as fibronectin, collagen
The basement membrane is found…
between the epithelium
and connective tissue.
Functions of the Basement Membrane
i. Supports the overlying epithelium
ii. Provides a surface along which epithelial cells migrate during
growth/ wound healing
iii. Acts as a physical barrier
The ABCD of melanoma warning signs:
- A for asymmetry: one half of a mole doesn’t match the other;
- B for border irregularity: edges are ragged, notched or blurred;
- C for colour: mix of brown, black, red, white, or blue;
- D for diameter greater than 6 mm
The basement membrane can act as a barrier to invasion from
_____.
melanoma.
Covering and lining epithelia form….
• Form the Outer Covering of the skin and some internal
organs.
• Form the Inner Lining of blood vessels, ducts and body
cavities, and the interior of the respiratory, digestive,
urinary and reproductive systems
Glandular epithelia make up the…
secretory portion of glands
(Glands consist of cells that secrete
substances into ducts, onto a surface or into blood.)
classifications of covering and lining epithelia
i. Simple (single layer)
Simple squamous*
Simple cuboidal*
Simple columnar* (ciliated and non-ciliated)
ii. Stratified
Stratified squamous* (keratinized and non-keratinized)
Stratified cuboidal
Stratified columnar
Transitional
iii Pseudostratified (actually a single layer)
Pseudostratified columnar* (ciliated and non-ciliated)
Endocrine glands secrete where?
Give example
Secrete directly into blood usually via traversing interstitial fluid Pituitary, pineal, thyroid, parathyroid
Exocrine glands secrete where?
Give example
Secrete into ducts that empty onto the surface of a covering or lining epithelium. Sweat and salivary glands; oil glands; wax glands; pancreas
Which gland can be both endocrine and exocrine?
Pancreas
describe structure of multicellular GLANDULAR EPITHELIA
i. Structure of duct (simple, branched,
ii. Structure of secretory area (tubular)
iii. Relationship between the two
