FORM & FUNCTION (Epithelial Tissues) Flashcards
Characteristics of epithelia:
-exhibit polarity with three domains (apical, basal and lateral)
>function will depend on the features in each domain
-avascular (devoid of blood vessels)
>ends in connective tissue under the epithelium
Apical domain: features
-directed to the lumen/external surface
-modifications likely present: cilia, stereocilia or microvilli
Microvilli:
-cytoplasmic processes that extend from cell surface
Ex. small intestinal epithelium
Stereocilia
-microvilli of unusual length
Ex. inner ear, testis
Cilia:
-motile cytoplasmic processes
Ex. respiratory epithelium
Lateral domain: features
-makes connections to the adjacent/neighbouring cells and communicates with them
-various types of junctions are present
>tight junctions (barrier function)
>anchoring junctions (mechanical stability)
>communicating junctions (direct communication between cells)
*paracellular pathway
Basal domain: features
-basement membrane
-contains basal lamina and lamina lucida
>contain secretions from the epithelial cells (eg. Proteoglycans and collagen: proteins and fibrous material)
Basal lamina:
-structural attachment site for overlying epithelial cells and underlying connective tissues
Epidermis:
-stratified squamous epithelium (based on the top layer)
-with and without keratin (produced by stratum granulosum)
Layers of epidermis:
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Stratum corneum
stratum basale
-uni-layer of stem cells (cubodial)
stratum spinosum
-prickle cells
stratum granulosum
-produces keratin
stratum lucidum
-flattened and tightly packed keratinocytes filled with keratin filaments
stratum corneum
-various layers of squamous cells
-secrete the keratin to the top
-no nucleus (‘dying’), will release keratin stored in them
Keratinocytes in stratum corneum:
-produces keratin
-when keratin is present on the surface=epithelium is named keratinized
Epitheloid tissues:
-tissues that appear epithelial, make contact with adjacent cells, but are devoid of the characteristic free surface
Example of epitheloid tissue:
*endocrine organs which develop from typical epithelia, but lost its connection to a surface during development
-pancreatic islet cells
-Leydig cells in testis
-anterior pituitary cells
-adrenal parenchyma cells
Why is epithelia so important?
-secretion
-absorption
-transport
-protection
-receptor
*problems with the form and/or function of epithelia lead to diseases
Secretion:
-columnar epithelium of gastric glands (enzymes for digestion)
Absorption:
-columnar epithelium of small intestine
Transport:
-respiratory and olfactory epithelia
Protection:
-stratified squamous epithelium of the skin (epidermis)
Receptor:
-epithelia of tongue (taste buds) and nasal mucosa (smell)
Simple squamous example:
-vascular system
>exchange
Simple cuboidal example:
-small ducts of exocrine glands
>absorption and secretion
Simple columnar example:
-small intestine and colon
>absorption and secretion
Pseudostratified example:
-trachea and bronchial tree
>secretion
>absorption
Stratified squamous example:
-epidermis, oral cavity, vagina
>barrier
>protection
Stratified cuboidal example:
-sweat gland ducts
>barrier
Stratified columnar example:
-largest ducts of exocrine glands
>barrier
Transitional example:
-renal calyces, ureters, bladder, urethra
>barrier
