8: Epithelial Tissue Flashcards
Which acidic dye is used to stain nuclear DNA & RNA, and why is this?
Haematoxylin as it binds acidic components of cells
Which dye is used to stain basic components of cells, e.g. proteins in cytoplasm?
Eosin
What is epithelial tissue? Where is it found?
A continuous layer of closely packed cells that covers the external body surface and lines body cavities (and generally marks off our insides from our outsides)
What are the 2 types of epithelial tissue? Can you describe their function?
Epithelia: layers of cells covering internal/external surfaces
Glands: structures that produce secretions
What are the 6 functions of epithelial tissues?
- Provide physical protection: from abrasion, deconstruction & dehydration
- Control permeability: selectively filter biochemical substances; e.g. capillaries & lung alveoli (diffusion of gases)
- Provide sensation (sensory epithelium which contains sensory cells - nose, ears, eyes)
- Absorbing nutrients from food in digestive tract
- Secretion (glandular epithelium - hormones, mucus, etc.)
- Transport: ciliated epithelia sweep mucus, cells & other particles along the surface of epithelium
Give 5 characteristics of epithelial tissue
- Polarity: apical & basal surfaces
- Specialised contacts: cell junctions, closely packed cells
- Attachment: via basal lamina to underlying connective tissue
- Avascularity: no blood vessels as not enough space (but richly innervated)
- Regeneration: can replace lost cells by cell division
Describe the apical surface of epithelial tissue
Is always free; contains microvilli (increasing SA for increased absorption of nutrients e.g. lining intestine & kidney tubules)
& also contains cilia (helps move materials e.g. mucus, etc, lining trachea)
Describe the basal surface of epithelial tissue
In contact with basement membrane
Explain why the characteristic ‘specialised contacts’ is important
For strength and impermeability, due to mechanical connections between cells (& not much extracellular space)
Explain the characteristic ‘attachment’, i.e. what is the basement membrane composed of?
2 components of the basement membrane:
- Basal lamina :(epithelium side) glycoproteins secreted by epithelial cells; selective filter for molecules between connective tissue & epithelium
- Reticular lamina :(connective tissue side) layer of extracellular material (collagen) produced by connective tissue, provides basement membrane strength
Explain the characteristic ‘avascularity’
= no blood vessels (as not enough space): nutrients arrive by diffusion from blood vessels in connective tissue
Explain the characteristic ‘regeneration’
Epithelial tissue has a high regenerative capacity (can reproduce rapidly), as these cells are exposed to mechanical friction, disruptive enzymes, toxic chemicals & bacteria. So regeneration is essential to maintain tissue integrity & is achieved via cell division from stem cells.
* Skin = renewed once every 35 days
* stem cells in the basal layer divide & migrate to outer layers
Explain the key features of stem cells
- They are undifferentiated cells (not committed to a specific cell type or function)
- Self renewable (able to go through cell division while maintaining undifferentiated state)
- After division each daughter cell can either remain a stem cell or can become a terminally differentiated cell
- Different tissues have different regenerative capacity: high in epithelial tissue but very low in cardiac & nervous tissue
Explain how epithelial tissue is differentiated (number of cell layers)
- Simple : one layer
- Stratified : more than one layer
Explain how epithelial tissue is differentiated (cell shape)
- Squamous : flat
- Cuboidal : cube
- Columnar : tall/column
Explain the differences between simple & stratified epithelia, in terms of function
- Simple = better for diffusion (shorter distance)
- Stratified = better for protection (more cells)
Give an example of where simple squamous epithelium is found and describe it’s function
Lines many body cavities e.g. found in the lining of alveoli of lung tissue. Also the endothelium (epithelium lining the entire vascular system/blood vessels/capillaries = exchange of nutrients & wastes between blood and tissue)
- Single layer of flat cells with a central disc shaped nuclei
- Allows material to pass by diffusion & filtration in sites where protection is not important
Give an example of where simple cuboidal epithelium is found and describe its function
e.g. lining kidney tubules, ducts and secretory portions of small glands
- Single layer of cube like cells with large, spherical central nuclei
- Function: secretion & absorption
Give an example of where simple columnar epithelium is found and describe its function
e.g. non-ciliated lines most of the digestive tract (stomach to rectum) & ducts of some glands; ciliated lines respiratory tract and uterus
- Single layer of tall cells with oval nuclei located near basement membrane. Some cells have cilia or microvilli; may contain mucus secreting unicellular glands (goblet cells)
- Function: (microvilli) absorption of nutrients; secretion of mucus, enzymes & digestive fluids; ciliated type move materials (mucus or eggs) by cilary action
Give an example of where stratified squamous epithelium is found and describe its function
e.g. lining oesophagus, mouth & vagina; keratinised type in epidermis of skin & outer surface of cervix
- Thick (several layers of flat cells). Basal cells are cuboidal or columnar, metabolically active, divide & produce cells of more superficial layers. In keratinised type, surface cells are full of keratin and dead
- Function: protects underlying tissues against abrasion, pathogens & chemical attack
Give an example of where stratified cuboidal epithelium is found and describe its function
- Generally 2 layers of cuboidal cells
- Location: (rare) : lines lumen of mammary glands and sweat glands
- Function: secretion
Give an example of stratified columnar epithelium and describe its function
- Several layers of cells in which basal cells are cuboidal and superficial cells are columnar
- Locations (rare): large ducts of mammary glands, salivary gland ducts and urethra
- Functions: secretion & protection
What is the difference between pseudostratified columnar epithelium and transitional epithelium?
- Pseudostratified columnar epithelium appears stratified but is not!
- Transitional epithelium : surface cells are dome shaped/flat (depending on stretch of bladder). Basal cells are cuboidal/columnar
Explain the description, function & location of pseudostratified columnar epithelium
Description: single layer of cells (some tall, some short); all in contact with basement membrane; some not reaching the free surface; nuclei seen at different levels; may be ciliated
Function: secrete substances, particularly mucus; movement of mucus by ciliary action (mucus traps dust in trachea)
- Location: lines part of the male reproductive tract & the respiratory system e.g. trachea
