Epithelial Tissue I & II Flashcards
Epithelium
Main Functions:
1. Protection
2. Transcellular transport
3. Secretion
4. Absorption
5. Sensory detection
*Its the main way we feel the world and sense what we’re doing
Epithelium Basic Structure:
Avascular
Covers body surfaces
Lines internal, closed body cavities
Constitutes glands
Polarity of Epithelium
Cells are closely apposed and attached to one another
Attached basally to a basement membrane
Apically faces into a lumen or the outside world
Epithelium Domains
- Apical Domain
- Lateral Domain
- Basal Domain
Apical Domain
Specializations of the plasma membrane often define the function of that epithelial
Microvilli
Used for absorption
Extends into lumen to increase surface area; often called striated or “brush border”
Has an actin core which is kept stiff by VILLIN
Glycocalyx
“Cell coat”
Associated with microvilli and aids in absorption
Carbohydrate chains linked to membrane proteins or lipids
Cilia
Movement along surfaces; very mobile hair-like structures that extend from dark basal bodies
Core of microtubules called basal bodies
Basal bodies
Part of cilia microtubules
Develop from procentriole organziers as “9 triplets”. As they extend into the cilium, they rearrange into a 9+2 arrangement (9 peripheral doublets and 2 central singlets)
Lateral Domain
Borders on neighboring cells and forms a selective barrier, adheres, and communicates
Interdigitations: Lateral surfaces show infolding that increases surface area
3 Complexes:
1. Zonula occludens (Tight Junction)
2. Zonula adherens ( Intermediate Junction)
3. Macula adherentes (Desmosomes/ “Spot” Junction)
Zonula Occludents/Tight Junction
Most apical part that separates the luminal space from the intercellular space
First line of defense; forms protective barrier between epithelial cells
Can be SUPER tight or kind of leaky depending on where they are in the body
Zonula adherens/Intermediate junction
Cells do NOT touch
Main function: cell to cell adhesion joined by linking proteins
Always affiliated with actin
Macula adherentes/Desmosomes
Most inferior of the complex but still very apical on the cell
Main function: cell to cell adhesion via attachment plaques which give stability and link through linking proteins
Always associated with intermediate filaments
Gap junction
Specialized lateral domain; “communicating juctions”/”nexus”
Main function: exchange or signaling between adjacent cells; direct passage of signaling molecules from one cell to another
Two way street between cells, but nothing can “leak” out
Basal domain
-Borders basement membrane, related to underlying tissues
-Specialized for cell-to-ECM adhesion; also exhibits infoldings
How does epithelial attache to the basal lamina?
“Spot Welds” aka Hemidesmosomes: 1/2 demisome that connects to basement membrane (intermediate filaments)
Associated w/ attachment plaques
Also via focal adhesions made of actin
Simple epithelium
One-layer thick; every cell touches the basement membrane
Pseudostratified columnar epithelium
Looks stratified but its actually simple b/c every cell touches basement membrane
Usually found in respiratory tract
Stratified epithelium
more than one layer; named for shape of cells in the apical layer
Non-keratanized epithelium
toughest covering for most things w/in the body
Keratanized epithelium
“not alive”; layer of protective epithelium
toughest layer (makes up most of the skin)
Transitional epithelium
the apical cells have a rounded shape
Most commonly found in the bladder
Shape of Epithelial cells
- Squamous (looks flat)
- Cuboidal
- Columnar
Two types of tissue to make glands from epithelial cells
- Parenchyma (general word for working part): epithelial cells
- Stroma: Connective tissue (supporting tissue)
2 major types of glands
- Endocrine
- Exocrine
Endocrine Glands
Secrete hormones into blood or lymphatic vessels located in CT
Polarized toward the basement membrane (REVERSE polarity)
Ductless (no lumen); produces hormones; secretion can be constitutive or regulated
Exocrine Glands
Secretes into ducts
Structure: often named for branching of ducts
1. simple (little or no branching)
2. Compound (multiple layers of branching)
3. Tubular
4. Acinar: “berry” or “flask-shaped”
Types of Exocrine Gland Secretion:
- Serous (watery): pyramida-shaped cells at light-level; basally located, round nuclei; basophilic basal cytoplasm
- Mucous: pale apical cytoplasm, darkly stained nuclei basally; lumen tend to be larger; mucous is heavy so its darker
