Epithelium Lecture Flashcards
1
Q
Types of Tissue
A
1) Epithelium
2) Connective Tissue
3) Muscle
4) Nerve
2
Q
Types of Connective Tissue
A
1) CT Proper
2) Cartilage
3) Bone
4) Blood
3
Q
Location of Epithelium
A
1) Cover exterior body surfaces
2) Line cavities
3) Line tubular organs
4) Cover external surfaces of organs
5) Line vascular system
6) Line ducts
4
Q
Characteristics of Epithelium
A
1) Typically have a free surface
2) Form a sheet by adhering to adjacent cells by junctional complexes and adhesion molecules
3) Rest on basal lamina
4) Exhibit polarity: apical, basal, and lateral
5) AVASCULAR
5
Q
Functions of Epithelium
A
1) Absorption
2) Secretion
3) Excretion
4) Protection
5) Contraction
6) Transport of material
6
Q
What is a basal lamina?
A
- It is like a rug
- Helps glue the epithelium to the connective tissue
7
Q
How to classify Epithelial Tissue?
A
- number of layers
- cell shape
- THEN modifications
8
Q
“Number of Layers” Classification
A
- Simple (one layer thick)
- Stratified (two or more layers)
- Pseudostratified (looks more than one, but all cells rest on basal lamina)
9
Q
“Shape” Classification
A
- Squamous (thin, flat cells)
- Cuboidal (cell that is the same width as height; square)
- Columnar (tall and thin; rectangle)
10
Q
Types of Modifications
A
1) Keratinized, non-keratinized
2) Cilia
3) Microvilli
4) Stereocilia
5) Goblet cells
11
Q
Types of Epithelia
Without Modifications
A
- Simple Squamous
- Simple Cuboidal
- Simple Columnar
- Stratified Squamous Keratinized
- Stratified Squamous Non-keratinized
- Stratified Cuboidal
- Stratified Columnar
- Pseudostratified Columnar
- Transitional [Urothelium]
12
Q
Simple Squamous
A
- Flat cell
- Shaped like a pancake
- Thin from side
- Large from surface
- Flat nucleus
- Endothelium: lines blood vessels and other vascular structures
- Mesothelium: covers organ surfaces
- Kidney (pariteal surface of Bowman’s, thin segment of loop of Henle)
13
Q
Simple Cuboidal
A
- Square cells
- Height = width
- Found in glands
- Found in kidney tubules
- Nuclear location: middle or bottom of cell
- Thyroid gland
- Kidney proximal convoluted tubule (brush border), distal convoluted tubule (basal striations), collecting ducts, collecting tubules
- Eyes (lens surface, corneal endothelium)
- Gland ducts in so many locations, kidney ducts and tubules
14
Q
Simple Columnar
A
- Rectangular cells
- Tall and thin cells
- In many organs from digestive to female reproductive
- USUALLY has apical modifications; microvilli or cilia
- Often will have goblet cells present
- Nuclear location: middle, bottom
- Gallbladder
- Gland ducts in many locations
- Surface lining of the stomach/large and small intestines, uterus, and endocervix
- Ciliated in oviducts (fallopian tubes), lungs (small bronchi and bronchioles)
15
Q
Stratified Cuboidal
A
- found in the ducts of glands
- salivary glands (large ducts)
- sweat gland ducts
16
Q
Pseudostratified Columnar
A
- Rectangular-ish cells
- Tall and thin cells
- Looks like someone shook a simple columnar epi.
- USUALLY have apical modifications; stereocilia, cilia
- May have goblet cells present
- Nuclear location: varies; which makes it confusing
- Ciliated in trachea and large bronchi
- Lines Eustachian tube
- Stereocilia in epididymis and vas deferens
17
Q
Stratified Squamous
A
- flat cells on top
- Skin epidermis (keratinized )
- Non keratinized (corneal epithelium, esophagus, exocervix, oral cavity lining)
18
Q
Transitional Epithelium
A
- Puffy round cells on top
- Cells small at the bottom
- Epi is found in the urinary system
- Allows distention for urine
- Urinary system (from renal calyx to proximal urethra)
19
Q
Stratified Columnar
A
Large ducts of glands, urethra (male)
20
Q
Basal Lamina
A
- Epithelial cells secrete majority of components
- Components: Collagens (Type 4 at least 50%, Type 3, and Type 7)
- Type 4 forms scaffold of basal lamina
- Type 3 and 7 anchor basal lamina to underlying connective tissue
- Type 3 is of non-epithelial origin
- Laminin: MAG that polymerizes on basal surface and interacts with Type 4 collagen to make a sheet like structure
- Fibronectin: MAG participates in binding integrins
21
Q
Basement Membrane
A
basal lamina + fibroreticular lamina
22
Q
Anchoring junctions
A
sites of adhesion; secure cells to the basal lamina or ECM
23
Q
Focal Adhesions
A
Integrin-associated adhesions that anchor intracellular actin filaments to fibronectin of ECM of BM
24
Q
Hemidesmosomes
A
- strong anchoring junction found in tissues subjected to abrasion and shearing forces (skin)
- Integrin-associated adhesion that anchors intracellular intermediate filaments to collgen type 4 and laminin in ECM of BM
25
What is the takeaway from these anchoring junctions?
- Integrins form the core of both of these junctions (transmembrane proteins found in the basal cell membrane)
- Extracellular side of these proteins contain receptors that help bind Type 4 collagen, laminin, fibronectin
26
Junctional Complexes in Lateral Domain
1. Zonula Occludens (Tight junctions): tight seal; zip-lock
2. Zonula Adherens (Adherens junctions): belt-like; six pack
3. Macula Adherens (desmosome): spot weld
4. Gap Junction: pipe between cells; chemically couples cells
27
The order of the junctions
1. Tight junction
2. Cell-Cell Anchoring Junctions (adherens or desmosomes)
3. Channel Forming Junction (gap)
28
Zonula Occludens (Tight junctions)
- Acts like a zipper between cells
- Forms a tight seal between cells
- Attaches to actin
- Defines apical vs. basolateral domains of cells
- Appears as a darkened line to adjacent cells
- Does not allow material to flow between cells
- Amount of the seal depends on the tissue type
- Formed by occludins and claudins
29
Zonula Adherens (sticking together junctions)
- Encircles cells like 6 pack rings/belt
- Formed by e-cadherin (transmembrane) and Catenin ( intracellular)
- Cadherin: Calcium Dependent Adhesion
- Cadherins are Calcium Binding Proteins
- Calcium is needed for the Cadherins to bind
- Adheres cells together via actin of terminal web
30
Macula Adherens (desmosomes)
- Spot welds cells together
- Desmoglein and Desmocollin (cadherins, calcium ion dependent adhesion, calcium binding proteins)
- Catenin-like = desmoplakin
- Desmoplakin binds the intermediate filaments
* **
- On the TEM, it looks like a black fuzzy caterpillar on each cell. Those fuzzy bits are intermediate filaments (cytokeratin)
31
Gap Junction
- Chemically couples cells (mechanically and electrically)
- Connexins are the major protein
- 6 connexins form a connexon
- Connexons form spots that acts as channels between cells
- Allows calcium and other ions to pass from cell to cell
* ***
- On TEM, it forms a very dark and thin line
32
Apical Specializations
- Microvilli (non-motile, more like straws)
- Stereocilia (just very long microvilli)
- Cilia (motile, sweeping motion like little brooms)
33
Microvilli
- Fingerlike projections of the apical plasma membrane
- Exaggerated glycocalyx (shows up as PAS + and shows up as HOT HOT pink)
- Increase surface area
- Usually absorptive
- Actin filaments form core
- Attached to terminal web (actin net)
34
Cilia
- Larger finger-like projections of apical plasma membrane
- They sweep material along the surface
- 9+2 arrangement of microtubules = 9 doubles and 2 singles
- Attached via basal bodies (BB=modified centrioles; 9 triplet microtubules)
35
Stereocilia
- Extra looooonnngggg microvilli
- Actin core
- Passive movement by fluid
- Absorptive
- Epididymis, vas deferens, inner ear
36
Hair cells
stereocilia of inner ear
37
What makes up the glandular epithelium?
- endocrine gland
| - exocrine gland
38
Endocrine Glands
- Secrete into blood stream (ENDOthelium)
- Do not have ducts
- Hormones are the main endocrine secretions
39
Exocrine Glands
- Secrete directly into the duct
- Some ducts modify he product
- Some ducts simply transport the secretion
- Product can be mucous, serous, or mixture
40
Functional Classification of Glands
Merocrine/Eccrine
- secrete via exocytosis
- most common
- plasma membrane is recycled
- secretory product is released; vesicle retained
******
Holocrine
- Whole cell is created
- Cells begin to die as they reach area of secretion
- Best example is the sebaceous gland around hair follicle
******
Apocrine
- portion of the apical membrane and the cytoplasm are secreted
- apical portion pinches off with product inside it
- loss of plasma membrane
- best example is lipid component of milk during lactation
41
Myoepithelial cells
- Contain actin, myosin, and cytokeratins; contractile
- Difficult to identify on H&E sections
- Associated with glands
- Assists with moving secretions from glands
- "Hugs" glandular elements to squeeze out contents
42
Renewal of Epithelium
- Most epithelial cells have a finite lifespan
- Skin turns over in 28 days
- Intestinal lining: 4-6 days
- Mitotic activity is visible in basal cell layers
- If injury or inflammation occurs, more mitotic figures are seen
- Also during dysplasia and neoplasia
