7 - Epithelia Flashcards
Two broad types of epithelia (divided by function)
1) Surface epithelia (line surfaces and lumena)
2) Glandular epithelia (involved in secretion)
How are glandular epithelia formed?
Invaginations of secreting cells
Epithelial cell functions 1) 2) 3) 4) 5)
1) Protection
2) Barrier, selective diffusion
3) Absorption
4) Secretion
5) Receptors e.g. smell, taste
Characteristics of epithelial cells 1) 2) 3) 4)
1) Exhibit polarity: apical, lateral and basal domains 2) Connected by cell junctions 3) Supported by a basement membrane 4) Avascular
Examples of simple squamous epithelium
Mesothelium, endothelium, lining of alveoli, glomeruli
Examples of simple cuboidal epithelium
Thyroid follicles, renal tubules
Examples of simple columnar epithelium
1) Non-ciliated e.g. stomach, small and large intestines,
gallbladder and bile ducts, endocervix
2) Ciliated: Fallopian tubes, bronchioles
Difference between stratified and simple epithelia
Simple epithelial cells all have contact with basement membrane.
Stratified epithelial cell basal layer only has contact with basement membrane
What are pseudostratified epithelial cells?
Epithelial cells that have nuclei in different places, and can appear stratified, but all all cells have contact with basement membrane
Examples of pseudostratified columnar epithelial cells
Respiratory tract (ciliated)
Examples of stratified squamous epithelial cells
Keratinising: skin
Non-keratinising: Oral cavity, oesophagus, anal cavity, vagina
Example of stratified epithelium where one cell type lies over a different cell type
Breast, sweat glands, salivary glands: Surface columnar layer overlying myoepithelial layer
Where does surface epithelium get nutrients?
From diffusion of blood vessels underlying basement membrane. Epithelial layers are avascular
Brush border
When there are lots of microvili on an epithelial layer.
Length of microvili
0.5 - 1μm in length
How much can microvili increase surface area by?
A factor of 20
Length of cilia
2 - 10 μm long
Can cilia move?
Yes. Have a core of microtubules
Types of intercellular junctions in epithelia
1)
2)
3)
1) Tight junctions
2) Adherens junctions
3) Gap junctions
Tight junctions
1)
2)
3)
1) Located at apical junction between epithelial cells
2) Link cells, limit what can pass between them
3) Made of occludin proteins
Difference in desmosome and hemidesmosome function
1) Desmosome (cell-cell)
2) Hemidesmosome (cell-basement membrane)
Components of a desmosome
1)
2)
1) Cadherens link two cells
2) Within cells, catenins link cadherens to intermediate filament cytoskeleton (catenins make up ‘plaque’)
Function of desmosomes and adherens junctions
Link the cytoskeletons of two cells (desmosomes - intermediate filaments, adherens junctions - actin)
Gap junction function
Allow continuous cytoplasm between linked cells (EG: for transfer of depolarisation between cardiac muscle cells)
Components of a gap junction
Connexin proteins form pores
Components of a hemidesmosome
1)
2)
1) Integrin proteins project from cell and anchor to basement membrane
2) Plaque within cell links integrins with intermediate filaments of cytoskeleton (link to laminins in basement membrane)
CAM function
Cell adhesion molecules
Link with CAMs on other cells to join together, communicate
Four types of CAMs
1) Cadherins: component of adherens junctions
2) Integrins: interact between actin and extracellular matrix
molecules
3) Selectins: mediate white blood cell-endothelial cell interactions
4) Immunoglobulin superfamily: mediate homotypic cell-cell
adhesions e.g. ICAM, CCAM, PECAM
Basement membrane
Interface between support tissues and parenchymal cells e.g. epithelia
What produces basement membrane?
Mainly produced by the cells being supported
Components of basement membrane
Extracellular matrix: predominantly collagen IV, heparan
sulphate and structural glycoproteins: laminins, fibronectin.
Underlying collagen VII and reticulin
Function of laminins and fibronectin in basement membrane
Laminins and fibronectin are involved in linking integrins of
epithelial cells to extracellular matrix
Function of collagen VII and reticulin in basement membrane
Link basement membrane to underlying tissue
Mucosa
Lines body passages that communicate with the exterior
– Surface epithelium with underlying supportive tissue, maybe with underlying smooth muscle (muscularis mucosae)
– Associated glands that secrete mucus or other secretions onto the epithelium
Serosa
Surface mesothelium and underlying supportive connective tissue
Examples of serosa
Lines pericardial, pleural, peritoneal cavities and tunica vaginalis
Two types of glandular epithelium
1) Exocrine - secrete into ducts
2) Endocrine - secrete into blood
Types of glandular epithelial cell shapes 1) 2) 3) 4) 5) 6) 7)
1) Simple tubular
2) Simple coiled tubular
3) Simple branched tubular
4) Simple acinar tubular
5) Compound acinar
6) Compound tubular
7) Compound tubuloacinar
Example of simple coiled tubular glandular epithelial cell
Sweat gland
Example of simple tubular glandular epithelial cell
Within colon
Example of a simple branched tubular glandular epithelial cell
In stomach
Two types of secretions from glandular epithelial cells
1) Serous secretion (proteins in water medium)
2) Mucosal secretion (glycoproteins in water medium)
Goblet cells
Mucus secreting cells full of membrane-bound mucous
droplets
Goblet cell appearance in H&E
1) Mucous membranes non-staining
2) Nucleus, organelles displaced basally
Acini 1) 2) 3) 4)
1) Serous cells can form a secretory unit called an acinus
2) Secrete into common, narrow lumen
3) Secretion carried away by a duct
4) Basophilic at base, acidophilic at apex
