Epithelial Cells 2 Flashcards
Review the Epithelium
Epithelial organs have associated ECM and connective tissue cells.
Layer of epithelia lies on the basal lamina.
Under the lamina you have interstitial connective tissue and extracellular matrix.
Epithelial cells make organised, stable cell-cell junctions to form continuous cohesive layers.
Epithelial layers line internal and external body surfaces.
How is the Epithelia classified?
SHAPE - e.g. cuboidal or columnar
LAYERING - e.g. single layer = simple; multi-layered = stratified
Describe the types of Simple epithelial cells?
- Simple Squamous SQUAMOUS = FLAT, SIMPLE = SINGLE LAYER (wider than they are tall) e.g. lung alveolar, mesothelium, endothelium
- Simple Cuboidal SIMPLE = One cell layer thick, CUBOIDAL = as wide as it is tall e.g. kidney collecting duct.
- Simple Columnar SIMPLE = One cell layer thick, COLUMNAR = taller than they are wide e.g. enterocytes
Types of Squamous Epithelia?
Stratified Squamous - STRATIFIED = lots of layers of cells The surface cells are use for the description therefore this is SQUAMOUS.
Two Main Types of Squamous Epithelia:
Keratinizing - e.g. epidermis (nuclei NOT VISIBLE in the surface cells)
Non-Keratinizing - e.g. linings of mouth (exactly the same but the nuclei are visible in surface layer cells)
What is Pseudo-stratified Epithelia?
Pseudostratified Columnar Epithelium e.g. upper airway (bronchi) epithelium.
Looks like there are two layers however all cells are connected to the basal lamina.
Function of Epithelial Polarity? Describe Epithelial Polarity?
Polarity is key for secretion, transport, absorption etc. because all these processes are usually unidirectional
Basal region is in contact with the matrix. The junctions are important in allowing the cells to maintain polarity.
Cells have an apical, basal and lateral surface.
Role of the Junctions in polarity?
TIGHT JUNCTION is important here.
close point of contact that prevents material passing between cells (paracellular pathway)
As a result material has to pass through the cell. The cell can now control passage.
Absorptive Epithelium
SB = Striated Border = brush border
It consists of lots of tiny projections of the plasma membrane (microvilli).
There is a flow from apical to basal.
ISC - Intestinal Stem Cells
ISCs are present in the crypt
There is a constant turnover of cells.
Cells are lost at the tip and are produced in the crypt.
It acts like an escalator - as the cells mature they move up towards the tip of the villus
Secretory Tissues?
The pancreas has both exocrine and endocrine functions.
Exocrine = apical —> duct
Granular ER and nucleus is usually in the basal part of the cell
There is a Golgi apparatus apical to the ER - it packages and processes the proteins produced.
Secretory granules are produced in the apical part of the cell and are destines for secretion.
Endocrine = basal —> circulation
Secretory granules are basal
Nucleus and ER are on the apical side
Golgi Apparatus is in between
Protective Epithelia?
STRATIFIED SQUAMOUS EPITHELIA (both keratinizing and non-keratinizing).
Skin: epidermis is the keratinizing stratified squamous epithelial layer. BARRIER to the environment and to mechanical damage
mechanical irritation the stem cells are stimulated to proliferate to replace the lost cells.
What’s Keratinizing SSE?
no nuclei visible in surface layer cells - they are dead cells and are made very tough by the production of several keratin proteins and lipids
What’s non-Keratinizing SSE?
nuclei are visible in the surface layer cells (e.g. oesophagus) - this is a wet epithelium.
Defects in Cytokeratins or Cell-Cell junctions =
BLISTERING DISEASES as a result of EPIDERMAL DAMAGE e.g. Epidermolysis Bullosa
