Epithelia Flashcards
What are the 4 tissue types
Epithelial, connective, nervous, muscle
How is epithelial fissure formed
From an uninterrupted layer of cells
What’s the function of epithelial tissue
Covers all internal and external body surfaces and forms boundaries between body compartments
Cells are joined by various…
Intercellular junctions
What is the basement membrane
Separates underlying connective tissue and epithelial cells.
Made of glycoproteins and collagen.
Produced partly from connective tissue cells and partly from epithelial cells
How are epithelial cells polarised?
They have an apical (free) surface that’s connected to the outside and a basal surface which is attached to the basement membrane.
Polarisation is particularly present in absorption or secretory cells because the intracellular organelles reflects the directional transport
How are epithelial tissues classed?
number of layers of cells in the epithelium
Shape of cells on the apical surface of the tissue
Specialisation of the cell surface
How are epithelial cells named based on the number of cells in the layer
Single layer of cells- simple
2 or more layers of cells- stratified
Looks like more than one layer but all cells are connected to the basement membrane- psedostatified
Why is there a limit to how thick an epithelial tissue can be?
Epithelial tissue is a vascular (no blood supply) this means nutrients must diffuse through capillaries from the basement membrane
How is epithelial tissue classed based on the shape of cells?
Cuboidal- as wide as they are tall
Columnar- taller than they are wide
Squamous- flat, scale like
Aspects of columnar cells
Involved in active transport or secretion (GI tract)
Aspects of squamous cells
Allow rapid diffusion but fragile
What’s transitional epithelium
Apical cells change shape as epithelium is stretched ex. Bladder
Empty- round or dome shaped
Full- stretched or flattened
How does specialisations on the surface of the cells affect the classification of epithelial tissue
Ex. Microvilli (increase surface area), cilia (for movement) or presence of protein keratin (waterproofing)
4 types of junctions
Tight, zonal adherents, desmosomes, gap junctions
Tight junctions
-prevent passage of molecules or ions through the space between epithelial cells. Must enter a cell by active transport or diffusion
- block movement of integral cell proteins between apical and basolateral surfaces.
Adhering junctions (Zonula adherens)
Completely surrounds cell providing stability,
Binds cells together at cytoskeleton to create a unit
Desmosome
Below adhering junctions and provides strong attachment of cells.
Found in tissues that are exposed to abrasion (skin) or physical stress (heart)
Disc shaped occurring as a row of spots around circumference of cells
Gap junctions
Have tiny pores to allow passage of small molecules between adjacent cells.
Means cells can respond to stimuli as a unit rather than individually
FOR INTERCELLULAR COMMUNICATION
Consists of 2 Connexons each made up of 6 connexin units
What’s a junctional complex
Tight junction, adhering junction and a desmosome
Mesothelium
Simple squamous epithelium lining the major body cavities
Provides a friction free surface by secreting a watery fluid (for movement)
Forms the serous membranes such as the pleura, pericardium and peritoneum
Endothelium
Simple squamous epithelium lining the walls of blood vessels, lymphatics and the heart.
Blood brain barrier
Restricts the passage of potentially harmful substances from the blood. Achieved through highly selective diffusion through but not between cells.
The endothelial cells metabolise harmful substances to prevent them from travelling to the brain.
How does the blood brain barrier make it very difficult to treat brain diseases
Blood brain barrier prevents antibodies from reaching the brain
Where are simple cuboidal cells mainly found
Lining tubules and ducts, sites involved in secretion, excretion and absorption.
Ex. Collecting duct of kidneys, salivary glands or pancreas
Where would you find the nucleus in a columnar epithelia cell
Central or basolateral
How can simple columnar cells be specialised?
Microvilli and goblet cells
Microvilli
Increase surface area by about 30x for absorption
Form a striated or a brush border which can be seen under the microscope
Goblet cell
Are modified columnar cells found in other cells in the epithelial tissue
Abundant in gastrointestinal and respiratory tracts
Secrete mucus which moistens surface of the respiratory tract
Pseudostratified columnar epithelium
Contains 3 cell types : basal, goblet and columnar ciliated. Vary in height and nuclei lie at different heights so looks stratified
Cilia
Longer than Microvilli
Move synchronous to provide movement
Can become damaged by common cold, smoking, cold air, old age
Why is stratified epithelium tissue not suitable for secretion
Multiple layer doesn’t allow forsecretion
Why would stratified squamous epithelium be keratinised
If it needs to be waterproof
Ex, outside layer of skin
Desquamation
When surface squamous cells die (sloughed) and replaced by mitosis in the basal cells of the tissue
Keratinisation
Epidermis consists mainly of keratinocytes which undergo mitosis in the basal layer of the epidermis. By cell division previously formed cells are pushed to the surface and fill with keratin. These cells’ junctions become filled with a waxy material which causes a lack of nutrients which then become hardened dead keratinised cells
