Epithelial Tissues Flashcards
What is the epithelia?
Lines and covers all body surfaces except tooth enamel and the anterior surface of the iris
What are the different characteristics of epithelia?
Shape = Squamous, cuboidal, columnar
Layer = Simple, stratified, pseudo-stratified
What is the makeup of the epithelium basement membrane?
Specialised ECM sheet structure and intertwining collagen fibres
What are the different kinds of cell junctions found in epithelia?
- Tight junctions = cell-cell, don’t allow passage of fluid / water, no diffusion
- Cell junctions = desmosomes and hemi-desmosomes, allow diffusion and account for structural integrity
- Gap junctions = holes for proteins / electrolytes
Cells will usually only have only one type of junction each
What are desmosomes?
Found in prickle cells of stratified squamous epithelium
- Cadherin proteins binding cells together at junctions
- Keratin filaments that join to the surface but also extend throughout the cell, weaving / linking together
- Channel formed between cells allows fluid to pass so is permeabel to water and ion
What are hemi-desmosomes?
- Very similar to desmosomes, but also have anchoring collagen fibres
- Used to anchor intermediate filaments in a cell to extracellular matrix
- Present in skin, intestines, and respiratory tract
NOTE: Desmosomes and hemi-desmosomes ARE NOT found in mobile cells (fibroblasts, endothelial cells)
What are tight junctions?
They are the glue connecting cells water tight
Forces most material to ener cells via diffusion or active transport
Found around things you don’t want leaking eg bladder, kidney, intestines, skin
What are gap junctions?
Tunnels formed between cells which are permeable to water and ions
Often found in cells that spread action potentials eg nerves and cardiac muscles
What are the different names of the layers found in stratified squamous epithelium (skin) from top to bottom?
Stratum Corneum = Keratinised Layer Stratum Granularis = Granular Cell Layer Stratum Spinosum = Prickle Cell Layer Stratum Basals = Basal Cell Layer Lamina Propria = Lamina Propria
What are the characteristics of the epidermis?
“Thick” skin (palms and soles) contains a 5th layer called the Stratum Lucidum
Epidermis contains no blood vessels
All cells, EXCEPT STRATUM BASALS, are keratinocytes, which manufacture and store keratin
What is keratin?
An intercellular fibrous protein found in hair, nails, and skin which gives it hardiness and water resistant properties
What are the characteristics of the stratum basale / basal layer of the epidermis?
Single layer of suboidal shaped stem cells
Precursor to keratinocyte layers
Two other cell types:
- Merkel cell = functional cell repsonsinble for stimulating sensory nerves which the brain receives as touch
- Melanocytes = Produces pigment melanin
Cells mature from basal layer through to surface layer where they shed
What are the characteristics of the stratum spinosum / prickle cell layer of the epidermis?
Spiny or pickly appearance post-fixationn due to high presence of desmosomes
Typically composed of 8 - 10 layers of keratinocytes interspersed with langerharn cells which are immune macrophages
Langerhan cells engulf bacteria, foreign particles, and other damaged cells found within this layer
What are the characteristics of the stratum granulosum / granular layer of the epidermis?
Keratinocytes look flatter and obtain a grainy appearance due to large amounts of granules from build up of keratin and keratohyalin
Produces lipid rich secretions
Nuclei and other cell organelles begin to disintegrate as the cell dies
What is the stratum corneum / keratinised layer of the epidermis?
Most superficial layer composed of 15 - 30 layers of cells
The dry and dead layabout helps prevent penetration of microbes and the dehydration of underlying tissue whilst also providing mechanical protection against separation
Cells are often shed and replaced periodically from the startum granulosum, replaced entirely approx every 4 weeks
