Epithelia Flashcards
Key functions of epithelia
Selective barriers
Secretory
Protection
Cell junctions
Tight junction Desmosome Hemidesmosome Adherens junction Gap junction
What are intermediate filaments made of
Keratin
What are microfilaments made of
Actin
Function of cytoskeleton
Strength, alter cell shape; link cytoplasm to membrane; tie cells together; muscle contraction
Features of tight junctions
Transmembrane sealing strands
Claudins and occludins key proteins
Join to actin and bind cytoskeletons of adjacent cells together
Electrically tight
Features of adherens junctions
More basal than tight junctions
Plaque layer of proteins on inside of cell
Cadherins span gap
Cadherins linked to actin by catenins
Function of adherens junction
Prevent separation of cells during contraction
Where do desmosome junctions occur
Lateral walls
Function of desmosomes
Resist shearing forces
e.g in cardiac muscle and epidermis
Features of desmosomes
Cadherins span gap
Cadherins attach to keratin which stretches across cell to desmosome on other side
Function of gap junctions
Direct connection between cells
Allow diffusion of material (1kDa)
Allow electrical signalling
Features of gap junctions
6 connexin proteins form a connexon/hemichannel
2 connexons form a gap junction
Function of hemidesmosome
Anchor basal surface to basement membrane
Features of hemidesmosomes
Integrin as transmembrane protein
Attaches to keratin in the cytoplasm and laminin in the basement membrane
Two structures of the basement membrane
Basal lamina
Reticular lamina
Formation and contents of basal lamina
Secreted by epithelial cells Laminins Collagen Proteoglycans Glycoproteins
Formation and contents of reticular lamina
Secreted by firoblasts
Fibrous proteins e.g fibronectin and collagen
Function of basement membrane
Support of overlying epithelium
Acts as surface along which cells can migrate during growth or healing
Filtration in kidneys
Cancer vs basement membrane
If a carcinoma pierces the basement membrane, chances of metastasis increase
ABCD of cancerous mole
Asymmetry
Border irregularity
Colour
Diametre
Types of epithelial tissue
Glandular
Lining/covering
Arrangements of epithelium and explanation
Simple - Single layer (absorption/secretion)
Stratified - multiple layers (protection)
Pseudostratified - Appears to have multiple layers (secretion)
Shapes of epithelium and general function
Squamous - diffusion
Cuboidal - Secretion/absorption
Columnar - Secretion/absorption
Transitional - Allow stretch
Features, appearance, and function of simple squamous epithelium
Most delicate
Irregular shaped, like a jigsaw
Filtration, secretion, diffusion
Special subtypes of simple squamous
Mesothelium - Lining of pericardial, pleural, and peritoneal cavities
Endothelium - Inside lining of blood and lymphatic vessels
Location of simple squamous
Bowman’s capsule
Cardiovascular and lymphatic systems
Alveoli
Visceral cavity linings
Feature of simple cuboidal
Secretion and absorption
Appear as hexagonal or cuboidal boxes
Location of simple cuboidal
Pancreatic ducts Parts of kidney tubules Smaller ducts Secretion chambers of thyroid Eyes
Features and appearance of simple cuboidal epithelium
Larger cytoplasm, so more organelles
Rectangular
Elongated nucleus near base of cell
Two major subtypes of columnar epithelium
Ciliated
Non-ciliated
Features and location of non-ciliated simple columnar epithelium
Microvili on apical surface
Goblet cells present
Found in gastrointestinal tract and gall bladder
Function of non-ciliated simple columnar epithelium
Secretion
Lubrication
Absorption
Function of ciliated simple columnar epithelium
Synchronous movement helps move foreign matter
Features and location of ciliated columnar epithelium
Also have goblet cells
Found in bronchioles, Fallopian tubes, sinuses, central canal of spinal cord and ventricles of brain
Features and function of stratified squamous epithelium
Located at areas of high mechanical stress
Protects against microbes
Lower layers may be cuboidal while higher layers are flat
Subtypes of stratified squamous epithelium
Keratinised - skin
Non-keratinised - mouth, throat, tongue, anus oesophagus, vagina
Features of pseudo stratified columnar epithelium
Not all cells reach apical surface
Nuclei at different levels
Can be ciliated or non-ciliated
Function and location of ciliated pseudo stratified columnar epithelium
Goblet cells present
Secrete and move mucus
Found in respiratory tract
Function and location of non-ciliated pseudo stratified columnar epithelium
No goblet cells
Absorption and secretion
Found in epididymis and part of male urethra
Function and location of stratified cuboidal
Rare
Found in ducts of adult sweat glands, esophageal glands, and part of male urethra
Function and location of stratified columnar epithelium
Uncommon
Only apical layer is columnar - basal layer short and irregular
Lines urethra, some esophageal glands, large excretory ducts and conjunctiva
Function and location of transitional epithelium
Variable shape
-Unstretched = stratified cuboidal
-Stretched = stratified squamous
Ideal for lining hollow surfaces as it can stretch without rupturing
Lines bladder and portions of ureter and urethra
Endocrine gland function and examples
Secrete directly into interstitial fluid
Pineal gland
Thyroid gland
Pituitary gland
Exocrine gland function and examples
Secrete onto surfaces or lining epithelium Sweat glands Salivary glands Sebaceous glands Pancreas
Different gland structures
Tubular Acinar Simple Coiled Compound
