Lecture 4: Epithelium Flashcards
Tissue
An aggregation of cells and extracellular substances
Epithelium
A tissue composed of closely aggregated cells with very little extracellular substance
4 basic types of tissue
Epithelial tissue
Connective tissue
Muscular tissue
Nervous tissue
3 categories of the epithelium
- Surface/Lining epithelia
- Glandular epithelia
- Special epithelia
Surface or lining epithelia
Form sheets that cover body surface and line luminal organs, tubular structures, and body cavities
Glandular epithelia
Secretory
Their functions are to synthesize, store, and release it’s product
Special epithelia
Receptors for taste and hearing (sensory for smell and vision have modified neurons)
7 functions of epithelial tissue
- Protection
- Secretion
- Absorption
- Diffusion
- Friction Reduction
- Cleaning
- Sensation
Protection
Protects underlying tissue from mechanical abrasion/injury, harmful chemicals, invading microbes, and from excessive loss of water
Secretion
In glands, specialized to secrete specific chemical substances such as enzymes, hormones, and lubricating fluids
Absorption
Those lining the small intestine absorb nutrients from the digestion of food. Second largest absorbing area are of kidney tubules
Diffusion
Simple squamous (square) epithelium promotes the diffusion of gases, liquids, and nutrients (ex. endothelium of capillaries and lungs)
Friction reduction
the smooth, tightly-interlocking endothelial cells that line the entire circulatory system reduce friction between the blood and walls of the blood vessels
Cleaning
Ciliated respiratory epithelium assists in removing dust particles/foreign bodies from air passages
Sensation
Specialized epi. tissue containing sensory nerve endings is found in the skin, ears, and on the tongue
Three germ layers in the developing embryo
- Ectoderm
- Mesoderm
- Endoderm
Ectoderm
Epidermis of the skin and its derivatives
2 parts of the mesoderm
Mesothelium
Endothelium
Mesothelium
Epitthelium lining three serious body cavities (peritoneal, pleural, and pericardial)
Endothelium
Epithelium lining blood and lymphatic vessels and heart chambers
Endoderm
Epithelial lining and glands for most of the GI tract, respiratory system, liver, pancreas, and urinary bladder
Epithelium has ____ cellular density
High
Endothelium has little _____cellular subastance
inter
Epithelial cell structure
polarized, cohesive, and closely associated to supporting connective tissue
Three surfaces of epithelial cells
Apical
Lateral
Basal
Where is the extracellular basal lamina
Lies at the interface of epithelial and connective tissue
Small blood capillaries never enter an epithelium across
a basal lamina
When components of a basal lamina are distinguishable in light microscopy, it is called
a basement membrane
Basal lamina
- Extracellular material, formed by the epithelial cells, separating epithelium from underlying connective tissue and acting as a selective barrier.
- Provides structural support
Basal lamina is visible in EM…
Only as a dense layer up to 100 nm thick
Basement membrane
- Basal lamina when it is visible with light microscopy
- Semi-permeable barrier (ex. blood-urine in placenta)
Basement membrane stain
PAS
Epithelial cells that are subject to pressure and traction have marked
Intercellular adhesion
Cohesiveness is due to (3)
- Transmembrane glycoproteins
- E-Cadherins
- Folds of plasma membrane between neighboring cells from intercellular adhesions
Three types of intercellular junctions
- Tight junctions
- Desmosomes
- Gap junctions
Tight junctions
- The membranes of neighboring cells are bound together by specific proteins
- Form continuous hermetic seals around the cell
- Prevent leakage of fluid across a layer of epithelial cells
Desmosomes
- Function like rivets, fastening cells together into strong sheets
- Intermediate filaments made of sturdy keratin proteins anchor desmosomes in place
- Adhere epithelial cells of the skin
Gap junctions
-Provide cytoplasmic channels or tunnels from one cell to adjacent cell
Gap junctions consist of
special membrane proteins that surround a pore through which ions, sugars, amino acids, and other small molecules may pass
Gap junctions are necessary for
communication (chemical and electrical signals) between cells in many types of tissue (ex. heart muscle)
