Lecture 15 - Epithelial Tissues Flashcards
What are tissues?
Groups of cells similar in structure and perform a common or related function
Histology
The study of tissues.
What are the four basic tissue types?
Connective, epithelial, nervous and muscle
Epithelium
Sheet of cells that covers body surfaces or cavities
Ex. Skin
Or as glandular epithelium that secretes substances
Ex. Salivary glands
Functions of epithelial tissue
Protection, absorption, filtration, excretion, secretion and sensory reception
Apical surface
The exposed, upper side of the epithelial tissue
Basal surface
Lower attached side that faces inwards toward the body and sits on a basal lamina
What is a basal lamina?
A non cellular adhesive sheet that attaches the epithelial cells to the rest of the body
Epithelial tissue characteristics
make continuous sheets that have little space between cells.
They form tight junctions and desmosomes with neighbouring cells
supported by a basement membrane
composed of the basal lamina and the reticular lamina.
Epithelial tissues are innervated (supplied by nerve fibres), but avascular (no blood vessels).
Epithelial tissue has a high regeneration capacity to repair damage due to friction or hostile substances
What is the reticular lamina?
a layer of extra- cellular material made of collagen fibres that is deep to the basal lamina
Simple epithelia (first part of name)
A single layer thick
functions in absorption, secretion, and filtration.
Stratified epithelia (first part of name)
Two or more layers thick and involve din protection
Ex. Skin
Squamous epithelia (second part of name)
Flattened and scale like
Cubodial epithelia (second part of name)
Box like or cube shaped
Columnar epithelia (second part of name)
Tall and column like
Where is Simple squamous epithelium located?
located where filtration or exchange of substances occurs.
Ex. In lungs
Where is Simple cubodial epithelium located?
forms the smallest ducts of glands or kidney tubules (found lining ducts of glands)
Where is simple columnar epithelium located?
lines the digestive tract. These cells in the intestines can have microvilli. (found lining intestinal tract)
Pseudostratified columnar epithelium
contains cells of varying heights that all sit on the basement membrane, giving the appearance of many layer (NOT STRATIFIED)
Found in trachea
What does Stratified squamous epithelium make up?
the external part of the skin, and extends into every body opening
Where is stratified cubodial epithelium found?
mostly in the ducts of some of the larger glands
Where is stratified columnar epithelium found?
in the pharynx, in the male urethra, and lining some glandular ducts.
Transitional epithelium
forms the lining of the urinary bladder and is specialized to allow cells to change shape and stretch.
Endocrine glands
Ductless glands that secrete hormones directly into the blood or lymph.
They secrete hormones, chemical messengers that bind to receptors in specific target organs to generate some response
Ex. Pituitary gland, adrenal glands
Exocrine glands
have ducts and secrete their products through an epithelial surface.
They are more numerous than endocrine glands.
Ex of secretions: mucous, sweat, oil, and salivary glands.
Even though your stomach is inside your body, it lined with epithelial tissue and is exposed to the outside world every time you eat and drink. Stomach acid and other gastrointestinal secretions are produced by exocrine glands.
Unicellular exocrine glands
most common unicellular glands are goblet cells.
They are found in epithelial linings of intestinal and respiratory tracts.
These cells produce mucin, a sugar-protein that can dissolve in water to form mucus, a slimy protective, lubricating coating.
Multicellular exocrine glands
consist of a duct and a group of secretory cells.
They are usually surrounded by supportive connective tissue that supplies blood and nerve fibers to the gland.
Classified by structure:
Simple vs. compound, tubular vs. alveolar
And By mode of secretion:
• Merocrine, holocrine or apocrine
Simple glands
Simple glands have an unbranched duct.
In tubular glands, secretory cells form long ducts that can be straight or coiled.
In alveolar or acinar glands, secretory cells form pockets or sacs Simple glands have an unbranched duct.
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Compound glands
In a compound gland, the duct branches to more than one group of secretory cells.
Tubuloalveolar glands have both tubular ducts and alveolar pockets or sacs
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Merocrine glands
Merocrine glands secrete products by Exocytosis as secretions are produced.
Ex. sweat, saliva, pancreatic juices
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Holocrine glands
Holocrine glands accumulate products within the cell and then rupture.
Ex. sebaceous oil glands
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Aprocrine glands
Apocrine glands release their secretions by budding off a portion of the cytoplasm. Ex. lactating mammary glands
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