W8- Lecture 43- Epithelial tissue Flashcards
what are epithelia tissues ?
Epithelia are tissues that serve as protective layers and/or secretory components of body organs and systems.
Formed into tightly cohesive cellular sheets.
Form functional units of secretory glands e.g. salivary, mammary, sweat.
what are the common attributes that epithelial tissues share ?
Limited intercellular space:
Specialised intercellular junctions hold cell membranes close together – effective barrier – blocks infiltration of fluids between cells.
Single or multiple layers of cells:
Form linings or coverings. Where diffusion/filtration is important, epithelia is a single layer – where protection e.g. abrasion is needed – multiple layers
Free apical surfaces:
All epithelia possess a free apical surface during development or at maturity. The apical surface is where cells of an epithelium face internal lumens.
Basement membrane:
Basal surface attaches to underlying tissues via basement membrane derived from underlying connective tissue.
Epithelia covering or lining tissues are constantly subjected to wear and tear. Mitotic capability enables repair and regeneration.
which 2 characteristics are epithelia described by ?
Cells layers:
Simple epithelium
Pseudostratified epithelium
Stratified epithelium
Cell shape: Squamous cells Cuboidal cells Columnar cells Transitional cells
describe the classification of epithelia based on layers
Simple epithelia – one cell thick
Stratified epithelia – many cells thick, but only bottom layer in contact with basement membrane.
Pseudostratified epithelia – appear more than one cell thick, but all cells rest on basement membrane
describe the classification of epithelia based on shape
Squamous – flattened cells like paving stones
Columnar – cells are taller than they are wide
Cuboidal – cells are of similar height, depth and width
Transitional – cells in layers which change their shape when they are stretched (only found in urological tract)
name two examples of Simple squamous epithelia
e.g. alveoli & capillaries of lungs
name an example of Simple cuboidal epithelia
e.g. kidney tubule
name an example of Simple Columnar
epithelia
e.g. small intestine
name an example of Transitional epithelia
only in urinary tract
stretches to accommodate fluid changes
name an example of Keratinised stratified Squamous epithelia
- only found in skin
name an example of Stratified Squamous
epithelia
oesophagus
name two examples of Pseudostratified
epithelia
- e.g trachea, nasal mucosa
name an example of Stratified cuboidal
epithelia
e.g. sweat gland duct
name an example of Stratified columnar
epithelia
e.g. Salivary gland duct
describe the Basal surface of epithelia
Basement membrane:
Separation from the underlying connective tissue – acts to support epithelia a selectively permeable filter between epithelium and connective tissue.
Anchors epithelium to connective tissue via cell-matrix adhesions.
Basal lamina:
Supportive sheet between epithelium and underlying connective tissue
describe the apical surface of epithelia(2)
example of each
Microvilli:
Finger like extensions of the plasma membrane of apical epithelial cell
Increase surface area for absorption (small intestine).
Cilia:
Whip like, motile extensions
Moves mucus, etc, over epithelial surface, in once direction. (trachea and respiratory bronchus).
describe the lateral surface of epithelia
Cells are connected to neighbouring cells via cell junctions:
Desmosomes:
Adhesive spots on lateral sides
Involves proteins called cadherins
Tight junctions:
Plasma membrane of adjacent cells fuse
Nothing passes
(GI tract doesn’t let enzymes from gut into blood stream)
Gap junction:
Present in many locations
Lets small molecules pass
(cardiac muscle tissue)
what is glandular epithelium ?
Aggregates of epithelial cells clustered together to perform specific secretory or excretory function.
Secrete wide range of products: Hormones Enzymes Milk Sweat Mucous oil
what are the two classifications of glands ?
Exocrine
Pour products into ducts that open into lumen of organ or onto the skin
Endocrine
Have no duct system – ductless glands – secrete into empty tissues spaces – eventually enter blood stream
what is the most common secretory mechanism ?
examples
impact on cell ?
Merocrine
e.g. salivary gland – secretion passes from cells without damage to plasma membrane – exocytosis
no damage to cell
describe how some glands excrete by holocrine mechanisms \
+ example
impact on cell ?
e.g. sebaceous gland – cellular debris part of secretion (sebum)
Involves death of the cell
describe how some glands excrete by
Apocrine mechanisms
examples
impact on cell ?
e.g. mammary gland
Apical end pinched off
describe the Morphological classification of epithelial cells
Simple – single tube Compound – branched duct system Branches Tubular Acinar/alveolar (grape like)
describe epithelial membranes (4 types)
Epithelial membranes contain epithelium
and an underlying connective tissue:
Mucous membranes – digestive system Serous membranes – body cavities Cutaneous membrane - skin Synovial membrane - joints (Synovial membranes contain only connective tissues and line the cavities of synovial joints)
