Epithelial Tissue Flashcards
What is a tissue?
A tissue is a group (aggregate) of cells organised to perform one or more specific functions.
What are cells within tissue connected by?
specialized anchoring junctions
What is the function of specialized anchoring junctions?
Helps cells to:
- SENSE their SURROUNDING extracellular environment
- COMMUNICATE with each other.
What are the three types of junctions?
1) Tight junctions
2) Desmosomes
3) Gap junctions
What are tight junctions?
Impermeable junctions which prevent molecules from passing through the intercellular space.
What are desmosomes?
anchoring junctions which bind adjacent cells together and help them form an internal tension-reducing network of fibres.
What are gap junctions?
Communicating junctions which allow ions and small molecules to pass from one cell to the next for intracellular communication.
State the four types of tissue.
1) Connective Tissue
2) Epithelial Tissue
3) Muscle Tissue
4) Nervous Tissue
What is connective tissue?
Connective tissue UNDERLIES and SUPPORTS the other three basic tissues, both STRUCTURALLY and FUNCTIONALLY.
- connects, muscle, epithelial and nervous tissue to create an organ.
What is epithelial tissue?
Epithelial tissue covers body surfaces, lines body cavities, and forms glands.
What is muscle tissue?
Muscle tissue is made up of contractile cells and is responsible for movement.
What is nervous tissue?
Nerve tissue receives, transmits, and integrates information from outside and
inside the body to control the activities of the body.
- COGNITIVE FUNCTIONS
What is epithelial tissue?
Avascular tissue composed of cells that:
- cover exterior body surfaces
- line internal closed cavities (including the vascular system)
- line body tubes that communicate with the exterior (the alimentary, respiratory, and genitourinary tracts).
What does epithelium tissue form?
the secretory portion of glands and their ducts
PARENCHYMA CELLS
What else do epithelial cells do?
they act as receptors for the special senses.
What are the three principal characteristics of epithelium tissue?
1) always connected with cell junctions
2) attached to a basement membrane (a protein-polysaccharide-rich layer)
3) exhibit functional and morphologic polarity
What are the 3 domains of epithelial tissue?
- an apical domain (free surface), (different depending on body part) (eg. microvilli, cillia)
- a lateral domain (necessary to make cell junctions: connections (communication + nutrition sharing),
- a basal domain (attach the cell to the membrane).
What are the two main factors used to classify epithelium?
1) the number of cell layers
2) the shape of the surface cells
What are the different names given to epithelium, depending on the number of cell layers?
simple - one layer thick
Stratified - two or more cell layers
What are the different names given to epithelium, depending on the shape of the surface cells?
- SQUAMOUS: width > height; (remember by “squa”shed)
- CUBOIDAL: width = depth = height;
- COLUMNAR: height > width (remember by “column”ar)
What is keratin?
The protein found in the skin, which makes the skin waterproof.
Keratin gives the cell protection and dehydration.
How else can Stratified Squamous Epithelium be characterized?
KERATINIZED and NON-KERATINIZED.
What does it mean for a cell to be “keratinized”?
When cells in the surface layers of stratified squamous epithelium lack nuclei and have increased keratin in their cytoplasm, the epithelium.
LACK NUCLEI, and are FILLED WITH KERATIN.
What is ‘pseudostratified epithelium’?
Epithelium which appears stratified, although some of the cells do not reach the free surface.
All epithelium cells rest on the basement membrane and it is actually a simple epithelium.
What is ‘transitional epithelium’? What is its different name?
Transitional epithelium (UROTHELIUM):
- epithelium lining the lower urinary tract,
- urothelium extends from the minor calyces of the kidney down to the proximal part of the urethra.
- Urothelium is a STRATIFIED epithelium with specific morphologic characteristics that allow it to distend.
(transitional: it looks stretched at times and unstretched at other times.)
What words should one use to explain the location of the epithelium?
1) endothelium
2) endocardium
3) mesothelium
What is endothelium?
Endothelium is the epithelial lining of the blood and lymphatic vessels.
What is endocardium?
Endocardium is the epithelial lining of ventricles and atria of the heart.
What is mesothelium?
Mesothelium is the epithelium that lines the walls and covers the contents of the closed cavities of the body (i.e., the abdominal, pericardial, and pleural cavities).
What are glands? How are they formed?
Cells which transport fluid have IN-FOLDINGS (at the BASAL CELL SURFACE).
They significantly increase the surface area of the basal cell domain, forming glands.
How are glands classified?
depending on how their SECRETORY PRODUCTS are RELEASED.
1) Endocrine glands
2) Exocrine Glands
What are endocrine glands?
- Endocrine glands LACK a DUCT SYSTEM.
- They SECRETE their PRODUCTS (hormones) INTO the BLOODSTREAM to reach a specific receptor on distant target cells.
- secrete HORMONES
What are exocrine glands?
- Exocrine glands SECRETE their products DIRECTLY onto a SURFACE through epithelial ducts that may modify their secretion (concentrating, removing, or adding substances).
- have DUCTS
- eg. sweat secretion
How are exocrine glands classified? (Based on what they secrete)
1) MUCOUS GLANDS, which produce mucous secretions,
2) SEROUS GLANDS, which produce protein-rich watery secretions.
How else are exocrine glands classified?
Based on SECRETION!
What are the three mechanisms of secretion of exocrine glands?
1) merocrine
2) apocrine
3) holocrine
Explain merocrine secretion.
secretory product is released by EXOCYTOSIS.
- eg. sweat glands
Explain apocrine secretion.
secretory product is released in VESICLES containing a THIN LAYER of CYTOPLASM,
- eg. mammary milk gland
Explain holocrine secretion.
secretory product is accompanied by CELL DEBRIS from the dying secretory cell.
- cell is damaged, remaining parts of cell are secreted.
How else are exocrine glands classified? (Based on the number of cells)
unicellular or multicellular
What are unicellular glands?
single cells distributed among other non-secretory cells.
eg. goblet cell
goblet cells are located in the surface lining and glands of the intestines and in certain passages of the respiratory tract.
What are “multicellular glands”? What are their two parts?
glands composed of more than one cell. (They exhibit varying degrees of complexity.)
they are composed of the:
- duct
- secretory portion
What are myo-epithelial cells?
- a mix of epithelial and muscle cells
- contract and expel the secretions of exocrine glands
How are glands classified (depending on ducts branched vs. not branched)?
1) SIMPLE: unbranched duct
2) COMPOUND: branched duct
How are glands classified (depending on shape)?
1) TUBULAR
2) ALVEOLAR / ACINAR (circular)
3) TUBULOALVEOLAR (tube ends in a sac-like dilation)
Where can one find pseudostratified epithelium?
In the intestinal tract of some animals. (eg. snails)
What are the three types of epithelial cells in pseudostratified epithelium?
1) basal epithelium
2) apical / surface epithelium
3) intercalated epithelium
What can one find on the surface of the intestinal tract?
cillia
What are the two different poles?
1) apical pole
2) basal pole
What type of tissue exists in a lot of ‘slides’?
connective tissue
What is the membrane called which surrounds cells?
the basement membrane
What is a specific feature of tissues in the kidneys?
1) renal tubes are present (can be cuboidal or columnar shape)
2) capillaries are present (might be filled with red blood cells
3) columnar epithelium (epithelocytes)
4) connective tissue
5) nuclei, basal pole, apical pole
What are special characteristics of the uterus of a cat?
looks like the small intestine
1) has the serosa, muscle layer (tunica muscularis), submucosa, mucosa, and lumen.
2) presence of tubular glands
3) arteries and veins present
What is the “fat gland” called?
“sebaceous” or “acinar” gland
What are the characteristics of human skin?
1) hair follicle
2) sebaceous (acinar) gland
3) erectile muscle (of the hair)
What is the Latin name for “basement membrane”?
Stratum basale
How do you say “membrane” in Latin?
Stratum
What is the spikey membrane called in Latin?
Stratum spinosum
What is the membrane called in Latin during which cells are being filled with keratin?
Stratum granulosum
In which membrane is keratin produced?
Stratum granulosum
What is the membrane called in which all vesicles are ruptured and filled with keratin?
Stratum lucidum
What is the final membrane of the epidermis called?
Stratum corneum
Is epithelium stable?
Epithelium is not stable! Cells are constantly being lost are regenerated.
Where are epithelial cells regenerated?
In the basal membrane (Stratum basale).
What is the principal function of keratin in keratinized cells?
it balances the water content of cells. it is water proof and so it doesn’t let any water in or out of the cell.
What type of epithelium is skin made out of?
squamous stratified keratinized epithelium
What does the thickness of skin depend on?
- species
- location on the organism
What is the thickness of the epithelium layer of the skin?
relatively thin
What are the main characteristics of the epidermis?
- STRATIFIED SQUAMOUS KERATINIZED EPITHELIUM
- connective tissue
- pipillae of the connective tissue
- excretory ducts of the sebaceous glands
- artefacts (not usually present in living tissue)
inside–>outside
1) Stratum basale
2) Stratum spinosum
3) Stratum granulosum
4) Stratum lucidum
5) Stratum corneum
What are the main characteristics of the cornea?
STRATIFIED SQUAMOUS NON-KERATENATED EPITHELIUM
- connective tissue
inside–>outside
1) basal membrane (Stratum basale)
2) Stratum spinosum
3) Stratum superficiale
What are the main characteristics of the urothelium?
TRANSITIONAL EPITHELIUM
(transitions between stretched and unstretched (not actually changing cells, just the physical appearance changes).
inside–>outside
1) basal layer (Stratum basale)
2) intermediate layer
3) superficial layer
Why can’t the urothelium be simple?
There must be a complete layer of cells once the urothelium is unstretched.
In the epidermal keratenized stratified squamous epithelium, what can be seen?
- connective tissue
- artefacts
- papillae of the connective tissue
- excretory ducts of sebaceous glands
5 layers:
1) stratum basale
2) stratum spinosum
3) stratum granulosum
4) stratum lucidum
5) stratum corneum
