Epithelial tissue Flashcards
wk 3
What are the three major functions of epithelial tissue?
selective barrier, secretory surface and protective surface
What are the two types of epithelial tissue?
covering and linning tissue and Glandular epithelium
what is covering and lining tissue?
outer cover of skin and internal organs
where might you find covering and lining tissue?
inner-lining of blood vessels, ducts and body cavities and in tracts such as respiratory, digestive and reproductive
what is glandular epithelium?
secreting portion of glands
what are the three types of surfaces in epithelia?
Apical, basal and lateral
What is the apical surface?
the most superficial layer of cells, attached to free surface and has surface specialisations.
what are the surface specialisations that are attached to the apical surface?
Microvilli, cilia, goblet cells and keratin
what is keratin?
protective layer that resists abrasive forces
what is microvilli and where is it commonly found?
increases the efficiency of absorption and most commonly found in small intestine.
what is cilia and where is it commonly found?
move substances over epithelial and found in the respiratory tract, brain and fallopian tube.
what are goblet cells?
mucous secreting cells
what are basal cells?
the deepest layer of cells that adhere to the basement membrane
What is the basement membrane?
a thin layer that attaches to and supports epithelial tissue.
what are the two components of the basement membrane?
basal lamina and reticular lamina
what and where is the basal lamina?
contans proteins and glycoproteins, molecules within it adhere to intergrin and is located close to epithelial cells.
Where is reticular lamina?
close to connective tissue
what are the structrual classifications of epithelial cells?
shape, layers and gland type
what are the four cell shape types?
Squamous, columnar, cuboidal and transitional
Describe squamous cells.
flat and thin to allow subtsnaces to pass easily. Can be identified by flat nuclei in microscope.
Describe Columnar cells.
rectangular, have specialisations (cilia/microvilli) and allow for protection, absorption and secretion.
Describe cuboidal cells.
square and cubed, contain microvilli and promote absorption and secretion.
Describe transitional cells.
change shape from squamous to cuboidal and again. Allows the surface to stretch.
What are the types of cell layers?
simple, stratified and pseudostratified
Simple Cell Layer
single layer in which things can pass through easily
Stratified Cell Layer
Two or more layers of cells, creates protection
Pseudostratified
appears to have many layers but indeed is simple. Usually in cells that have high mitotic activity (trachea)
What are the two types of glands?
Endorcrine and exocrine glands
Where are endocrine glands?
within the body
Where are exocrine glands and describe them
outside the body, release into a duct and mostly in the epithelia.
How can the two glands be classified?
If they are unicellular or multicellular
what are the unicellular exocrine glands?
goblet cells
what is a unicellular endocrine hormone?
enteroendocrine hormones
what are multicellular glands classified by?
Branching (branched/unbranched) and shape (tubulor or rounded)
What is the mode of secretion for merocrine glands?
secretion synthesised by ribosomes on RER –> packed by GA –> released via exocytosis
What is an example of a merocrine gland?
salivary gland
What is the mode of secretion for Apocrine Glands
Accumulates secretory products at the apical (top) –> end of cell pinches off via exocytosis –> repairs itself
What is an example of a Holocrine Gland?
Sebaceous gland (near the skin)
What is the mode of secretion for Holocrine Glands?
accumulates secretory products in cytosol –> cell ruptures –> releases products
What is an example of an Apocrine Gland?
mammary gland
What are the two main membranes involved in the epithelia?
Serous and mucous
Where is the Serous membrane?
Lines cavities that do NOT open DIRECTLY to EXTERIOR and the organs within the cavity
What are examples of cavities that the serous membrane lines?
Thoracic and abdominal
What is the purpose of the serous membrane?
secrets serous fluid which sits between the two layers of membrane to allow for lubrication
Where is the Mucous membrane?
Lines all cavities that OPEN to the EXTERIOR
What are example of cavaites that are lined by the Mucous Membrane?
Respiratory, reproductive, digestive and most of the urinary tract.
Structure of Tight Junctions
Uses transmembrane proteins that bind to the plasma of adjacent cells.
Purpose of Tight Junctions
Seal very tightly and prevent things from moving in
What organs have Tight Junctions?
Stomach, bladder and intestines
Structure of adherens
Cadherin inserts into microfilaments plaque on one cell to cadherin on the adjacent cell.
What is the prupose of adherens?
resists separation during contractive actions
What organs have adherens?
intestines
What is the structure of Desmosomes?
cadherins join to plaque made from intermediate filaments
What is the purpose of Desmosomes?
resist separation under tension
What organs have Desmosomes and Hemidesmosomes?
Heart and epidermis
What are Hemidesmosmes?
junctions between the bottom of the cell and basal lamina?
What is the purpose of hemidesmosomes?
anchor cells to the basement membrane
What is the structure of Gap Junctions?
Connexions creat Connexons (fluid-filled tunnels) that allow for direct connection via cytoplasm.
what is the purpose of Gap Junctions?
allows for rapid communication which is vital when things need to occur in sync (e.g beating heart)
Where are Gap Junctions found?
Muscles in heart, GI tract and uterus.
What transmembrane protein is found in adheren junctions?
Cadherins
Where in the body would you find stratified squamous epithelia?
Vagina
What type of secretion does the pancreas use?
merocrine secretion
What is an example of apocrine secretion?
Milk production in the mammary glands.
What is the function of microvilli?
To increase SA of an epithelia for absorption
What are the advantages of glandular secretion over unicellular?
Increased volume of secretion, control of timing of release and ability to store rather than have continuous release.
What is keratin?
protein that creates extra protection for an epithelia from heat, microbes, chemicals and water loss.
What is an example of a mucous membrane?
Respiratory tract.
Where in the body would you find simple cuboidal epithelia?
pancreas.
Where in the body would you find simple columnar epithelium?
Duodenum
what type of cell junction contains intergin proteins?
Hemidesmosomes
what is the function of cillia?
move trapped particles across the surface of the epithelia
What is the name of the superfcial layer of basement membrane?
basal lamina
In which type of epithelial membrane would you find a lamina propria?
Mucous membrane
What type of connective tissues underlies the epithelia of the body?
Loose areolar
What type of epithelium would you find in the urinary bladder?
transitional
What type of epithelia would you find forming the serous membranes of the body?
simple squamous
Does the epithelia receive direct blood supply?
No- it is avascular
