Epithelia Flashcards
- State the structural arrangements, classifications, and functions of epithelial tissues, and state their general structural relationships (orientation) to connective tissue, blood vessels, muscle, and neurons
(peripheral nervous tissue). - Describe the cellular basis for apical-basal polarity of epithelial cells and describe the functions of epithelial polarity.
- State the different cell junctions that connect epithelial cells to one another and to the basal lamina, and describe their key components and functions.
- State the types and functions of the different cell surface modifications on epithelial cells.
- Describe basal laminae by stating their basic components, their functions, the basis of their diversity, and their structural relationship to epithelia and other tissues.
- Compare and contrast exocrine and endocrine glands in terms of their development, general structure, and functions, and for both types of glands, trace the path that a secreted molecule must take from its synthesis to its destination, and describe all the barrries/structures the molecule must cross en route.
- Describe the epithelial to mesenchymal transition during development.
- Describe how epithelial tissues are maintained and regulated, and describe the properties, functions, regulation and development of epithelial stem cells.
- State the general terms for epithelial-derived cancer, and describe how defects in epithelial cell regulation can contribute to cancer.
xxx
Endocrine glands are unique in that….?
They are no longer physically attached to the epithelial surface. Endocrine glands function to secrete into the blood, so they must secrete out of the basolateral surface, across the basal lamina, through the connective tissues, through the basal lamina of the blood vessels etc.
[Exocrine glands have only to secrete directly into the lumen]
2 broad categories of secretions from epithelial glands:
Serous (tears)
Mucous (yeah)
What are the acini?
Functional secretory engines of an exocrine gland.
Epithelia serve several different functions including:
- A barrier that protects internal tissues against abrasion, infection, harmful chemicals or radiation (e.g. sunlight).
- Selective absorption and transport of various molecules from the environment.
- Selective secretion of various molecules and fluids.
- Movement of particles and mucous through passage ways.
- Biochemical modification of molecules (e.g. liver)
- Communication to (and from) other tissues and organs
- Reception of sensory stimuli (e.g. smell, taste and touch).
A tissue that faces blood and lymph is called_____
endothelium
heets of cells that line the enclosed internal spaces of the body cavities are called the_____-.
mesothelium
Epithelia are derived from ____
all three primary germ layers (ectoderm, mesoderm, endoderm)
embryonic epithelia often disassemble and move into the mesenchymal (connective) tissues; there they may migrate to other locations to form new epithelia, or they may transform into distinct non-epithelial cell lineages that give rise to other tissues. This process is known as the_____
epithelial to mesenchymal transition.
-Transitional epithelia
(found around the bladder) are a special case: these epithelia are stratified, but when stretched change their shape from cuboidal to squamous, and appear to decrease the layering: this is indicative of a tightly adherent epithelium that is very resilient and stretchable.
Key core proteins of tight junctions are
occludins and claudins
Tight junctions
Tight barriers ensure that substances absorbed or secreted must pass through the epithelial cell by specific transport pathways.
Adherence junctions (zonula adherens): Promote attachment, but also polarity, morphological organization and stem cell behavior within the epithelial sheet. Adherence junctions contain specific _____ that link to actin filaments and other adapter/signaling proteins in the cytoplasm.
cadherins
Desmosomes (macula adherens): Promote ______ and promote the structural organization of the epithelial sheet. Core components of these junctions include a different class of cadherins that link to intermediate filaments
mechanical strength and resist shearing forces
Gap junctions:
Promote rapid communication between epithelial cells, through diffusion of
ions and small molecules.
tight junction complexes tend to reside near the ___- surface
apical
What is the importance of cell polarity?
unidirectional secretion and absorption
Transcytosis
movement that transverses a cell (eg crosses basolateral and apical membranes)
An unusual type of microvillus, called_____, are found in the epididymis and in sensory cells in the ear. These are extremely long, actin-filled microvilli, and are not related to cilia.
stereocilia (unfortunate nomenclature)
In the ear, stereocilia function in the reception of sound.
Basal laminae are formed by a special type of network-forming collagen, a fibrous protein. This type of collagen forms sheets of thin fibers that are interwoven with a variety of other extracellular glycoproteins. Network-forming collagen (especially “type IV”) and some other glycoproteins including ____ and_____ are common to most basal laminae.
laminins; entactin
[It is thought that most of the basal lamina components are actually synthesized and secreted by epithelial cells. However, some extracellular components of the connective tissue (made by fibroblasts) bind to and possibly organize elements in the basal lamina.]
Basal laminae have several important functions:
- They mediate attachment of epithelia to the underlying connective tissue.
- Basal laminae often contribute to selective filtration of substances diffusing to or from the epithelia.
- They are necessary for the establishment and maintenance of epithelial cell polarity.
- They can serve as specific “highways” for the migration of cells through connective tissue.
- They provide a barrier to movement of invading microbes or cancerous cell into other tissues. 6. They control the gene expression of cells to affect their proliferation or development.
- They control the development, morphogenesis, and organization of epithelial cells, providing a sort of “tissue scaffolding” function. Thus, they are critical to the repair of epithelial tissue following damage by injury or disease.
Epithelial cells directly connect to basal laminae by attachment of ______ and focal adhesions on the basal surface of the epithelial cell to components of the basal lamina. The key class of proteins that form these connections are the ____ (distinct proteins from the cadherins that mediate cell-cell linkage).
hemidesmosomes; integrins
Many stem cells produce daughters that also proliferate themselves (undergo cell division cycles), often at faster rates; these transitional intermediates are called ______ .
transit amplifying cells
Total cell disintegration, which leads to the entire cellular contents becoming part of the secretion; glands of this sort are less common, and are sometimes called _____.
holocrine glands
(examples include the secretion of oily sebum onto hair and skin).
The first main component of an exocrine gland is the secretory unit. Secretory units can be organized into bowl or flask-shaped lobules called ____, or they may be organized into tubes, and are called _____. Some glands have both tubular and alveolar character and are called tubuloalveolar.
alveoli or acini, and are called alveolar or acinar glands; tubular glands
The second main component of an exocrine gland is ducts. Ducts are tubular structures that emanate from the secretory units. Ducts function as passageways to conduct secretions to their destinations. There are categorizations:
Glands that possess a single duct are classified as simple glands, whereas those with multiple branched ducts are called compound glands.
Cancers of epithelial origin are called ____, and cancers derived from glandular epithelium are known as _____.
carcinomas; adenocarcinomas
A disease called _____ is an autoimmune disease in which antibodies are produced against components of desmosomes in skin, leading to extensive blistering.
pemphigus
