Flashcards in Epithelia III Deck (22):
Epithelial stem cell fx.?
Self-renew (regenerate stem cells with each cell division)
Produce differentiated cell types
Often same process that occurs in development!
What are transit amplifying cells?
Stem cells produce daughters that also proliferate (often faster) these are transitional intermediates.
They then produce differentiated cells. (there are always more amplifying cells than there are stem cells b/c stem cells are so tightly regulated)
In which phase of cell division to stem cells spend the most time?
Stem cells regulated by? (general)
Cell to cell communication and cell signaling pathways (can be local in same epithelia or a different one, endocrine, from nervous system).
Features stem cell regulatory pathways?
Similar to embryogenesis/development (like Wnt, Sonic hedgehog etc.)
-Most pathway components are shared by several stem cell lineages
-Single signaling pathways leads to diff. outcomes in diff lineages
Why do you get diff outcomes with same signaling pathway in stem lineages?
-Diff developmental histories (cells can maintain diffs in chromatin/cytoplasmic states)
-Diff enviro stem cell is in (niche)
-Diff in levels of extracell ligands, receptors, downstream components
ex given in lecture: Wnt pathway having totally diff effects in colon and lung cancer.
Where are signaling mlcs released?
can be secreted or membrane bound (wnt sonic notch etc.). Go into ECM and interact with receptor, alter things in cell.
Glands are derived from...
Epithelial tissue! Fun.
2 major types of epithelial glands
1.) Exocrine: secrete materials onto surface (epithelial lined)
2.) Endocrine: secrete into blood stream
How do glands secrete substances?
1.) Exocytosis (glands that do this often called merocrine or apocrine)
2.) Total cell disintigration (whole cell becomes part of signal)... holocrine glands (like oil into your hair)
Diff in development of exocrine and endocrine glands?
Exocrine basically are the epithelium invaginating in and forming ducts etc.
Endocrine is invagination but then it pinches OFF so not connected anymore.
Which side of epithelial cell secretes in endocrine and exocrine glands?
Related to development.
In exocrine get secretion from apical side.
In endocrine, from the basolateral side (significant b/c then secretions must pass through basal lamina, blood vessel walls etc... so more barriers!)
How many cells in exocrine glands?
Typically multicell. But can be unicellular. Like those lining interal passages (goblet cells)
Components of multicellular exocrine glands?
1.) Secretory units- can be organized into bowl (alveoli) or flask (acini) shaped units. Or into tubes (tubular). Called alveolar, acinar, tubular glands. Some glands can be tubuloalveolar. (Some glands have single secretory unit, some have more)
2.) Ducts- tubular structures emanating from secretory units. Passages that conduct secretions. Can have secretory/ion transport properties to alter secretion as it passes.
Simple vs compound glands
Single have 1 dict. Multiple ducts are compound.
Types of exocrine glands of the body "tubes"? (alimentary canal, respiratory, urogenital)
1.) Mucous: viscous glyco-protein rich fluid
2.) Serious: water, salts and specific proteins
Secretory epithelial cells secrete these materials unidirectionally from APICAL surface (exception is holocrine secretion).
Have no ducts. Secrete into blood.
Mostly specific hormones.
Generally organized as clumps/chords of cells that are embedded with/surrounded by connective tissue containing extensive capillary networks. Each clump surrounded by basal lamina.
Remember these hormones must pass barriers!
Regulation of glandular secretions
Typically by ANS, hormones from blood, or both.
Exocrine often secrete constantly at low level (can be promoted to enhance secretion volume).
Endocrine: tightly regulated by hormones/neurons.
Why are epithelia so important to disease?
They are essential to organ/tissue fx, high turn over rate requiring stem cell driven renewal, and their exposure to external damage.
Most common cancers. Epithelial origin.
Tumors start in epithelium then can invade/metastasize. Often tumors retain some qualities from tissue of origin. (why histology is imp).
Arise from defects in regulatory pathways that control epithelial stem cells and their progeny during tissue development/maintenance.
From glandular epithelium.