Epithelial tissue Flashcards
Is epithelial tissue vascularized?
no, it’s avascular
What are the functions of epithelia?
- barrier that protects internal tissue
- selective absorption and transport of various molecules from the environment
- selective secretion of various molecules and fluids
- movement of particles, solutions and cell elements
- large scale biochemical modification/conversion/metabolism (e.g. liver, kidney, intestine)
- communication
- reception of sensory stimuli
What is endothelia?
linings blood and lymphatic vessels that face blood and lymph
What are the sheets of cells that line enclosed internal spaces of body cavities?
mesothelium
What is the epithelial to mesenchymal transition?
- embryonic epithelia disassemble and move into the mesenchymal (connective) tissues
- then they may migrate to other locations to form new epithelia or may transform into distinct non-epithelial cell lineages that give rise to other tissues
Where is connective tissue?
under the basal lamina
What runs through the connective tissue?
blood vessels, nerves, lymph, muscles
- each is surrounded by its own basal laminae that attach to their own neighboring connective tissue
What are the two layers of mucosa?
- outer epithelium
- the connective tissue directly underneath called lamina propria (beneath is submucosa that has bigger vessels and muscles)
What is the general relationship with the layers of epithelia tissue?
space(lumen)-epithelia-epithelial basal lamina-CT-other CT embedded tissues (blood vessels, muscles, nerves, each with their own basal laminae that connects them with CT)
What are tight junctions?
- provide highly selective barrier that limits or prevents diffusion of substances between epithelial cells
- key proteins - occluding and Claudine
- ensure substances must pass through the epithelial cell by specific transport pathways
What are adherence junctions?
- contain specific cadherins that link to actin filaments and other adapter/signaling proteins in the cytoplasm
- cadherins extracellular domains interact with each other (cytoplasmic tails that bind to adapters and actin filaments)
- some cadherin proteins control various aspects of epithelial polarity, development and function
What are desmosomes?
- promote mechanical strength and resist shearing forces and promote structural organization of the epithelial sheet
- different class of cadherins that link to intermediate filaments and other adapter proteins
What are gap junctions?
promote rapid communication between epithelial cells through diffusion of ions and small molecules
Is the cytoskeleton asymmetric or polar in orientation?
yes, particularly microtubules
Why is epithelial cell polarity crucial?
to allow unidirectional secretion and/or absorption of molecules to or from one side of the epithelium
What is transcytosis?
- endocytosis of substances from one membrane region, followed by trans-cellular transport of the vesicles and their exocytosis from another membrane region
What does basal laminae do?
- lines basal surface of epithelial tissue
- surrounds blood vessels, muscle and nerve tissue
What is basal laminae made of?
network forming collagen interwoven with a variety of glycoproteins (laminin and enactins)
What are the functions of basal laminae?
- mediate attachment of epithelia to underlying connective tissue
- contribute to selective filtration of substances diffusing to or from the epithelia
- necessary for the establishment and maintenance of epithelial cell polarity
- serve as highways for the migration of cells through connective tissue
- provide barrier to movement of invading microbes or cancer cells
- control the gene expression of cells to affect their proliferation or development
- critical to repair of epithelial tissue following injury (control development, morphogenesis and organization of epithelial cells)
How do epithelial cells directly connect to the basal laminae?
- key class is integrins
- attachment of hemidesmosomes and focal adhesions
What do focal adhesions regulate?
- integrins of focal adhesions connect to actin filaments inside the epithelial cell
- regulate epithelial polarity and function through signaling mechanisms
What are the key properties of all stem cells?
- competent for cell division
- must self renew (one mother stem cell is regenerated with each division)
- produce anywhere from one to many distinct, differentiated cell types specific to each tissue
What are transit amplifying cells?
daughter stem cells that proliferate at faster rates
- transitional intermediates
Where do most stem cells reside in vivo?
stem cell niche - a specific tissue subcompartment
What are two important principles to understand about stem cell signaling?
- each pathway controls multiple, different stem cell systems
- a single signaling pathway will have different developmental outcomes in different stem cell lineages
How do epithelial glands secrete their substances?
- exocytosis
- total cell disintegration (secretion of sebum)
Where do exocrine glands secrete their materials?
apical side of epithelial surfaces
What are secretory units (in relation to exocrine glands)?
- clumps of secretory epithelial cells that produce the bulk of the exocrine secretion
- can be organized into alveoli or acini (bowl shaped lobules) or tubular glands (tubes)
What are ducts (in relation to exocrine glands)?
- tubular structures that emanate from the secretory units
- passageways to conduct secretions to their destination
- simple glands - one duct
- compound ducts - multiple, branched ducts
What are the three types of exocrine glands of the body tubes (alimentary canal, respiratory, and urogenital system)?
- mucous - produces viscous glycoprotein rich fluids
- serous - produces low viscosity watery fluids carrying specific enzymes
- mixed - both kinds, typically from different cell types within the gland’s secretory units
Where do endocrine glands secrete substances?
- directly into the blood stream (have no ducts)
- hormones must cross the basal surface and basal lamina of the epithelium
- most endocrine cells secrete these molecules from the basolateral membrane
What generally regulates secretions from both exocrine and endocrine glands?
autonomic nervous system, hormones, or both
What are adenocarcinomas?
cancers derived from glandular epithelium
