Tissues Flashcards
Tissues
collections of specialized cells and their extracellular matrix (non-cellular extracellular substance surrounding them) that perform a relatively limited number of function.
whats the 4 tissues types
epithelial, connective, muscle and nervous
Epithelial tissues
• covers all surfaces and lines all hollow structures
Cellularity of epithelial tissues
composed almost entirely of cells with very little extracellular matrix and closely bound by specialized junctions
Polarity of epithelial tissues
has distinct surfaces
Apical surface
= free surface not attached to any other cells
• faces external environment (atmosphere) or internal environments such as fluid in tubes
• microvilli =
non-motile projections of the cell membrane (containing microfilaments) on most epithelia
• increase surface area for absorption and secretion
• so dense in the first portion of the kidney tubule known as the “brush border”
cilia
motile projections on the apical surface of the cells that can sweep substances such as mucus along the tube – e.g. pseudostratified ciliated columnar epithelium of the trachea
lateral surface
site of specialized attachment to neighbouring cells
basal surface
site of attachment to basal lamina
Basal lamina (attachment)
specialized type of extracellular material secreted by epithelial and connective tissue cells (Fig 3.3)
• important role in tissue repair
avascular (epithelial)
contains no blood vessels therefore relies on diffusion of gases and nutrients from blood vessels located in underlying connective tissue
arrangement (epithelial)
sheets or layers
regeneration (epithelial)
continually replaced by division of stem cells found close to basal lamina
Function of epithelial cells
- protection of underlying structures
- acting as a barrier – prevents certain substances from crossing, barrier to water and limits water loss from body
- allows passage of certain substances– readily exchanges oxygen and carbon dioxide through lung epithelium and others epithelium are more selective – filtering at the kidney
- secretion – mucus glands, sweat glands, and enzyme-secreting portions of the pancreas are all composed of epithelial cells that secrete their products onto surfaces or into ducts
- absorbing substances – contain specialized carrier proteins on their membranes that allow specific components to be transported – e.g. intestinal epithelium
classification of epithelial cells
- most epithelium classified by two names: the first indicates the number of layers and the second indicates the shape of the cell
- others may have other descriptors added based on the presence of specialized features such as microvilli or cilia
simple epithelium
single layer of cells
• relatively thin and fragile
• found where secretion, absorption or filtration occurs
• provides smallest diffusion distance
stratified epithelium
more than one layer of cells
• found in areas subjected to significant mechanical or chemical stresses
stratified epithelium can be classified as :
- nonkeratinized = moist
- keratinized = dry, durable and moisture resistant and found in the skin where the outer most layers are composed of dead cells
transitional epithelium
unique type of stratified epithelium that lines the urinary bladder, ureters, pelvis of the kidney and superior portion of the urethra. Shape of the cells and the apparent number of layers vary with the amount of stretch on the bladder.
o pseudostratified (pseudo = false) columnar epithelium
is actually one layer of cells with all cells attached to the basement membrane but appears to be multilayered because some cells are shorter and do not extend to the free surface
• usually ciliated
• Shape of the Superficial Cells
quamous (Fig 3.4) = flat or pancake like o cuboidal (Fig 3.5) = cube-shaped – as wide as they are tall o columnar (Fig 3.6) = tall and thin – similar to a column
Glandular epithelium - secretory organs
o primarily composed of epithelium with supporting network of connective tissue
exocrine glands
glands that contain ducts (lined with epithelium) – dump their products into ducts that empty onto external surfaces (such as the skin) or into organ lumen (such as the intestine)
o categorized by nature of secretions
serous glands
watery solution usually containing enzymes
muscous glands
secrete glycoprotein mucin