Epithelial Tissue Flashcards
Epithelial Tissues
- large sheets of cells covering all surfaces of the body exposed to the outside world and lining the outside of organs
- also forms much of the glandular tissue of the body
- skin, airways, urinary/reproductive system, hollow organs, and body cavities that don’t connect to the exterior of the body (blood vessels, serous membranes)
- nearly completely avascular (no blood vessels
where do they derive from?
- all 3 major embryonic layers
- epithelia lining skin, parts of mouth and nose and anus develop from ectoderm
- cells lining airways and most of digestive system originate in endoderm
- epithelium that lines vessels in the lymphatic and cardiovascular systems derives from mesoderm –> called endothelium
what structural and functional features do they share?
- tissues are highly cellular
- little or no extracellular material between cells
- adjoining cells form cell junction
- exhibit polarity with differences in structure/function between the exposed surface of the cellj
cell junction
adjoining cells form specialized intercellular connection between cell membranes
apical
surface of the cell and basal surface close to underlying body structures
basal lamina
mixture of glycoproteins and collagen
- provides attachment site for epithelium, seperates it from underlying connective tissue
- attatches to reticular lamina to form basement membrane
basement membrane
basal lamina attatched to reticular lamina
- holds everything together
how do epithelial tissues get nutrients?
- nutrients come by diffusion or absorption from underlying tissues or the surface
- capable of rapidly replacing damaged and dead cells
–> characteristic of surface epithelium that allows our airways and digestive tracts to rapidly replace damaged cells w new cells
what is the body’s first line of protection from physical, chemical and biological wear and tear?
epithelial tissues
- act as gatekeepers of body to control permeability and allow selective transfer of materials across physical barrier
functions of epithelium
- first line of protection
- gatekeepers
- selective transport
- capable of secretion and release of mucous
- releases digestive enzymes (in the small intestine)
- cells lining the respiratory system secrete mucous that traps incoming microorganisms and particles
- glandular epithelium contains many secretory cells
Epithelial Cells
- characterized by polarized distribution of organelles and membrane-bound proteins between their basal and apical
- certain structures found in epithelial cells are an adaptation to specific functions: certain organelles are segregated to basal sides, other organelles and extensions (like cilia) are on apical surface
cilia
- microscopic extensions of the apical cell membrane that are supported by microtubules
- they beat in unison and move fluids and trapped particles
ciliated epithelium
- lines the ventricles of brain where it helps circulate the cerebrospinal fluid
- The ciliated epithelium of your airway forms a mucociliary escalator that sweeps particles of dust and pathogens trapped in secreted mucous toward the throat
mucociliary escalator
- sweeps dust particles and pathogens trapped in mucous towards the throat
- called escalator bc it continuously pushes mucous with trapped particles upward
nasal cilia
sweeps the mucous blanket down towards your throat
common between nasal cilia and mucociliary escalator
- transported materials are usually swallowed
- end up in acidic environment of your stomach
what are the 3 types of cell junctions
- tight junctions
- anchoring junctions
- gap junctions
what are tight junctions
- separates the cells into apical and basal compartments
- two adjacent epithelial cells form a tight junction
- no extracellular space between them
- movement of substances through the extracellular space between cells is blocked
- enables epithelia to act as selective barriers
what are anchoring junctions
- several types of celljunctions that help stabilize epithelial tissues
- common on lateral and basal surfaces of cells where they provide strong and flexible connections
- 3 types: desmosomes, hemidesmosomes, adherens
what are desmosomes?
- type of anchoring junctions
- occurs in patches on membranes of cells
- patches are structural proteins on inner surface of cells membrane
- the adhesion molecule (cadherin) is embedded in patches and projects through cell membrane to link with cadherin molecules of adjacent cells
- these connections are especially important in holding cells together
hemidesmosomes
- type of anchoring junction
- look like half a desmosome
- link cells to extracellular matrix (like basal lamina)
- similar in appearance but they include adhesion proteins called integrins instead of cadherins
- use either cadherins or integrins depending on contractile protein actin located on cytoplasmic surface of cell membrane
- actin can connect isolated patches or form belt-like structure inside the cell
- these junctions influence the shape and folding of epithelial tissue
gap junction
- not the same as tight and anchoring junctions
- forms intercellular passageway between membranes of adjacent cells to facilitate the movement of small molecules and ions between cytoplasm of adjacent cells
- junctions allow electrical and metabolic coupling of adjacent cells, which coordinates function in large group cells
how are epithelial tissues classified?
according to shape of cells and number of cell layers formed
what are the different cell shapes?
- squamous (flattened and thin)
- cuboidal (boxy, as wide as it is tall)
- columnar (rectangular, taller than it is wide)
what is it called when it has more than one layer
stratified
pesudostratified
- pseudo: false
- tissue with single layer of irregularly shaped cells that give appearance of more than one layer
transitional
- form of specialized stratified epithelium in which the shape of cells can vary
true or false: shape of cells in single cell layer of single epithelium reflects the function
true
what does squamous cell nuclei look like
flat, horizontal, elliptical (mirrors form of cell)
endothelium
- epithelial tissue that lines vessels of lymphatic and cardiovascular system
- made up of a single layer of squamous cells
simple squamous epithelium
- thin scale like cell
- present where rapid passage of chemical compounds is observed
ex: alveoli of lungs, segments of kidney tubules, lining of capillaries
mesothelium
- simple squamous epithelium that forms surface layer of serous membrane that lines body cavities and internal organs
- function: provide smooth and protective surface
mesothelial cells
- squamous epithelial cells that secrete fluid that lubricates mesothelium
what does simple cuboidal epithelium
- nucleus of box-like cells appears round
- located near center of cell
- epithelia are active in secretion and absorptions of molecules
EX: observed in lining of kidney tubules and ducts of glands
simple columnar epithelium
- nucleus of tall column-like cells tends to be elongated and located in basal end of cells
- epithelium is active in absorption and secretion of molecules
- forms the lining of some secretions of the digestive system and parts of the female reproductive tract
ciliated columnar epithelium
- simple columnar epithelial cells with cilia on apical surfaces
- found in lining of fallopian tubes and parts of respiratory system
- function: beating of cilia helps remove particulate matter
pseudostratified columnar epithelium
- appears stratified but instead consists of single layer of irregularly shaped and differently sized columnar cells
- nuclei of neighboring cells appear at different levels rather than clustered in basal end
- all cells are in contact w basal lamina (even tho it doesnt look like it), some dont reach apical surface
EX: respiratory tract (some have cilia)
true or false: simple and pseudostratified cuboidal epithelia are heterogeneous bc they include additional types of cells interspersed among epithelial cells
false – simple and pseudostratified columnar epithelia
goblet cell
- mucous-secreting unicellular ‘gland’ interspersed between columnar epithelial cells of mucous membranes
stratified epithelium
- several stacked layers of cells
- protects against physical and chemical wear and tear
- named by shape of most apical layer of cells (closest to free space)
stratified squamous epithelium
- most common tpype of stratified epithelium in human body
- apical cells are squamous
- basal layer mgiht be columnar or cuboidal
- top layer: covered with dead cells filled with keratin
EX: mammalian skin
stratified cuboidal epithelium and stratified columnar epithelium
- found in certain glands and ducts
- uncommon in human body
transitional epithelium
- another kind of stratified epithelium
- gradual changes in shapes of apical cells as bladder fills with urine
- only found in urinary system: ureters and urinary bladder
- when bladder is empty: epithelium is convoluted and has cuboidal apical cells w convex umbrella-shaped apical surfaces
- bladder filled: epithelium loses its convolutions and apical transition from cuboidal and squamous, more stretched out and less stratified
Gland
structure made up of one or more cells modified to synthesize and secrete chemical substances
- consist of groups of epithelial cells
- can be classified as endocrine or exocrine glands
endocrine gland
- ductless gland that releases secretions directly into surrounding tissues and fluids
- secretions of endocrine glands are hormones
–> released into interstitial fluid, diffused into bloodstream and dleivered to targets (cells that have receptors to bind the hormones) - part of major regulartory system coordinating the regulation and integration of body responses
ex: anterior pituitary, thymus, adrenal cortex, gonads
exocrine glands
- secretions that leave through duct that opens directly/indirectly to external environment
- release contents through duct that leads to epithelial surface
EX of secretions: mucous, sweat, saliva, and breast milk - all discharged through tubular ducts
- secretions into lumen of the gastrointestinal tract (technically outside the body)
glandular structure
- exocrine are either unicellular or multicellular
unicellular glands
- scattered single cells
- such as goblet cells (found in mucous membranes of small and large intestine
multicellular exocrine glands
- aka serous glands
- develop from simple epithelium to form a secretory surface that secretes directly into an inner cavity
- glands line the internal cavities of the abdomen and chest and release their secretions directly into the cavities
- other multicellular exocrine glands release their contents through a tubular duct (duct is single in a simple gland but in compound glands, is divided into one or more glands)
- tubular glands –> ducts can be straight or coiled
- alveolar (acinar) –> tubes that form pockets (an exocrine portion of the pancreas)
- combination of tubes and pockets are known as tubuloalveolar (tubuloacinar) compound glands
- branched gland: duct connected to more than one secretory group of cells
what do the exocrine glands mode of secretion and nature of released substances look like?
- merocrine secretion
- apocrine secretion
- holocrine secretion
merocrine secretion
merocrine secretion: most common type of exocrine secretion
- secretions are enclosed in vesicles that move to the apical surface of cell where ocontents are released by exocytosis
EX: watery mucous containing the glycoprotein mucin is a lubricant that offers some pathogen protection is a merocrine secretion
- eccrine glands that produce and secrete sweat are another example
apocrine secretion
- accumulates near the apical portion of the cell
- that portion of the cell and its secretory contents pinch off from the cell and are released
- apocrine sweat glands in the axillary and genital areas release fatty secretions that local bacteria break down (causes body odor)
what happens in both merocrine and apocrine glands
both continue to produce and secrete their contents with little damage caused to the cell because the nucleus and gogi regions remain intact after secretion
holocrine secretion
- involves the rupture and destruction of the entire gland cell
- cell accumulates its secretory products and releases them only when it bursts
- new gland cells differentiate from cells in the surrounding tissue to replace those lost by secretion
- the sebaceous glands that produce the oils on the skin and hair are holocrine glands/cells
Serous Gland
- produces watery, blood-plasma-like secretions rich in enzymes such as alpha amylase
- common in salivary glands of mouth
- mixed exocrine glands have both serous and mucous glands and release both types of secretions
Mucous Gland
- releases watery to viscous products rich in the glycoprotein mucin
- common in salivary glands of the mouth
- mixed exocrine glands have both serous and mucous glands and release both types of secretions
