Chp 4, Epithelial Tissue Flashcards
Tissues and the (4) basic types
- group of cells with similar in structure that perform common/related function
1. Epithelial
2. Connective
3. Muscle
4. Nervous
Histology
study of tissues
Epithelial Tissue / Epithelium
- sheet of cells that covers a body surface / lines a body cavity
- Two forms in the body:
1. Covering and lining epithelia - on external/internal surfaces
2. Glandular epithelia - secretory tissue in glands - Main function: protection, absorption, filtration, excretion, secretion, and sensory receptors
(5) Shared characteristics of Epithelial Tissue
- Polarity
- Specialized Contacts
- supported by connective tissues
- avascular, but innervated
- regeneration
apical surface
- the upper, free surface of epithelial tissue exposed to the body exterior or cavity of an internal organ
- typically smooth, but can also have microvilli / cilia
basal surface
- lower, attached side of epithelial tissue, faces inward toward the body
- attaches to the basal lamina
basal lamina
- adjacent to the basal surface, this is a thin support sheet that holds the basal surface to underlying cells
- acts as a selective fiber that determines which molecules diffuse from underlying connective tissue are allowed to enter the epithelium
- upper part of the basal basement
Polarity of Epithelial Cells
-a top (apical) and bottom (basal) surface that different in structure and function
Specialized Contacts
- epithelial cells fit closely together to form sheets (except for glandular epithelial). they are connected
- The are connected by lateral contacts tight junctions and desmosomes.
- Tight junctions prevent passant of material between the cells
- desmosomes give structural support and help prevent tearing
Connective Tissue that supports Epithelial cells
- epithelial cells rest on/are supported by connective tissue called the ‘basement membrane’
- basement membrane is a layer of basal lamina and deep to that is the reticular lamina
Avascular, but innervated
- epithelial tissue do not contain any blood vessels
- they are supplied by nerve fibers
- get nourished by substances diffusing from blood vessels in the underlying connective tissue
Regeneration
- epithelial cells have a high regenerative capacity (cell division - mitosis)
- stimulated by loss of apical-basal polarity and broken lateral contacts
Classification of Epithelia (two names)
- The first name is the number of cell layers (simple or stratified)
- Second name is shape of cells or shape of apical layer if stratified
Shapes of Epithelial cells
- squamous - flattened and scale like
- cuboidal - box-like, cube
- columnar - tall, column-like
Simple epithelia
-single layer epithelia involved in absorption, secretion, or filtration
endothelium
- simple squamous epithelia found in lining of lymphatic vessels, blood vessels, and heart
- the thinness encourages the efficient exchange of nutrients and wastes between bloodstream and surrounding cells
Mesothelium
-simple squamous epithelium that are found in serous membranes, membranes lining the ventral cavity and covering the organs in the cavity
simple squamous epithelia
- single layer with flat cells and sparse cytoplasm
- very thin and permeable, found where filtration/exchange by rapid diffusion is needed - kidneys/lungs
simple cuboidal epithelium
- single layer of cuboidal cells
- involved in secretion and absorption
- this epithelium forms the walls of small ducts of glands and kidney tubules
simple columnar epithelium
- single layer of column shaped epithelium cells - these are tall, closely packed cells.
- associated with absorption and secretion
- some have microvilli/cilia (which make it good for absorption and secretion)
- lines digestive tract, gall bladder, ducts of some glands, bronchi, and uterine tubes
psuedostratified columnar epithelium
- columnar cells have varying heights (which makes it look stratified) but all of them rest on the basement membrane - so actually simple
- secretes and absorbs
stratified epithelium tissue
- two or more layers of cells
- new cells regenerate from below (old cells on top)
- more durable than simple epithelium
- protection is the mane role
stratified squamous epithelium
- most widespread of stratified epithelia
- many layers
- apical layer is squamous, with deeper layers cuboidal/columnar
- located in areas of wear/tear like skin
- keratinized cells - have the the tough protein keratin OR
- non-keratinized - without keratin
Stratified cuboidal epithelia
- pretty rare
- found in sweat and mammary glands
- usually only 2 layers
stratified columnar epithelium
- very limited
- small amounts in pharynx, male urthera, and line some glandular ducts
- only apical layer is columnar
transitional epithelium
- forms lining of hollow urinary organs - bladder, ureters, urethra
- these cells can compress/stretch, allowing more volume in the organ
- basal layer are cuboidal/columnar
Gland and gland classification
- one ore more cells that make and secrete a product
- classified by site of product releases (endocrine/exocrine) and number of cells (unicellular/multicellular)
endocrine glands
- glands that secrete internally, like hormones
- ductless
- released by exocytosis into extracellular space where it can enter blood, lymphatic fluid, or to specific target organs and prompt a certain response
- mostly multicellular with a few unicellular (part of diffuse endocrine system)
exocrine glands
- gland that secrete externally onto body surfaces (skin) or into body cavities
- more numerous than endocrine glands
- these secrete into ducts
- can by unicellular / multiceullar
Unicellular exocrine glands
- goblet and mucous cells
- found in epithelial linings of intestinal and respiratory tracts
- both cells produce mucin, that dissolves in water forming mucous
Multicellular exocrine glands
- have two parts - a duct and a secretory unit
- usually surrounded by supportive connective tissue that supplies blood and nerve fibers to gland
- the connective tissue also forms fibrous capsule around gland and extend into the gland, dividing into lobes
- classified by structure (simple/compound &secretory unit) and mode of secretion
Simple vs. Compound multicellular exocrine Glands
Classification of multicellular exocrineglands by structure:
simple glands - unbranched duct
compound glands - branched duct
secretory units of multicellular exocrine glands - 3 types
- tubular
- aveolar / acinar - sacs
- tubuloalveolar
modes of secretion of multicellular exocrine glands (3)
- merocrine
- holocrine
- apocrine
merocrine
multicellular exocrine gland form of secretion by exocytosis
ex - sweat, pancreas
holocrine
- mode of secretion of multicellular exocrine glands where the product accumulates in duct until it ruptures releasing product and dead cell fragments
ex. sebaceous oil glands
apocrine
mode of secretion of multicellular exocrine glands
-product accumulates within duct, but only apex ruptures
not actually sure if this exists in humans, maybe mammary cells
