Anatomy-Ch.4 Tissues (Epithelial Tissue)
functions of the basal lamina
-acts as a selective filter determining which molecules from capillaries in the underlying connective tissue are allowed to enter the epithelium -acts as scaffolding along which regenerating epithelial cells can migrate
6 special characteristics of epithelia (distinguish from other tissue types)
1) Cellularity. Epithelia are composed almost entirely of cells. 2) Specialized contacts. Adjacent epithelial cells are directly joined at many points by special cell junctions. 3) Polarity. All epithelia have a free apical surface and an attached basal surface. The structure and function of the apical and basal surfaces differ, a characteristic called polarity. The apical surface abuts the open space of a cavity, tubule, gland, or hollow organ. The basal surface lies on a thin supporting sheet, the basal lamina, which is part of the basement membrane. 4) Support by connective tissue. All epithelial sheets in the body are supported by an underlying layer of connective tissue 5) Avascular but innervated. Whereas most tissues in the body are vascular (contain blood vessels), epithelium is avascular, meaning it lacks blood vessels. Epithelial cells receive their nutrients from capillaries in the underlying connective tissue. Although blood vessels do not penetrate epithelial sheets, nerve endings do; that is, epithelium is innervated. 6) Regeneration. Epithelial tissue has a high regenerative capacity. Some epithelia are exposed to friction, and their surface cells rub off. Others are destroyed by hostile substances in the external environment such as bacteria, acids, and smoke. As long as epithelial cells receive adequate nutrition, they can replace lost cells quickly by mitosis, cell division
5 Lateral surface features
1) cell junctions 2) tight junctions 3) adhesive belt junctions 4) desmosomes 5) gap junctions
4 special features on the epithelial cell surfaces
1) cilia 2) microvilli 3) cell junctions 4) basal lamina
epithelial tissue occurs in 2 forms
1) covering and lining epithelium 2) glandular epithelium
4 basic types of tissue
1) epithelial tissue 2) connective tissue 3) muscle tissue 4) nervous tissue
2 apical surface features
1) microvilli 2) cilia
epithelia classified based on 2 factors
1) number of cell layers 2) cell shape
6 functions of epithelia
1) protection of underlying tissue 2) secretion (release of molecules from cells) 3) absorption (bringing small molecules into cells) 4) diffusion (movement of molecules down their concentration gradient) 5) filtration (passage of small molecules through a sieve-like membrane) 6) sensory reception
2 types of epithelia
1) simple 2) stratified
4 types of simple epithelia
1) simple squamous 2) simple cuboidal 3) simple columnar 4) pseudostratified columnar
3 shapes of cells
1) squamous cells 2) cuboidal cells 3) columnar cells
3 types of stratified epithelia
1) stratified squamous 2) stratified cuboidal and columnar 3) transitional
an epithelial cell is joined to adjacent cells by 3 common types of cell junctions
1) tight 2) desmosomes 3) gap
transitional function in simple epithelial tissues
NONE
tissue =
a group of cells of similar structure that perform a common function
epithelium =
a sheet of cells that covers a body surface or lines a body cavity
simple columnar epithelium function
absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action; active movement of molecules; thin enough to allow large numbers of molecules to pass through quickly yet thick enough to house the cellular machinery needed to perform the complex processes of molecular transport
how are stratified epithelia named?
according to the shape of the cells in the apical layer
tight junctions
adjacent cells are so close that some proteins in their plasma membranes are fused; the fusion forms a seal that closes off the extracellular space; tight junctions prevent molecules from passing between the cells of epithelial tissue; don't need to be entirely impermeable, some more leaky than others and may let certain types of ions through
most organs contain what tissue
all 4 types
simple squamous epithelium function
allows passage of materials by diffusion and filtration in sites where protection is not important; produces lubricating fluid in serosae; thin and often permeable allowing small molecules to pass through membrane quickly
where is the basal lamina
at the border between the epithelium and the connective tissue
infections and toxins that destroy epithelial cells usually don't destroy the ___________
basal lamina
why are simple epithelia easy to classify by cell shape?
because all the cells in the layer usually have the same shape
stratified epithelia regenerate from...
below; the basal cells divide and push apically to replace the older surface cells
tissues are the ___________ of the body's organs
building blocks
what do tissues consist of
cells and extracellular matrix (nonliving material between the cells)
a sheet of closely joined epithelial cells rests on __________
connective tissue
simple epithelia =
contain a single layer of cells, with each cell attached to the basement membrane
stratified epithelia =
contain more than one layer of cells; the cells on the basal surface are attached to the basement membrane; those on the apical surface border an open space
broad functional term for nervous tissue
control
broad functional term for epithelial tissue
covering
covering and lining epithelium
covers the outer and inner surfaces of most body organs
cuboidal cells =
cube-shaped cells with spherical, centrally located nuclei
in stratified epithelia, the cell shapes usually differ among...
different cell layers
squamous function in simple epithelial tissues
diffusion and filtration
Squamous cells are found where _______ or ________ are important. Why?
diffusion, filtration; because these are distance-dependent processes so the thinner the layer the more quickly the process occurs
epithelia occur at the boundary between 2 different ________
environments
without the basal lamina, __________ is more difficult
epithelial regeneration
most substances that enter into the body or are released from the body must pass through an _________
epithelium
different tissues are woven together to form the "______" of the human body
fabric
squamous cells =
flat cells with flat, disc-shaped nuclei
glandular epithelium
forms most of the body glands
gap junctions
function in intercellular communication by allowing small molecules to move directly between neighboring cells
stratified cuboidal epithelium description
generally 2 layers of cubelike cells; rare tissue type
the epidermis of the skin lies between the _______ and _______
inside, outside of the body
all functions of epithelia reflect their roles as __________ tissues
interface
adhesive belt junctions
junction reinforces the tight junctions, particularly when the tissues are stretched
simple squamous epithelium location
kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae)
simple cuboidal epithelium location
kidney tubules; ducts and secretory portions of small glands; ovary surface
stratified cuboidal epithelium location
largest ducts of sweat glands, mammary glands, and salivary glands
transitional epithelium location
lines the ureters, bladder, and part of the urethra; lines inside of hollow urinary organs
desmosomes
main junctions for binding cells together
broad functional term for muscle tissue
movement
ciliated epithelia function to propel material, for example ______
mucus
microvilli are abundant on epithelia that secrete _______, where they help to...
mucus; anchor the mucous sheets to the epithelial surface
epithelia contain ________ but no _______
nerve endings, blood vessels
pseudostratified columnar epithelium location
nonciliated type in male's sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract
simple columnar epithelium location
nonciliated type lines most of the digestive tract (stomach to rectum), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus
stratified squamous epithelium location
nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane
where do microvilli occur
on almost every moist epithelium in the body
where are microvilli the longest and most abundant?
on epithelia that absorb nutrients (small intestine) or transport ions (in the kidney)
stratified epithelial tissues function to ________
protect
squamous function in stratified epithelial tissues
protection
stratified cuboidal epithelium function
protection
major role of stratified epithelia
protection (not only role)
stratified columnar epithelium function
protection; secretion
transitional function in stratified epithelial tissues
protection; stretching to accommodate distension of urinary structures
cuboidal/columnar function in stratified epithelial tissues
protection; these tissue types are rare in humans
stratified squamous epithelium function
protects underlying tissues in areas subjected to abrasion
cilia on an epithelium bend and move in coordinated waves which...
push mucus and other substances over the epithelial surface
stratified columnar epithelium location
rare in the body; small amounts in male urethra and in large ducts of some glands
transitional epithelium description
resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending on degree of organ stretch
directly deep to the basal lamina is a layer of _________ belonging to the underlying connective tissue
reticular fibers
basement membrane =
reticular fibers + basal lamina
cuboidal/columnar function in simple epithelial tissues
secretion and absorption; ciliated types propel mucus or reproductive cells
simple cuboidal epithelium function
secretion and absorption; same as simple columnar epithelium
Columnar and cuboidal cells are found in tissues involved in ________ and _______. Why?
secretion, absorption; larger cells are needed for additional cellular machinery needed to produce and package secretions and to produce the necessary energy for these processes
pseudostratified columnar epithelium function
secretion, particularly of mucus; propulsion of mucus by ciliary action; like simple columnar epithelium is functions in secretion or absorption
stratified columnar epithelium description
several cell layers; basal cells usually cuboidal; superficial cels elongated and columnar; rare tissue type
one layer of epithelia
simple epithelial tissues
pseudostratified columnar epithelium description
single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting goblet cells and bear cilia; all cells rest on basement membrane
simple cuboidal epithelium description
single layer of cubelike cells with large, spherical central nuclei
simple squamous epithelium description
single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia
simple columnar epithelium description
single layer of tall cells with round to oval nuclei; some cells bear silica; layer may contain mucus-secreting unicellular glands (goblet cells)
what 2 tissue types are rare
stratified cuboidal and stratified columnar epithelia
more than one layer of epithelia
stratified epithelial tissues
what type of epithelium is the thickest and best adapted for protection?
stratified squamous epithelium
_________ epithelia are more durable than _______ epithelia
stratified, simple
transitional epithelium function
stretches readily and permits distension of urinary organ by contained urine; urinary organs like the urinary bladder stretch as they fill with urine
broad functional term for connective tissue
support
microvilli maximize ________
surface area across which small molecules enter or leave cells
columnar cells =
taller than they are wide, like columns; the nuclei of columnar cells are located near the basal surface and are commonly oval in shape, elongated from top to bottom
what is the basal feature
the basal lamina
stratified squamous epithelium description
thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers
what is the basal lamina
thin noncellular sheet consists of proteins secreted by the epithelial cells
in simple epithelia, the shape of the cells indicates ________
tissue function
the word tissue derives from the the French word meaning "_________"
to weave
multiple layers of cells protect what?
underlying connective tissues in areas where abrasion is common
cilia =
whiplike, highly motile extensions of the apical surface membranes of certain epithelial cells