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