2.2 Epithelium and glands

cuboidal epithelial tissue

Embryonic origin of epithelium

all 3 germ layers

Epithelium originating from ectoderm

•Skin

•Oral and nasal mucosae

•Mammary glands

Epithelium originating from endoderm

•Lining of gut, respiratory tract

•Liver

•pancreas

Epithelium originating from mesoderm

•Lining of blood and lymph vessels, chambers of the heart (endothelium) and body cavities (mesothelium)

•Kidney tubules

2 types of epithelia

Surface
Glands

•Surface Epithelia

–Sheets of cells covering internal or external surfaces

Cancer of surface epithelia

carcinoma

Glands

–Structures that produce secretions

–Originate from invaginated epithelial cells

Cancer of glands

adenocarcinoma

Surface epithelium can invaginate to form

glands that secrete substances.

Exocrine glands

retain connection to surface epithelium and secrete products through ducts.

Endocrine glands

do not retain connection to surface epithelium and release their products directly into the bloodstream.

Basement membrane

Thin, non-cellular layer consisting of basal lamina and lamina reticularis of variable thickness

Function of basement membrane

lies at interface between epithelium and connective tissue functions in support

Components of basement membrane

Lamina basal and lamina reticularis.

Components of lamina lucida

integrins
Laminins
Collagens XVII, IV
Dystroglycans

Components of lamina dense

Collagen IV
Enactin/nidogen
Perlecan
Heparin surface proteoglycans

Components of lamina reticularis

Collagen I, III, V
Proteoglycans

Basal lamina includes which layers

lamina lucida
lamina densa

The basal lamina components are made by

epithelial cells

The lamina reticularis components are made by

connective tissue cells like fibroblasts

Vasculaity of surface epithelium

avascular, get nutrients from underlying CT capillary beds

Regeneration of skin epithelium

28 days

Regeneration of small intestine epithelium

approximately 2-3 days

Polarity of epithelium

Apical face
Basolateral space

Apical face

faces lumen

BAsolateral face

faces basement membrane

Sheet of epithelium are connected via

tight junctions

Closely packed, continuous sheets of epithelium

–Little intercellular material

–Little ECM

•Cover surfaces, line cavities and tubes epithelium

–Mesothelia – line body cavities

–Endothelia – line vessels

Surface epithelium is always adjacent to

open space

SImple

one layer

stratified

multiple layers

Pseudostratified

looks like more than 1 layer but all cells rest on BM and some cells don’t reach surface

Generally, thick layer of epi cells

protection

Generally, thin layer of epi cells

diffusion and filtration

Squamous

fried egg with bulging nuclei and scant cytoplasm

Cuboidal

as tall as wide

Columnar

taller than wide

In stratified layer, cell morphology is based on which layer

is at the apical surface.

Simple squamous function

PERMEABILITY
Fluid transport, gas exchange, lubrication

simple squamous epithelium

Simple squamous cytoplasm

highly attenuated and only approximated

Simple squamous nuclei

bulge into the lumen

Examples of simple squamous epithelium

Endothelium, lung air spaces, mesothelium

ENdothelium

Thin layer of cells lining blood vessels and lymphatic vessels

Mesothelium

Simple squamous epithelium lining body cavities

Simple Cuboidal function

•For Ion Pumping

Secretion, absorption

Simple cuboidal membranes

•Lateral cell membranes evident

Simple cuboidal nuclei

•Round centrally located nuclei

Where to find simple cuboidal

Ducts, covering of ovary, form kidney tubules

simple cuboidal epithelium

Simple Columnar function

•For High Volume Secretion

Transportation, absorption, secretion

Simple columnar nuclei

–Oval

–Uniform height

Where to find simple columnar

Digestive tract, gallbladder, large ducts, oviducts, uterus, small bronchi

simple columnar epithelium

Stratified Squamous keratinized function

•Protection, barrier

Top layer of stratified squamous keratinized

flat, fried egg appearance that contain nuclei

Stratified squamous keratinized basal layer

more cuboidal shaped with HIGH MITOTIC ACTIVITY

Where to find non keratinized stratified squamous

Mouth, epiglottis, esophagus, vocal folds, vagina

non-keratinized stratified squamous epi

Stratified squamous keratinized function

protection

Top layer of keratinized stratified squamous

top layer is flat with NO NUCLEI (filled with keratin instead)

Nonliving layer of keratinized stratified squamous epithekium

top part that is NONLIVING, no nucleus, filled with keratin

Where to find keratinized stratified squamous epithelium

Epidermis of Skin

keratinized stratified squamous epithelium

Stratified Cubodial function

•Absorption, secretion

Stratified cuboidal cell boundaries

•Cell boundaries not apparent

Stratified cuboidal nucelei

•Layering of round nuclei

Where to find stratified cuboidal

duct of sweat glands

stratified cuboidal epithelium

Stratified columnar function

secretion and absorption

Frequency of stratified columnar

very rare

Examples of stratified columnar

Large excretory ducts, conjunctiva of eye, portions of male urethra

stratified columnar

Pseudostratified function

•Secretion, absorption, lubrication, transportation

Pseudostratified nuclei

not uniformly arranged in different layers of cells

Dead giveaway of pseodostratified

presence of ciliacil

cilia are never found on

stratified epithelium

Pseudostratified columnar epithelium location

male urethra, epididymis, and larger excretory ducts of glands

Pseudostratified ciliated columnar epithelium

Pseudostratified ciliated columnar epithelium

lining most of the trachea and primary bronchi, the auditory tube, part of the tympanic cavity, the nasal cavity, and the lacrimal sac

Transitional epithelium function

•Distensible

Transitional epi morphology

•Dome-shaped surface cells (cobble stone like)

Transitional epi nuclei

can sometimes form double nucleated surface cells

Where to find transitional epi

urinary tract

transitional epithelium

Mucous membranes

line cavities that open to exterior

Serous membranes

line cavities that do NOT open to exterior

Examples of serous membranes

•Pericardium

•Pleura

•peritoneum

Examples od mucous membranes

•Oral cavity

•Nasal cavity

•Respiratory tract

•Gastrointestinal tract

•Urinary tract

Cutaneous membrane

skin surface

Modifications of apical surface epithelium

–Keratin

–Microvilli (striated or brush border)

–Cilia

–Flagella

–Stereocilia

Modifications of basolateral surface of epithelium

junctions

Examples of basolateral junctions

•Occluding, adhering, communicating

BAsal surface mods

–Adhering junction -- hemidesmosomes

Keratin

•Intermediate filament

Tonofilaments

•Type of keratin fibers found in epithelial cells

Bundles of tonofilaments form a

tonofibril