Epithelium Flashcards
Epithelial tissue
Covers the body surface/ lines body cavities
Avascular
Derive nutrients via diffusion from blood vessels in the underlying CT
What is the function of epithelial tissue cells in the intestine?
Absorption
What is the function of epithelial tissue cells in glands?
Secretion
What is the function of epithelial tissue cells in the skin?
Protection
What is the function of epithelial tissue cells in the neuroepithelium?
Sensory
What is the function of epithelial tissue cells in the myoepithelial?
Contractility
Basement Membrane
Separates the epithelial tissue from CT
Basal lamina, collagen, glycoproteins and heparin sulphate form the BM
PAS-positive and seen with LM
How can you classify epithelium?
Simple, stratified, and pseudostratified
Simple Epithelium
All cells life on the basal lamina
3 types: squamous, cuboidal and columnar
Stratified Epithelium
Has more than one layer and cell on the bottom layer lie on the basal lamina
4 types of stratified: squamous cuboidal, columnar and transitional
Pseudostratified
All cells lie on the basal lamina but appear stratified because their nuclei are in different locations
What can change the epithelium from one type to another?
A continuous abrasion or irritation.
Ex: stratified squamous non-keratinized to keratinized in the esophagus when milk diet is replaced by roughage in young animals
Or
Pathological change
Ex: pseudo-stratified columnar to stratified squamous in respiratory tract because of continuous smoke inhalation (metaplasia)
What is the most prevalent epithelium?
stratified squamous (keratinized or nonkeratinized)
How often is epithelia replaced?
Continuously replaced but the rate of replacement is variable
Microvilli
1 micrometer high and 80 nm wide
Function: increase the surface area of absorptive cells (intestine and kidney) by 15-40 times
ABSORPTION
Brush border
Microvilli grouped together, individual microvilli cannot be seen under the LM
AKA striated border
Stereocilia
10- 20 um
Long immotile microvilli
Present in the epididymus
Function: absorb testicular fluid
Cilia
Hair like processes 7-10um high, 0.2 um diameter
Consists of 2 central microtubules and 9 peripheral microtubule pairs
Function: moving cells and fluid past the cells
What does each peripheral microtubule pair have?
2 little dynein arms and a motor protein that used energy from ATP to hook up the next pair of microtubules
Kartagener Syndrome (Immotile Cilia Syndrome)
When a patient genetically lacks dynein arms
They’re infertile
More prone to respiratory syndrome
Flagellum
Lagrer than cilium
Present in the sperm tail
Intercellular Junctions
Provide adhesions between cells and restrict movement of materials in and out of the lamina
Junctional Complex (terminal bar)
Membrane-associated structures that function in cell-to cell attachment of simple epithelia
3 components: Zonula occludens, Zonula adherens, and macula adherens
Zoluna Occudens (ZO)
Surrounds the entire apical circumference of adjacent cells
Function: prevents substances from moving into the intercellular space from the lumen
Zonula adherens (ZA)
Intermediate Junctions
Surrounds the entire circumference of adjacent cells
Variation: fascia adherens
Function: binding of adjacent cells, linking cells to form a network
Macula adherens (MA)
Desmosome
Function: Provides firm binding between cells
Well developed in the stratifed epithelia (skin)
Hemidesmosome
Variation of a desmosome
Binds the epithelium with the underlying CT
Gap Junction
Couple adjacent cells metabolically and electrically
Made of 6 connexins
Communication between cells of signaling molecules (ions, hormones, AMP and GMP)- coordination
Exocrine Glands
Secrete via a duct on the epithelium of its origin
EX: salivary glands
Modes of secretion: Holocrine, merocrine and aponcrine
Endocrine glands
Not connected to epithilial surface, no duct and secrete into the bloodstream
EX: paracrine and autocrine glands
Location: thyroid glands
where do paracrine and autocrine glands secrete?
Into the local extracellular space
P: acts on nearby cells (not the ones that produce them)
A: acts on the same cell that secretes it
Mucus secretion
Viscous material that protects/ lubricates cell surfaces
Serous Secretion
Watery secretion that is often rich in enzymes
Mixed Secretion
Contains both mucus and serous
Merocrine cells
Release only secretory granules by exocytosis with no loss of cytoplasm
99% of secretion
Apocrine cells
Release secretory product with some apical cytoplasm
Sweat glands in domestic animals
Holocrine Cells
Release secretory product with all cytoplasmic contents (these cells die)
What is the difference between Basil Lamina and the Basement Membrane?
BL is made of type 4 collagen and glycoproteins and is seen on the EM level
BM is made of basal lamina and type 1 collagen fibers and can be seen on the LM level
Simple gland
Duct does not brach
Compound gland
Duct branches
What controls the secretion of hormones by the endocrine glands?
Metabolic factors, secretion of other hormones and the nervous system
Ciliogenesis
Centrioles duplicate, each centriole moves near the apical cell membrane (now called basal body) and gives rise one cilium.
Simple Squamous
C: one layer, flat, spaced out
L: blood vessels (endothelium), body cavities (mesothelium)
F: Diffusion
Simple Cuboidal
C: one layer, tightly connected, cubed/ rounded
L: kidney, salivary glands, pancreas
F: Absorption
SC: microvilli
Simple Columnar
L: small intestine, stomach, respiratory tract
F: secretion and absorption
C: Tall, central nuclei
Simple Columnar Ciliated
L: uterus
F: ovum transport, propels particles over epithelium surface
C: Columnar, tall
SC: cilia
Pseudostratified Columnar (ciliated)
C: looks like more than one layer, nuclei at different places
L: bronchus, epididymus
F: cilia propels mucus and particles to the pharynx
SC: cilia, goblet cells
Stratified Squamous
C: multilayer, cuboidal based, polygonal middle, flat squamous superficial
L: oral cavity, skin, pharynx, vagina
F: Withstand abrasion and water proof
SC: keratinized or non keratinized
What has keratinized stratified epithelium?
skin
Stratified Cuboidal
C: multilayer, cuboidal/rounded,
L: exocrine gland ducts
F:Provides robust lining
Stratified Transitional
C: 4-5 layers thick
L: bladder
F: stretch and withstand urine toxicity
Dynein Arms
Motor proteins that uses energy from ATP to hook up to the next pair of micro tubules
