Epithelium

Question 1

A simple explanation of epithelial tissue structure

Answer 1

Contiguous cells - cell junctions mediate strength & communication - little extracellular matrix - supported by connective tissue (separated by basement membrane) - avascular, innervated. Apical surface may contain microvilli, cilia, basal surface connected to basal lamina

Question 2

Functions of epithelia?

Answer 2

Protection, transcellular transport, secretion, absorption, immune defence

Question 3

Where is epithelial tissue found?

Answer 3

Covers body surfaces & cavities - invaginated epithelia = glands

Question 4

What causes a brush-border effect?

Answer 4

Microvilli on the apical surface of cells

Question 5

What is the apical surface?

Answer 5

The outer surface of the epithelium - faces the lumen or externally

Question 6

What is the basal/basolaterlal surface of the epithelium?

Answer 6

Surface in contact with the basement membrane

Question 7

Do epithelial cells reproduce rapidly or slowly?

Answer 7

Rapidly

Question 8

What are the two segments of the basement membrane?

Answer 8

Basal lamina & lamina reticularis

Question 9

Explain the breakdown of the basal lamina?

Answer 9

Lamina lucina (50nm) - just below epithelium - extracellular glycoproteins e.g. laminin & entactin
Lamina densa (50nm) - Type 4 collagen

Question 10

What is the function of the lamina reticularis?

Answer 10

Fixes lamina densa to connective tissue - thickness varies e.g. thick in skin

Question 11

How are epithelia classified by layers?

Answer 11

Simple - 1 cell - transport of substance between tissues - absorption & secretion

Stratified - >1 cell - protection - layer of high abrasion

Question 12

What are the different morphologies of epithelial cells?

Answer 12

Squamous, cuboidal, columnar, transitional

Question 13

Are functions the same in all areas of epithelial tissue?

Answer 13

Apical domain & basolaterlal domain - modifications to carry out specific functions

Question 14

Explain simple squamous epithelium?

Answer 14

1 layer thin flat cells with bulging nuclei - fluid transport, gaseous exchange, ion exchange(rapid diffusion), lubrication, & lining membranes

Question 15

Where is simple squamous epithelium found?

Answer 15

Loop of Henley, alveoli, parietal layer of Bowman’s capsule, endothelium of blood vessels, mesothelium of pleural, pericardial, & peritoneal cavities

Question 16

Explain simple cuboidal epithelium?

Answer 16

Cube shapes centrally places nucleus - 1 layer - rapid diffusion - secretion, absorption, protection

Question 17

Where is simple cuboidal epithelium found?

Answer 17

Ducts of glands, thyroid, covers of ovaries, kidney tubules

Question 18

Explain simple columnar epithelium?

Answer 18

1 layer - hexagonal solids - nuclei usually in the basolateral domain - may contain microvilli on apical plasma membrane (increase surface area for absorption) & cilia (propel liquid) - transportation, absorption, secretion, protection

Question 19

Where is the simple columnar epithelium found?

Answer 19

Microvilli - small intestine
Cilia - uterine tubes (move ova) - respiratory tract (move mucous)
GI tract gall bladder, large ducts of glands

Question 20

Explain stratified squamous epithelium?

Answer 20

Protective barriers - areas of mechanical stresses - basal cells are cuboidal, apical cells are squamous - keratinised, para-keratinised, non-keratinised

Question 21

Explain keratinised stratified squamous epithelium?

Answer 21

Apical cells are dead, lack nuclei, filled with keratin (keratinocytes) - tough & water resistant - epidermis of skin

Question 22

Explain stratified squamous para keratinised epithelium?

Answer 22

Apical cells contain nuclei - pyknotic

Question 23

Explain non-keratinised stratified epithelium?

Answer 23

Apical cells alive with nuclei - basal cells cuboidal & touch basal lamina - areas of stress kept moist - mouth, throat, oesophagus, vagina, & anus

Question 24

Explain stratified cuboidal epithelium?

Answer 24

2 layers - sweat glands

Question 25

Explain stratified columnar epithelium?

Answer 25

2 layers - apical cells are columnar, basal cells are cuboidal - conjunctiva, cornea, salivary glands, male urethra

Question 26

Explain transitional epithelium?

Answer 26

Many layers - apical layer = domed and flattened when bladder is distended in urine - basal cells = cuboidal - binucleated

Question 27

Explain pseudostratified columnar epithelium?

Answer 27

Nuclei appear at various heights - all cells in contact with basal lamina - not all have an apical surface - cilia located on apical membrane - respiratory, nasal tract & epididymis

Question 28

Explain Tight Junctions/Occluding Junctions/ Zonula Occludens

Answer 28

Integral proteins (claudins, Occluding necktons, junctional adhesive molecules) of 2 cells - lock together - seal around apical perimeter of cells - impermeable - cells tightly packed - prevent macromolecules passing intercellularly - proteins can't move between apical & basal domains - tight & leaky

Question 29

What Junctions are found in cardiac muscle cells?

Answer 29

Fascia adherents - similar to Zonula adherents - not around circumference - connected at longitudinal terminals

Question 30

Explain Zonula Adherens/ Adherence

Answer 30

Located basal of Zonula Occludens - encircle cell circumference - space between outer membranes occupied by E-cadherins - intracellular aspects bind to bundle of actin filament in cell running parallel to membrane - connects cytoskeleton of adjacent cells

Question 31

Explain Desmosomes/ Macula Adherens ?

Answer 31

Randomly distributed on lateral cell membranes - 2 disc shaped plaques on cytoplasmic side - extracellular space in 30nm occupied by transmembrane proteins - in the presence of Ca2+ ions form bonds with proteins of adjacent cells = extracellular core - appears as electron dense area using EM - allow materials in EC fluid to pass through - attached to the intermediate filaments of the cytoskeleton

Question 32

What ion is required to form desmosomes & hemidesmosomes?

Answer 32

Ca 2+

Question 33

Explain Gap Junctions/Nexus Communicating Junctions?

Answer 33

Pores/protein channel between cells for ions & small substance s- intercellular communication for cardiac cells to contract together - 6 closely packed channel forming proteins = connexion (hemi-channel) - 2 connexions fuse to form gap junction

Question 34

Explain hemidesmosomes?

Answer 34

Attach basal membrane to basal lamina - 1/2 desmosome - presence of Ca2+ ions - Type 1 & 2