Epithelia

Question 1

4 basic types of tissue

Answer 1

muscular
nervous
connective
epithelia

Question 2

where is epithelia found?

Answer 2

at boundaries of body - cover surfaces, line cavities, form glands
separate controlled internal environment from uncontrolled external

Question 3

how does epithelia develop?

Answer 3

from all germ layers:
endoderm = GI lining
mesoderm = lining of CV system
ectoderm = epidermis

Question 4

epithelia functions

Answer 4

protection - skin
diffusion - lungs
absorption - small intestine
secretion - glands

Question 5

common properties (4)

Answer 5

1 - polarity
2 - basement membrane
3 - cell adhesion and communication
4 - cell replacement

Question 6

polarity in epithelium

Answer 6

entirely cellular, avascular, without extracellular fibres

apical surface to external environment, specialisation on basolateral or apical related to function

Question 7

epithelia basement membrane

Answer 7

vital component, separates from underlying connective tissues (collagen IV)
consists of:
basal lamina - secreted from epithelial cells
reticular lamina - secreted by fibroblasts - reticular fibres anchoring basal lmaina to underlying connective tissue

Question 8

cell adhesion and communication in epithelia

Answer 8

lateral communication throu gap junctiond of water, ions and small molecules
cell matric attacements bond epith tissue ti connective tissue
strong adhesion between cells
stress bearing cytoskeletons linked from cell to cell by adhesive junctions
adhering junctions form belt around cell linked to bundles of actin filaments
myosin filaments can pull on actin to contract cell

Question 9

tight junctions

Answer 9

seals gap between epithelial cells
forms network of sealing strands, more than 50 types if proteins, myosin can loosen junction
transmembrane Claudius in stomach link to small intestine, claudins change, each part of GI tract has diff function so diff tightness of junctions needed

Question 10

cell replacement in epithelia

Answer 10

more hostile external env = greater cell death
tissue homeostasis through continual cell replacement from stem cellssubstantial variation among diff epithelia:
epithlia of intestine completely self renews in 5 days
inter follicular epidermis takes 4 weeks
lung wpithelia takes up to 6 months

Question 11

regulation of epithelial cell fate

Answer 11

epithelial - meschymal interactions
2 way process
assembly of ep cells is reversible,
epithelium = surface tissue
mesenchymal = underlying tissue
transition allows polarised epith cells that interact with basememnt membrane to undergo multiple changes and assume mesenchymal cell phenotype
after degredation of basement membrane, cells have:
- enhanced migratory potential
- invasiveness
- increased resistance to apoptosis and inc production of ECM components
naturally happens in embryogenesis and tissue repair
most cancers originate in epithelia and only become malignant when it escapes epithelia and infects other cells

Question 12

classification of epithelia

2 types

Answer 12

1 - simple = single layer of cells e.g. lung
2 - stratified = many layers e.g. skin
(some dont easily fit into either, pseudostartified = upper respiratory tract, transitional = urothelium)

Question 13

types of epithelial cells (7)

Answer 13

simple squamous 
simple cuboidal
simple columnar
pseudostratified columnar
stratified squamous
stratified cuboidal
stratified columnar

Question 14

simple squamous

Answer 14

thin scales
facilitates rapid passage of molecules
lining of capillaries, lung air sacs etc
nuclei as flat as cell 
e.g. alveoli and serosa

Question 15

simple cuboidal

Answer 15

secretion and absorption of molecules requiring active transport
nucleus in centre of cell
e.g. lining of kidney tubules and ducts of glands

Question 16

simple columar

Answer 16

forms most of digestive tract
with and without cilia/microvilli
absorption and secretion of molecules requiring active transport
nucleus at bottom, basal end
e.g. most of GI tract, Fallopian tubes

Question 17

pseudostratified columnar

Answer 17

irregular nature of nuclei - stratified but all cells in touch with basal membrane, only some reach apical.
cilia/no cilia, ciliated cells can be interspersed with goblet cells
e.g. respiratory tract, male reprodcutive tract

Question 18

stratified sqaumous

Answer 18

most common in body
thin and flattened apical cells with cuboidal cells on basal membrane
top layer often dead, with keratin
in high ares of abrasion
e.g. upper skin layers - keratinised, oesophagus - not keratinised

Question 19

stratified cuboidal

Answer 19

rare
found in glands
e.g. ducts, tubes of glands

Question 20

stratified columnar

Answer 20

rare
allows tissues to stretch and contract
e.g. conjunctiva, pharynx, anus, male urethra and embryos

Question 21

transitional epithelia

Answer 21

round when relaxed e.g. when bladder is empty

allows change in distention

Question 22

glandular epithelia

• glands definition
• secretion pathways for exo and endocrine

Answer 22

gland = structure made up of one or more type of cells that have been modified to secrete chemicals
secretion - ducts - exocrine - tissues that secrete through ducts
secretion - ductless - endocrine - hormones in interstitial fluid into blood stream, straight into tissues

Question 23

goblet cells

Answer 23

embedded in other tissues

individual cells that may be surrounded by ciliated columnar etc

Question 24

glands that secrete mucus

Answer 24

mucus glands

Question 25

glands that secrete proteins

Answer 25

serous glands

Question 26

types of goblet cells

Answer 26

unicellular - seen around edge as bulbous

multicellular = acinar/acinus