Epithelial tissues

Question 1

explain the classification of epithelia based on cell shape

Answer 1

Squamous - the cells are wider than they are tall, thin.

Simple squamous - one layer of cells - allows exchange, endothelium, alveolar, mesothelium

cuboidal - all cells a similar shape. kidney and other ducts

columnar - taller than they are wide, irregular from above enterocytes (intestinal absorbtive) and other absorbtive and secretory

Question 2

explain the classification of epithelia based on stratification

Answer 2

pseudostratified - all cells connected to basal lamina trachea and bronchi, urinary and reproductive tracts. often ciliated.
stratified - lots of layers of cells, squamous relates to top layer of cells
keratinised - skin (epidermis) , top layer no nucleus because cells are dead, makes more sturdy
non-keratinised - (mouth, oesophagus) can see nucleus in top layer because the cells are still alive.
Simple squamous - one layer of cells - allows exchange, endothelium, alveolar, mesothelium

Question 3

How is absorption determined by the epithelia

Answer 3

columnar shaped cells.
Intestine/kidney nephron
carriers are on microvillus brush-border

Question 4

how is secretion determined by the epithelia

Answer 4

vesicles at the top, near the lumen so that they can transport substances out of the cell exocrine
vesicles at basal lamina, nucleus at top - substances travel into cell via blood. endocrine
tubules and glands of varying complexity
stimulated [pancreas/adrenal gland] or constitutive [plasma proteins by hepatocytes]
polarity - plasma membrane has a different composition of lipids and proteins on the apical and basal side meaning that absorption and secretion can only occur in one direction.
these are separated by tight junctions [apical junctions] between epithelial cells.
has to be done through cells rather than paracellularly - allows some control

Question 5

how is fluid transport determined by the epithelia

Answer 5

mitochondria arranged vertically, in line with foldings to allow active transport - site of ATP synthesis
infoldings increase surface area
tubular increase SA by being longer and with infoldings, eg microvilli

Question 6

how is protection determined by the epithelia

Answer 6

keratinised squamous cells - top layer is dead stratified, hard and provides protection in epidermis.
if desmosomes and cytoskeleton are ineffective - lead to blistering and so fragile skin.
epidermis, dermis, hypodermis

Question 7

describe epithelial cell turnover

Answer 7

balance between proliferation and cell death

over proliferation can cause adenomas (polyp) and then more likely malignant tumours

Question 8

describe turnover over villi

Answer 8

glands, crypts - stem cells produce new cells to replace those at the top that have died.

Question 9

describe turnover of epidermis

Answer 9

surface cells lost, replace by those at the bottom that undergo a series of differentiation