Chapter 3

Question 1

What are epithelial cells specialised for?

Answer 1

Epithelial cells are specialized for absorption, secretion or to act as a barrier. Epithelial cells form very cohesive sheets of cells, called ‘epithelia’, which function mainly as:
* A covering or lining for body surfaces, e.g. skin, gut and ducts
* The functional units of secretory glands, such as salivary tissue and liver.
Epithelial cells are firmly joined together by adhesion specializations. These special structures serve to anchor the cytoskeleton of each epithelial cell to its neighbours and to anchor the epithelium to underlying or surround- ing extracellular matrix materials.
Epithelial cells are further specialized by modifica- tions of their surfaces to fulfil their specific role, which may be absorption or secretion or to act as a barrier

Question 2

Epithelial cell shape

Answer 2

These groups are: squa- mous (flat plate-like, Fig. 3.1); cuboidal (height and width similar, Fig. 3.2); and columnar (height 2–5 times greater than width, Fig. 3.3).

Question 3

Simple and stratified epithelium

Answer 3

Epithelial cells form either a single layer in which all of the cells contact underlying extracellular matrix (simple epithelium), or several layers, where only the bottom layer of cells is in contact with the extracellular matrix (stratified epithelium,

Question 4

Pseudostratified and transitional epithelium

Answer 4

Pseudostratified epithelium (Fig. 3.5) contains epithe- lial cells that appear to be arranged in layers but which are all in contact with the extracellular matrix. A transi- tional epithelium is a further special type of stratified epithelium, which is mainly restricted to the lining of the urinary tract (see Ch. 15), and varies between cuboi- dal and squamous depending on the degree of stretching.