Introduction to Epithelial and Glands


Epithelium

The approach is to begin with simple epithelia, then to look at more complex examples. After, we'll add glands to the mix. Make frequent use of the web site, your text and the atlas to aid in identification of the epithelia and glands described below.

Important Reminder: Concentrate on the epithelia - not the organs they reside in. We'll cover the organs later.

Slide 166 - Three selected samples.

This slide has three portions cut from various organs (which we are not interested in). From left to right with the bare slide, there are examples of epithelia which are -


In the stratified squamous epithelium, the cells progress from cuboidal or columnar at the base to flat (squamous) at the surface. Epithelia are labelled by the upper-most layer of cells, so this is a squamous epithelium. Note the increased basophilia (blue-purplish color) to the basal layer, reflecting active production of proteins and active nuclei. As the cells flatten out, in the successive layers, they keratinize and die, forming a hard, multicellular layer to protect the tissues below.


The simple columnar epithelium is highly folded, and sometimes appears to have multiple cell layers. This is an artifact of tissue orientation. Find the simplest presentation of a tissue, and you'll probably have the correct presentation.

The larger chunk of tissue is a series of ducts. Some of them have cuboidal lining cells, and the rest have squamous epithelia. These should be easily distinguished.


Slide 6 - Neonatal Rat Head

In this slide, we shall examine three different epithelia. Look at the top of the head, inside the oral cavity, and inside the nasal cavity - specifically at the ventral aspect of the nasal cavity.

The top of the head has stratified squamous epithelium (epidermis) with hairs and glands (which we'll look at later). The oral cavity has stratified squamous without hairs or glands (a mucous membrane). The ventral portion of the nasal cavity has pseudostratified, columnar epithelium, with kinociliated cells and goblet cells. This is an example of respiratory epithelium.



Slide 131 - Canine Ureter

The urinary system has an epithelium of its own, transitional or urinary epithelium. Compare the epithelium in this example of canine ureter with the diagrams in your notes. The epithelium has an appearance of being stratified, but in fact is a highly folded single layer of cells. The outermost layer never quite becomes squamous, having oval-to-pear shapes instead.


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