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LABORATORY 4 - EPITHELIUM - (first of two laboratory sessions)
This lab has an associated homework assignment that is posted on
Blackboard. If you have not done this assignment already, it would
make this lab more efficient if you did so.
OBJECTIVES: LIGHT MICROSCOPY - Recognize: Simple epithelia including: simple squamous, cuboidal, columnar and pseudostratified columnar epithelium Stratified epithelia including: stratified squamous (keratinized and non-keratinized), stratified cuboidal, stratified columnar and transitional epithelium Surface modifications including: apical surface, striated border, cilia, stereocilia, "intercellular" bridges, basal surface, basement membrane Glandular epithelium: serous, mucous and serous demilune glandular secretory units
ELECTRON MICROSCOPY: Recognize types of epithelia (as above) and characteristic features of surface specializations that occur on apical, basal and lateral surfaces including the following: Apical surface: Microvilli, cilia, stereocilia, striated border, glycocalyx Basal surface: Hemidesmosomes and basal lamina Lateral surface: Cell junctions, zonula occludens, zonula adherens, macula adherens (desmosome), gap junction, glycocalyx
ASSIGNMENT FOR TODAY’S LABORATORY
GLASS SLIDES SL 63 (Heart with atrioventricular valve) simple squamous epithelium (lines heart) SL 137 (Ovary) Simple cuboidal epithelium (covers ovary) - varies in height SL 14 (Small intestine) Simple columnar epithelium SL 15B (Trachea) Pseudostratified columnar epithelium with goblet cells SL 156 (Epididymis) Pseudostratified columnar epithelium with stereocilia SL 16 (Esophagus) Stratified squamous epithelium, non-keratinized SL 9 (Auricle of ear) Stratified squamous epithelium, keratinized SL 25 (Sole of the foot) Stratified squamous epithelium, keratinized SL 92 / 93 (Salivary glands) Stratified cuboidal and stratified columnar epithelium (large ducts) SL 18 (Ureter) and SL 57 (Bladder) Transitional epithelium lines these organs
ELECTRON MICROGRAPH EM 9 (small intestine) simple columnar epithelium
POSTED ELECTRON MICROGRAPHS
5 Organelles
9 Epithelial cell apical surface modifications
10 Lateral surface modifications
30, # 30a Autoradiography
Lab 4 Posted EMs
HISTOLOGY IMAGE REVIEW - available on computers in HSL Chapter 4, Epithelial Tissue Frames: 156-
EPITHELIUM
Epithelia line tubes or cover surfaces. They are composed of closely apposed cells, held together by one or several types of junctions, interdigitation of the lateral membranes, and a small amount of self-secreted glycocalyx (cell coat) that may aid in cell adherence. The "free surface" (top or apical surface) of an epithelium is exposed to the external environment (as in skin) or to fluid (internal cavities, ducts, tubes). The basal surface of epithelia rests on a basement membrane. The basement membrane (J. Figs. 4-1, 4-2, 4-3; R. Figs. 5.1, 5.28, 5.29) serves as a means of anchoring the epithelium to underlying tissue.
Epithelia are classified according to the number of cell layers:
- SIMPLE = 1 layer
- STRATIFIED = 2 to many layers
The shape of the cells also determines the name of the epithelium - in stratified epithelia only the top layer of cells is considered:
- SQUAMOUS = flattened, scale-like cells with a flattened or absent nucleus
- CUBOIDAL = cells about as tall as their width with a round nucleus
- COLUMNAR = cells taller than their width, usually with an oval nucleus
I. SIMPLE EPITHELIA: a single layer of cells. Each cell has three different surfaces: 1) an apical (upper) surface ("free surface") that faces a lumen, 2) lateral surface that contacts neighboring cells and 3) a basal surface that lies against the basement membrane. Each of these surfaces may have specialized characteristics that enable it to perform the specific functions required for its location.
A. SIMPLE SQUAMOUS EPITHELIUM (J. Fig. 4-11; R. Plate 1). SL 63 : (Heart with atrioventricular (AV) valve). Locate the projecting green-stained valve (arrow in diagram, red arrow) and note the thin, pink-staining simple squamous epithelium covering the surface. The nuclei (basophilic) stain deep blue or purple. This layer of simple squamous epithelium is the endothelium that lines the chambers of the heart and continues as the lining of all blood vessels (scan, med, red arrows, high, red arrows).
B. SIMPLE CUBOIDAL EPITHELIUM (J. Fig. 4-12; R. Fig. Plates 1, 2) SL 137: (Ovary) Simple cuboidal epithelium covers much of the ovary; observe how this epithelium (mesothelium) varies in different regions from simple squamous to cuboidal to columnar. (scan, med, high, red arrow)
III. STRATIFIED EPITHELIA: two or many layers of cells. Only the surface layer of cells is exposed to the air or lumen; the basal layer of cells rests on the basement membrane. The shape of the cells on the surface layer determines the name of the epithelium; cells beneath this layer may be quite different in shape.
A. STRATIFIED SQUAMOUS EPITHELIUM (J. Fig. 4-14; R. Fig. Plates 2, 3)
- SL 16: (Esophagus). One surface of this section is covered by an epithelium that is composed of many layers of cells (red arrow). It is important to observe that the cells in the surface layer have nuclei. The presence of the nuclei in these surface cells indicates that this tissue is non-keratinized stratified squamous epithelium and indicates that the epithelium is derived from a region of the body that has a wet or moist surface (scan, high).
- SL 9: (Auricle of ear). The surface cells of this epithelium (on the auricle of the ear) lose their nuclei and become scale-like. This type of epithelium is called keratinized stratified squamous epithelium. Note that cells in the lowest levels of this epithelium are cuboidal-columnar, thus it is essential to know the shape of surface cells when categorizing stratified epithelia (scan, high, epithelium in red rectangle).
- SL 25: (Skin of the sole of the foot). In this slide, the keratinized layer is much thicker (entire epithelium indicated by the red brackets, keratinized portion indicated by the blue brackets), providing extra protection for this region.
B. STRATIFIED CUBOIDAL EPITHELIUM (J. Fig. 4-14d; R. Plate 3) and STRATIFIED COLUMNAR EPITHELIUM. These epithelia are relatively limited, occurring mostly as large ducts in glands.
- SL 92: (Submandibular Gland). This salivary gland has ducts of various sizes. The largest ducts are stratified cuboidal or columnar, and are found in the connective tissue outside the lobes of gland (scan, low, high).
- SL 93: (Sublingual Gland). Look for gradations in duct size and epithelial cell variations from simple cuboidal to stratified columnar (scan, high 1, red arrow, high 2, red arrow).
C. TRANSITIONAL EPITHELIUM (J. Fig. 4-15; R. Plate 3) Limited to excretory passages. Transitional epithelium is generally considered to be stratified. When transitional epithelium is greatly distended it may appear to be only 2 to 3 cell layers thick.
- SL 18: (Ureter). The star-shaped lumen of this contracted ureter appears to be lined by many layers of cells. The cells adjacent to the lumen appear rounded, cuboidal-columnar, and many cells appear to bulge out into the lumen (med, red arrow high, blue arrow). Binucleate surface cells are characteristic for this epithelium. Compare with true stratified squamous epithelium in esophagus (SL 16) (scan, high).
- SL 57: (Bladder) (scan). The bladder is lined with transitional epithelium, also. Observe the same characteristics that are indicated for the ureter.
OBJECTIVES FOR LABORATORY 4: EPITHELIUM I
- Using the light microscope or digital slides, identify:
Epithelial types Simple epithelia Simple squamous Simple cuboidal Simple columnar Pseudostratified columnar Pseudostratified ciliated columnar with goblet cells Pseudostratified with stereocilia Stratified epithelia Stratified squamous Non-keratinized Keratinized Stratified cuboidal / stratified columnar Transitional For all types, recognize apical, lateral, and basal surfaces
- On electron micrographs, identify:
Cilia Microtubule core Basal body Microvilli Microfilament core Junctional complex Zonula occludens (tight junction) Zonula adherens (belt desmosome) Macula adherens (spot desmosome, or just desmosome) Autoradiography (understand the procedure and be able to interpret)
