LAB ONE: CELL ORAGANELLES AND EPITHELIUM

A. Nuclei (liver, slide 50)

The nuclei (N) of the liver cells depicted below appear as small, purple staining dots. In many of the nuclei, nucleoli (NU) are visible. Note that the cytoplasm (pink) appears to be granular or non-uniform, indicating the presence of cytoplasmic organelles that cannot be resolved at this magnification.

 

B. Microvilli, or striated-brush border (jejunum, slide 4)

Below is a small section of an intestinal villi. Intestinal villi are fingerlike outgrowths of the mucosa projecting into the lumen of the small intestine. Microvilli, or brush border (arrows), are extensions of absorptive cells (simple columnar cells) that are often seen in the small intestine. Microvilli greatly increase the surface area of cells, thereby increasing the tissues absorptive efficiency.

 

C. Cilia (trachea, slide 8)

Cilia (arrow) are elongated, motile structures found on the surface of certain epithelial cells, specifically "respiratory epithelium." They are much longer than microvilli and different in structure. Cilia have a rapid back-and-forth movement that helps propel fluid or particles over the epithelium.

 
D. Simple Squamous Epithelium (kidney, slide 52)

A single layered, termed "simple", epithelium is shown below surrounding a renal corpuscle in the kidney. Simple squamous epithelial cells (arrow) are thin and flat, allowing for increased diffusion and absorption. This type of epithelium is also found in serous membranes, in the lining of blood vessels, and in the alveoli of the lungs. In the lymphatic and cardiovascular system simple squamous epithelium is referred to as endothelium. In the lining of the peritoneal, pleural, and pericardial cavities, simple squamous epithelium is called mesothelium.

 

E. Simple Cuboidal Epithelium (kidney, slide 52)

The kidney is a maze of tubules, all of which are lined with "simple" epithelium. Depicted below are collecting tubules lined with simple cuboidal epithelium, as found in the kidney medulla. These types of epithelial cells (arrow) are cuboid in shape and have large, centrally placed nuclei (purple). Simple cuboidal epithelium functions in secretion and absorption, and may also be seen lining secretory ducts, or in the thyroid gland.

 
F. Simple Columnar Epithelium (jejunum, slide 4)

The simple columnar epithelial cells (arrow) seen below in this small intestine specimen, are taller than they are wide. Simple columnar epithelium lines most of the digestive tract and the gallbladder. Notice that the nuclei are uniformly located at the base of the cells. Often seen projecting from the cells surface are microvilli, or brush border. These cellular modifications help to further increase the absorptive surface area of the cell.

 
G. Stratified Squamous Nonkeratinized Epithelium (esophagus, slide 1 and vagina, slide 60)

Stratified squamous nonkeratinized epithelium (brackets) lines wet, exposed cavities such as the mouth, anal canal, esophagus, and the vagina. This type of epithelium provides protection against abrasion by building up multiple cell layers. Compare and contrast esophagus and vagina (they are often confused). The esophagus slide, on the left, is characterized by mucus-secreting glands that are absent in the vagina specimen on the right.

 
H. Stratified Squamous Keratinized Epithelium (skin, slide 2)

Stratified squamous keratinized epithelium (brackets) is found mainly in the skin. Its cells form many layers, and the cells closer to the underlying connective tissue are usually cuboidal or columnar. Cells become irregular in shape and flatten as they get closer to the surface, where they are thin and squamous. The keratinized layer (arrow) appears detached from the epithelium and often lacks nuclei and organelles.

 

I. Pseudostratified Ciliated Columnar, or Respiratory Epithelium (trachea, slide 8)

Pseudostratified ciliated columnar epithelium lines the trachea and bronchi of the respiratory tract. The cilia help to move materials such as mucous and dust across the tissue surface. All cells in the epithelium reach the bottom (sit on the basement membrane), but not all cells reach the surface. The staggered height of cells within the tissue can make it appear stratified, when in reality it is "simple" in organization. In contrast to the evenly distributed nuclei found in simple columnar epithelium, the nuclei of respiratory epithelium cells are unevenly distributed.

J. Transitional Epithelium (urinary bladder, slide 11)

Transitional epithelium (brackets) lines organs, such as the urinary bladder, which must expand and shrink repeatedly. The cells have a variety of shapes and sizes, with the surface cells having a cuboid appearance. Unlike respiratory epithelium, not all transitional epithelial cells contact the basement membrane. Transitional epithelial surface cells take on a dome-shaped appearance when relaxed and a squamous shape when stretched.