In observing epithelial cells under a microscope, the cells are arranged in a single layer and look tall and narrow, and the nucleus is located close to the basal side of the cell. The specimen is what type of epithelial tissue?

A. Columnar

B. Startified

C. Squamous

D. Transitional

Tall, narrow cells arranged in a single layer correspond to a simple columnar epithelial tissue.

Explanation:

According to the arrangement of cells, epithelial tissues can be classified as:

- Simple epithelium, formed by a single cellular layer which is in contact with the basement membrane

- Stratified epithelium, formed by two or more cellular layers. The cellular shape and high vary from one layer to the other. In classification, only the superficial layer is considered.

- Transitional epithelium. In this case, the epithelial cells vary in shape and size allowing the tissue to stretch.

Classification of epithelial tissues according to the cell shape:

- Squamous epithelium: Epithelial cells are flat and thin. Their nucleus is narrow and centered. This epithelium can be found in endothelium, mesothelium, pericardium, and peritoneum.

- Cuboidal epithelium: Epithelial cells are cubic shaped: their width, length and high are about equal. Their nucleus is rounded and centered. This epithelium can be found in kidney tubules, Malpighi tubules, thyroid gland, salivary glands, and pancreas.

- Columnar epithelium: Epithelial cells are tall, rectangular and/or column-shaped, longer than width. Their nucleus is ovoid and near to the base. This epithelium can be found in the stomach, intestine, duct of glands, Fallopian trumps, etc. Their functions are related to secretion, absorption, protection, motility.

Types of epithelium tissue:

- Simple squamous epithelium

- Simple cuboidal epithelium

- Simple columnar epithelium

- Stratified squamous epitheliums

- Stratified cuboidal epitheliums

- Stratified columnar epitheliums

- Transitional epithelium