Question

The inner lining of the kidney tubules has
(A) Cuboidal epithelium
(B) Columnar epithelium
(C) Squamous epithelium
(D) None of the above

Answer 1

Hint: Epithelial tissue is a tissue made of one or more layers of compactly arranged cells that covers a body surface (external or internal) and which is underlined by a basement membrane.

Complete answer:
In cuboidal epithelium cells are cubical in shape. The nuclei are rounded and lie in the centre of the cells. The cells of cuboidal epithelium often form microvilli on their free surface. This gives a brush like appearance to their free border called brush bordered cuboidal epithelium. Microvilli increase absorptive surface area. In ovaries and seminiferous tubules of testes it is called germinal epithelium because it produces gametes (ova and sperms respectively).
The cuboidal epithelium is present in the small salivary and pancreatic ducts, thyroid vesicles, parts of membranous labyrinth, proximal and distal convoluted tubules of the nephrons of kidneys, ovaries, seminiferous tubules, and ciliary bodies, choroid and iris of eyes. Other sites of cuboidal epithelium are the inner surface of the lens and the pigment cell layer of the retina of the eye.
In columnar epithelium the cells are elongated and placed side by side like columns. The outer free space of each cell is slightly broader. The nuclei are somewhat elongated along the axis of the cells. Nuclei lie near the bases of the cells. Certain cells of this epithelium contain mucus and are called goblet cells as they look like goblet. The epithelium containing mucus secreting cells, along with the underlying supporting connective tissue is called mucosa or mucous membrane. The intestinal mucosa has microvilli to increase the absorptive surface area and is called brush-border columnar epithelium which is highly absorptive. It lines the stomach, intestines, gallbladder and bile duct. It also forms the gastric glands, intestinal glands and pancreatic lobules where it has secretory role and is called glandular epithelium.
Squamous epithelium is also called pavement epithelium because the cells are flat, polygonal and fitted together like the tiles of the floor. Central nucleate region may show protrusion. It is present in cavities of mouth, oesophagus, alveoli and blood vessels.

So, the correct answer is option A) Cuboidal epithelium.

Note:
Columnar epithelium is a single layer of columnar cells attached to the basement membrane. Its nuclei is located in the basal region. In humans, columnar epithelium lines the digestive tract including the stomach, small intestine, and large intestine.