Types of Epithelium — Cell Shape, Nucleus & Basement Membrane

Epithelial tissue (epithelium) covers body surfaces and lines cavities, ducts and organs. It is broadly divided into simple epithelium (a single cell layer — squamous, cuboidal, columnar, and their ciliated/pseudostratified forms) and compound epithelium (many layers — stratified and transitional). All epithelia have a free (apical) surface and rest on a basement membrane.

It comes down to cell shape and nucleus. Squamous cells are flat and thin with a flattened central nucleus (found in alveoli and blood vessels, for diffusion). Cuboidal cells are cube-shaped with a round central nucleus (gland ducts and nephron, for secretion/absorption). Columnar cells are tall and pillar-like with an oval nucleus near the base (stomach and intestine lining, for secretion/absorption).

Pseudostratified epithelium looks multi-layered but is actually a single layer — every cell touches the basement membrane, but the cells are of different heights, so their nuclei lie at different levels and give a false impression of stratification ('pseudo' = false). It is usually ciliated and lines the trachea, bronchi and nasal cavity, where it moves mucus and trapped particles.

Glandular epithelium is made of secretory cells. A unicellular gland is a single isolated secretory cell — the classic example is the goblet cell of the alimentary canal, which secretes mucus. A multicellular gland is a cluster of secretory cells, such as the salivary gland, where cells form an acinus that drains its secretion through a duct.

The basement membrane is a thin, non-cellular layer made of collagen fibres and glycoproteins that lies beneath every epithelium, attaching it to the underlying connective tissue. It is present in all epithelia without exception, provides structural support, and acts as a selective barrier. In this lab it is shown as the orange layer under every type.

Transitional epithelium is specialised for stretching. Its surface cells are large and dome-shaped when the organ is relaxed, and they flatten as the organ fills, allowing the wall to expand without breaking. This makes it ideal for the urinary bladder, ureters and renal pelvis, which must change volume as urine collects.

Yes. Epithelial tissue is part of the Class 11 chapter 'Structural Organisation in Animals.' NEET regularly tests cell shape, nucleus position, the location and function of each type, the simple-versus-compound distinction, glandular epithelium (goblet cells and exocrine/endocrine glands), and the universal presence of the basement membrane.