Skip to main content

Unfortunately we don't fully support your browser. If you have the option to, please upgrade to a newer version or use Mozilla Firefox, Microsoft Edge, Google Chrome, or Safari 14 or newer. If you are unable to, and need support, please send us your feedback.

Publish with us
Cells of Nervous Tissue



Read more

Quick Facts

The nucleolus is a rounded, dense body, present in the nucleus of eukaryotic cells during interphase, that is the site of ribosomal RNA (rRNA) synthesis and ribosomal subunit assembly. It consists of (a) a fibrillar center, containing the rRNA genes, surrounded by (b) the pars fibrosa, a dense fibrillar component where transcription occurs, and (c) the pars granulosa, a granular component where the ribosomal subunits are assembled. Multiple nucleoli occur in some cells (Dorland, 2011).

Complete Anatomy
The world's most advanced 3D anatomy platform
Try it for Free
Related parts of the anatomy

Structure and/or Key Features

The most predominant, non-membranous structure in the nucleus is the spherical nucleolus. It surrounds rRNA genes that are transcriptionally active. The nucleolus is the site of synthesis of ribosomal ribonucleic acid (rRNA), ribosomal production and assembly. The diameter of the nucleolus is 1–2 mm, but this varies within different populations of cells. In cells that are most active in synthesizing proteins, the nucleolus is well developed and prominent. It is not uncommon for some cells to contain more than one nucleolus (Mescher, 2013).

Like heterochromatin, the nucleolus stains with basic dyes and hematoxylin.

Anatomical Relations

The nucleolus is located at the center of the nucleus.


The nucleolus synthesizes and assembles ribosomal ribonucleic acid (rRNA).

Clinical Correlates

Nucleoli house proteins for ribosome synthesis and oncogenes and tumor suppressor genes that control cell proliferation. Structural and functional faults in nucleoli have been the basis of a number of disease processes including some types of cancers (McKinley, O'Loughlin and Pennefather-O'Brien, 2016).


Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

McKinley, M. P., O'Loughlin, V. D. and Pennefather-O'Brien, E. E. (2016) Human Anatomy. 5th edn.: McGraw-Hill Education.

Mescher, A. (2013) Junqueira's Basic Histology: Text and Atlas. 13th edn.: McGraw-Hill Education.

Complete Anatomy

The world's most advanced 3D anatomy platform

Complete Anatomy