List of abbreviations		 Vocabulary
of micros-
copic
anatomy
specialist terms
explained in
English +
German

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!
dieser Seite

Editor:
Dr. med.
H. Jastrow
Conditions
of use
Overview nucleus (Nucleus):
Pages with explanations (still in German) are linked to the text below the images when available
nucleus of a
lymphocyte (rat)		 nucleus with pores
(gut epithelial cell, rat)		 nucleus of a
Schwann cell (monkey)		 nucleus with 2 nucleoli
(ganglion cell, guinea pig)
segmented nucleus
of a human granulocyte		 nucleus of a parietal cell
(stomach, rat)		 nucleus of a
lymphocyte (monkey)		 nucleus of a glial cell
(brain, rat)
segmented nucleus of a hu-
man eosinophilic granulocyte		 characteristic horse-wheel like aggre-
gation of chromatin (plasma cell, rat)		 a similar human plasma
cell nucleus		 nucleus of a smooth muscle
cell (arteriole from rat brain)		 nucleus of a hepa-
tocyte (monkey)		 nucleus of a Sertoli
cell (testis, rat)		 syncythiotrophoblast
(human placenta)
Euchromatin spermiogenesis
(testis, rat)		 Sertoli- and other cells
(testis, rat)		 nucleus of a spine
cell in human skin		 nucleus of a rat basophil
granulocyte (spleen)		 nuclei of rods
(human retina)		 euchromatin & prominent nucleolus
(adenohypophysis, rat)		 changes in euchromatin before onset
of a mitosis (adrenal gland, rat)
highly condensed heterochromatin
of a spermatozoon (monkey)		 long nuclei: fibrocytes,
smooth muscle cells (rat)		 flat and round nuclei of
different layers of skin (rat)		 nucleus of a rat oocyte irregular shaped nucleus of a podocyte
and endothelial cell (kidney, rat)		 nuclei of different cells
of a lung alveole (rat)
thin and long nucleus of a resting cell
of the connective tissue (human fibrocyte)		 Part of a discoid nucleus
skeletal muscle (pig)		 nucleus of a
liver cell (rat)		 nucleus of an
egg cell (rat)		 trinucleated cell of Zona fas-
ciculata adrenal gland (rat)		 extracellular space appears
to be inside the nucleus (rat)
A nucleus (Terminolgia histologica: Nucleus) is the cell compartment that contains the genetic information (desoxy ribonucei acid = DNA) bound to chromatin and usually one or more nucleoli. It is limited by the nuclear membrane.
All cells contain nuclei with two exceptions: red blood cells (erythrocytes) and platelets (thrombocytes).
Most cells only contain one nucleus. However, two nuclei may be encountered in the following cells: liver cells (hepatocytes), superficial cells of the transitorial epithelium (of the urinary system), parietal cells (of the stomach), chondrocytes, heart muscle cells. Cells with many nuclei derive from cells that melt together during development to form a syncythium:
the syncythiotrophoblast which is the surface epithelium of the placenta, osteoclasts (bone resorbing cells), chondroclasts (cartilage resorbing cells) and all skeletal muscle cells. Whereas the first 3 different cell types contain 3 to about 8 nuclei, the skeletal muscle cells possess some hundreds to a few thousand nuclei located close to the cell surface since some of them they are several millimetres long.
The nuclear membrane separates the nucleus from the surrounding cell fluid with its organelles, the cytoplasm. The fluid inside the nucleus called karyoplasm or karyolymph embeds the more or less dense network of the chromatin and the nuclear bodies, called nucleoli.
The average diameter of a nucleus is about 5 to 10 µm. The nuclear volume comprises 5 - 10 % of the cellular volume with considerable variation depending on cell type. The relation of nuclear to cell volume also depends on cell function. In very small cells, e.g., lymphocytes or mikroglia cells the nucleus-plasma relation is over 50 %, in univacuolar fat cells it may be less than 1 % in times of high lipid storage. Most cells have a simple chromosome set, this means they are diploid (every chromosome is present twice), some cells, e.g. liver cells or heart muscle cells may become polyploid containing then more than a single set of chromosomes. The nucleus-plasma relation is of importance for judgement of dignity of tumour cells that often develop multiple sets of chromosomes. The nuclear volume increases with cell activity as is the active part of the chromatin where, in the transcription process, genetic information is copied to messenger ribonucleic acid (m-RNA) for being transported into the cytoplasm for protein synthesis in a process called translation.
The shape of a nucleus usually adapts to that of the whole cell. Thus, e.g., long cells like fibrocytes have long nuclei, round cells like lymphocytes spherical nuclei as have cuboid epithelial cells. Unusual shapes of nuclei are seen in the band-shaped and lobed granulocytes that belong to the white blood cells. The shape of a nucleus is dynamic in smooth muscle cells that show a straight long nucleus in rest phase and a corkscrew like shape during contraction. In univacuolar fat cells a large lipid droplet pushes the disc like nucleus aside from the centre of the cell. Some cells,e.g. megacaryocytes (which are the precursors of blood platelets = thrombocytes) have large lobed nuclei. Nuclei of other cells show invaginations of cytoplasm, e.g. cells of the pineal gland (pinealocytes) or transitorial epithelial cells of the urinary bladder.
In the light microscope nuclei appear as homogenous structures with with partial densities. The latter are the nucleoli or chromatin granules. After fixation and staining of tissues the sour (due to richness of nucleic acids) chromatin is basophilic, i.e. may be stained with basic colouring agents. It is in many cases more intensely stained than the cytoplasm. The chromocentres appear as fine fibres or bigger lumps of the fibrils from chromosomes as brighter euchromatin or more densely packed heterochromatin. These two forms of chromatin are best visible in the electron microscope. Some cells in females show a dense aggregation of heterochromatin attached to the nuclear membrane, the X-chromatin (Barr's corpuscule). It comprises an inactivated female sex- = X-chromosome.
During cell devision (Mitosis or Meiosis) the genetic material is doubled. The characteristic stages of these processes can be distinguished from the changes in the nucleus due to formation of chromosomes. The majority of cells that s not in atate of division are in a stage called interphasis.

--> nuclear membrane, nuclear pore, karyoplasm, euchromatin, heterochromatin, chromosomes, nucleolus
--> Electron microscopic atlas Overview
--> Homepage of the workshop

Three pictures were kindly provided by Prof. H. Wartenberg; other images, page & copyright H. Jastrow.