Overview primary lysosomes (Lysosoma
Pages with explanations are linked to the
text below the images if available! (Labelling is in German)
|"granules" of an eosinophil are
in fact lysosomes (rat)
|lysosomes + mitochondria
heart muscle cell (monkey)
|exocytosis of a zy-
mogen vesicle (monkey)
|lysosomes of a baso-
philic granulocyte (rat)
Lysosomes (Terminologia histologica: Lysosomae), which
are also called prelysosomes and primary lysosomes in former days, are
relatively electron-dense organells homogenously filled with very tiny
granules and usually spheres in three-dimensional shape. Lysosomes have
median diameters of 25 to 200 nm and thus on average are
considerably smaller than
Lysosomes are enzyme filled vesicles originating from terminal cisterns
of the trans-side of Golgi-apparatuses.
They contain a high concentration of digestive, i.e. lytic enzymes which
were synthetised in rough endoplasmic reticulum
transferred via small vesicles to cis-sides of Golgi-apparatuses
and packed there into lysosomes. Lysosomes are present in all cells of
animals with exception of red blood cells (erythrocyten).
Their number is high in microphages (e.g. neutrophilic
granulocytes) and macrophages as well
as in other phagocyting cells of the reticulohistiocytic and reticuloendothelial
systems. Further they are numerous in cells of the liver
and kidney as well as in nerve-,
and muscle cells.
|RER and lysosomes
of a human plasma cell
|dictyosomes form lysosomes
human plasma cell
of a human plasma cell
|lysosomes of a human
|lysosome of a human
The specific "granules" of neutrophilic,
or basophilic granulocytes are lysosomes as
well (see images above).
More than 50 different enzymes have been demonstrated inside
lysosomes most of which are acid hydrolases. The most important
lysosomal enzymes are: acidic phosthatase (most characteristic enzyme),
alpha-aminopeptidase and other proteases, beta-glucuronidase, esterases,
sulfatases, desoxyribonucleases, ribonucleases, cathepsin D, collagenases,
triglyaridlipases, neuraminidases, phospholipases, sphingomyelinase, glucosidase,
N-acetyl-hexosaminidase and hyaloronidase. These enzymes have optimal effectiveness
under acidic pH 4-5. For this reason an ATP driven protone pump is located
inside the double membrane which borders the lysosomes in order to pump
H+ ions into their lumen.
Lysosomes serve for degradation of foreign organic substances
(heterophagy / foreign body defense) internalised by endocytotic
processes. Further they are responsible for destruction of cell own material
(autophagy of organells).
Since during endocytosis (pinocytosis
or phagocytosis) the membranes
of lysosomes fuse with the internalised material lysosomes decrease in
number. The term degranulation of lysosomes means that the electron-dense
content of the lysosomes fuses with endosomes. Thereby the enzymes are
released and attack the content of the endosome which now is called heterolysosome
(Terminologia histologica: Heterolysosoma). Heterolysosomes are
the second stage of lysosomes in which intracellular digestion takes place.
Some lysosomes are secreted from cells by exocytosis
(e.g. as zymogen vesicles in the pancreas;
see above or as mast cell vesicles). In this
case they release their enzymes to help in extracellular digestion or to
reduce viscosity of secretions. Glucocorticoids (like Cortison) "stabilise"
the membranes of lysosomes and thus inhibit inflammatory processes.
--> secondary- - telo-
or tertiary lysosomes, cytoplasm,
--> Electron microscopic atlas Overview
--> Homepage of the workshop
Two images were kindly provided by Prof. H. Wartenberg;
other images, page & copyright H. Jastrow.