Page 82 - Atlas of Histology with Functional Correlations

Lysosomes are cytoplasmic organelles that contain many hydrolyzing or

digestive enzymes called acid hydrolases. Lysosomal hydrolases are
synthesized in the rough endoplasmic reticulum and transferred to the Golgi
apparatus, where they are modified and packaged into membrane-bound
lysosomes. They are highly variable in appearance and size. To prevent the
lysosomes from digesting the cytoplasm and cell contents, a membrane separates

the lytic enzymes in the lysosomes from the cell cytoplasm. The main function
of lysosomes is the intracellular digestion or phagocytosis of substances taken
into the cells. Lysosomes digest phagocytosed microorganisms, cell debris, cells,

and damaged, worn-out, or excessive cell organelles, such as rough endoplasmic
reticulum or mitochondria. During intracellular digestion, a membrane surrounds
the material to be digested. The membrane of the lysosome then fuses with the
ingested material, and their hydrolytic enzymes are emptied into the formed
vacuole. After digestion of the lysosomal contents, the indigestible debris in the

cytoplasm is retained in large membrane-bound vesicles called residual bodies.
Lysosomes are very abundant in such phagocytic cells as tissue macrophages
and specific white blood cells (leukocytes) such as neutrophils.

Peroxisomes

Peroxisomes are cell organelles that appear similar to lysosomes, but are
smaller. They are found in nearly all cell types. Peroxisomes contain several

types of oxidases, which are enzymes that oxidize various organic substances to
form hydrogen peroxide, a highly cytotoxic product. Peroxisomes also contain
the enzyme catalase, which eliminates excess hydrogen peroxide by breaking it
down into water and oxygen molecules. Because the degradation of hydrogen
peroxide takes place within the same organelle, peroxisomes protect other parts

of the cells from this cytotoxic product. Peroxisomes are abundant in the cells of
the liver and kidney, where much of the toxic substances are removed from the
body. They detoxify, degrade alcohol, oxidize fatty acids, and metabolize

various compounds.

CELL CYTOSKELETON

The cytoskeleton of a cell consists of a network of tiny protein filaments and
tubules that extend throughout the cytoplasm. The cytoskeleton serves the cell’s
structural framework. Three types of filamentous proteins, microfilaments,

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