Fat Body Cells

Adipocytes (trophocytes) are the predominant cell type associated with metabolic and storage functions. In young cells, a few inclusions can be detected and the nuclei are round. As the cells mature and accumulate nutritional reserves, they become vacuo-lated and the nuclei are compressed. The colors of adipocytes, which depend on the insect species and change with maturation, range from white, yellow, tan, and brown to blue.

Urocytes are special cells common in cockroaches, which sequester uric acid (the main end product of nitrogen metabolism in terrestrial insects) for excretion and storage. They are degenerate cells, which unlike adipocytes, lack organelles such as mitochondria, ribosomes, or the endoplasmic reticulum.

Mycetocytes are cells that harbor symbiontic microorganisms and may serve for nutritional purposes. Mycetocytes are in proximity to urocytes, a spatial organization that implies some sort of physiological—biochemical interaction.

The adipocytes are arranged in two or three layers in the periphery of the fat body lobe, and the more metabolically active cells face the circulatory system. The mycetocytes are located in the center of the lobe surrounded by urocytes.

Other cell types associated with the fat body, including various blood cells, can be found adhered to fat body cells. Oenocytes, which are large ectodermally derived cells, have also been observed to be attached to adipocytes. Their exact physiological role is unresolved.

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