Soft tissue
Histology-white and brown adipose

Topic Completed: 1 August 2012

Minor changes: 15 September 2020

Copyright: 2002-2020,, Inc.

PubMed Search: White fat [title]

Vijay Shankar, M.D.
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Cite this page: Shankar V. Histology-white and brown adipose. website. Accessed October 24th, 2020.
  • Also called White Adipose Tissue (WAT)
  • Cells are called adipocytes
  • See also Brown adipose tissue (topics are being merged)
  • Subcutaneous, mediastinum, abdomen, retroperitoneum
  • Main function is energy storage as lipid, which is mobilized to other tissues depending on metabolic needs
  • Triglycerides circulate in blood as chylomicrons; the enzyme lipoprotein lipase, produced by adipocytes and present on luminal surface of endothelium, converts triglycerides to free fatty acids; free fatty acids are taken up by adipocytes and converted to triacylglycerol, which is stored within cytoplasmic lipid droplet of adipocytes
  • Adipocytes also secrete leptin and IL6, but their effects in humans are not well defined
  • Stromal cells also convert androstenedione to estrone, the main source of estrogen in men and postmenopausal women
Gross description
  • Homogeneous, yellow, greasy surface, faint fibrous septa
Microscopic (histologic) description
  • Uniform large spherical cells up to 120 microns; lipid droplet pushes nucleus to periphery and deforms it to a thin crescent
  • Cytoplasm usually has single, clearly delimited vacuole
  • Cells are clear because cytoplasmic fat dissolves during tissue processing
  • Nucleus may have central vacuole or Lochkern
  • Very thin membranes are present between cells
Microscopic (histologic) images

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White adipose tissue and vasculature

White adipose tissue

Fat emboli in lung-Oil Red O stain

Mature adipose tissue

Positive stains
  • Vimentin (nonspecific), S100 (primarily for mature adipocytes), calretinin (also stains lipoma and liposarcoma) (Hum Pathol 2006;37:312)
  • Oil red O and Sudan Black stain neutral fat (must use frozen tissue because tissue processing removes fat); Oil red O also stains most carcinomas
  • Nile blue sulfate stains neutral fat pink-red, and stains fatty acids / phospholipids blue
  • Basement membrane is highlighted by PAS and reticulin
Electron microscopy description
  • Pre-adipocytes - spindle cells with abundant endoplasmic reticulum and small spherical mitochondria
  • Mature adipocyte - large lipid droplet flattens nucleus against cytoplasmic membrane, variable pinocytotic vesicles; capillaries are close to adipocyte basement membrane
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