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Adipose Tissue (white and brown fat)

Adipose Tissue (white and brown fat)

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Adipose Tissue
  • Type of Connective Tissue.
  • Comprises adipocytes (fat cells).
  • Located throughout the body.
White Adipose Tissue
  • Most common in the body
  • "Bubble-like" matrix of large adipocytes that contain a fat droplet when mature.
– White adipocytes are called "unolocular" because of single fat droplet. – Fat is usually removed in slide preparation by the alcohol, leaving empty vacuole. – Nucleus is pushed to periphery. – Other cellular organelles (Golgi, ER, etc.) are also present (not shown in our example).
  • Rich vascularization.
  • Located throughout the body:
– Subcutaneous deposits with noticeable accumulations in certain areas (breasts, thighs, hips, abdomen). – Visceral deposits (esp. kidneys, eyeballs; excessive depositions may occur around heart and abdominal viscera, for example).
Functions
  • Largest stores of energy
– Triglycerides – Fatty acids from diet, adipocytes can also synthesize fatty acids from glucose. – Mitochondria, smooth ER required for lipid uptake and storage.
  • Responds nervous and endocrine system cues.
– Releases fatty acids/glycerol into blood. Adipocytes release leptin* – "Satiety factor" regulates appetite.
  • Thermal insulation
– Poor heat conduction
  • Cushions and maintains organ placement
– Absorbs shock
Brown Adipose Tissue
  • Numerous fat droplets in adipocytes = "Multilocular"
  • Brown adipocytes are smaller than white adipocytes.
  • Abundant mitochondria in each cell.
  • Central nuclei
  • Sympathetic innervation
  • Scarce in adults (around collarbones, mediastinum, and kidneys/adrenal glands).
  • More prevalent (and more important) in newborns (and hibernating animals).
Functions:
  • Nonshivering thermogenesis:
– Mitochondria have thermogenin (aka, uncoupling protein) in inner membranes, which promotes heat production. – Close association with capillaries allows for heat dissipation via the bloodstream.
  • Brown adipose can increase as part of cold adaptation.

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