16th_Ed_Junqueira's_Basic_Histology_Text_and_Atlas_McGraw_Hill_Education

White Adipose Tissue

Composition: Contains primarily one large lipid droplet (unilocular); nucleus and cytoplasm pushed against plasmalemma.
Fatty Acid Release: Fatty acids are released by lipase from white adipocytes when nutrients are needed; transported by plasma proteins (e.g., albumin).
Leptin: A polypeptide hormone released from white adipocytes, targets hypothalamus, regulates eating behavior.

Proportion: Comprises 5% of newborn body weight, less in adults.
Adipocyte Characteristics: Smaller cells with many small lipid droplets (multilocular), numerous mitochondria, and central nucleus.
Function: Brown fat metabolizes fatty acids in mitochondria for thermogenesis instead of ATP production, utilizing uncoupling protein-1.

Definition: Adipocytes are large cells from mesenchyme specialized for energy storage in lipid droplets (triglycerides).
Lipid Sources: Lipids are stored from dietary fats (chylomicrons), liver triglycerides (VLDLs), and locally synthesized fatty acids.
Mobilization: Hormone-sensitive lipase hydrolyzes triglycerides under norepinephrine and peptide hormone influences.
Support Structure: Reticular fibers and connective tissue septa divide adipose tissue into lobules.
Types: White fat and brown fat; white fat constitutes about 20% of adult body weight.

Thermogenesis: Main function is heat production through nonshivering thermogenesis, primarily in hibernating animals and newborns.
Mechanism: Norepinephrine triggers hydrolysis of triglycerides; fatty acids are oxidized rather than released.

Development: Arises from mesenchyme in a different embryonic location (paraxial) than white adipose tissue; appears earlier in fetal development.
Age and Activity: Amount decreases after childhood but can increase during cold adaptation, showing as clusters of multilocular cells in white adipose tissue.
Differentiation: Autonomic nerves promote brown adipocyte differentiation and prevent apoptosis in mature cells.