Adipose Tissue: Functions and Characteristics

Adipose Tissue

• Adipose tissue is a type of connective tissue that accounts for 10-25% of an adult's body weight, with a main function of passive storage of excess calories in the form of triglycerides.
• It serves as a metabolic energy reserve, characterized by a double energy density (calories/gram) compared to carbohydrates and proteins.
• Adipose tissue also produces and releases adipokines, hormones, and growth factors, making it an endocrine organ.

Distribution and Characteristics

• The distribution of adipose tissue varies by sex, age, and genetic factors, with women having a higher concentration of subcutaneous fat, particularly during pregnancy.
• Triglycerides are not stationary, but are continuously mobilized and redeposited every 10-15 days.
• The average lifespan of adipocytes is approximately 6 months, with a 10-60% renewal rate.

Types of Adipose Tissue

• White Adipose Tissue (WAT) is composed of distinct cells, with adipocytes accumulating to form deposits classified as subcutaneous and visceral adipose tissue.
• WAT has a fundamental role in regulating the balance between nutrient availability and demand, storing excess calories.

Subcutaneous Adipose Tissue

• Also known as hypodermis, it accounts for 80-85% of total adipose tissue, located beneath the dermis, and has thermal and mechanical protective functions.
• It is found in the plantar surface of the foot, palmar surface of the hand, abdomen, buttocks, thighs, breasts, orbits, and pericardium, contributing to sex-specific body shapes.

Visceral Adipose Tissue

• Accounts for 10% of total adipose tissue, with higher metabolic activity, and is concentrated in the abdominal cavity, including the omentum, mesentery, and retroperitoneal space.
• Its accumulation, known as abdominal obesity, is particularly dangerous for cardiovascular diseases, as it is immunologically dynamic, hosting numerous leukocytes.

White Adipose Tissue Cells

• Characterized by polyhedral cells, 70-100 microns in diameter, capable of accumulating fatty acids.
• Fatty acids derive from three main sources: dietary, synthesized in the liver, and synthesized in adipocytes from glucose.
• The large lipid droplet formed is composed of triglycerides and beta-carotene, which can be stained with Sudan black.
• The citoplasma is reduced, and the nucleus is compressed to the periphery, with a basal membrane and a cellular membrane rich in vesicles and caveolae.

Regulation of Metabolism

• Triglycerides can be deposited into cells through two pathways: absorption from plasma or formation ex novo from glucose.