Adipose Tissue Overview

Adipose Tissue

• Adipose tissue is connective tissue primarily composed of adipocytes (fat cells)
• Adipocytes store lipids, mainly triglycerides
• Two main types: white adipose tissue and brown adipose tissue

White Adipose Tissue

• Function: Primarily for long-term energy storage
• Structure: Uni-locular, meaning a single large lipid droplet fills most of the cell; this gives it a white appearance
• Location: Throughout the body; subcutaneous layers, visceral fat, and other locations.
• Role: Energy storage, insulation, cushioning, and organ support.
• Lipids: triglycerides, cholesterol, and other lipids; these are insoluble in water, allowing for efficient storage
• Hormonal regulation: responds to hormones and nervous stimuli; releases hormones and other substances, functioning as an endocrine organ
• Important: important for nutritional homeostasis; plays a significant role in regulating energy balance
• Medical application: Lipomas (benign tumors) can develop from these cells

Brown Adipose Tissue

• Function: Primarily for thermogenesis (heat production); important for maintaining body temperature
• Structure: Multilocular, meaning multiple small lipid droplets are present along with abundant mitochondria, which is why it has a darker appearance
• Location: Abundant in newborns; concentrated in the neck, back, and around certain organs in the body
• Role: Crucial for thermoregulation, especially in newborns.
• UCP1: uncoupling protein-1 (also called thermogenin); these proteins in the inner mitochondrial membrane enable the transport of protons, which releases heat energy from these organelles rather than ATP
• Hormonal regulation: norepinephrine stimulates thermogenesis in brown fat cells
• Medical application: These cells are sometimes referred to as 'hibernomas' in fetal tissue

Histogenesis of Adipose Tissue

• Adipocytes are derived from mesenchymal stem cells
• White adipocytes and brown adipocytes originate from different progenitor cells, and arise from the mesoderm in the embryo
• Beige adipocytes are generally intermediate between white and brown adipocytes, which can switch between these states depending on the environmental conditions.

Lipid Storage and Mobilization

• Lipids enter adipocytes from three sources: dietary fats, lipids synthesized by the liver (VLDL), and fatty acids
• Mobilization of lipids from adipocytes is stimulated by norepinephrine, promoting the release of fatty acids
• Proteins and hormones like albumin aid the transport of mobilized lipids out of the cells

Hormonal Regulation

• Adipocyes function as an endocrine organ and release various hormones and other factors
• Leptin released by adipocytes, impacts eating behavior and energy expenditure.
• Insulin is involved with glucose uptake by the adipocytes and promotes triglyceride synthesis
• Other peptide hormones and growth hormone (GH) contribute to balancing lipid synthesis and mobilization.

Medical Application

• Adipose tissue plays an important role in obesity and related health conditions.
• Obesity is associated with chronic low-grade inflammation, with the release of factors from visceral fat.