Histology · Connective tissue, cartilage and bone

Adipose tissue: white and brown fat !

Tissue

Fat tissue stores energy, insulates and cushions the body, makes hormones, and in its brown form produces heat.

Updated 2026-11-01

See it in 3D: Breast fat · Infrapatellar fat pad

What it is

Adipose tissue is a connective tissue made mostly of adipocytes held in a fine net of reticular fibres and capillaries. White fat is the main energy store of the adult and an endocrine organ that releases leptin and adiponectin. Brown fat burns lipid to make heat; it is abundant in newborns and persists in small depots in adults.

Structure

White adipocytes are unilocular: one large lipid droplet fills the cell and pushes a flattened nucleus to the edge, giving a signet-ring look.
In routine sections the lipid dissolves during processing, so white fat looks like a net of empty polygonal spaces with thin pink rims.
Brown adipocytes are multilocular: many small droplets, a central round nucleus and pink, granular cytoplasm packed with mitochondria.
Brown fat is richly vascular and supplied by sympathetic nerves.

Function

Stores triglyceride and releases fatty acids when energy is needed.
Insulates and cushions organs and the soles and palms.
Secretes leptin (signals satiety to the hypothalamus) and adiponectin (improves insulin sensitivity).
Brown fat: uncoupling protein 1 lets protons leak across the inner mitochondrial membrane, so energy is released as heat instead of ATP.

White vs brown fat

Feature	White fat	Brown fat
Droplets	One large (unilocular)	Many small (multilocular)
Nucleus	Flattened, at the edge	Round, central
Mitochondria	Few	Many, with uncoupling protein 1 (thermogenin)
Main job	Energy storage, insulation, cushioning, hormones	Non-shivering heat production
Where	Subcutaneous tissue, around viscera, breast, marrow	Newborns: neck, between the scapulae, around the kidneys; adults: small neck and supraclavicular depots

Clinical notes

In obesity adipocytes enlarge and visceral fat fills with macrophages; this low-grade inflammation is linked to insulin resistance and type 2 diabetes.
Adiponectin falls as visceral fat rises.
Newborns, especially preterm ones, rely on brown fat to keep warm, which is one reason they are prone to hypothermia.
Lipomas are benign tumours of mature white fat; liposarcoma is the malignant counterpart.

Test yourself

Think of the answer, then tap the question to see it.

Why do white adipocytes look like signet rings?

A single huge lipid droplet fills the cell and pushes the flattened nucleus to one edge.

Which protein lets brown fat produce heat instead of ATP?

Uncoupling protein 1 (thermogenin), which lets protons leak back across the inner mitochondrial membrane.

Why does fat appear as empty spaces on a routine H&E slide?

Alcohols and clearing agents used in paraffin processing dissolve the lipid, leaving only the cell membranes and nuclei.

Which hormone from adipose tissue signals satiety to the hypothalamus?

Leptin.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

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Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: 4.3 Connective Tissue Supports and Protects (OpenStax, 2022); Connective Tissue (National Cancer Institute, SEER Training Modules, 2024).

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Representative model, for educational purposes only.