Cells with one big oily droplet that squeezes the nucleus to the edge, so that each looks like a signet ring
Adipose tissue — white adipocytes.
Anatomy · Cells & tissues
Adipose tissue
The body's fat
Connective tissue · beneath the skin and around organs
A loose connective tissue that consists mostly of fat-storing cells called adipocytes. White adipocytes hold a single large droplet of triglyceride that pushes the nucleus and the rest of the cytoplasm to a thin rim; brown adipocytes hold many small droplets and many mitochondria and burn fat to make heat. Beyond storing energy, the tissue insulates, cushions and packs the spaces between organs, and acts as an endocrine organ, releasing hormones such as leptin and adiponectin.
How to spot them
- ▸In a stained section, a honeycomb or 'chicken-wire' of large empty-looking round cells with thin pink walls
- ▸Each cell's nucleus is squashed into a thin crescent at the edge, giving a 'signet ring' look
- ▸The lipid is dissolved away during slide preparation, leaving the cell looking empty
- ▸Fine strands of connective tissue and capillaries run between the fat cells and group them into lobules
- ▸Brown fat is different: smaller cells with a central round nucleus and many tiny lipid droplets
What to know
The body's main energy store, holding about nine kilocalories in every gram
Adipose tissue — triglycerides give roughly 9 kcal (37 kJ) per gram.
A form full of mitochondria and a protein called thermogenin, which burns fat to make heat in newborns and hibernators
Adipose tissue — brown fat, with UCP1, gives non-shivering thermogenesis.
Hormone discovered in 1994 after the mouse 'obese' gene was cloned, which signals fullness to the brain (1994)
Adipose tissue — leptin, found by Jeffrey Friedman and colleagues.
A cushion in the heel pad, the palm and behind the eyeball, as well as an insulating layer under the skin
Adipose tissue — the subcutaneous layer forms the hypodermis.
The variety that packs around the intestines and organs of the abdomen is more linked to metabolic disease than the variety under the skin
Adipose tissue — visceral fat.
The number of its cells is largely set in childhood and adolescence, and roughly one in ten is replaced each year
Adipose tissue — research by Kirsty Spalding and colleagues in 2008.
Key ideas
- Insulin promotes storage: adipocytes take up glucose and fatty acids and build triglyceride; when energy is needed, hormones such as adrenaline and glucagon trigger lipase enzymes to break the store down.
- Adipose tissue is also an endocrine organ, releasing leptin, adiponectin and other signals that influence appetite, insulin sensitivity and inflammation.
Quick-fire facts
- •White adipocytes may be 70–120 micrometres across, and can enlarge many times
- •Brown fat is abundant in babies, mainly between the shoulder blades, and small deposits persist in the neck and upper chest of adults
- •Fat is stored in two main depots: subcutaneous (under the skin) and visceral (around the organs)
- •Adipose tissue is highly vascular, and each fat cell is in contact with a capillary
- •Leptin was identified in 1994; a lack of it causes severe obesity in mice and rare cases in humans
- •Adipocyte number in adults is fairly stable; weight gain mostly enlarges existing cells
- •'Beige' adipocytes are a third type that can acquire brown-like features in the cold
- •The word 'adipose' comes from Latin adeps, meaning fat
Drill it — 7 cards
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