Pl. II · Laxus adiposus — adipose tissue

The plate

The specimen, drawn

Pl. II

Cells that have given up everything else to hold one drop. The cytoplasmThe gel-like substance within a cell that contains organelles and cytosol. is a rim, the nucleusThe control center of the cell that contains DNA and directs cellular activities. is pressed flat against the wall.

Habitat & range

Where it lives

Body map

Adipose sits where the body wants either a fuel store, a cushion, or a blanket — and often all three at once.

Range

• The subcutaneous layer, under the whole skinThe body’s largest organ, providing protection and regulation. — the layer you can pinch.
• A packing cushion around each kidney, holding it in place.
• The breast, and the omental apron hanging over the gut.
• Behind each eyeball, and in the palms and soles as shock padding.
• Brown fat between the shoulder blades in newborns, for heat rather than storage.

Collection record

• Add your slide numbers here.

Niche

What it does for a living

Storage, insulation, and padding — and, lately, hormone signalling. An adipocyte is a cell that has committed almost its whole volume to one lipid droplet. It is not inert packing: adipose releases leptinA hormone involved in regulating energy balance and puberty onset. and other signals that tell the brain how much fuel is on hand, and brown fat burns its own stores to make heat instead of ATPThe energy currency of cells used for muscle contraction..

field collected specimen

How to know it on sight

• Empty-looking circles — the fat dissolved out in processing and left the space behind.
• Each cell is a thin rim of cytoplasm around that space, like a signet ring.
• Nuclei squashed flat and pushed against one side, never central.
• Cells packed close with almost no matrix between them; capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. squeeze through the corners.

Specimen 1

From a recto-anal junction. Find one cell and trace the rim all the way round; the nucleus is the bulge on one side.

Specimen 2

H&E. The clear spaces are where lipid used to be before the solvents took it.

Specimen 3

High power. Look at how little actual cell there is around each space.

People keep calling her by the wrong name

Look-alikes

Two plates. Read the line underneath each one before you decide.

Areolar connective tissue

Areolar has open space too, but it is unbounded gaps between fibres; adipose space is bounded — every gap has its own cell wall round it.

Spongy bone and marrow

Marrow has fat cellsThe basic structural and functional units of life. in it, so the circles look familiar — but marrow also has bony trabeculae and developing blood cells, and adipose has neither.

Examine it yourself

The virtual slide

This is brown fat, not the usual white. Compare it with the slides above: the droplets are many and small rather than one and large, and the nucleus is still roughly central. Ask yourself what burning fat for heat requires that storing it does not.

Virtual slide courtesy of Histology Guide.

Field notes

Why this organism

A honeypot ant replete spends its life hanging from the roof of the nest with its abdomen swollen into a translucent globe of food. It cannot walk, it cannot forage, it cannot do anything else — it has given over its whole body to being a container, and the colony lives off it when the season turns. An adipocyte makes exactly the same bargain: everything that was cell gets pushed to the edges so the cargo can have the middle.