Lung Under the Microscope (top section)

Lung (top section), Homo sapiens

Lung (top section), prepared microscope slide

This is a frozen section of human lung tissue stained with H&E. It shows the tiny air sacs (alveoli) where oxygen passes into the blood, and it also shows the tears and folds that often happen when soft, airy tissue is frozen and cut.

Frozen section of lung. The parenchyma forms an open, lace-like network of thin alveolar septa around widely patent airspaces — well-aerated peripheral lung at its most delicate. Denser, darker bands of collapsed alveoli follow the subpleural margin along the left of the section, and a small focus of septal congestion stains red at the lower left. The section has folded on itself in places during cryosectioning, producing the darker creases that cross the tissue; between folds the fine alveolar architecture, septal capillaries, and scattered alveolar macrophages can be followed at high power.

What to look for

Alveoli: Many small, open, empty-looking spaces that give lung tissue a lacy, honeycomb look.
Alveolar walls (septa): Very thin pink walls between the air spaces, dotted with purple nuclei.
Blood vessels: Tubes of various sizes, some filled with bright pink to red blood cells.
Collapsed areas: Darker, denser patches where the air spaces have closed up, often near the edges.
Folds and tears: Darker creases and gaps caused by cutting frozen tissue, not by the lung itself.

At each magnification

Low power (about 4x)

A lacy pink network with lots of open white space, plus darker bands and folds.

Medium power (about 10x)

The pattern of alveoli and the blood vessels running between them.

High power (about 40x)

Thin alveolar walls with flattened cells, purple nuclei, and red blood cells in tiny capillaries.

Questions and answers

What does lung tissue look like under a microscope?

Lung tissue looks like lace or a sponge. Most of it is tiny air sacs called alveoli, separated by very thin walls. With H&E stain, the walls are pink with purple nuclei, and blood in the vessels is red.

Why are alveolar walls so thin?

Oxygen and carbon dioxide move between the air and the blood by diffusion, which only works well over very short distances. The thin walls put the blood in tiny capillaries very close to the air.

What is a frozen section?

A frozen section is made by freezing tissue and slicing it right away instead of embedding it in wax. It is fast, but soft or airy tissue like lung often tears or folds, so some of the gaps and creases on this slide come from the cutting process.

Based upon data generated by the TCGA Research Network (https://www.cancer.gov/tcga) and made available through the NCI Genomic Data Commons (GDC). See credits.

Category: Histology and Tissue
Scan magnification: 20x
Stain: H&E
Tags: normal lung tissue, alveoli, alveolar septa, pneumocytes, alveolar capillaries, subpleural atelectasis

Viewing this slide in class

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