Lung (bottom section) Slice 2 Under the Microscope

Lung (bottom section) Slice 2, Homo sapiens

Lung (bottom section) Slice 2, 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.

This frozen section of normal human (Homo sapiens) lung is stained with H&E. Most of the tissue looks like lace. The open spaces are alveoli, the tiny air sacs where oxygen enters the blood, and the thin walls between them hold capillaries. Along one edge the tissue has collapsed into a darker, denser band where the air sacs are squeezed shut. Pink strands of connective tissue and small red vessels run through the slice, and the streaks and tears come from cutting frozen, air-filled tissue.

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.

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

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