Histological section of a human fetal lung at the stage of 12 weeks of gestation. Staining with an anti cytokeratin 7 antibody, in brown, and with hematoxylin (for nuclear DNA), en blue. Magnification: 250x. At this stage the lung is immature and the future airways (e.g. bronchi) look like glands. The parenchyma and the forming cells (visualized by their nuclei in blue), have no significant density that usually is found in adults. The epithelium (colored in brown with an anti E-cadherin (specific) antibody is in monolayer, not stratified and undifferentiated since there is no distinct cell types such as mucous, brush, etc. The cells possess big vacuoles and a nucleus (in purple) that is oriented towards the bronchiolar opening.
