The lungs are the elastic respiratory organs of vertebrates that breathe air. In humans, the lungs are paired in the chest cavity on opposite sides of the heart. The right lung is divided into three lobes and the left is composed of two lobes.

A membranous lining called the pleura covers the human lungs, as well as the upper body cavity. A small amount of watery fluid is generally present in the pleural cavity that keeps the pleura lubricated and allows the lungs to move smoothly in the chest cavity during the breathing process. Lung infections and related problems can cause an inflammation of the pleura, known as pleurisy, to occur.

Humans continuously carry out the processes of inspiration and expiration. Inspiration, or the movement of air into the lungs, is accomplished via diaphragm contraction that enlarges the chest, which reduces the external pressure on the respiratory organs and allows them to expand. The expansion generates suction and fresh air is taken into the lungs. In contrast, expiration occurs as the diaphragm returns to its resting place and the thoracic cavity decreases in size. This process increases external pressure on the lungs and squeezes air out of them.

The sample of human lung tissue illustrated in the digital image above was labeled with wheat germ agglutinin (WGA) conjugated to Texas Red-X. WGA, which selectively binds to N-acetylglucosamine and N-acetylneuraminic (sialic acid) residues, is well suited for staining the Golgi complex in mammalian cells. The tissue sample was also labeled with Alexa Fluor 488 conjugated to phalloidin (targeting F-actin) and DAPI (targeting DNA in cell nuclei). Images were recorded in grayscale with a 12-bit digital camera coupled to either a Nikon E-600 or Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.

Targeting the Golgi Apparatus in Lung Tissue Samples with Wheat Germ Agglutinin - The human lung tissue sample presented in this section was labeled with Alexa Fluor 350 conjugated to the lectin wheat germ agglutinin. Fluorescent wheat germ agglutinin conjugates are often used as probes for the Golgi network in mammalian cultures. The specimen was also labeled with Alexa Fluor 488 conjugated to phalloidin and the nucleic acid stain SYTOX Orange, which target filamentous actin and DNA, respectively.