The reconstructions have better contrast and signal-to-noise ratio (there’s less unwanted information). But 3-D histological serial section reconstruction (building up a picture from thin slices of tissue) remains a very important technique. There are other modern 3-D reconstruction methods that are faster, cheaper and easier to use. We stained and mounted them onto glass slides, photographed sections and aligned the images for reconstruction using open-source software. We cut 2,689 serial sections of a chicken lung at a thickness of 8 micrometres (each micrometre is one millionth of a metre). We used the method on a chicken lung because this is the model animal for study of the biology of birds. Because it takes time, a lot of materials and specialised skills, it’s not often used in biological studies. 3-D reconstructionģ-D reconstruction entails preparing a spatial model of a structure from 2-D images. Our 3-D serial section reconstruction supplied new details and underscored the value of the technique for investigating complex biological structures. This maintains a high pressure that drives oxygen into the blood circulating across the lung. ![]() During every respiratory cycle, the air in the lung is replaced with “clean” air. The lungs are ventilated continuously and in one direction (from back to front) with “fresh” air by coordinated actions of the very large air sacs. The design of the bird’s lungs forms a highly efficient gas exchange system with large functional reserve. The compact entwining of the capillaries increases respiratory surface area while minimising the thickness of the blood-gas barrier. We were able to get a much clearer view of the shapes and connections of the air capillaries and blood capillaries in the lung. The various branches of the airway system do not interconnect and neither do the branches of the blood system. John Ndegwa Mainaģ-D reconstruction showed us that the airways and blood vessels track each other and supply specific parts of the bird’s lung. Plate 1: airways, arteries and veins of the fowl lung. ![]() More recently, 3-D reconstruction methodologies have revolutionised various fields of biology. In the late 1970s, the South African-born Nobel prize winner Sydney Brenner was the first to apply computing to reconstruct series of sections. The approachįor hundreds of years, scientists could only study biological structures in two dimensions – sections of tissue were placed under a transmission microscope. We were then able to see what makes the bird lung so efficient at taking up the oxygen needed to release energy – key to survival. Because they are so small and so tightly entangled with each other, it wasn’t possible to see their shapes and connections clearly until we used 3-D reconstruction. Using this technique showed us that the tiny structures (air- and blood capillaries) between which oxygen is exchanged are not the shape they were long thought to be. Three-dimensional (3-D) serial section computer reconstruction is one of them. To explore these aspects of the avian lung, my colleagues and I have used a variety of techniques. They relate to how the airways and blood vessels are shaped, arranged and connected, and how air flows around the lung. ![]() Flying uses a huge amount of energy and some birds fly nonstop over very long distances or at very high altitudes where there is little oxygen.Įven after extensive study, questions about the bioengineering of the avian respiratory system have persisted. Their lungs are what allows birds to fly. ![]() They are structurally very complex and functionally efficient. One of the aspects of bird biology that has long interested scientists is their lungs. Biology explains why animals behave the way they do and what threatens their survival. Knowledge of bird biology and their place in ecosystems contributes to devising conservation efforts. BirdLife International’s State of the World’s Birds Report for 2022 says that about half of all bird species are decreasing and more than one in eight of them are at risk of extinction. Since they can easily escape from unsuitable habitats, birds are important “sentinel” animals: the number and diversity of species indicates environmental health. Birds feature prominently in the history of painting, poetry, commerce and music. They have also shaped the advancement of human societies culturally, philosophically, artistically, economically and scientifically. As predators, pollinators, seed dispersers, scavengers and ecosystem bioengineers, the world’s 11,000 species of birds play critical roles in the food chain and therefore the existence of animal life.
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