gas exchange

• The need for specialised exchange surfaces arises as the size of the organism and its surface area to volume ratio increases
• In single-celled organisms, substances can easily enter the cell as the distance to be crossed is short, while in multicellular organisms, the distance is larger due to a higher surface area to volume ratio, requiring specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• Features of an efficient exchange surface include large surface area, thinness, and a good blood supply/ventilation to maintain a steep gradient
• The mammalian gaseous exchange system involves lungs with a large surface area located in the chest cavity, surrounded by the rib cage, and inflated by the ability to inflate
• The air enters through the nose and passes along the trachea, bronchi, and bronchioles, structures well adapted to enable the passage of air into the lungs
• Gaseous exchange takes place in the walls of alveoli, tiny sacs filled with air and surrounded by capillaries with a constant flow of blood to maintain the concentration gradient
• The trachea and bronchi are composed of several layers, mostly cartilage, glandular and connective tissue, elastic fibers, smooth muscle, and blood vessels
• Bronchioles are narrower than bronchi, with only the larger bronchioles containing cartilage, while the smallest bronchioles have alveoli clusters at the ends
• Structures and functions of the mammalian gaseous exchange system include cartilage, ciliated epithelium, squamous epithelium, goblet cells, smooth muscle, and elastic fibers