An organ system, (sometimes simply system), is a group of organs that work together to carry out a particular task. In humans and other animals, the organ systems are integumentary system, lymphatic system, muscular system, nervous system, reproductive system, urinary system, respiratory system, skeletal system, and immune system.
The respiratory system is an organ system associated with respiration (breathing) or gas exchange. In terrestrial vertebrates, the respiratory system is typically comprised of pharynx, larynx, bronchi, lungs and diaphragm. The lungs have about a million of alveoli (small air sacs) where gas exchange occurs. The lungs of birds though are different from most of the vertebrates. Their lungs do not expand or contract. Rather, they have air sacs throughout their body that act as the bellows ventilating the lungs. In humans and other mammals, the respiratory system is the respiratory tract. The upper part is comprised of nose, nasal cavities, sinuses, pharynx, and the part of the larynx above the vocal folds. The lower part consists of larynx, trachea, bronchi, bronchioles, and alveoli. The alveoli are rich in blood supply and allow a close contact with the blood to facilitate gas exchange. In aquatic vertebrates such as fish, the gills are the respiratory structure. In amphibians, the respiratory organs are the lungs and the skin.
In invertebrates, such as the arthropods, the respiratory organ is a gill-like structure called brachiostegal lung. The spiders and mites respire through their body surface. Larger spiders and scorpions have the so-called primitive book lung. Many insects have holes in the exoskeleton called spiracles, which they use for breathing.
- respiratory apparatus
- ventilatory system