Respiration : a systematic supply of oxygen

• The respiratory system is responsible for bringing in oxygen from the atmosphere, transferring it into the bloodstream for distribution, and the expulsion of carbon dioxide – a waste product of the respiration reaction – back to the atmosphere
• Organs involved in respiration : nose, mouth, nasal cavity, sinuses, pharynx, larynx, trachea, primary bronchi, secondary bronchi, bronchioles, alveoli, lungs
• Nose & mouth : air enters and leaves through these openings. Nose hairs help "capture" large particles
• Nasal cavity : divided into halves by the nasal septum. Lined by mucous membranes, which are continuous with the mucous membranes of the sinuses. The membrane is composed of pseudostratified epithelium, which has many goblet cells that secrete mucous to capture other particles. They are well vascularized so that incoming air is heated by the blood. The air is also moisturized by water evaporating from the mucous lining.
• Sinuses : air filled spaces in the skull, act as resonant chambers
• Pharynx : junction between nasal cavity, oral cavity, esophagus and trachea
• Larynx : the "voice box;" composed of cartilage and smooth muscle (vocal cords). The epiglottis is supported by the epiglottic cartilage, and it covers the triangular slit called the glottis. Vocal cords work by vibrating as air is forced past them.
• Trachea : is the cartilage-ribbed tube that extends into the lungs. It is ~2.5cm in diameter and ~12.5cm long. It is also lined, like the nasal cavity, with a ciliated pseduostratified epithelium, filled with goblet cells. It filters out scum that has escaped detection so far.
• Bronchial tree : consists of the branches from the trachea. The first two branches are the primary bronchi, which branch into the secondary bronchi, which divide and divide into smaller and smaller passageways, the smallest of which are bronchioles that end in alveoli, small air sacs where gas exchange takes place.
• Lungs : the "housing" of the bronchial tree. The visceral pleura is a serous membrane attached to each lung. It folds back to become a parietal pleura, lining the pleural cavity found between the two membranes. The cavity is filled with a thin film of serous fluid to reduce friction during breathing.