Air passes from our nostrils into the throat (pharynx), down through the opening of the vocal cords (glottis), into the windpipe (trachea), passing through the left and right bronchi. The bronchi in turn branch into smaller branches called branchioles which finally terminates in small sac like structures of the lungs called alveoli. Only in the alveoli does actual gas exchange takes place.
Nose and Pharynx
Within the nose inhaled air is conditioned by warming and moistening. Hairs and hairlike structures called cilia trap dust particles and purify the air. The nasal chambers open into a cavity at the rear of the mouth called the throat (pharynx). Tonsils and adenoids are pockets of lymphatic tissue inside the pharynx which trap and filter microorganisms.Trachea
After passing through the pharynx, air passes through the opening of vocal cords (glottis) down to the windpipe (trachea). A thin flap of tissue called the epiglottis folds over the opening during swallowing and prevents food from entering the trachea. |
| human respiratory system |
The trachea has smooth muscle and rings of cartilage that maintain its structure and prevent it from collapsing. At its lower end, the trachea branches into two large bronchi. Both left and right bronchi also have smooth muscle and cartilage rings. The right bronchi is usually more straight than the left one, making it easier for aspirated food or foreign material to enter it. The bronchi then branch into smaller bronchioles, forming a bronchial tree before they eventually terminate in the air sacs known as alveoli.
Lungs
Human lungs are composed of approximately 300 million alveoli, which are small sac like structures that are surrounded by a network of capillary blood vessels. Oxygen can pass through the alveoli walls and enters the red blood cells inside the capillaries to bind with hemoglobin. In exchange, carbon dioxide leaves the capillaries and enters the alveoli.When a person inhales, the rib muscles and diaphragm contract to increase the volume of the chest cavity. This increase leads to reduced air pressure in the chest cavity, and air rushes into the alveoli, forcing them to expand and fill. During exhalation, the rib muscles and diaphragm relax, the chest cavity area diminishes, and the internal air pressure increases. The compressed air forces the alveoli to close, and air flows out.
Normally an adult person breathes 12-20 times per minutes. Breathing rate is determined by the amount of carbon dioxide in the blood. A high carbon-dioxide concentration leads to an increased breathing rate and the person will feel short of breath.
