Describe the structure of a mammalian respiratory system. Include in your discussion the mechanisms of inspiration and expiration.

Describe the structure of a mammalian respiratory system. Include in your discussion the mechanisms of inspiration and expiration.

From the nasal cavity and pharynx inhaled air passes through the larynx, trachea, and bronchi to the bronchioles, which end in microscopic alveoli lined by a thin, moist epithelium. branches of the pulmonary arteries convey oxygen poor blood to the alveolar, branches of the pulmonary veins transport oxygen rich blood from the alveoli back to the heart. Air enters through the nostrils and is then filtered by hairs warmed, humidified, and sampled for odors as it flows through a maze of spaces in the nasal cavity. As the external intercostals & diaphragm contract, the lungs expand. The expansion of the lungs causes the pressure in the lungs (and alveoli) to become slightly negative relative to atmospheric pressure. As a result, air moves from an area of higher pressure (the air) to an area of lower pressure (our lungs & alveoli). During inspiration Diaphragm and intercostal muscles contract. The diaphragm moves downwards. The intercostals muscles make the rib cage move upwards. These two processes increase the volume of the thoracic cavity and also reduces the air pressure to below atmospheric pressure allowing air to rush into the airways then into the alveoli. Expiration is the opposite of inspiration as in the diaphragm and intercostal muscles relax, this allows the diaphragm to move upwards and the intercostal muscles let the rib cage relax to its resting state. The volume within the thoracic cavity now decreases. This decrease in volume now causes an increase in pressure above atmospheric pressure which forces air out up the airway.