Part One

1. The cardiovascular and respiratory systems share responsibility for supplying the body with oxygen and disposing of carbon dioxide. The respiratory organs oversee the gas exchanges that occur between the blood and the external environment.

2. The organs of the respiratory system include the nose, pharynx, larynx, trachea, bronchi, and the lungs. Since gas exchanges with the blood happen only in the alveoli, the other structures are really just conducting passageways that allow air to reach the lungs.
However, they purify, humidify, and warm incoming air.

3. During breathing, air enters the nose by passing through the external nares, or nostrils. The olfactory receptors for the sense of smell are located in the mucosa, in the slitlike superior part of the nasal cavity, below the ethmoid bone.

3. (continued) The function of the respiratory mucosa is to warm the air as it flows past. In addition, the sticky mucus produced by the mucosa’s glands moistens the air and traps incoming bacteria and foreign debris.

4. The nasal cavity is surrounded by a ring of paranasal sinuses, located in the frontal, sphenoid, ethmoid, and maxillary bones. They produce mucus, which drains into the nasal cavities.

5. The pharynx, commonly called the throat, serves as a common passageway for food and air.

6. If the pharyngeal tonsils become inflamed and swollen, it forces the person to breathe through the mouth.
In this situation, air is not properly moistened, warmed, or filtered before reaching the lungs.

7. The larynx, or voice box, is formed by 8 rigid hyaline cartilages and a spoon-shaped flap of elastic cartilage called the epiglottis. The epiglottis protects the superior opening of the larynx. When we swallow, the larynx is pulled upward and the epiglottis tips, forming a lid over the larynx.
This routes food into the esophagus posteriorly.

8. If anything other than air enters the larynx, a cough reflex is triggered to expel the substance and prevent it from entering the lungs.

9. The trachea is lined with ciliated mucosa. The cilia beat continuously and in a direction opposite to that of incoming air. They propel mucus away from the lungs to the throat, where it can be swallowed or spat out.

10. The trachea is rigid because its walls are reinforced with c-shaped rings of hyaline cartilage. The solid portions of the rings support the trachea walls and keep it patent, or open, in spite of the pressure changes that occur during breathing.

11. The right and left primary bronchi are formed by the division of the trachea. The right primary bronchus is wider, shorter, and straighter than the left.

12. Each lung is divided into lobes by fissures. The left lung has 2 lobes, and the right lung has 3 lobes.

13. The surface of each lung is covered with a visceral serosa called the pulmonary, or visceral, pleura, and the walls of the thoracic cavity are lined by the parietal pleura. These pleural membranes produce pleural fluid, which allows the lungs to glide easily over the thorax wall during breathing movements and causes the pleural layers to cling together.

14. After the primary bronchi enter the lungs, they subdivide into smaller and smaller branches (bronchii), finally ending in the smallest of the conducting passageways, the bronchioles.

15. The terminal bronchioles lead into respiratory zone structures, even smaller conduits that eventually terminate in alveoli.

16. The respiratory zone is the only site of gas exchange. All other respiratory passages are conducting zone structures, which serve as conduits to and from the respiratory zone.

17. The walls of the alveoli are composed largely of a single, thin layer of squamous epithelial cells.
The external surfaces of the alveoli are covered with a “cobweb” of pulmonary capillaries.

18. Gas exchanges occur by simple diffusion through the respiratory membrane. Oxygen passing from the alveolar air into the capillary blood and carbon dioxide leaving the blood to enter the gas-filled alveolus.