Anatomy and Physiology Notes: Respiratory System

Primary functions of the respiratory system
1. Provides oxygen for metabolism in the tissues
2. Removes carbon dioxide, the waste product of metabolism

Secondary functions of the respiratory system
1. Facilitates sense of smell
2. Produces speech
3. Maintains acid-base balance
4. Maintains body water levels
5. Maintains heat balance

Upper respiratory tract
1. Nose: Humidifies, warms, and filters inspired air

2. Sinuses: Air-filled cavities within the hollow bones that surround the nasal passages and provide resonance during speech

3. Pharynx
a. Passageway for the respiratory and digestive tracts located behind
the oral and nasal cavities
b. Divided into the nasopharynx, oropharynx, and laryngopharynx

4. Larynx
a. Located above the trachea, just below the pharynx at the root of
the tongue; commonly called the voice box
b. Contains two pairs of vocal cords, the false and true cords
c. The opening between the true vocal cords is the glottis.
d. The glottis plays an important role in coughing, which is the most
fundamental defense mechanism of the lungs.

5. Epiglottis
a. Leaf-shaped elastic structure attached along one end to the top of
the larynx
b. Prevents food from entering the tracheobronchial tree by closing
over the glottis during swallowing

Lower respiratory tract
1. Trachea: Located in front of the esophagus; branches into the right
and left main stem bronchi at the carina

2. Main stem bronchi
a. Begin at the carina
b. The right bronchus is slightly wider, shorter, and more vertical than the left bronchus.
c. The mainstem bronchi divide into secondary or lobar bronchi that enter each of the five lobes of the lung.
d. The bronchi are lined with cilia, which propel mucus up and away from the lower airway to the trachea, where it can be expectorated or swallowed.

3. Bronchioles
a. Branch from the secondary bronchi and subdivide into the small terminal and respiratory bronchioles

b. The bronchioles contain no cartilage and depend on the elastic recoil of the lung for patency.
c. The terminal bronchioles contain no cilia and do not participate in gas exchange.

4. Alveolar ducts and alveoli
a. Acinus (plural acini) is a term used to indicate all structures distal to the terminal bronchiole.
b. Alveolar ducts branch from the respiratory bronchioles.
c. Alveolar sacs, which arise from the ducts, contain clusters of alveoli, which are the basic units of gas exchange.
d. Type II alveolar cells in the walls of the alveoli secrete surfactant, a phospholipid protein that reduces the surface tension in the alveoli; without surfactant, the alveoli would collapse.

5. Lungs
a. Located in the pleural cavity in the thorax
b. Extend from just above the clavicles to the diaphragm, the major muscle of inspiration
c. The right lung, which is larger than the left, is divided into three lobes, the upper, middle, and lower lobes.
d. The left lung, which is narrower than the right lung to accommodate the heart, is divided into two lobes.
e. The respiratory structures are innervated by the phrenic nerve, the vagus nerve, and the thoracic nerves.
f. The parietal pleura lines the inside of the thoracic cavity, including the upper surface of the diaphragm.

g. The visceral pleura covers the pulmonary surfaces.
h. A thin fluid layer, which is produced by the cells lining the pleura, lubricates the visceral pleura and the parietal pleura, allowing them to glide smoothly and painlessly during respiration.
i. Blood flows through the lungs via the pulmonary system and
the bronchial system.

6. Accessory muscles of respiration include the scalene muscles, which elevate the first two ribs, the sternocleidomastoid muscles, which raise the sternum, and the trapezius and pectoralis muscles, which fix
the shoulders.


Respiratpry Process
a. The diaphragm descends into the abdominal cavity during inspiration, causing negative pressure in the lungs.
b. The negative pressure draws air from the area of greater pressure, the atmosphere, into the area of lesser pressure, the lungs.
c. In the lungs, air passes through the terminal bronchioles into the alveoli to oxygenate the body tissues.
d. At the end of inspiration, the diaphragm and intercostal muscles relax and the lungs recoil.
e. As the lungs recoil, pressure within the lungs becomes higher than atmospheric pressure, causing the air, which now contains the cellular waste products carbon dioxide and water, to move from the alveoli in the lungs to the atmosphere.
f. Effective gas exchange depends on distribution of gas (ventilation) and blood (perfusion) in all portions of the lungs