Respiratory System Anatomy

Respiratory System

• The respiratory system consists of tissues and organs that bring air to the gas exchange surface where oxygen is absorbed and carbon dioxide is released.
• The respiratory system can be divided into two parts: the upper respiratory system (nose, nasal cavity, paranasal sinuses, and pharynx) and the lower respiratory system (larynx, trachea, bronchi, and lungs).

Anatomy of the Respiratory System

• The respiratory tract can be divided into two parts: conducting portion (from nasal cavity to terminal bronchioles) and respiratory portion (respiratory bronchioles and alveoli) where gas exchange occurs.
• The respiratory system has six main functions: providing a gas exchange surface, moving air to and from the exchange surface, protecting respiratory surfaces from the environment, defending against invasion by pathogens, producing sound, and involvement in regulation of blood volume and pressure, and control of body pH.

Breathing (Pulmonary Ventilation)

• Inhalation (inspiration) draws gases into the lungs, and exhalation (expiration) forces gases out of the lungs.

Gas Conditioning

• As gases pass through the nasal cavity and paranasal sinuses, inhaled air becomes turbulent, warmed to body temperature, humidified, and cleaned of particulate matter.

Produces Sounds

• The larynx, nasal cavity, paranasal sinuses, teeth, lips, and tongue work together to produce sound, which allows for speech, singing, and nonverbal communication.

Provides Olfactory Sensations

• When airborne molecules are inhaled and dissolve in the mucus in the nose, they bind to receptors in the olfactory epithelium, allowing for the sensation of smell.

Protects the Body

• Hairs, twisted pathways, goblet cells, mucous glands, and lysozyme in the mucus help defend the body against infection by airborne pathogens.

Larynx (Voice Box)

• The larynx is a component of the respiratory tract, located in the anterior neck, suspended from the hyoid bone, and spanning between C3 and C6.
• The larynx is continuous inferiorly with the trachea and opens superiorly into the laryngeal part of the pharynx.
• The larynx is formed by a cartilaginous skeleton, held together by ligaments and membranes, and is divided into three sections: supraglottis, glottis, and subglottis.

Innervation of the Larynx

• The larynx receives both motor and sensory innervation via branches of the vagus nerve (CN X), including the recurrent laryngeal nerve and superior laryngeal nerve.

Vocal Cord Paralysis

• The vocal cords are responsible for the production of speech, and their movement is controlled by the intrinsic muscles of the larynx, which are innervated by the recurrent laryngeal nerve.
• Causes of recurrent laryngeal nerve palsy include apical lung tumor, thyroid cancer, aortic aneurysm, cervical lymphadenopathy, and iatrogenic (particularly during thyroid surgery).

The Tracheobronchial Tree

• The tracheobronchial tree consists of the trachea, bronchi, and bronchioles, which form a system of airways that allow passage of air into the lungs, where gas exchange occurs.
• The trachea marks the beginning of the tracheobronchial tree, arising as a continuation of the larynx and traveling inferiorly into the superior mediastinum, bifurcating at the level of the sternal angle (forming the right and left main bronchi).

Trachea

• The trachea is held open by cartilage, in C-shaped rings, and is lined by ciliated pseudostratified columnar epithelium, interspersed by goblet cells, which produce mucus.
• The combination of sweeping movements by the cilia and mucus from the goblet cells forms the functional mucociliary escalator, which traps inhaled particles and pathogens, moving them up out of the airways to be swallowed and destroyed.

Bronchi

• At the level of the sternal angle, the trachea bifurcates into the right and left main bronchi, which undergo further branching to produce the secondary bronchi.
• Each secondary bronchi supplies a lobe of the lung, and gives rise to several segmental bronchi.
• The right main bronchus is wider, shorter, and descends more vertically than its left-sided counterpart, resulting in a higher incidence of foreign body inhalation.

Bronchioles

• The segmental bronchi undergo further branching to form numerous smaller airways, called bronchioles.
• The smallest airways, bronchioles, do not contain any cartilage or mucus-secreting goblet cells, but instead, club cells produce a surfactant lipoprotein, which is instrumental in preventing the walls of the small airways from sticking together during expiration.
• Bronchioles eventually end as terminal bronchioles, which branch further into respiratory bronchioles, distinguishable by the presence of alveoli extending from their lumens.

Alveoli

• Alveoli are tiny air-filled pockets with thin walls (simple squamous epithelium), and are the sites of gaseous exchange in the lungs.
• There are approximately 300 million alveoli in adult lungs, providing a large surface area for adequate gas exchange.

Lungs

• The lungs are the organs of respiration, responsible for oxygenating blood.
• The lungs lie either side of the mediastinum, within the thoracic cavity, and are surrounded by a pleural cavity, which is formed by the visceral and parietal pleura.
• Each lung is divided into lobes, with the right lung having superior, middle, and inferior lobes, and the left lung having superior and inferior lobes.

Vasculature

• The lungs are supplied with deoxygenated blood by the paired pulmonary arteries, and once the blood has received oxygenation, it leaves the lungs via four pulmonary veins (two for each lung).

Pulmonary Embolism

• A pulmonary embolism refers to the obstruction of a pulmonary artery by a substance that has traveled from elsewhere in the body, resulting in a reduction in lung perfusion, decreased blood oxygenation, and accumulation of blood in the right ventricle of the heart.
• The most common emboli are thrombus, fat, and air, and treatment involves anticoagulation and thrombolytic therapy.

Pleurae

• The pleurae refer to the serous membranes that line the lungs and thoracic cavity, permitting efficient respiration.
• There are two pleurae in the body, one associated with each lung, each divided into two parts: visceral pleura (covers the lungs) and parietal pleura (covers the internal surface of the thoracic cavity).

Mediastinum

• The mediastinum is a visceral compartment of the thoracic cavity, completely separating the two pleural cavities by being placed longitudinally between them.
• The mediastinum extends from the superior thoracic aperture to the diaphragm, and its main contents are the heart, esophagus, trachea, thoracic nerves, and systemic blood vessels.
• The mediastinum can be split into the superior and inferior mediastinum.