Anatomy of Alveoli and Lungs

The Alveoli

• Alveoli are small, grapelike clusters found at the end of each bronchiole, also known as air sacs
• They are responsible for the exchange of oxygen and carbon dioxide
• Each lung contains millions of alveoli

Lungs

• The lungs are the essential organs of respiration, located in the thoracic cavity
• The right lung has three lobes: superior, middle, and inferior
• The left lung has two lobes: superior and inferior, and is slightly smaller than the right lung due to the space taken up by the heart

The Pleura

• The pleura is a thin, moist, and slippery membrane that covers the outer surface of the lungs

Respiration

• Respiration is the exchange of oxygen and carbon dioxide that is essential to life
• A single respiration consists of one inhalation and one exhalation
• Inhalation occurs when the diaphragm contracts and pulls downward, causing the thoracic cavity to expand and drawing air into the lungs
• Exhalation occurs when the diaphragm relaxes, moving upward and causing the thoracic cavity to become narrower, forcing air out of the lungs
• Respiratory rate is the number of breaths taken in one minute, with a normal rate in healthy adults being roughly 12 to 20 breaths per minute

Functions of the Respiratory System

• Deliver air to the lungs
• Bring oxygen from the inhaled air into the blood for delivery to the body cells
• Expel the waste products returned to the lungs by the blood through exhalation
• Produce the airflow through the larynx that makes speech possible

Structures of the Respiratory System

• Upper respiratory tract: nasal cavity, paranasal sinuses, pharynx, and larynx
• Lower respiratory tract: trachea, lungs, bronchi, and bronchioles

Nose and Nasal Cavity

• The nasal cavity is the main route of air entry
• The nostrils are the external openings of the nose
• The nasal septum is a wall of cartilage that divides the nose into two equal sections
• Cilia filter incoming air to remove debris
• Olfactory receptors are nerve endings that act as the receptors for the sense of smell
• Mucous membranes line the nose and produce mucus to moisten, warm, and filter the air as it enters

Paranasal Sinuses

• Air-filled cavities lined with mucous membrane, located in the bones of the skull
• There are four nasal sinuses: maxillary, frontal, sphenoidal, and ethmoidal
• Functions of the sinuses include making the bones of the skull lighter, producing sound, and producing mucus to provide lubrication for the tissues of the nasal cavity

Pharynx

• The pharynx receives air after it passes through the nose or mouth, as well as food
• It is divided into three regions: nasopharynx, oropharynx, and laryngopharynx
• The nasopharynx is used only by the respiratory system for the transport of air and opens into the oropharynx
• The oropharynx is shared by the respiratory and digestive systems and transports air, food, and fluids downward to the laryngopharynx
• The laryngopharynx is shared by both the respiratory and digestive systems and continues downward to the openings of the esophagus and trachea

Larynx

• The larynx is a triangular chamber located between the pharynx and the trachea
• It contains the vocal cords
• During breathing, the cords are separated to let air pass
• During speech, they close together, causing the cords to vibrate against each other and produce sound as air is expelled from the lungs

Trachea, Bronchi, and Bronchioles

• The trachea is the tube located directly in front of the esophagus that extends from the neck to the chest
• The trachea divides into two primary bronchi, which then divide and subdivide into smaller bronchioles within the lung