Tracheobronchial Tree Anatomy

• Air passageways decrease in size but increase in numbers as they branch in the tracheobronchial tree.
• Cartilage rings are replaced with cartilage plates, which are then replaced with smooth muscle as branching occurs.

Tracheobronchial Tree Parts

• Trachea: the "trunk" of the tree.
• Carina: first bifurcation with a sensitive membrane that initiates a cough reflex; 16-18 branches past the Carina.
• Primary (main) bronchi: first branch past the carina, leading into the left and right lungs.
• Secondary (lobar) bronchi: second branch, splitting to serve each of the lobes (3 on the right, 2 on the left).
• Tertiary (segmental): third branch; 9-10 branches within each lobe
• Bronchioles: smaller branches supplied by nerves and bronchial blood vessels.
• Terminal bronchioles: endpoint of the conducting system, surrounded by smooth muscle for air control into gas exchange.

Respiratory Zone

• Respiratory bronchioles: first area of gas exchange.
• Alveolar ducts: "hallways" with alveoli sticking out.
• Alveolar sacs: main gas exchange areas, multiple alveoli bunched together like grapes to create a high surface area.
• Alveoli: structures in contact with pulmonary capillaries for gas exchange, which change in size during ventilation.

Alveoli Details

• Pulmonary capillaries: branch off the pulmonary artery to associate closely with the alveolar sacs.
• Elastic fibers: surround the alveoli for recoil.
• Connective tissue: layer associated with visceral pleura surrounds the alveoli.

Alveoli Main Cell Types

• Type I pneumocyte: simple squamous epithelium that creates a thin layer for gas exchange.
• Type II pneumocyte: larger, cube-shaped cells that secrete alveolar fluid that line alveolar lumen.
• Macrophages (dust cells): wandering cells that remove dust and debris.
• Alveolar epithelium: made of type I and II pneumocytes

Respiratory Membrane

• The layers that gas must pass through to reach the blood, very thin overall
• Alveolar fluid: surfactant-containing fluid produced by type II pneumocytes.
• Alveolar epithelial cells: thin simple squamous cells.
• Alveolar basement membrane: stabilizes alveolar epithelial cells.
• Interstitial space: small region.
• Capillary basement membrane: stabilizes capillary epithelial cells.
• Capillary endothelium: epithelial cells facing the capillary lumen.

External Lung Features

• Base: inferior, sits on top of the diaphragm and is concave.
• Apex: superior, near the clavicle, and pointy.
• Hilum: region on the medial surface where external structures enter the lung.
• Root of the lung: hilum and entering structures (bronchi, pulmonary blood vessels).
• Right lung: has three lobes (superior, middle, and inferior).
• Horizontal fissure: separates the superior and middle lobes.
• Oblique fissure: separates the superior and inferior lobes.
• Left lung: has two lobes (superior, inferior), allowing space for the heart.
• Oblique fissure: separates the superior and inferior lobes.
• Cardiac impression: carved-out shape of the heart on the medial side.
• Cardiac notch: indentation on the anterior side to accommodate the heart.

Thoracic Cavity Layers

• Parietal pleura: serous membrane adhering closely to the thoracic wall.
• Pleural cavity: filled with pleural fluid to reduce friction when the lung moves and creates a suction effect.
• Visceral pleura: serous membrane adhering closely to the lungs.

Lung Volumes measurements

• Spirometer: measures volume of air inspired and expired (mL) in a given amount of time.
• Tidal volume: 500 mL, volume breathed during quiet ventilation.
• Inspiratory reserve volume: 3.1 L, difference between tidal volume and maximum inspiration.
• Maximum inspiration: maximal amount of air held by lungs.
• Expiratory reserve volume: 1.2 L, difference between tidal volume and maximum expiration.
• Maximum expiration: biggest exhale possible (must recruit muscles), even at this point, the lungs are not completely empty.
• Residual volume: 1.2 L, volume of air leftover after maximum expiration to prevent collapse.

Lung Capacities

• Lung capacities: sum of multiple lung volumes.
• Total lung capacity: 6 L, all volumes added together.
• Vital capacity: 4.8 L, total minus residual, or the difference between maximum inspiration and expiration.
• Inspiratory capacity: 3.6 L, tidal volume + inspiratory reserve, the total the volume you can breathe in.
• Functional residual capacity: 2.4 L, residue volume + expiratory reserve volume in lungs

Ventilation Details

• Minute ventilation: 6000 mL/min, total air moved into and out of the respiratory system per minute.
• Respiratory rate: 12/min, number of breaths per minute.
• Alveolar ventilation (V_A): volume of air available for gas exchange using (tidal volume minus anatomic dead space) * respiratory rate.
• Anatomic dead space: 150 mL, conducting zone (where no gas exchange can take place).