Respiratory System Anatomy Quiz

Anatomy of the Lungs

• Lungs are located in the lateral parts of the thoracic cavity.
• Each lung is surrounded by pleura.
• Right lung has 3 lobes; left lung has 2 lobes.
• Each lung receives a main bronchus, one pulmonary artery, and two pulmonary veins.
• These structures subdivide within the lung.
• Lungs also receive nerves and lymphatics.
• The root of the lung is where the lung connects to the trachea and heart.
• The hilum of the lung is where the bronchi and pulmonary vessels enter.
• The lung conforms to the thoracic cavity's shape; its costal surface is convex, and the diaphragmatic and mediastinal surfaces are concave.
• The apex of the lung extends about 2.5cm above the clavicle.

The Principal Bronchi

• The right main bronchus is shorter, wider, and more vertical than the left.
• Inhaled foreign objects are more likely to enter the right lung due to this structure.
• Before entering the right lung's hilum, the right main bronchus branches off into a superior lobar bronchus.
• Upon entering the hilum, it further divides into middle and inferior lobar bronchi.
• The left main bronchus is narrower, longer, and more horizontal.
• It is located below the arch of the aorta and divides into a superior and inferior lobar bronchus.

The Bronchial Tree

• The trachea branches into the right and left main bronchi.
• The main bronchi further divide into lobar bronchi, and then segmental bronchi.

Lobes and Fissures

• The right lung is slightly larger than the left lung.
• The right lung is divided into 3 lobes by oblique and horizontal fissures.
• The horizontal fissure runs horizontally across the fourth costal cartilage.
• The oblique fissure runs from the inferior border to the posterior border of the lung.
• The left lung is divided into 2 lobes by an oblique fissure.

The Bronchopulmonary Segments

• These are the anatomical, functional, and surgical units of the lung.
• Each lobe is supplied by a lobar bronchus.
• A lobar bronchus divides into segmental bronchi, supplying the bronchopulmonary segments.
• Each bronchopulmonary segment has connective tissue, a segmental bronchus branch, and pulmonary vein/artery tributaries.
• The segments are pyramidal in shape, with the apex towards the lung root.

The Bronchioles

• Segmental bronchi repeatedly divide, becoming smaller.
• They lose their cartilage and become bronchioles.
• Bronchioles are less than 1mm in diameter.
• They lack cartilage and are lined with a ciliated columnar epithelium.
• Bronchioles contain smooth muscle fibers.
• Bronchioles develop into terminal bronchioles and eventually respiratory bronchioles, where gas exchange begins.

The Bronchioles (continued)

• As bronchioles get smaller, the epithelium becomes simple ciliated columnar.
• Goblet cells decrease, and cartilage is absent.
• There’s a thickening of smooth muscle.
• Very small bronchioles have a simple cuboidal epithelium.

The Bronchopulmonary Segments (continued)

• Respiratory bronchioles branch into alveolar ducts leading to alveolar sacs.
• Alveoli are chambers lined by simple squamous epithelium, facilitating gas exchange between air and capillaries.

The Lung Hila

• Lung hila are at the level of the 3rd and 4th costal cartilages and at T5, T6, and T7.
• The hila contain the entrances for pulmonary vessels, bronchi, lymphatics, and nerves.
• Right hilum is grooved by azygos vein and superior vena cava.
• Left hilum is grooved by the aorta, aortic arch, and subclavian vessels.

Nerve supply to Lungs

• Autonomic nerve fibers (sympathetic and parasympathetic) form pulmonary plexuses at the hila.
• The plexuses divide into anterior and posterior plexuses.
• Parasympathetic nerves induce cough reflexes and cause bronchoconstriction and vasodilation.
• They also stimulate mucous glands.
• Sympathetic nerves cause bronchodilation and vasoconstriction.

Lymphatic Drainage

• Lymphatic drainage occurs via superficial and deep plexuses.
• Draining onto bronchopulmonary lymph nodes, then tracheobronchial nodes.
• Drainage continues via the bronchomediastinal lymph trunk.

The Trachea

• The trachea is approximately 10 cm long and 2.5cm in diameter (15cm during inspiration)
• It's a fibrous tube with U-shaped cartilage rings.
• The posterior free ends of the incomplete cartilage rings are joined by trachealis muscle.
• It begins at the level of the cricoid cartilage of the larynx.
• It terminates at the level of the sternal angle (T4/5), where it divides into the right and left main bronchi.
• Lined by pseudostratified ciliated columnar epithelium.

The Trachea (continued: Relations)

• Posterior: Esophagus
• Anterior: Sternum and Thymus, Left Brachiocephalic vein, Aortic arch and its branches
• Right Side: Azygos Vein, Right Vagus
• Left Side: Aortic arch, Left common carotid and left subclavian arteries, Left vagus and left phrenic nerves

The Pleurae

• Pleura comprises two layers – parietal and visceral – surrounding the lungs.
• Parietal pleura lines the thoracic cavity, diaphragm, mediastinal surfaces, and cervical pleura.
• Visceral pleura covers the outer surfaces of the lungs and extends into the interlobar fissures.
• The two layers meet at the hilum, forming the pulmonary ligament.

The Pleurae (continued)

• The pleural cavity is a potential space between the parietal and visceral pleura, containing pleural fluid.
• Types of parietal pleura: cervical, diaphragmatic, mediastinal.
• Recesses: costodiaphragmatic and costomediastinal.

The Alveoli

• Respiratory bronchioles branch into alveolar ducts and sacs.
• Alveoli contain simple squamous epithelium to facilitate gas exchange.

Alveolar Cells

• Type I pneumocytes form the majority (90%) of the alveolar surface, are thin, and form the blood-air barrier.
• Type II pneumocytes (septal cells) are cuboidal, secrete surfactant, and are important for maintaining alveoli stability.
• Macrophages/dust cells remove foreign particles from the alveoli.

Pulmonary Surfactant

• Surfactant is a phospholipid and protein fluid.
• It decreases surface tension in alveoli, helping them inflate during inspiration.
• It prevents collapse during expiration.
• Secreted constantly and removed by type I pneumocytes and macrophages. A key component dipalmitoylphosphatidylcholine (DPPC).

Bronchopulmonary Segments (continued: Specific Segment Names)

• Segments are listed by lung and lobe in a specified order by the notes.

Blood-Air Barrier

• Thin layer of surfactant.
• Cytoplasm of Type I pneumocytes.
• Basement membrane of pneumocytes.
• Connective tissue.
• Basement membrane of capillary endothelial cells.
• Cytoplasm of endothelial cells.

The Lung in Disease (Examples)

• Pleural effusions involve fluid accumulation in the pleural cavity.
• Lobar pneumonia exhibits lung inflammation.
• Pneumothorax involves air in the pleural space, collapsing the lung.
• Lung malignancy (cancer) involves cancerous growth in the lung.
• Chronic Obstructive Pulmonary Disease (COPD) is characterized by chronic lung inflammation and damage (often connected to smoking).