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Lung structure.
Structure of lungs, bronchi and pleura.
| Question | Answer |
|---|---|
| Where is the trachea situated? | Palpable anteriorly, above suprasternal notch. |
| What is the structure of the trachea? | C-shaped rings of hyaline cartilage supporting a fibro-elastic and muscular aair-transport tube. |
| Where does the trachea start and end? | Starts at C6, ends at T 4/5 (sternal angle) at carina. |
| What alters the tracheal diameter? | The trachealis muscle (posteriorly positioned). |
| How many lobes do the left and right lungs have? | The left has 2 lobes while the right has 3 lobes. |
| What is the structure of the bronchus? | Each lung has one bronchus. The right main bronchus is slightly more vertical, shorter and wider than the left. |
| Which lung is more likely to be entered by a foreign body? | The right lung because of its size and shape (bronchus of right lung is more vertical so easier for foreign bodies to travel straight down it). |
| How many secondary lobar bronchi does the left lung have? | 2. |
| How many secondary lobar bronchi does the right lung have? | 3. |
| How are the bronchi supplied with blood? | The bronchi are supplied with oxygenated blood via the bronchial arteries. |
| What do the lobar bronchi divide in? | Segmental bronchi. |
| What do the bronchi divide into? | Conducting bronchioles then terminal bronchioles and then respiratory bronchioles, decreasing in diameter and finally becoming alveoli. |
| What is the histology of the trachea? | Pseudostratified, ciliated, columnar epithelium, with goblet cells for mucous secretion. |
| What is the histology of the bronchi? | Pseudostratified, ciliated columnar epithelium, but the height is decreased (flattened) compared to the trachea. |
| What happens to the histology as the bronchi branch into the lungs? | The C-shaped cartilage rings are replaced by cartilage plates. |
| What is the histology of the bronchioles? | Very thin lumen <1mm in diameter. The epithelium changes to become ciliated columnar (thinner/flatter) and there is a surrounding band of smooth muscle. |
| What holds the bronchioles open? | The cartilage and glands disappear and the bronchiole is held open by the surrounding lung tissue. |
| What happens in the bronchioles in asthma? | The smooth muscle in the bronchioles may excessively narrow the lumen. |
| What is the histology in the terminal and respiratory bronchioles? | The epithelium becomes non-ciliated cuboidal (thinner and flatter) and goblet cells disappear). |
| What are alveoli? | The basic structural and functional unit of the lung where gaseous exchange takes place. |
| Where are the alveoli found? | They are found as outpocketings of respiratory bronchioles, alveolar ducts and alveolar sacs. |
| What separates the alveoli? | Separated by septae (alveolar wall) which is a thin membrane containing capillaries. The septae is the air-blood barrier for gas exchange. |
| What are pleura? | The membranes which cover/line the organs within the cavity as well as the cavity walls. |
| What is the pleural cavity? | The space between the layers of pleura. |
| What does the pleural cavity consist of? | It contains fluid to lubricate the pleural surfaces allowing for smooth, gliding movements between surfaces. |
| What does the visceral/pulmonary pleura refer to? | The pleura covering the lungs. |
| What is the parietal pleura? | The membranes which cover/line the cavity walls. |
| What are the layers of the pleura called? | Parietal (outside) and visceral (inside). |
| What separates the two lungs? | The mediastinum. |
| How is the shape of the left lung different to the right? | The left lung is slightly longer and narrower than the right lung, predominantly to make room for the heart and pericardium. |
| What is the name of the space that separates the superior and inferior lobes in the left lung? | The oblique fissure. |
| What is the top of a lung called? | The apex. |
| How is the lymph drained from the lung? | Via the sub-pleural plexus and a plexus alongside the bronchi to hilar lymph nodes. |
| How do the lungs make room for the heart? | The heart sits in the lingula. |
| What is the root of the lung called? | The hilum. |
| What is the hilum? | Allows structures (bronchus, pulmonary artery and pulmonary veins) pass into and out of the lung. |
| How does de-oxygenated blood enter the lungs? | Via the pulmonary arteries. |
| How does oxygenated blood leave the lungs? | Via the pulmonary veins. |
| How is the shape of the right lung different to the left lung? | The right lung is slightly wider but shorter than the left lung. |
| What causes the difference in shapes between the lungs? | Due to the diaphragm being higher on the right side. |
| What are the descending fissures in the right lung called? | Horizontal/transverse fissure and oblique fissure. |
| Where are the apex of the lung and pleura in relation to the clavicle? | Above the clavicle. |
| Where are the pleura and lungs in relation to the ribs? | The pleura extend down to the costal margin while the lungs end 2 rib spaces higher. |
| How is the thoracic cavity expanded? | Intercostal muscles between the ribs assist in respiration by expanding the thoracic cavity. |
| What do the intercostal muscles do? | They raise the ribs (pushing the sternum up as well), but may also act in forced expiration to help lower the ribs. |
| What is the structure of the diaphragm? | Muscular at its periphery, but tendinous centrally and it has left and right domes. |
| What happens to the diaphragm during inspiration? | The domes descend, causing negative intrathoracic pressure, but raising intra-abdominal pressure. |
| What is the nerve that supplies the diaphragm? | Motor and sensory supply is by the phrenic nerve. |
| What is a pneumothorax? | Occurs when air enters into the pleural cavity. |
| What does a pneumothorax result in? | A collapsed lung. |
| How is a collapsed lung treated? | The air must be removed to allow the lung to expand again: a needle is inserted just above the rib to avoid damage to the neurovascular bundle that runs just inferior to each rib. |