Normal Lung, Congenital Abnormalities, Acute Lung Injury, and RDS Flashcards
How are the bronchi structurally distinct from the bronchioles?
Bronchi have submucosal glands and cartilage.
Bronchioles do not
In the primary bronchi, what are the layers from lumen –> cartilage?
Lumen Pseudostratified columnar epithelium Lamina propria Muscularis Submucosa (with glands) Cartilage
Describe the normal sequence from terminal bronchioles –> alveoli?
Terminal bronchioles Respiratory bronchioles Alveolar duct Alveolar sac Alveoli
What is the main function of type I pneumocytes?
Gas exchange
What is the main function of type II pneumocytes?
Surfactant production
Can divide and regenerate type I cells in cases of injury
What is the main function of the mucociliary escalator?
Goblet cells secrete mucus and cilia rhythmically beat upwards to push mucus out of airway
Reaches as far down as the respiratory bronchioles
What might be a cause of lung agenesis or hypoplasia?
Oligohydramnios (kidney agenesis) –> low amniotic fluid –> bad lung development
Could also result from decreased intrathoracic space
What are Bronchogenic cysts?
Foregut buds that become disconnected from the tracheobronchial tree, enlarge over time, and form a cystic mass
What is CCAM? What is seen on gross imaging of lungs? Histology?
Congenital Cystic Adenomatoid Malformation
See multiloculated cysts all over the lungs, replacing the entire lobes
The alveoli are lined by epithelium more similar to bronchiole epithelium (much thicker)
What is pulmonary sequestration? What are the consequences of this happening?
Discrete mass of lung tissue without connection to the airway system
May be intralobar or extralobar
Lots of mucus will plug up the mucosa
Inflammation
Recurrent respiratory infections
What are some causes of atelectasis in adults?
Resorption
Compression
Contraction
Describe Resorption Atelectasis
Some obstruction in the respiratory tract blocks some alveoli. That part of the lung resorbs inward and shrinks.
Mediastinum shifts TOWARDS the affected lung
Describe Compression Atelectasis
Something in the pleura (air, effusion) is compressing the lung space
Mediastinum shifts AWAY from the affected lung
Describe Contraction Atelectasis
Lung parenchyma is destroyed and you get fibrosis of the lung
Describes the different types and the pathophysiology of Pneumothorax
Could be spontaneous or traumatic
Causes compression, collapse, and atelectasis, leading to respiratory distress
If a solid object is aspirated, which bronchus is is most likely to fall down? Which lobe is it likely to end up in?
Likely to fall down R mainstem bronchus and lodge in the R lower lobe
What is the most common cause of pulmonary edema?
L sided heart failure
What is the normal weight of a lung?
350-450 g
What does pulmonary edema look like on histology?
All the normal air spaces are pink with fluid. Vessels are highly congested
What are the three main characteristics of acute lung injury (non-cardiogenic pulmonary edema)?
- Acute onset dyspnea
- Hypoxemia
- Bilateral pulmonary infiltrates in absence of cardiac failure
What is ARDS?
Acute Respiratory Distress Syndrome
Rapid onset of life threatening respiratory insufficiency
Cyanosis
Severe arterial hypoxemia
May progress to organ failure
List the common causes of ARDS
A- Aspiration, Acute Pancreatitis, Air/Amniotic fluid embolism
R- Radiation
D- DIC, drugs, drowning
S- Sepsis, shock, smoke inhalation
How do you treat ARDS?
Treat the cause and give the patient symptomatic management
ARDS is a clinical term. What do pathologists say to describe the same phenomenon?
DAD = Diffuse Alveolar Damage
Describe the pathogenesis of Acute Lung Injury
Macrophages enter, release TNF and IL-8.
PMNs are recruited, they degranulate, producing proteases and leukotrienes.
Causes injury to endothelial cells, leading to protein leakage in the alveolar space.
Hyaline membrane forms
How does ARDS appear on histological stain?
Hyaline membrane formation around the alveolar spaces (smudgy pink crayon appearance)
Septa are widened
How does ARDS progress over time?
Over time, progresses to a late proliferative and a fibrotic stage
What is the primary cause of neonatal respiratory distress syndrome?
Deficient surfactant production
What are some predisposing factors to neonatal RDS?
Prematurity
Maternal diabetes
C-section
What is the main function of surfactant?
Reduce surface tension in the alveoli, keeping them inflated
About when should the fetus be producing sufficient amounts of surfactant?
34 weeks gestation
How can surfactant production be measured prenatally?
Look at the amniotic fluid L:S (lethicin:sphingomyelin) ratio
Above 2:1 means the baby is ready for delivery
Describe the pathogenesis of Neonatal RDS
No surfactant production leads to atelectasis. V/Q mismatch in the lung will cause pulmonary vasoconstriction. Leads to hypoxia and acidosis.
Endothelial and epithelial damage occur, leading to plasma leak and buildup of hyaline membranes
How does maternal diabetes affect neonatal RDS?
High glucose levels lead to high insulin production from the fetal pancreas, which may decrease surfactant production
How do glucocorticoids affect neonatal RDS?
Babies delivered by C section are not subjected to the stress (and glucocorticoid release) associated with vaginal delivery. The glucocorticoids increase production of surfactant, so babies delivered by C section do not have that stimulus to make more surfactant
How do you treat neonatal RDS?
Best to prevent it by delaying delivery as long as you can to allow for fetal lung maturity. Once the infant is born, you can give exogenous surfactant to treat
What is Acute Interstitial Pneumonia? When is it diagnosed?
You cannot diagnose this disease until you have ruled out all other causes.
Has the same histology and clinical features as acute ARDS
