Pulmonary Anatomy & Embryology (Wondisford) - 11/28/16 Flashcards
Lung Development
General Overview
How many stages?
Occurs in 5 stages:
- Embryonic (wks 4-7)
- Pseudoglandular (wks 5-16)
- Canalicular (wks 16-26)
- Saccular (wks 26-birth)
- Alveolar (wks 32-8 yrs)
Initial development:
- Respiratory bud comes off foregut:
- Development of lung bud from distal end of respiratory diverticulum during Week 4 [embryonic stage]
- Lung bud divides into 2 bronchial buds that branch off into bronchi
Important developments in each stage
-
Embryonic (wks 4-7)
- Lung bud → trachea → mainstem bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi
- Errors at this stage → TE (tracheoesophageal) fistula
-
Pseudoglandular (wks 5-16)
- Endodermal tubules → terminal bronchioles
- Surrounded by modest capillary network
- NO RESPIRATION, incompatible w life
-
Canalicular (wks 16-26)
- Terminal bronchioles → respiratory bronchioles → alveolar ducts
- Surrounded by prominent capillary network
- Airways increase in diameter
- RESPIRATION POSSIBLE AT 25 WKS
-
Saccular (wks 26-birth)
- Alveolar ducts → terminal sacs
- Terminal sacs separated by primary septae
- Pneumocytes develop
- Alveolar ducts → terminal sacs
-
Alveolar (wks 32-8 yrs)
- Terminal sacs → adult alveoli (due to secondary septation)
- In utero, “breathing” occurs via aspiration and expulsion of amniotic fluid → inc. vascular resistance through gestation
- At birth, fluid gets replaced with air → dec. in pulmonary vascular resistance
alveoli at birth vs. by 8 years
At birth: 20-70 million alveoli
By 8 yrs: 300-400 million alveoli
Congenital lung malformations (2)
Pulmonary hypoplasia
- Poorly developed bronchial tree
- Abnormal histology usually involving right lung
- Associated w congenital diaphragmatic hernia, bilateral renal agenesis (Potter Syndrome)
Bronchogenic cysts
- Caused by abnormal budding of foregut and dilation of terminal/large bronchi
- Discrete, round, sharply defined and air-filled densities on CXR
- Drain poorly
- Cause chronic infections
Pneumocytes
Type I cells vs. Type II cells vs. Club cells
Type I cells
- 97% of alveolar surfaces
- Line the alveoli
- Squamous; thin for optimal gas diffusion
- Collapsing pressure (P) = [(2*surface tension)/radius]
Type II cells
- Secrete surfactant → dec. alveolar surface tension, prevent alveolar collapse
- Dec. lung recoil
- Inc. compliance
- Cuboidal and clustered
- Precursors to type I cells and type II cells
- Type II cells proliferate during lung damage
Club cells
- Nonciliated
- Low-columnar/cuboidal with seretory granules
- Found in bronchioles, not alveoli
- Secrete component of surfactant
- Degrade toxins
- Act as reserve cells for bronchiolar epithelium
Pulmonary surfactant
Complex mix of lecithins (the most important = dipalmitoylphosphatidylcholine)
Synthesis begins around wk 26 of gestation
Mature levels achieved around wk 35
Prevents atelectasis (lung collapse) and increases lung compliance at low lung volumes
Neonatal respiratory distress syndrome
General description
Screening tests
Risk factors
Complications
Treatment
Therapeutic supplemental O2
SURFACTANT DEFICIENCY →
Inc. surface tension → alveolar collapse (“ground-glass” appearance of lung fields)
Screening tests for fetal lung maturity: lecithin-sphingomyelin (L/S) ratio in amniotic fluid
- >2 = healthy
- <1.5 predictive of NRDS
Risk factors:
- Prematurity
- Maternal diabetes (due to inc. fetal insulin)
- C-section delivery (dec. release of fetal glucocorticoids)
Complications:
- Metabolic acidosis
- PDA
- Necrotizing enterocolitis
Treatment:
- Maternal steroids before birth
- artificial surfactant for infant
Therapeutic supplemental O2 can result in (RIB):
- Retinopathy of prematurity
- Intraventricular hemorrhage
- Bronchopulmonary dysplasia
Respiratory Tree
Conducting zone vs. Respiratory zone
Conducting zone
- Large airways: nose, pharynx, larynx, trachea, bronchi
- Small airways: bronchioles → terminal bronchioles
- Large numbers in parallel → least airway resistance
- Warms, humidifies, filters air
- NO GAS EXCHANGE → “anatomic dead space”
- Cartilage and goblet cells extend to end of bronchi
- Pseudostratified ciliated columnar cells (bronchus epithelium) → extend to beginning of terminal bronchioles → transition to cuboidal cells
- Mucociliary escalator (clear mucus and debris from lungs)
- Airway smooth muscle cells extend to end of terminal bronchioles (sparse beyond this point)
Respiratory zone
- Lung parenchyma
- Consists of respiratory bronchioles, alveolar ducts, alveoli
- Cilia terminate in respiratory bronchioles
- Alveolar macrophages clear debris, participate in immune response
Lung lobe relations
- R lung = 3 lobes separated by oblique and horizontal fissures
- L lung = 2 lobes separated by oblique fissure + lingula (homolog of R middle lobe)
Which lung is the more common site for an inhaled foreign body?
Right lung b/c R main stem bronchus is wider and more vertical than left
If you aspirate a peanut…
- While upright → enters inferior segment of RLL (2)
- While supine → enters superior segment of RLL (6)
- Can also enter superior segment of LLL
Relation of pulmonary artery to the bronchus at each lung hilum
RALS (Right Anterior, Left Superior)
Diaphragm Structures
Structures perforating diaphragm
At T8: IVC
At T10: esophagus, vagus (CN 10; 2 trunks)
At T12: aorta, thoracic duct, azygos vein
I (IVC) ate (8) ten (10) eggs (esophagus) at (aorta) twelve (12)
Innervation of the diaphragm
C3, 4, and 5 (phrenic nerve)
Pain from diaphragm irritation (e.g. air, blood, pus in peritoneal cavity) can be referred to shoulder (C5) and trapezius ridge (C3, 4)
Common biFOURcations (3)
C4: common carotid
T4: trachea
L4: abdominal aorta
What structures grow medially and divide the pleural spaces from the pericardial cavity forming a definitive pericardial cavity?
Pleuropericardial folds
Folds come in from the side → heart becomes anterior to lungs
The pleural cavities are still open to the peritoneal cavity until diaphragm is fully formed.
What are the four parts of the diaphragm?
- Septum transversum
- Dorsal mesoderm
-
Pleuroperitoneal membranes
- Pair grow from posterior body wall, meet the septum transversum, close pericardioperitoneal canals, and form definitive pleural and peritoneal cavities
- Muscle from adjacent body wall that grows inward
What can cause a diaphragmatic hernia on the left?
Result?
Contraindication of treatment?
Defect most often occurs through failure of pleuroperitoneal membrane to form completely
Result: abdominal contents may herniate through → prevent normal development of the left lung
Contraindication of a bag mask to ventilate: air can enter small intestine → cause further shift of the heart to the R, compressing the R lung
(Harder to herniate through R side → liver on R)
Law of Laplace
P = 2T/r
Pressure in alveoli is directly proportional to tension and inversely proportional to radius.
Without surfactant, small alveoli generate more pressure (smaller radius) and “collapse” into large alveoli → decrease gas exchange
With surfactant, surface tension is reduced and collapse of smaller alveoli minimized.
What replaces goblet cells in bronchi?
Club cells in bronchioles
Rib cage movement
- Pump handle (AP dimension)
- Bucket handle (Lateral dimension)
Muscles of respiration
Quiet breathing vs. Exercise
Quiet breathing:
- Inspiration - diaphragm ONLY
- Expiration - passive
Exercise:
- Inspiration
- External intercostals
- Scalene muscles
- SCM
- Expiration:
- Rectus abdominis
- Internal and external obliques
- Internal intercostals
Pt experienced hoarseness for the past month. CXR reveals a mass at the aortopulmonary window.
Which nerve is most likely compressed?
Left recurrent laryngeal
Close proximity b/w aortopulmonary window and left recurrent laryngeal n.
