9/11- Lung Embryology, Histology, Anatomy Flashcards
What are the main phases of lung development with their time periods?
- Embryonic (26 d - 5 wks)
- Pseudoglandular (6 - 16 wks)
- Canalicular (17-28 wks)
- Saccular (29 wks - birth)
- Alveolar (36 wks - 4 yrs)
What happens during the Embryonic phase (26 d - 5 wks)?
MAJOR AIRWAYS
LRT begins as a laryngotracheal diverticulum from primitive pharynx; major airways begin to form
What happens during the Pseudoglandular phase (6 - 16 wks)?
TERMINAL BRONCHIOLE
Major airways to the level of the terminal (membranous) bronchi
What happens during the Canalicular phase (17-28 wks) ?
PULMONARY ACINUS
Pulmonary acini and vascularization develop; by week 24 respiratory bronchioles form & respiration is possible, but chances of survival are slim
What happens during the Saccular phase (29 wks - birth)?
DISTAL AIRSPACES
Terminal sacs (alveolar ducts, alveoli) & adjacent lymphatic/capillary network develop, lined by type I & II pneumocytes; type II
What happens during the Alveolar phase (36 wks - 4 yrs)?
MATURE ALVEOLI
Newborn infant has only 1/6 to 1/8 of the adult number of alveoli; 95% of alveoli maturing after birth
When does surfactant reach adequate/functional levels?
2 weeks before birth
What is seen here?
7 week fetus (pseudoglandular): three lobes (left) & primitive tubular structure (right)
What is seen here?
18 week fetus (canalicular): pulmonary acini and vascular system form
What is seen here?
4 day old infant; resembles adult lung
What are the functions of the airways?
- Conduits for air
- Moisturizing and warming functions
- Evacuation of foreign material via mucociliary escalator
Where (what vertebral level) does the trachea branch into R/L main stem bronchi? What is this called?
Carina
- T4 - T5
Which main bronchi is longer/narrower? more vertical?
Left: longer, narrower
Right: more vertical
T/F: Aspirate material more frequently enters left vs. right lung
False! More into right (fatter, straighter)
How many lobar branches are there off the bronchi? Segmental bronchi?
Lobar bronchi: 3 on right, 2 on left
Segmental bronchi- 10 bronchopulmonary segments per lung
Describe bronchi histology
- Cartilaginous airways
- > 2 mm in diameter
- Cartilage in walls that prevent their collapse (circumferential rings/plates)
Adventitia: Cartilagionous plates (as opposed to C-shaped cartilage in trachea) Submucosa: mucous glands
Muscular mucosa
Mucosa
1. Lamina propria
2. Respiratory epithelium: pseudostratified, ciliated columnar epithelium (90%) and goblet cells, neurosecretory (Kulchitsky) cells, clara, basal, and brush cells
Describe bronchiole histology
- < 2mm in diameter
- Lack cartilage and submucosal glands
- No goblet cells
- Lined by simple rather than pseudostratified epithelium
Membranous (terminal) bronchioles:
- 0.5 - 1 mm
- smooth muscle wall
- lamina propria
- Ciliated cuboidal cells and nonciliated secretory (Clara) cells
Respiratory bronchioles:
- 0.15-0.2 mm
- have alveolar ducts and alveoli budding from their walls
- Cuboidal cells
- Epithelium and alveoli; no smooth muscle!
- +/- cilia along one side; alveoli along the other
- Give rise to alveolar ducts (composed only of alveoli)
- Forms part of pulmonary acinus
T/F: The right lung has 3 lobes while the left has 2
True
Which lobe does the lingula stem from?
Left upper lobe
Lungs are covered by what?
Visceral pleura
- Parietal pleura covers the thoracic wall
Define:
- Pneumonectomy
- Lobectomy
- Segmentectomy
- Wedge
Resection of:
- Pneumonectomy: entire lung
- Lobectomy: single lobe
- Segmentectomy: bronchopulmonary segment
- Wedge: less than a segment
What is a pulmonary lobule?
- Shape
- Airway components
- Clinical correlations
Smallest gross anatomic component
- Polygonal shape, 1-2 cm diameter
- Best visualized along pleural surface, bounded by connective tissue interlobular septa
- Each lobule contains 3-5 terminal bronchioles and up to 30 pulmonary acini
- Lobular architecture important for distinguishing major forms of emphysema
What is seen here?
Can easily see polygonal pulmonary lobules
- Can see pleural puckering from metastatic carcinoma
- Anthracosis (carbon pigment deposition)- especially around these septal units
What is seen here?
Normal lung
- Alveolar septa
- Clear alveolar spaces
Describe the trachea histology
Adventitia: C-shaped cartilage
Submucosa: mucous glands Muscular mucosa
Mucosa
- Lamina propria
- Respiratory epithelium: pseudostratified, ciliated columnar epithelium (90%) and goblet cells, neurosecretory (Kulchitsky) cells, clara, basal, and brush cells
What is the pulmonary acinus?
Functional unit of gas transfer (because lined by alveoli)
- Pulmonary acinus = R.B. + A.D. + Alveoli
Which epithelium is shown on the left? right?
Left: bronchiole epithelium
Right: tracheal and bronchi epithelium
Pick out the:
- Membranous bronchioles
- Respiratory bronchioles
- Alveolar ducts
What are the cells of the alveoli (and their histological characteristics/functions)?
Type I pneumocytes
- Flat squamous cells
- Cover ~ 95% of alvoelar surface
Type II pneumocytes
- Cuboidal cells that serve two functions:
1. main cell type involved in alveolar repair
2. source of surfactant
Alveolar macrophages
- Loosely attached to epithelial surface or free in alveolar space
- Phagocytic function
What is surfactant?
Phospholipid that decreases alveolar surface tension; facilitating alveolar expansion
Describe the content of alveolar interstitium
- Capillaries
- Elastic fibers
- Myofibroblasts (support alveolar framework)
What is the alveolar-capillary barrier?
Thinnest point for gas diffusion (0.2-2.5 um)
What is this?
Type I pneumocyte
What is this?
Type II pneumocyte
What are Pores of Kohn?
Develop after birth; connect adjacent alveoli
- Involved in collateral ventilation
- 13-21 per alveolus
What are Lambert’s canals?
Direct communication between airway (bronchiole) and adjacent alveoli
- Involved in collateral ventilation
T/F: the lung has a dual vascular supply?
True
What are pulmonary arteries?
Where do they come from? Where do the go?
Accompany airways to lung periphery
- Form capillary network around alveoli
- Bring deoxygenated blood from right side of heart
- About the same size of adjacent bronchiole
- Dual elastic lamina
What are bronchial arteries?
Where do they come from? Where do the go?
Systemic in origin arising from intercostal arteries and aorta
- Form plexus around trachea and bronchial wall as far as respiratory bronchioles
- Also supplies visceral pleura (supply nutrition to airways/lung)
What are pulmonary veins? (where do they go)
Return oxygenated blood to the heart
- Travel with interlobular septa
- Single elastic lamina
What are bronchial veins? (where do they go)
Deoxygenated blood to systemic circulation via azygos and intercostal veins
What is seen here?
Membranous bronchiole with accompanying arteriole
- “Bronchovascular channel”
- Observe that they’re about the same size
How to distinguish between pulmonary artery and vein?
Artery has two elastic lamina
What is seen here?
Left: pulmonary artery
Right; pulmonary vein
Describe the lymphatics of the lung
Two systems:
1. Superficial lymphatic drainage
- Present along pleural surface
2. Deep (intrapulmonary) lymphatic drainage
- Present adjacent to bronchovascular bundle and along interlobular septa
Connections exist between both forms of lymphatic drainage
What is seen here?
Membranous bronchiole with pulmonary artery (bronchovascular channel)
- Can see lymphatic channels (intraparenchymal)
What is seen here?
Lymphatic channels (filled with metastatic cancer)
(:
