Embryology of the Respiratory Tract Flashcards
What are the lungs derived from?
- Primitive gut tube
What is the term used for the developing lungs?
Respiratory diverticulum
What is the direction of growth for the respiratory diverticulum?
Ventral
- Forward form both
What part of the gut tube is the oesophagus derived from?
- Mid-gut
How do the trachea and oesophagus separate?
- Tracheo-oesophageal septuplets which then forms them as two separate entities
Which week do the two lung buds begin to bifurcate?
- Week 6
- Origins of left and right lung
Name the opening of the respiratory diverticulum
Laryngeal orifice
- Changes from hole to T shape
- Above epiglottis and below trachea
What does the thyroid gland develop from?
Forman cecum
Describe the branching of the bronchi
- Dichotomous branching
- 2 sets on left lung and 3 sets on right
- Primary to secondary
What does dichotomous branching of bronchi mean for the size of lung?
- Lateral enlargement of the lung
- Pushes into the coelomic cavity
Describe the two layers of the coelomic cavity
- Visceral (inside)
- Parietal pleura (outside)
What is the name of epithelium derived from the foregut?
- Endoderm
What is the mesoderm?
(splanchnic)
- Muscles, cartilage, connective tissue
At what week does definite trachealis muscle develop?
- Week 13
What is the trachea-oesophageal fistula?
- False passage between two spaces
Describe oesophageal atresia
- 4 types
- No opening
What is the danger in oesophageal atresia types C, D and E?
- Direct connections to lungs
- Any milk swallowed goes directly to fill the lungs
- Needs surgical repair
What can atresia cause?
- Polyhydramnios- excess fluid in amniotic sac
- Foetus not swallowing the fluid- pre-term, respiratory distress
What does the diaphragm form from?
- Septum transversum- inferior to heart
- Pleuroperitoneal canals- connect primitive thorax from primitive abdomen
How does the septum transverses grow?
- Grows dorsally (backwards) cuts off peritoneal canals
What are the embryological components of the diaphragm?
- Front–> septum transversum
- Centrally –> oesophageal mesoderm peritoneal membrane
- Circumferentially –> body wall mesoderm
What is a diaphragmatic hernia?
- Improper meeting of septum transverses and peritoneal cavity (more on left) 80%
- Stomach and intestines herniate through opening into thorax
- Reduce space for lung and reduce diaphragmatic action
- Heart moved
What are the 4 stages of respiratory tract development?
- Pseudoglandular stage
- Canalicular stage
- Saccular stage
- Alveolar stage
Describe the pseudo glandular stage
- 5-17 weeks
- No development of respiratory bronchi
- At birth- no survival, only conducting tissue
Describe the canalicular stage
- 16-25 weeks
- Terminal sacs formed- limited respiration (cuboidal epithelium) possible if infant is born here
Describe the saccular stage
- 24 weeks- birth
- Alveolar sacs develop- increases SA
- Epithelium gets smaller
- Blood-air-barrier is thin
- Production of surfactant
Describe the alveolar stage
- Late foetal to age 8
- Formation of alveoli, type 1 pneumocystis, fusion of basal alumina between capillaries and type 1 cells
How many generations of dichotomous branching are there in uterine life?
- 17
How many generations of dichotomous branching are there after birth?
- 6
What is pulmonary hyperplasia?
- Incomplete development of the lungs
- Decreased number/size of segments/alveoli
- Respiratory function is low
Describe infant respiratory distress syndrome
- After 25 weeks- surfactant should be produced (phospholipid)
- Before birth lungs are normally filled with fluid- surfactant or amniotic
- If there is no surfactant- alveolar collapse/lung collapse and t2 pneumocystis failure
- Decreased SA–> Poor respiration
