Respiratory Embryology Flashcards
Describe the origin of the lung bud
Develop from the ENDODERM (lining of larynx, trachea, bronchi and lungs)
All other lung tissue (cartilaginous, connective and muscular tissue components of the trachea and lungs) are of MESODERM origin
Describe the communication between respiratory and digestive tracts in the adult and how this changes
Initially, lung bud is in open communication with the foregut
DIVERTICULUM (common with gut tube initially) expands caudally and two ridges, TRACHEOESOPHAGAL RIDGES, separate it from the foregut
Ridges fuse to form TRACHEOESOPHAGEAL SEPTUM - foregut is divided into oesophagus (dorsal) and the trachea & lung buds (ventral portion)
What remains as the point of communication at the larynx?
Laryngeal orifice allows the respiratory primordium to maintain its communication with the pharynx (around this is the cartilage, epiglottis, etc)
Development of the lung buds and bronchial tree?
Essentially is BRANCHING that carries the mesoderm with it to give rise to other structures
By the end of week 4, will have trachea and bronchial buds (enlarge to form right and left main bronchus)
Over next few days, branching forms the lobar bronchi (right lung - 3, left - 2)
Tertiary buds give rise to segmental bronchi
Branching continues after birth as well
Time taken for development and maturation of the lungs?
By end of the embryonic period, gross respiratory structures have developed but the system takes a longer time to mature
Most likely respiratory congenital defect?
Abnormalities in partitioning of the oesophagus and trachea by the tracheoesphageal septum
Results in oesophageal atresia (blind-ending) with/without tracheoesophageal fistulas (TEFs - communication)
Different respiratory congenital defects due to common problem?
Upper oesophagus ends with a blind pouch and the lower segment forms a fistula with the trachea (deal with promptly to allow feeding)
Trachea forms normally but oesophagus splits, so upper end has blind pouch and lower end starts with blind pouch
H-type TEF - split does not form completely so trachea still has a small communication location with the oesophagus
Proximal end of the oesophagus communicates with the trachea but the distal end does not (has a blind pouch)
Oesophagus can have 2 separate communications (fistulas) with the trachea
Time period and events occurring during embryonic period?
26 days-6 weeks
Respiratory diverticulum forms
Initial branching occurs, to give lungs, lobes and segments
Time period and events occurring during pseudoglandular period?
6-16 weeks
(Looks, histologically, quite glandular)
14 more generation of branching occur to form all the way to the terminal bronchioles
Time period and events occurring during canalicular period?
16-28 weeks
Terminal bronchioles each give rise to 2 respiratory bronchioles, which give rise to 3-6 alveolar ducts
Time period and events occurring during saccular period?
28-36 weeks
Terminal sacs (alveoli) start to form; capillaries establish close contact
Alveolar walls are still too thick
Time period and events occurring during alveolar period?
36 weeks to early childhood
Alveoli mature and alveolar walls thin
Describe alveoolar development before birth
Ducts lead to terminal sacs (primitive alveoli) that are surrounded by cuboidal epithelium and are in close contact with capillaries
Cells lining the sacs, AKA Type I alveolar cells, become thinner to produce thin squamous epithelium and surrounding capillaries protrude into alveolar sacs (BLOOD-AIR BARRIER)
At end of the month, Type II alveolar cells develop (PRODUCE SURFACTANT - prevents alveolar collapse by reducing surface tension)
Mature alveoli are not present before birth
Problems in the newborn?
RESPIRATORY DISTRESS SYNDROME (~20% of deaths in newborns)
Surfactant not produced until late in pregnancy, so premature babies may not have enough surfactant (alveolar surface tension is high and alveoli collapse during expiration)
