Resp - embryology Flashcards
When does the embryonic stage of lung morphogenesis take place?
3-8 weeks
When does the pseudo-glangular stage of lung morphogenesis take place?
5-17 weeks
When does the canalicular stage of lung morphogenesis take place?
16-26 weeks
When does the saccular stage of lung morphogenesis take place?
24-38 weeks
When does the alveolar stage of lung morphogenesis take place?
36weeks - 2-3 years
What is a zygote?
Where the sperm and ovum have fused to form a diploid cell called the zygote
What is a Morula?
The ball of cells formed from mitotic division of the zygote
How does the morula transform into a blastocyst?
As the morula continues to grow, nutrition to centre becomes difficult
Therefore a cavity called the blastocystic cavity forms
Cells accumulate at one end, called inner cell mass
What is a trophoblast?
The outer lining of cells of the blastocyst
When is the blastocyst ready for implantation?
Where does this usually take place?
Day 5-6
Inside uterine endometrial layer
How does hte blastocyst implant?
The blastocyst begins to bury itself into the endometrium of the womb with the chorion playing an important part
What eventually forms the placenta?
The chorion
What does the chorion secrete?
Human Chorionic gonadotrophin (hCG)
How does the chorion develop?
Trophoblast forms two layers
Goes on to form chorion
Develops chorionic villi
What happens to the inner cell mass?
They form the bilaminar disc
Thus separating the blastocyst cavity into two
>Amniotic cavity
>Yolk sac
What is the maternal part of the palcenta?
Decidua basalisof endometrium
Rough + maternal blood vessels
What is the foetal part of the placenta like?
Smooth with foetal blood vessels + endo of umbilical cord
When does the placenta mature?
18-20 weeks
What are dizygotic twins?
Twins from two separate ovum
What are monozygotic twins?
Twins fom same ovum (identical)
Share placenta, may not share amniotic/chorionic sac
What is the primitive streak?
A dipping of cells of the epiblast (invagination) in the midline
Forms axis of embryo
How are the three germ layers formed?
Epiblast cells migrate to space between epiblast + hypoblast
Displace hypoblast
Forms trilaminar disc = three germ layers
>Ectoderm
>Mesoderm
>Endoderm
What is the notochord?
Cells from the primitive streak sink down forming a solid tube of cells
This is called the Notocord
What is neurulation?
Formation of the neural tube
How does the neural tube form?
Neural plate sinks down from ectoderm
Invaginates to form a tube
This is induced by the notocord
How does the mesoderm develop?
The neural tube induces the mesoderm to thicken It then splits into three parts >Paraxial mesoderm >Intermediate plate mesoderm >Lateral plate mesoderm
What does the lateral plate mesoderm split into?
A somatic splanchinic mesoderm
And somatic mesoderm
Space between is the intraembryonic coelom
What does the paraxial mesoderm go on to form?
Somites
What does the intermediate plate mesoderm go on to form?
Urogenital system
What does the lateral plate mesoderm go on to form?
Body cavity and coverings
>Peritoneum
>Pleura
When does the heart start to beat?
Day 24
What is the gut formed from?
Endoderm
How many pairs of somites are there?
43
What folds does the embyro go under?
Lateral fold
Head and tail fold
What do the somites divide into?
Dermatome
Myotome
Sclerotome
What does the ectoderm form?
Epidermis of skin
Neural tube
What does the endoderm form?
Gut
Respiratory system
When is the foetus most sensitive to teratogens?
Weeks 3-8
Where does the respiratory system develop from?
Ventral wall of foregut
How does the respiraotry primordium develop?
A median outgrowth of foregut called laryngotracheal groove
>Develops caudal to 4th pair of pharyngeal pouches
How does the larynx develop?
The laryngotracheal groove becomes the paryngeal inlet
With arytenoid swellings + laryngeal cartilages growing off the 4th and 6th pharyngeal arches
The epiglottis then forms from the caudal part of the hypopharyngeal eminence
What is laryngeal atresia?
A rare birth defect due to a failure of recanalisation
Obstructs foetus’ upper airway
How does the lung bud develop?
Laryngotracheal groove gives rise to laryngotracheo diverticulum
This becomes invested with mesoderm and enlarges to form a lung bud
From where does the trachea develop?
The endoderm of the laryngotracheal tube forms the pulmonary epithelium and glands of trachea
The splanchnic mesenchyme forms the cartilage, muscles and connective tissue
What is a tracheo-oesophageal fistula?
Where the trachea and oesophagus do not separate properly, leaving an abnormal passage.
Either blind end (atresia), or connections.
What is the pseudoglandular stage of lung development?
Lung resembles exocrine gland
Major structures formed, but nor gas exchange
What happens in the embryonic phase of lung development?
Trachea has formed
The main bronchi have formed
All the way to tertiary bronchi
What happens in the canalicular stage of lung development?
Lumina of bronchi and terminal bronchioles enlarge
Vascularity increases
Respiration possible by end of stage
Foetus may survive in ITU
What happens in the saccular stage of lung development?
More terminal sacs develop
Capillaries invade these sacs + squamous epithelium develop at sac ends
Forms Type 1/2 pneumocytes
Blood/air barrier developed
When does surfactant production begin?
Week 20-22
What is respiratory distress syndrome?
Surfactant deficiency where child’s lungs don’t inflate
Common in premature children
What happens in the alveolar stage of lung development?
Formation of alveoli from terminal sacs
Alveoli enlarge
Continues after birth
>Increase in size and number
What are the congenital conditions of lung development?
Lobe of azygous vein Congenital lung cysts Agenesis of lungs Lung hypoplasia Accessory lung
What components does the diaphragm develop from?
Septum transversum
Pleuroperitoneal membranes
Dorsal mesentary of oesophagus
Muscular ingrowth from lateral body walls
Why is the phrenic nerve root values C3-C5?
Septum transversum originally opposite C3-C5 somites
Migrates caudally during diaphgram development
Brings with it the C3-C5 spinal nerves
What are common defects of the diaphgram?
Posteriolateral defect
Congeital hiatus hernia
Retrosternal hernia
Acecssory diaphgram
What abnormalities can form in the embryonic phase of lung development?
Pulmonary agenesis
Tracheo-oesophageal fistula
Tracheal/laryngeal stenosis
What abnormalities can form in the pseudoglandular phase of lung development?
Pulmonary sequestration
cystadenomatoid malformation
cyst formation
When does the diaphgram close?
By around 18 weeks
Which side is a diaphragmatic hernia more likely to be on? What does it lead to?
Left more than right
Leads to pulmonary hyerplasia
+ Persistant pulmonary hypertension
How do you treat respiratory distress syndrome?
Antenatal glucocorticoids Surfactant replacement Oxygen CPAP Mechanical ventilation
What is chronic neonatal lung disease associated with?
Increased bronchiolitis severity
Asthma
Future COPD