S12- Development of thoracic viscera Flashcards
When and where does the respiratory tract begin to develop from?
Begins to develop in the third week of foetal life, begins in the floor of the primitive pharynx and separates from the developing oesophagus
Where and when does the development of the lower respiratory tract begin?
It begins in the 4th week of foetal life and forms from the base of the primitive pharynx. It the deepens and is seperated from the developing oesophagus. in the middle of the 5th week the lung bud splits into two bronchial buds.
What are the four stages of lung developments and what happens in each?
The psuedogladular period (weeks 5-17)-tissue has distinct glandular appearance and is divided as far as the terminal bronchioles.
The canalicular period (weeks 16-25)-alveolar ducts begin to develop and tissue becomes highly vascularised.
The terminal sac period (weeks24-Birth)- the simple cuboidal epithelium differentiates to type I and type II squamous alveolar cells.
The alveolar period (latte foetal - 8 years)-alveolar walls continue to thin and adjacent capillaries bulge to form immature alveoli. 95% of alveoli devvelop after birth.
What is the formation of the lungs after the diverticulum forms?
It branches into left and right bronchial buds. These sub divide into secondary bronchial buds (three on right and two on left). These subdivide into tertiary bronchial buds which represent the future bronchopulmonary segments.
What are the 5 regions of the heart tube?
Sinus venosus Primitive atrium Primitive ventricle Bulbus cordis (forms future RV) Truncus arteriosus
What is the anchorage of the heart at the caudal and rostral ends?
It is anchored at the rostral end by the formation of the aortic arches. It is anchored at the caudal end by being partly embedded in septum transcersum which forms the central tendon of the diaphragm.
What does the sinus venosus drain in the primitive heart?
Drains the umbilical veins, vitelline veins (drains yolk sac) and common cardinal veins (involved in yolk sac blood).
When does the heart tube divide into 2 chambers and how does this occur?
At around week 4 the atrioventricular endocardial cushions form from which septae grow to seperate the right and left atrioventricular canals. The atria are seperated by the septum primum and the septum secundum with the foramen ovale through them. The ventricles are sepeerated by a muscular ridge that forms the interventricular spetum.
How do the aorta and pulmonary artery form?
The bulbus cordis and the truncus arteriosus are divided longitudinally by a spiral septum. This fuses in midline to produce two seperate arteries.
How do the valves form?
Subendocardial tissue swellings form at the sites of future valves.
How does the foramen ovale shut?
From the increased pressure in the left atrium.
What do atresia, fistulae and oesophageal aplasia mean?
- Atresia-is a structure that doesnt completely form.
- Fistulae-abnormal communication between two epithelial lined surfaces.
- Oesophageal aplasia-Complete lack of formation.
What is a tracheo-oesophageal fistula?
Abnormal connection between tracheal and oesophageal lumina. Results from failure of seperation. Would present with coughing and choking as food would go into lungs.
What is the result of cycstic fibrosis on the lungs?
There is a mutation in the CFTR ion channel gene so this results in thick sticky mucus that makes it hard to breathe.
What is respiratory distress syndrome and why does it occur?
Inadequate production of surfactant usually due to premature birth (<24 weeks) this is because this is the point that type II alveolar cells begin to produce it. Results in no reduction in surface tension so the alveolar sacs collapse.
