Development of lungs

Question 1

Start of respiratory development

Answer 1

Respiratory primordium develops as a ventral groove in the floor of the foregut (originally from the gut tube)

Question 2

Foregut

Answer 2

Region from mouth to pancreas

Question 3

Respiratory primordium

Answer 3

Gives rise to the trachea, larynx, lungs

Question 4

General development steps of respiratory system

Answer 4

1. Respiratory primordium develops as a ventral groove in floor of foregut
2. Groove deepens and forms elongated outgrowth called laryngo-tracheal groove
3. The laryngo-tracheal groove becomes separated from the foregut by two trachea-oesophageal grooves (one on each side). These two grooves move towards each other and fuse to form the trachea-oesophageal septum and form the laryngo-tracheal tube. The portion of the foregut that was cut off from this will become the pharynx
4. Laryngo-tracheal tube becomes the primitive trachea and eventually splits into two bronchial buds
   - Primitive trachea- mesenchyme (neural crest derived) gives rise to cartilaginous tracheal rings and smooth muscle of the trachea. Endodermal lining becomes ciliated, pseudostratified respiratory epithelium with goblet cells.
5. Lung buds grow caudo-laterally becoming principle bronchi (left bud will be more lateral; right more caudal).
6. Principle bronchi bud into lobar bronchi.
7. Lobar bronchi will push into developing pleural cavity, become surrounded by mesenchyme and form the pleura
8. Lobar bronchi will bud into segmental bronchi
9. Segmental bronchi divide up to 20 times (species dependent) into terminal bronchioles (which are lined with endodermal derived epithelium)
10. Terminal bronchioles divide further into respiratory bronchioles
11. More divisions create secondary tubules called canalicules or alveolar ducts
12. Canaliculi form terminal saccules. These divide further into blind saccules that will differentiate into alveoli (saccular phase) OR the alveoli differentiation will occur first on the terminal saccules (alveolar phase).
13. Primitive alveoli that allow newborn to breath initially are developed into mature alveoli

Question 5

Primitive trachea

Answer 5

• Endodermally lined. Becomes ciliated, pseudostratified respiratory epithelium with goblet cells
• Mesenchyme around it is neural crest derived and gives rise to cartilaginous tracheal rings and smooth muscle of trachea.

Question 6

Periods of bronchi and lungs development

Answer 6

• Embryonic- primordium of lungs and bronchi formed
• Fetal- ramified bronchi are formed and preliminary structures produced for gas exchange
• Postnatal- definitive structures for gas exchange called alveoli develop and lungs take on their adult form. Marked by extensive growth of respiratory bronchioles, accules and alveolar development.

Question 7

Fetal period development subdivisions

Answer 7

Pseudo-glandular
- Segmental bronchi divide lots into terminal bronchioles

Canalicular
- Terminal bronchioles divide into respiratory bronchioles. Further divisions create secondary tubules called canalicules or alveolar ducts

Saccular
- Terminal saccules divide further into blind saccules that will differentiate into alveoli

Alveolar
- alveoli differentiation will occur first on the terminal saccules

Question 8

Tracheal bronchus

Answer 8

develops from the trachea to supply right cranial lobe in cattle, sheep, and pigs

Question 9

Pleural cavity development

Answer 9

• heart and lungs will originally be surrounded by left and right segments of pleuro-pericardial cavity
• Pleuro-pericardial folds (folds of mesoderm) will grow medially into the left and right parts of the pleuro-pericardial cavity and will eventually fuse to separate the two cavities
• heart will be suspended in one pericardial cavity. Lungs will be in the pleural cavity

Question 10

What lines terminal bronchioles?

Answer 10

Lined with endodermal derived epithelium

Question 11

Lungs during gestation

Answer 11

Lungs were filled with fluid secreted from developing alveolar cells and glands in system, and from amniotic fluid that was aspirated by fetus.

Question 12

Lungs in postnatal period

Answer 12

• Fluid is expelled
• Anything left over is absorbed by epithelial cells

Question 13

Subdivisions of canine lungs

Answer 13

Linked by lobar branches
Left
- Cranial lobe (has a cranial Lobe and a caudal lobe)
- Caudal lobe

Right
- Cranial lobe
- Middle lobe
- Accessory lobe
- Caudal lobe

Question 14

Subdivisions of porcine lungs

Answer 14

Linked by lobar bronchi except the right cranial lobe

Left
o Cranial lobe (has a cranial Lobe and a caudal lobe)
o Caudal lobe

Right
o Cranial lobe- Linked by tracheal bronchus
o Middle lobe
o Accessory lobe
o Caudal lobe

Question 15

Subdivisions of ovine lungs

Answer 15

Left
- Cranial lobe (has a cranial part and a caudal part)
- Caudal lobe

Right
- Cranial lobe (has a cranial and caudal part)- Linked by tracheal bronchus
- Middle lobe
- Accessory lobe
- Caudal lobe

Question 16

Subdivisions of equine lungs

Answer 16

Linked by lobar branches

Left
- Cranial lobe
- Caudal lobe

Right
- Cranial lobe
- Accessory lobe
- Caudal lobe
- No middle lobe as missing bronchus

Question 17

Subdivisions of bovine lungs

Answer 17

Left
- Cranial lobe (cranial and caudal parts)
- Caudal lobe

Right
- Cranial (has cranial and caudal parts)- Linked by tracheal bronchus
- Middle lobe
- Accessory lobe
- Caudal lobe

Question 18

Emphysema

Answer 18

• Damage to walls of alveoli
• Loss of lobes. Alveoli compress together and there is a loss of surface area. Decrease in gas exchange and therefore breathing issues