Respiratory System Development

pharyngeal arches

Week 4-5

5 pairs: 5th arch does not develop

Muscular system + cranial nerves + arteries

Layers of Pharyngeal Arches

Ectoderm outer surface

Endoderm inner surface

Mesoderm in between

Mesenchymal tissue of pharyngeal arch

Derivatives of 1st pharyngeal arch

CN V (trigeminal)

Mastication muscles

Mandible malleus, incus

Meckel's cartilage

Derivatives of 2nd pharyngeal arch

CN VII (facial)

Facial expression muscles

Stapes, styloid process

Derivatives of 3rd pharyngeal arch

CN IX (glossopharyngeal)

Stylopharyngeus muscle

Greater horn of hyoid bone

Derivatives of 4th to 6th pharyngeal arch

CN X

Cricothyroid + muscles of larynx

Laryngeal cartilages

respiratory diverticulum

Appears in day 25

Lung bud

From anterior wall of foregut

tracheoesophageal ridges

Separate respiratory diverticulum (trachea) and foregut (esophagus) during development

laryngeal orifice

communication between pharynx and respiratory tract

Larynx

4-6 pharyngeal arches

Phases of lung development

Pseudoglandular stage

5-16 weeks

Formation of bronchial tree

canalicular stage

16-26 weeks

Development of respiratory bronchioles (cuboid)

terminal sac stage

26 weeks to birth

Cuboidal → squamous, in contact with endothelium of blood vessels

Alveolar stage

developed epithel-endothel contact

airway development

Lung bud → 2 main bronchi → secondary bronchi → tertiary bronchi → terminal bronchioles → respiratory bronchioles → alveolar duct → primitive alveolar

type 1 alveolar cells

simple squamous epithelium

type 2 alveolar cells

secrete surfactant

What parts of the lower respiratory tract are derived from endoderm?

epithelium, glands

What parts of the lower respiratory tract are derived from the splanchnic mesoderm?

cartilage, smooth muscle, connective tissue

The laryngeotracheal diverticulum is made of ___________ lined internally by ___________.

Mesoderm, endoderm

Distal end of the laryngeotracheal groove

Lung bud

pharyngeal pouches

1

endodermal epithelium

Lines internal surfaces like GI tract and lungs.

2

pharyngeal clefts

Ectodermal epithelium

5