Embryonic Development + Respiratory Development

Events of week 1

Fertilization, cleavage, blastocyst forms

What does the inner cell mass of blastocyst form

Embryo

What does trophoblast of blastocyst form

Placenta

Event of week 2

Implantation, formation of bilaminar disc (epiblast and hypoblast) 

What is epiblast

Forms the amniotic cavity (dorsal)

What is hypoblast

Forms yolk sac (ventral)

Event of week 3

Gastrulation; primitive streak forms into mesoderm → mesoderm forms into endo and ectoderm

What does ectoderm form

Skin, nervous system

What does mesoderm form

Muscle, bone, connective tissue, cardiovascular

What does endoderm form

Epithelium that lines gut and respiratory system

What forms the nervous system

Neural plate folds → Neural groove and neural fold → Neural tube

Events of week 4-8

Organogenesis; folding of embryo creates foregut, midgut and hindgut

When does the lung start developing

In week 4 → Endoderm forms gut tube → respiratory diverticulum/lung bed forms from ventral foregut

Where does the larynx begin forming

between 4th and 6th laryngeal arch

What does endoderm, mesoderm and arches form for larynx

Endoderm → Epithelium and glands; mesoderm → Laryngeal cartilage, arches → vagus nerve branches

Event of week 5

T shaped opening forms → Laryngeal orifice → Has laryngeal ventricle that become vocal cord

Event of week 6

Epiglottis begins to form above laryngeal orifice

Event of week 12

Laryngeal orifice adult shape forms; creates cartilage (thyriod, cricoid, arytenoid)

Development of lung bud

Trachoesophageal ridge appear and fuse → Divides into dorsal esophagus and ventral trachea and lung bud

What does the endoderm and mesoderm form in the lung bud

Endoderm: Epithelium and gland; mesoderm: muscle, cartilage, and CNT

Phases of lung development

Pseudoglandular, canalicular, terminal sac, alveolar phases

Event of pseudoglandular phase

5-16 wk; Branches continue to form terminal bronchiole

Event of canalicular phase

16-26 wk; Terminal bronchiole form alveolar duct; vascularity increases

Difference between primitive and adult alveoli

Primitive made of CUBOIDAL EP, adult made of pseudostratified COLUMNAR EP

Event of terminal sac phase

26 wk to birth; capillary connect to alveoli → forms blood air barrier

Event of alveolar phase

Eight months post birth to 8 years old; complete development of epithelium

Difference between lung before and after birth

Before: Breathes amniotic fluid; after: fluid is absorbed into capillary, surfactant is left behind