1. A midline diverticulum that forms along the ventral aspect of the pharyngeal gut, between the 4th and 6th pharyngeal arches at 3.5 weeks

2. Enveloped by splanchnic mesoderm

1. At 4.5 weeks, the lung bud bifurcates to form the right and left mainstem bronchi

2. Soon thereafter, further bifurcations result in the secondary bronchi, two on the left and three on the right

1. Divide another 17 times

2. Beginning at about 18 weeks of fetal life, these terminal bronchioles produce epithelial outpouchings which eventually form the alveoli

Differentiates into the supporting tissue: blood vessels, cartilage, and smooth muscle

1.Produced by the lining cells of the airspaces at 28 weeks

2. Phospholipid material acts as a wetting agent and is critically important in decreasing surface tension of the aqueous surface of the airspaces and thereby facilitating lung inflation

1. Formed from the growth of shelves of septum transversum

2. Diaphragm is of both somatic and splanchnic mesodermal origin

1. This septum is of splanchnic mesoderm origin

2. The very first plate of tissue that begins the separation of thoracic and abdominal cavities

3. It contributes tissue mostly to the anterior and midline regions of the diaphragm, specifically the central tendon

The lateral, muscular portions of the diaphragm are formed by two shelves of somatic mesoderm coming from the chest wall

1. Splanchnic mesoderm origin

2. Fills in the dorsal region of the diaphragm in the region of the aorta, inferior vena cava, and the esophagus

1. The pleuroperitoneal fold fails to develop

2. Happens more frequently on the left side

3. The defect is lateral in location

4. As a result of this defect, abdominal organs herniate up into the left chest, pushing the heart and lungs to the right and more importantly, compressing the lungs

5. Results in pulmonary hypoplasia

Causes pulmonary insufficiency (and often death)

1. Results in pulmonary hypoplasia

2. Severe fetal edema causing pleural effusions

3. May be due to a chromosomal abnormality, such as Trisomy 21 of monosomy X, or it can be due to viral infection

1. Means "little amniotic fluid"

2. Causes external compression of the lungs and thus produces pulmonary hypoplasia