Embryologic Derivatives — Endoderm

Endoderm derivatives:

Epithelial lining of “the stuff on the inside” is derived from endoderm, including:

1. Gastrointestinal tract:

- Foregut: pharynx, esophagus, stomach, proximal 2nd part of duodenum

- Midgut: distal 2nd part of duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal two-thirds of transverse colon

- Hindgut: distal one-third of transverse colon, descending colon, sigmoid colon, rectum, anal canal proximal to pectinate line

2. Respiratory tract: larynx, trachea, bronchi, lungs

3. Caudal end of genitourinary tract:

- urinary bladder

- female urethra, lower two-thirds of vagina

- male urethra (except the most distal aspect of the male urethra, which is formed by an invagination of ectoderm), bulbourethral (Cowper’s) glands, urethral (Littre’s) glands

The parenchyma of the following structures is derived from endoderm:

- Submandibular and sublingual salivary glands

- Thyroid gland—follicular cells are derived from endoderm, parafollicular C cells are derived from neural crest

- Liver, biliary tree, gallbladder

- Pancreas

Branchial (pharyngeal) pouches are lined by endoderm ∴ the following branchial-pouch derivatives originate from endoderm:

1st branchial pouch → epithelial lining of auditory (eustachian) tube, middle ear cavity, mastoid air cells

2nd branchial pouch → epithelial lining of palatine tonsils

Dorsal wings of 3rd pouch → inferior parathyroid glands

Dorsal wings of 4th pouch → superior parathyroid glands

Ventral wings of 3rd pouch → thymus