[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Head and neck: pharyngeal arches](https://durgical.com/en/embryology/#a-head_neck) › Pharyngeal pouches: tonsil, thymus, parathyroids and C cells

[Embryology](https://durgical.com/en/embryology/) · [Head and neck: pharyngeal arches](https://durgical.com/en/embryology/#a-head_neck)

# Pharyngeal pouches: tonsil, thymus, parathyroids and C cells

- Embryonic structure

Pouches are inner pockets of the embryo's pharynx. They form the middle ear, tonsil, thymus, parathyroids and part of the thyroid.

Updated 2026-11-01

**See it in 3D:** [Auditory tube](https://durgical.com/en/anatomy/auditory-tube/) · [Palatine tonsils](https://durgical.com/en/anatomy/palatine-tonsil/) · [Thymus](https://durgical.com/en/anatomy/thymus/) · [Parathyroid glands](https://durgical.com/en/anatomy/parathyroid-glands/) · [Thyroid gland](https://durgical.com/en/anatomy/thyroid-gland/)

## Key points

- 1st: middle ear and auditory tube.
- 2nd: palatine tonsil.
- 3rd: thymus and inferior parathyroids.
- 4th: superior parathyroids and C cells.
- 3rd and 4th fail in 22q11.2 deletion.

## What it is

The pharyngeal pouches are outpocketings of pharyngeal endoderm that push between the arches. There are four well-formed pairs, and their lining gives the tympanic cavity, palatine tonsil, thymus, the four parathyroids and the thyroid C cells. The third-pouch crossover (inferior parathyroids that start higher than the superior ones) and the pouches' role in 22q11.2 deletion are classic questions.

## Key facts

- The inferior parathyroid comes from the 3rd pouch and the superior from the 4th: the names 'cross'.
- Because of its long journey, the inferior parathyroid is the most variable: it may stay in the thymus, the mediastinum or near the carotid bifurcation.
- The thymus grows until puberty and is then replaced by fat.

## Structure

- Endodermal lining; each gland's connective tissue comes from neural crest mesenchyme.
- The 3rd and 4th pouches have a dorsal and a ventral wing.
- The 5th pouch is rudimentary and is usually absorbed into the 4th.

## What it becomes

- 1st: tubotympanic recess → tympanic cavity and auditory tube; its end helps form the tympanic membrane.
- 2nd: epithelial buds invaded by lymphocytes → palatine tonsil; the rest of the pouch remains as the tonsillar fossa.
- 3rd: inferior parathyroids and thymus.
- 4th: superior parathyroids and the ultimobranchial body, which joins the thyroid and gives the parafollicular (C) cells that make calcitonin.

## Step by step

- Weeks 4–5: pouches form front to back, guided by FGF and retinoic acid.
- Week 5: the dorsal wing of the 3rd pouch gives the inferior parathyroid, the ventral wing the thymus.
- Weeks 6–7: the thymus descends to the anterior mediastinum and drags the inferior parathyroid along.
- The 3rd-pouch parathyroid ends up below the 4th-pouch one, which has a shorter descent.
- Week 7: the parathyroids settle on the back of the thyroid.
- Between the third and fifth months the tonsil fills with lymphoid tissue.

## What each pharyngeal pouch forms

| Pouch | Derivatives |
| --- | --- |
| [1st](https://durgical.com/en/conditions/acute-otitis-media/) | Tympanic cavity (middle ear), auditory tube, mastoid air cells |
| [2nd](https://durgical.com/en/conditions/peritonsillar-abscess/) | Epithelium of the palatine tonsil and tonsillar fossa |
| [3rd](https://durgical.com/en/conditions/digeorge-syndrome/) | Dorsal wing: inferior parathyroids; ventral wing: thymus |
| [4th](https://durgical.com/en/conditions/thyroid-cancer/) | Dorsal wing: superior parathyroids; ventral wing: ultimobranchial body (C cells) |

## Markers

- TBX1
- HOXA3
- PAX9
- PAX1
- GCM2
- FOXN1
- EYA1

## Clinical notes

- 22q11.2 deletion (DiGeorge): pouches 3 and 4 fail; small or absent thymus (T-cell deficiency) and hypocalcaemia from hypoparathyroidism.
- Ectopic parathyroids: a common cause of persistent hyperparathyroidism after surgery.
- Thymic or parathyroid rests in the neck from incomplete migration.
- C cells give medullary thyroid carcinoma (calcitonin as marker), part of multiple endocrine neoplasia type 2.
- Auditory tube dysfunction (1st pouch): otitis media with effusion, especially with cleft palate.

## Memory aid

Run them top to bottom like a day's work: 'hear, swallow, defend, manage calcium' (ear, tonsil, thymus, parathyroids and C cells).

## Test yourself

Think of the answer, then tap the question to see it.

## Which pharyngeal pouch gives the inferior parathyroid glands?

The third pouch (dorsal wing), together with the thymus (ventral wing).

## Why do third-pouch parathyroids end up below fourth-pouch parathyroids?

The thymus drags them down as it migrates to the mediastinum, a longer journey.

## Where do the thyroid C cells come from?

From the ultimobranchial body, which arises from the ventral wing of the fourth pouch.

## What comes from the first pharyngeal pouch?

The tympanic cavity (middle ear), the auditory tube and the mastoid air cells.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/pharyngeal-pouches-tonsil-thymus-parathyroids-and-c-cells/)

## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Auditory tube](https://durgical.com/en/anatomy/auditory-tube/)
- [Palatine tonsils](https://durgical.com/en/anatomy/palatine-tonsil/)
- [Thymus](https://durgical.com/en/anatomy/thymus/)
- [Parathyroid glands](https://durgical.com/en/anatomy/parathyroid-glands/)
- [Thyroid gland](https://durgical.com/en/anatomy/thyroid-gland/)

## Related

- [The pharyngeal apparatus: arches, pouches, clefts and membranes](https://durgical.com/en/embryology/the-pharyngeal-apparatus-arches-pouches-clefts-and-membranes/)
- [Pharyngeal arches: nerve, muscles, skeleton and artery (the table)](https://durgical.com/en/embryology/pharyngeal-arches-nerve-muscles-skeleton-and-artery/)
- [Pharyngeal clefts and membranes: external ear and cervical sinus](https://durgical.com/en/embryology/pharyngeal-clefts-and-membranes-external-ear-and-cervical-sinus/)
- [22q11.2 deletion (DiGeorge): the third and fourth pouches](https://durgical.com/en/embryology/22q11-2-deletion-the-third-and-fourth-pouches/)
- [Thyroid gland: from the foramen cecum to the neck](https://durgical.com/en/embryology/thyroid-gland-from-the-foramen-cecum-to-the-neck/)
- [Ear: inner, middle and external ear](https://durgical.com/en/embryology/ear-inner-middle-and-external-ear/)
- [Branchial cleft cysts, sinuses and fistulas](https://durgical.com/en/embryology/branchial-cleft-cysts-sinuses-and-fistulas/)

## Related conditions

- [DiGeorge syndrome (22q11.2 deletion syndrome)](https://durgical.com/en/conditions/digeorge-syndrome/)
- [Hypoparathyroidism (incl. post-thyroidectomy hypocalcaemia)](https://durgical.com/en/conditions/hypoparathyroidism/)
- [Hypocalcaemia](https://durgical.com/en/conditions/hypocalcaemia/)
- [Acute otitis media](https://durgical.com/en/conditions/acute-otitis-media/)
- [Thyroid cancer (papillary)](https://durgical.com/en/conditions/thyroid-cancer/)
- [Multiple endocrine neoplasia (MEN 1, 2A, 2B)](https://durgical.com/en/conditions/multiple-endocrine-neoplasia/)

[← All of embryology](https://durgical.com/en/embryology/)

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: [Embryology, Pharyngeal Pouch - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK557724/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Embryology, Parathyroid - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK554580/) (StatPearls Publishing (NCBI Bookshelf), 2023); Langman's Medical Embryology, 13th ed., ch. 17: Head and Neck (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/embryology/pharyngeal-pouches-tonsil-thymus-parathyroids-and-c-cells/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/pharyngeal-pouches-tonsil-thymus-parathyroids-and-c-cells/