Development of Pharyngeal appratus | Embryology | First Aid Lectures | Lec9 #firstaidlectures
Channel: Dr. Jamil Lectures
Date: 2023-04-26

In this lecture ee will discuss about pharyngeal appratus ,Buccopharyngeal membrane,Pharyngeal clefts/groove,Pharyngeal arches and Digeorge Syndrome.

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Development of Pharyngeal Apparatus
● Gill-like structure at the cranial end of a sagittal section
of an embryo is called a pharyngeal apparatus that
consists of following parts.
1. Buccopharyngeal membrane →an area of
ectoderm directly fused to the endoderm in the cranial
region of the embryo and forms buccopharyngeal
membrane that gives rise to the mouth.
3. Pharyngeal arches → There are 6 arches that are lined with mesoderm
(mesenchymal tissue) → These pharyngeal arches develop into following tissues.
➢ Muscles
● 1st arch gives rise to following muscles
Muscle of mastication supplied by trigeminal nerve (Medial and lateral
pterygoids,Masseter & Temporalis)
Mylohyoid / anterior belly of digastric (Suprahyoid muscles)
Tensor veli palatini muscles that control the movement of soft palate during
swallowing.
● 2nd arch gives rise to following muscles
Stapedius muscles of the middle ear that control the sensitivity of hearing.
Muscles of facial expression
Stylohyoid / posterior belly of digastric muscle (Suprahyoid muscles).
● 3rd arch gives rise to following muscles
Stylopharyngeus muscles that are supplied by the glossopharyngeal nerve
and help in deglutition (the process of swallowing).
➢ Nerves
● 1st arch gives rise to trigeminal nerve ( Cranial nerve 5)
● 2nd arch gives rise to facial nerve (Cranial nerve 7)
● 3rd arch gives rise to glossopharyngeal nerve (Cranial nerve 9)
● 4th and 6th arches give rise to vagus nerve (Cranial nerve 10)
while Superior laryngeal nerve is developed by 4th arch and
Recurrent laryngeal nerve is developed by 5th arch.
➢ Arteries
● 1st arch gives rise to maxillary artery
● 2nd arch gives rise to the hyoid artery that becomes a stapedial
artery→Only 10% adults keep this artery and usually it does not remain in adulthood.
● 3rd arch gives rise to the common carotid artery and proximal portion of internal
carotid artery.
● Right 4th arch gives rise to the Subclavian artery and the left 4th arch gives rise to
the Aortic arch.
● Right 6th arch gives rise to the right pulmonary artery and the left 6th arch gives rise
to the left pulmonary artery and ductus arteriosus (connects the pulmonary trunk with
aorta).
4. Pharyngeal Pouches → There are 4 pharyngeal pouches that are lined with
endoderm → The 3rd and 4th pouches split into dorsal pouch and ventral pouch →
pouches gives rise to
● 1st pouch develops into epithelium of the middle ear like tympanic cavity and
eustachian tube (drains into nasal cavity).
● 2nd pouch develops into lymphatic tissue called tonsils (Pharyngeal
tonsil,Palatine, tubal and lingual tonsils) → endoderm of 2nd pouch
also lines the naso-oral cavity.
● 3rd pouch splits into dorsal and ventral pouches
Dorsal pouch develops into Inferior parathyroid glands.
Ventral pouch develops into a thymus that starts in the neck
then moves down to the chest where T-cells mature.
● 4th pouch also splits into dorsal and ventral pouches
Dorsal pouch gives the superior parathyroid gland
Ventral pouch develops into the ultimo pharyngeal body that forms the
parafollicular cells (C-cells) → C-cells secrete calcitonin which helps in
regulation of calcium blood level.
Digeorge Syndrome
● syndrome in which 3rd and 4th Pharyngeal pouch do not develop during embryo
development → as 3rd pharyngeal pouch develops into thymus so thymus will be
missing, T cells will not get mature, number of T cells decreases and patient will be
having immunity issues due to impaired T-cell development →3rd pharyngeal pouch
also develops into inferior parathyroid gland and 4th pharyngeal pouch develops into
superior parathyroid gland, so in this syndrome parathyroid gland will not be present,
PTH will not produce leading to hypocalcemia(decrease calcium in blood) and can
result in Tetany →In this syndrome patients often include congenital heart problems
as well → parafollicular C- cells will not form leading to abnormal calcium
metabolism.

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