FCPS part 1 Medicine solved mcqs with explanation Q24

Thymus is derived from:

a) 4^th Pharyngeal pouch

b) 2^nd pharyngeal pouch

c) 3^rd pharyngeal pouch

d) Tuberculum impar

Correct Answer: c

Explanation:

Derivatives of pharyngeal pouches:

• 1^st pouch: Middle ear cavity, Eustachian tube, mastoid air cells
• 2^nd pouch: epithelial lining of palatine tonsil
• 3^rd pouch: inferior parathyroid gland + thymus
• 4^th pouch: superior parathyroid gland

NOTE: It might seem strange that the inferior parathyroid glands arise from the 3^rd pouch while the superior parathyroid glands arise from the 4^th pouch. But this is how it is.