Which deficiency is associated with squamous metaplasia in the eyes or bronchus?

Squamous metaplasia, particularly in the eyes or bronchus, is primarily associated with a deficiency of vitamin A. This vitamin plays a crucial role in maintaining the integrity and functioning of epithelial tissues. In the case of vitamin A deficiency, the normal columnar epithelial cells can undergo metaplasia, transforming into squamous cells, which is not ideal for the function of these tissues.

In the eyes, a lack of vitamin A can lead to conditions such as xerophthalmia, where the conjunctival epithelium undergoes squamous metaplasia instead of maintaining its normal structure. This can compromise the eye's ability to stay lubricated and protected from environmental factors.

In the bronchus, the normal respiratory epithelium, which is ciliated columnar epithelium, may also experience squamous metaplasia in response to chronic irritation or deficiency, further disrupting airway clearance and increasing susceptibility to infection.

Other vitamin deficiencies listed do not typically cause squamous metaplasia as a primary symptom. Vitamin C deficiency is more associated with scurvy and impacts collagen synthesis; vitamin E deficiency affects neurological function and red blood cell membrane integrity; and vitamin D deficiency primarily relates to bone health and calcium metabolism.