Step 1: Identify the asana.
Sarvangasana (shoulder stand) is an inverted posture with the chin pressed toward the chest ({jalandhara bandha}) and the neck flexed.
Step 2: Yogic rationale.
Classical yoga texts describe Sarvangasana as {stimulating the thyroid and parathyroid} by increasing circulation and gentle compression in the neck region—hence it is traditionally recommended for thyroid-related dysfunctions (especially sluggish metabolism in hypothyroidism).
Step 3: Scope and caution.
It is a {supportive} practice, not a substitute for medical treatment. Contraindications include cervical spine issues, uncontrolled hypertension, glaucoma, and late pregnancy.
Step 4: Conclude.
\[
\boxed{\text{Thyroid gland (Option D).}}
\]