GWEN SHOCKEY / SCIENCE SOURCE / SCIENCE PHOTO LIBRARY GWEN SHOCKEY / SCIENCE SOURCE / SCIENCE PHOTO LIBRARY
Illustration comparing primary hypothyroidism with secondary hypothyroidism. Primary hypothyroidism (left) occurs when the thyroid cannot produce enough hormones for the pituitary gland (represented by the thick green arrow). Secondary hypothyroidism (right) occurs when the thyroid is not stimulated by the pituitary gland to produce necessary hormone levels (represented by a thinner green arrow).
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