Thyroid Gland

Key:

  1. Colloid
  2. Follicular cells (encircling the colloid to form a follicle)
  3. Parafollicular cells

A follicle is made of colloid surrounded by follicular cells.  The colloid is the storage region for thyroid hormones.  It is mostly made of Thyroglobulin and the hormones T3 (Triiodothyronine) and T4 (Thyroxine) are made and stored within it.  The thyroid hormones are released when called upon to increase basal metabolic rate.  The parafollicular cells (Aka: C cells) are located between the follicles.  They produce and secrete Calcitonin (Aka: Thyrocalcitonin) which decreases the activity of osteoclasts, stimulated osteoblasts, and causes the kidneys to filter calcium ions out of the blood and dump them into the urine.  All will decrease blood calcium levels.