Thyroid-Parathyroid – Tutorial

Please read Unit 6 – Introduction to Endocrine Tissues prior to completing the activities in this chapter.

Introduction to the Thyroid Gland

The thyroid gland consists of two lobes partially wrapped around the antero-lateral surfaces of the trachea just below the laryngeal cartilages in the neck.  The two lobes of the thyroid are connected anteriorly by a narrow band of thyroid tissue known as the isthmus.

The thyroid gland contains numerous storage chambers known as thyroid follicles which are lined with simple cuboidal epithelium.  The cuboidal epithelial cells, also known as follicular cells, remove amino acids and iodine from the blood and store them in thyroid follicles as a globular protein called thyroglobulin which can be easily converted to thyroid hormones.  When stimulated by thyroid stimulating hormone (TSH), follicular cells remove thyroglobulin from the storage follicle and use it to produce two different hormones for secretion into the bloodstream.  The thyroid gland typically secretes larger amounts of the hormone thyroxine (tetraiodothyronine or T₄) and smaller amounts of triiodothyronine (T₃).  However, it is T₃ that is mainly responsible for affecting the activity of target cells all around the body since most T₄ is converted to T₃ before it arrives at peripheral tissues.

Another hormone produced by the thyroid gland is calcitonin.  Calcitonin is produced by cells known as parafollicular cells located in the interstitial spaces between thyroid follicles.  Since the parafollicular cells that produce calcitonin are slightly larger and stain lighter than follicular cells they are also referred to as clear cells, or simply C-cells.

Introduction to the Parathyroid Glands

Four parathyroid glands exist bilaterally as two pairs of small, oval shaped tissue patches embedded on the posterior superficial surfaces of the thyroid gland.  Each of the four parathyroid glands is typically about the size of a small pea and they secrete parathyroid hormone (PTH).  The thyroid and parathyroid glands will be discussed together in the tutorial activities that follow due to their close anatomical association in the human body and the fact that they are commonly sectioned together for study on microscope slides.

Tutorial:  Use the image slider below to learn more about the characteristics of the thyroid and parathyroid glands. 

Microscopy:  Use the image slider below to learn how to use a microscope to study the thyroid and parathyroid glands on a microscope slide.

Tutorial:  Use the hotspot image below to learn more about the thyroid and parathyroid glands and the hormones they secrete. 

Tutorial:  Use the hotspot image below to learn more about the thyroid gland and the hormones it secretes as viewed on a high power image.

Tutorial:  Use the image slider below to study numerous examples of thyroid-parathyroid tissue.