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1 Label the structures of the thyroid and parathyroid glands in Figure (a) and (b). 2 Label the photomicrographs of the sections of thyroid and parathyroid glands in Figure (a) and (b).
(b) Posterior view 201 10 Dissection Shawn Miller, Photograph Mark Nielsen
The Correct Answer and Explanation is:
1. Label the Structures of the Thyroid and Parathyroid Glands
Figure (a): Anterior View of the Neck (Thyroid Gland Visible)
- Thyroid Gland: Butterfly-shaped gland located anteriorly in the neck, inferior to the larynx and spanning across the trachea. It consists of two lobes (right and left) connected by an isthmus.
- Isthmus: The central portion of the thyroid gland that bridges the two lobes over the trachea.
Figure (b): Posterior View
- Parathyroid Glands: Typically four small, oval glands located on the posterior surface of the thyroid lobes—two on each lobe (superior and inferior parathyroid glands).
- Thyroid Lobes (Posterior View): The right and left lobes of the thyroid can be seen from the back, providing the location reference for the parathyroid glands.
2. Label the Photomicrographs
Figure (a): Thyroid Gland Photomicrograph
- Thyroid Follicles: Spherical structures filled with colloid, which stores thyroglobulin (precursor to thyroid hormones T3 and T4).
- Follicular Cells: Surround the follicles; responsible for synthesizing and secreting thyroid hormones.
- Parafollicular (C) Cells: Located between follicles; secrete calcitonin, which lowers blood calcium levels.
Figure (b): Parathyroid Gland Photomicrograph
- Chief Cells: Small, dark-staining cells that secrete parathyroid hormone (PTH), which increases blood calcium levels.
- Oxyphil Cells: Larger, lighter-staining cells with unknown function; increase in number with age.
- Capillaries: The parathyroid gland is richly vascularized, allowing rapid hormone transport.
Explanation
The thyroid and parathyroid glands play essential roles in endocrine regulation, particularly involving metabolism and calcium homeostasis. The thyroid gland is located in the anterior neck, just below the larynx. It consists of two lobes connected by an isthmus and is responsible for producing thyroid hormones (T3 and T4), which regulate metabolic rate, and calcitonin, which lowers blood calcium levels. Microscopically, the thyroid is composed of follicles lined with follicular cells and filled with colloid—a storage form of thyroid hormones. Parafollicular (C) cells between the follicles produce calcitonin.
The parathyroid glands, usually four in number, are found embedded on the posterior surface of the thyroid lobes. They are much smaller than the thyroid but play a vital role in calcium regulation. These glands secrete parathyroid hormone (PTH), which raises blood calcium levels by increasing calcium reabsorption in the kidneys, stimulating osteoclast activity in bones, and enhancing calcium absorption in the intestines through activation of vitamin D.
In histological sections, the thyroid can be recognized by its round follicles filled with colloid, whereas the parathyroid gland shows clusters of chief cells and larger oxyphil cells without the presence of follicles. The distinction between the two is crucial in histological diagnosis and surgical procedures to avoid damaging the parathyroid glands during thyroidectomy. Understanding these glands’ anatomy and histology is fundamental in diagnosing and managing endocrine disorders such as hypothyroidism, hyperthyroidism, and hyperparathyroidism.
