Anatomy and Location
The
thyroid gland is a butterfly-shaped endocrine organ located in the anterior neck, just below the larynx. It consists of two lobes connected by an isthmus. The gland is highly vascularized and enclosed in a fibrous capsule.
Histological Structure
Histologically, the thyroid gland is composed of numerous spherical or oval
thyroid follicles. These follicles are the functional units of the gland, each lined by a single layer of
follicular cells and filled with a colloid containing
thyroglobulin. The colloid is a glycoprotein precursor to thyroid hormones.
Cell Types
There are two main types of cells in the thyroid gland:Hormone Synthesis and Secretion
Thyroid hormone synthesis involves the uptake of iodine, its incorporation into thyroglobulin, and the coupling of iodotyrosines to form T3 and T4. The hormones are stored in the colloid until needed, at which point they are endocytosed by follicular cells, processed, and released into the bloodstream. T3 is the more active form, while T4 is converted to T3 in peripheral tissues.Regulation
The activity of the thyroid gland is primarily regulated by
thyroid-stimulating hormone (TSH) from the anterior pituitary gland. TSH stimulates the follicular cells to produce and release thyroid hormones. Feedback mechanisms involving circulating levels of T3 and T4 help maintain homeostasis.
Clinical Significance
Histological examination of the thyroid can reveal various pathological conditions: Hyperthyroidism: Characterized by an overactive thyroid, often resulting in enlarged follicles and reduced colloid.
Hypothyroidism: An underactive thyroid, leading to increased colloid and reduced follicular cell activity.
Thyroid Nodules: Localized growths within the gland, which can be benign or malignant.
Thyroiditis: Inflammation of the thyroid, which can be autoimmune (e.g., Hashimoto's thyroiditis) or due to infection.
Histological Techniques
Common histological techniques used to study the thyroid include
hematoxylin and eosin (H&E) staining, which highlights the overall structure of the gland. Immunohistochemistry can be used to detect specific hormones or markers within the tissue, providing further insight into functional states and pathological conditions.
