Page 779 - Atlas of Histology with Functional Correlations

SECTION 2 • Thyroid Gland, Parathyroid

Glands, and Adrenal Gland

THYROID GLAND

Located in anterior neck region and consists of two large, connected lobes
Consists of follicles surrounded by follicular cells that fill the lumen with
colloid

Colloid contains thyroglobulin, an iodinated inactive storage form of thyroid
hormones
Follicular cells controlled by thyroid-stimulating hormone (TSH)
Iodide is an essential element in the production of thyroid hormones

Low levels of thyroid hormones stimulate the release of TSH from
adenohypophysis
Iodide is taken from blood, oxidized to iodine, and transported into follicular
lumen

Iodine combines with tyrosine groups to form iodinated thyroglobulin
Triiodothyronine (T ) and tetraiodothyronine (T ) are main thyroid gland
3
4
hormones
Release of thyroid hormones involves endocytosis of thyroglobulin and
hydrolysis of thyroglobulin
Thyroid hormones bound to thyroxin-binding protein
T is produced, but T is physiologically more potent than T 4
3
4
Thyroid hormones increase metabolic rate, growth, differentiation, and body
development
Parafollicular cells (C cells) are located in follicular peripheries of thyroid

gland
Parafollicular cells (C cells) secrete calcitonin to lower blood calcium by
inhibiting osteoclasts

Parafollicular cells (C cells) act independent of pituitary gland hormones but
depend on calcium levels

PARATHYROID GLANDS

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