Table of Contents
Definition / general | Drawings | Parathyroid hormone physiology | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stainsCite this page: Roychowdhury M. Anatomy & histology. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parathyroidanatomy.html. Accessed January 18th, 2021.
Definition / general
- 4 glands in 2 pairs usually close to upper and lower poles of thyroid lobe
- Discovered in 1880 by Ivar Sandström, a Swedish medical student (Am J Surg Pathol 1996;20:1123)
- May be found anywhere along pathway of descent of branchial pouches
- 10% have 2 - 3 glands; 5% have 5 glands, 0.2% have 6 glands
- Upper pair arises from fourth branchial cleft and descends with thyroid gland; usually at cricothyroid junction
- Lower pair arises from third branchial cleft and descends with thymus; usually near inferior thyroid
- Other locations: carotid sheath, anterior mediastinum, intrathyroidal; glands tend to be bilaterally symmetrical
- Stromal fat increases to 30% at age 25; percent fat is related to constitutional percent fat but reduced in dying individuals; mean is 17% with wide variation (Hum Pathol 1982;13:717)
Drawings
Parathyroid hormone physiology
- Release controlled by ionized calcium level with negative feedback system
- 84 amino acids, derived from cleavage of prepro PTH; biologic activity due to 34 amino acids at amino terminus; other portions are inert but may give false positives in detection systems
- Binding of PTH to its receptor stimulates cAMP and phosphatidylinositol diphosphate
- Note: PTH related protein is rarely produced by benign lesions (Am J Clin Pathol 1996;105:487)
Five major actions:
- Activates and increases the number of osteoclasts, which mobilizes calcium from bone
- Increases renal tubular reabsorption of calcium
- Increases conversion of vitamin D to active dihyoxy form in kidneys
- Increases urinary phosphate excretion, which reduces calcium loss
- Increases GI calcium absorption
Hypercalcemia of malignancy (breast, lung, kidney, myeloma) due to
- Release of PTH related protein, usually in advanced disease, or
- Osteolytic metastases with local release of cytokines (IL1, TNF alpha)
Gross description
- Yellow-brown, 25 - 40 mg each gland
Microscopic (histologic) description
- Composed primarily of chief cells and fat with thin fibrous capsule dividing gland into lobules
- May have a pseudofollicle pattern resembling thyroid follicles (pink material is PAS positive)
Chief cells:
- 6 - 8 microns, polygonal, central round nuclei, contain granules of parathyroid hormone (PTH)
- Basic cell type, other cell types are due to differences in physiologic activity
- 80% of chief cells have intracellular fat
- Chief cell is most sensitive to changes in ionized calcium
Oxyphil cells:
- Slightly larger than chief cell (12 microns), acidophilic cytoplasm due to mitochondria
- No secretory granules
- First appear at puberty as single cells, then pairs, then nodules at age 40
Water clear cell:
- Abundant optically clear cytoplasm and sharply defined cell membranes
- Chief cells with excessive cytoplasmic glycogen
Microscopic (histologic) images
Positive stains
- Chromogranin A, glycogen, keratin, PTH