Thyroid & parathyroid

Parathyroid - general

Anatomy & histology-parathyroid

Topic Completed: 1 January 2013

Minor changes: 14 June 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: (Anatomy[TI] OR histology[TI]) parathyroid[TI]

Page views in 2020: 10,024

Page views in 2021 to date: 10,681

Table of Contents

Cite this page: Roychowdhury M. Anatomy & histology-parathyroid. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parathyroidanatomy.html. Accessed December 6th, 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

Images hosted on other servers:

Embryological pathway of parathyroid migration, showing possible locations for lower parathyroid glands

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: