Thyroid & parathyroid

Parathyroid - general

Anatomy & histology-parathyroid


Editorial Board Member: Marc Pusztaszeri, M.D.
Deputy Editor-in-Chief: Andrey Bychkov, M.D., Ph.D.
Truong Phan Xuan Nguyen, M.D.

Last author update: 24 August 2023
Last staff update: 21 September 2023

Copyright: 2003-2024, PathologyOutlines.com, Inc.

PubMed Search: Anatomy / histology parathyroid

Truong Phan Xuan Nguyen, M.D.
Page views in 2023: 17,106
Page views in 2024 to date: 3,106
Cite this page: Nguyen TPX. Anatomy & histology-parathyroid. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parathyroidanatomy.html. Accessed February 22nd, 2024.
Definition / general
Essential features
  • 4 tiny glands located on the posterior surface of the thyroid
  • Histologically composed of a parenchyma of chief cells, oxyphils and transitional cells, and stromal fat
  • Regulate calcium homeostasis through synthesis and secretion of parathyroid hormone (PTH)
Terminology
  • Glandulae parathyroidae (by Ivar Sandström, 1880), Epithelkörperchen (by Kohn, 1895)
Physiology
  • Genes involved in differentiation and growth of parathyroid glands
  • Synthesis and secretion of parathyroid hormone (PTH), an 84 amino acid peptide derived from a large precursor of 115 amino acids (preproPTH); only the 34 N terminal amino acids have biologic activity (J Endocrinol 2005;187:311)
  • Main function of PTH is regulation of serum calcium which mediated by the calcium sensing receptor (CaSR); hypocalcemia activates CaSR, inducing increased PTH synthesis and secretion (Biochem Biophys Res Commun 1995;214:524, Proc Natl Acad Sci USA 1995;92:131)
  • PTH acts by increasing calcium resorption into blood from bone, kidney and the gut
    • Acting on the PTH receptor (PTHR1) that stimulates renal tubular reabsorption of calcium
    • Enhances calcitriol formation in kidney by stimulating 1α vitamin D hydroxylase to convert 25(OH) vitamin D to 1α25(OH)2 vitamin D, resulting in increased gut absorption of calcium
    • Prolong life and increase activity of osteoblast, while osteoblast signaling activates osteoclasts, indirectly causing bone resorption; PTH activates osteocytes, causing lysis of perilacunar bone (Mills: Histology for Pathologists, 5th Edition, 2020)
Diagrams / tables

Images hosted on other servers:

Embryological pathway of parathyroid migration

Anatomy

Anatomy

Laboratory
Gross description
  • Small, smooth, soft, flattened ovoid or bean shaped structures (4 - 6 mm long, 3 - 4 mm wide, 1 - 2 mm thick), yellow-tan
  • Each gland weighs ~30 - 40 mg but can also extremely variable; inferior glands are slightly larger
    • 60 mg is the upper limit of normal weight for a parathyroid gland, although weight > 40 mg can be considered abnormal (J Am Coll Surg 2006;203:758)
  • Parenchyma is yellow to orange-tan depending on the amount of stromal fat, percent of oncocytic cells and vascularity
  • Reference: Lindberg: Diagnostic Pathology - Normal Histology, 3rd Edition, 2022
Gross images

Contributed by Truong Phan Xuan Nguyen, M.D.
Normal parathyroid gland

Normal parathyroid gland

Frozen section description
  • Parathyroids often sent for intraoperative consultation: 1) identification of parathyroid tissue to preserve the glands in situ or for autotransplantation to avoid postoperative hypoparathyroidism and 2) evaluation during surgery for primary hyperparathyroidism to verify abnormal glands
  • Parathyroid to be differentiated from fat, lymph nodes, thymus, thyroid and other tissue (Arch Pathol Lab Med 2005;129:1575)
  • Parathyroid consists of a mixture of parenchymal cells (chief, oxyphil) and fat
  • Near infrared fluorescence imaging with indocyanine green imaging is a useful tool for intraoperative detection of parathyroid by surgeon (In Vivo 2020;34:23)
Microscopic (histologic) description
  • Thinly encapsulated with fibrous septa extending into parenchyma dividing gland into vague lobules
  • Parenchyma has 3 cell types: chief cells, oxyphils and transitional cells; these are all variants of the chief cells that have differing degrees of oncocytic change
    • Parenchymal cells arranged in nests and cords
  • Chief cells
    • Functional cells, responsible for the synthesis and secretion of PTH
    • 8 - 12 μm in diameter, round to polygonal with centrally located nuclei, coarse chromatin and small nucleoli
    • Cytoplasm varies from clear to amphophilic or faintly eosinophilic
      • Clear vacuolated appearance is due to accumulation of glycogen or lipid
    • Arranged in small nests and thin cords and separated by stromal adipose tissue
  • Oxyphil cells
    • Typically appear at puberty and increase in number with age
    • Larger than chief cells, measuring 12 - 20 μm in diameter
    • Singly, in small clusters or as large nodules and sheets
    • Abundant granular eosinophilic cytoplasm due to the accumulation of numerous mitochondria
  • Transitional cells
    • Intermediate forms that have features of chief cells and partial oncocytic change
  • Water clear cell
    • Found in the fetal gland but are not present in normal adult glands
    • Found usually only in pathologic states (hyperplasia and adenoma)
    • Very large, measuring 15 - 20 μm and up to 40 μm
    • Represent chief cells with excessive cytoplasmic glycogen
  • May have cysts and follicles filled with proteinaceous material that resembles colloid of the thyroid gland
    • Positive with periodic acid-Schiff (PAS)
    • Do not contain birefringent calcium oxalate crystals (polarized light)
  • Stroma comprised of stromal fat cells and fibroconnective tissue with rich vascular supply
  • Age related changes: increased stromal fat cells, accumulation of fibroconnective tissue, more oxyphils
  • Reference: Lindberg: Diagnostic Pathology - Normal Histology, 3rd Edition, 2022
Microscopic (histologic) images

Contributed by Truong Phan Xuan Nguyen, M.D.
Normal parathyroid gland Normal parathyroid gland

Normal parathyroid gland

Chief cells Chief cells

Chief cells


Oxyphils cells Oxyphils cells

Oxyphil cells

Transitional cells

Transitional cells

Water clear cells

Water clear cells

Colloid type material, without oxalate crystals

Colloid type material, without oxalate crystals

Virtual slides

Images hosted on other servers:

Parathyroid gland

Frozen section

Positive stains
  • Histochemistry
    • PAS (chief cells contain abundant glycogen, colloid-like material in cysts and follicles)
    • Oil red O (chief cells contain intracytoplasmic lipid droplets - frozen section)
  • Immunohistochemistry
Negative stains
Electron microscopy description
  • Chief cells: contain relatively few secretory granules
  • Oxyphil cells: the cytoplasm is filled with numerous mitochondria
  • Transitional cells: have fewer mitochondria than fully developed oncocytic cells but more than chief cells
  • Reference: Mills: Histology for Pathologists, 5th Edition, 2020
Electron microscopy images

Images hosted on other servers:

Parathyroid gland

Videos

Histology of parathyroid

Board review style question #1
Which cell type of parathyroid glands is round to polygonal with centrally located nuclei, coarse chromatin, small nucleoli and cytoplasm that ranges from clear to amphophilic or faintly eosinophilic?

  1. Chief cell
  2. Oxyphil cell
  3. Transitional cell
  4. Water clear cell
Board review style answer #1
A. Chief cell. These features are suitable for the chief cell's function of producing and releasing PTH hormone. Answer B is incorrect because oxyphil cells have granular eosinophilic cytoplasm. Answer C is incorrect because transitional cells have partial features of chief cells and oxyphil cells. Answer D is incorrect because water clear cell has foamy cytoplasm.

Comment Here

Reference: Anatomy & histology - parathyroid
Board review style question #2

In which type of parathyroid glands are water clear cells found?

  1. Ectopic glands
  2. Fetal glands
  3. Normal adult glands
  4. Supernumerary glands
Board review style answer #2
B. Fetal glands. Water clear cells are usually found in fetal parathyroid glands with excessive cytoplasmic glycogen. Answers A, C and D are incorrect because they only comprise 3 cell types (chief cells, oxyphil cells and transitional cells) of normal adult parathyroid glands.

Comment Here

Reference: Anatomy & histology - parathyroid
Back to top
Image 01 Image 02