The parathyroid glands are four small endocrine glands that regulate calcium homeostasis. They secrete parathyroid hormone (PTH) which increases blood calcium levels. The parathyroid glands were first accurately described in 1849 and their role in calcium metabolism was established through later discoveries in the late 19th and early 20th centuries. They have complex embryological development and anatomy with variable positioning. Histologically, they contain chief cells and oxyphil cells. The parathyroid glands, PTH, calcitonin, and vitamin D work together to tightly regulate extracellular calcium levels which is essential for many physiological functions.

1. PARATHYROID GLANDS
Dr. KALICHARAN
S5 Unit
Guide: Dr. Sailaja Rani M.S. (Prof.)
Co-Guide: Dr. Renuka M.S. (Asst. Prof.)

2. HISTORY
• 1849,Sir Richard Owen- first accurate description of normal
parathyroid in animals
• 1879,Ivar Sandstrom- glandulae parathyroideae
• 1891,Gley- development of tetany after removal
• 1908,MacCallum-calcium metabolism
• 1923,Hanson-isolation of PTH
• 1926,Edward Churchill-first parathyroid surgery
• 1928,Isaac Y. Olch- first successful surgery

3. EMBRYOLOGY
• Parathyroid IV or Superior parathyroid
• Parathyroid III or Inferior parathyroid
• Inferior parathyroid glands have longer line of
descent

6. ANATOMY
• Most humans have 4 glands
• Akerstrom and colleagues,in autopsy series of 503
cadavers, found-
84% have 4 glands
13% supernumerary glands, mc in thymus
3% had <4 glands
• Normal parathyroid glands weigh 30-50mg and are approx
size of rice grain (3-5mm)

7. • Normal parathyroids are gray and semitransparent in
newborns
• In adults they appear golden yellow to light brown
• Their color mainly depends on cellularity, fat content,
vascularity
• Often embedded in and sometimes difficult to discern
from surrounding fat
• Bilateral symmetry- 80% in superior glands and 70% in
inferior glands

8. Position :
• Superior glands -more consistent, 80% near post
aspect of thyroid at the level of cricoid cartilage
• Approx 1% of normal sup. glands – in
paraesophageal or retroesophageal space
• Enlarged sup. glands may descend in
tracheoesophageal groove and come to lie caudal
to inferior glands

9. • Inferior glands – within 1cm from a point
centered where ITA and RLN cross
• Approx 15% of inf glands are found in the thymus
• Inf glands can be found as high as skull base,
angle of mandible or as low as pericardium
• Sup glands are located dorsal to RLN where as Inf
glands are located ventral to RLN

12. Histology
• Composed of chief cells and oxyphil cells arranged in
trabeculae , stroma composed primarly of adipose cells
• Infants and children- mainly chief cells, produce PTH
• Acidophilic, mitochondria-rich oxyphil cells are derived
from chief cells, seen around puberty and adulthood
• Water-clear cells - rich in glycogen
• Functional significance unknown

14. Blood supply:
• 80% cases , all 4 receive blood supply from
Inferior Thyroid Artery
• Each gland has its own end arterial branch that
are vulnerable to injury during procedures
• 20% cases alternate blood supply to superior
glands from Superior Thyroid Artery
• Venous drainage parallels that of thyroid, with
the superior, middle and inferior thyroid veins

19. PHYSIOLOGY
• Most abundant cation - Calcium
• Levels in ECF >>>>ICF by 10,000 folds
• Regulated by PTH, Calcitonin & Vit D
• Extra cellular calcium role in
1. Excitation contraction of muscles
2.Synaptic transmission
3.Coagulation
4.Hormone secretion

20. • Intracellular calcium role in :
Second messenger regulating
- Cell division
- Motility
-Membrane trafficking and secretion

21. • Calcium exists in 2 forms
- Ionized (50%)
- Bound (albumin -40%) ,
(Phosphate,citrate-10%)
• Total S. Calcium - 8.5 to 10.5mg/dl
• Ionized calcium – 4.4 – 5.2mg/dl, regulated by hormones
• Acidosis increases ionized Ca level while Alkalosis increases bound
Ca level

23. PTH
• Synthesized as precursor hormone preproPTH
• Cleaves into Pro PTH then into 84 amino acid PTH
• Half life 2-4 min
• Metabolized in liver into
1.Active N terminal component
2.Inactive C terminal component
• PTH stimulated by low levels of calcium ,
Hypomagnesemia, catecholamines, 1,25hydroxyvit D

24. • PTH has 3 target organs-bone , kidney and gut
• It increases bone resorption by stimulating osteoclasts –
increase serum Ca & Phosphate
• PTH acts on DCT to limit Ca excretion, inhibits phosphate
and bicarb reabsorption at PCT
• It also inhibits Na/H antiporter- M.Acidosis in HyperPTH
states
• PTH and hypophosphatemia enhance 1-hydroxylation of
25-hydroxyvitaminD which inturn acts on intestine

26. CALCITONIN
• Secreted by Parafollicular C cells
• Antihypercalcemic hormone by inhibiting osteoclasts
• Stimulated by Ca and Pentagastrin, catecholamines,
CCK ,Glucagon
• At kidney it inhibits phosphate reabsorption
• Very useful as marker for MTC and in treating Acute
Hypercalcemic crisis

27. VITAMIN D
• Refers to vit D2 and vit D3- produced by photolysis of
naturally occurring sterol precursors
• Vit D2 pharmaceutically available
• Vit D3 m.imp physiologic compound produced from7-
dehydrocholesterol
• Metabolized in liver to 25-hydroxyvit D, further
hydroxylated in kidney to 1,25-dihydroxyvitD
• Vit D stimulates absorption of Ca and phosphate from gut
and resorption of Ca in bone

28. THANK YOU