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Parathyroid Gland 


  1. Normal calcium level in the body
    1. Normal serum Ca = 9 – 11 mg%,
    2. Ionized Ca = 50%,
    3. Ca bound to protein = 40%,
    4. Ca bound to anions - 10%

Table . Distribution (mmol/L of Calcium in Normal Human Plasma).


Total diffusible 



Ionized (Ca2+)



Complexed to HCO3-, citrate, etc



Total nondiffusible (protein-bound) 



Bound to albumin



Bound to globulin



Total plasma calcium 



  1. Normal histology of the bone
    It has three types of cells
    1. Osteoblast  - These are the bone forming cell. Whenever there is increase activity of osteoblast it causes raised level of serum alkaline phosphatase (MCQ). That is why level of serum alkaline phosphatase is raised in children and pregnancy (MCQ). Have receptors for PTH. Help in forming new bone.
    2. Osteocytes  -  They are the bone maintaining cells. They regulate bone activity.
    3. Osteoclast  -  They cause bone resorption (MCQ). In Multiple myeloma there is increase activity of osteoclast that is why there are lytic lesion and Hypercalcemia in MM (MCQ)

Important Points:

  1. In MM there is no increase activity of osteoblast.
  2. That’s why serum alkaline phosphatase level (ALP) are normal in MM and bone scan is also normal. (FAQ)
  3. Other bone condition with increase ALP = 1. Paget disease, 2. Bone metastases, 3. Rickets, osteomalacia,
  4. Osteogenesis imperfecta,
  5. Osteogenic sarcoma.
Extra Edge:

ALP level is normal in osteoporosis and multiple myeloma.

Parathyroid Hormone

Basic physiology

(PTH) is normally secreted in response to low ionized Ca2+ levels, by 4 parathyroid glands situated posterior to the thyroid.

PTH acts by :-

  1. osteoclast activity releasing Ca2+ & PO43- from bones
  2. Ca2+ & PO43- reabsorption in the kidney;
  3. Active 1,25 dihydroxy-vitamin D3 production. 

Biochemical Markers of Bone Metabolism in Clinical Use (Ref. Hari. 18th ed., Pg - 3126) 

  1. Bone formation
    1. Serum bone-specific alkaline phosphatase
    2. Serum osteocalcin
    3. Serum propeptide of type I procollagen
  2. Bone resorption
    1. Urine and serum cross-linked N-telopeptide
    2. Urine and serum cross-linked C-telopeptide
    3. Urine total free deoxypyridinoline



  1. (Primary hyperparathyroidism
    Ca, PO4, PTH
    1. The most common cause of primary hyperparathyroidism is parathyroid solitary adenoma.
    2. A single solitary abnormal gland is the cause of approximately 80% of patients
    3. The abnormality of the gland is usually a benign neoplasm or adenoma and rarely a parathyroid carcinoma.

Important Point

  1. Adenomas are most often located in the inferior parathyroid gland. (MCQ)
  2. Chief cells are predominant in both hyperplasia and adenoma. 
  1. Secondary hyperparathyroidism : Ca2+, PTH (MCQ) PO4 (In CRF)
    Ca , PTH ,   PO4 (In malnutrition, ricket osteomalacia)

Causes Low vitamin D intake, chronic renal failure, Rickets, osteomalacia, malabsorption (FAQ)

(Note: Rugger Jersey spine is seen in CRF)


The "trade-off hypothesis" for Ca2+/PO42– homeostasis with progressively declining renal function. (Ref. Hari. 18th ed., Pg-2289)


In CRF, serum calcium level decreases and serum phosphate level increases.

  1. Tertiary hyperparathyroidism :   Ca2+, PTH (FAQ) PO4


  1. Occurs after prolonged secondary hyperparathyroidism, causing glands to act autonomously having undergone hyperplastic or adenomatous change.
  2. This causes Ca2+ from secretion of PTH unlimited by feedback control. Seen in chronic renal failure.
  1. Malignant hyperparathyroidism
    1. Causes: Parathyroid-related protein (PTHrp) is produced by some squamous cell lung cancers, breast and renal cell carcinomas. (FAQ) 
Extra Edge: 

Hypercalcemia in malignancy occur due to increase level of PTHrp. In this PTH level are not raised (AIIMS Nov 12).


Important Points: Most patient’s of hyperparathyroid are “asymptomatic


Manifestations of Hyperparathyroidism


Renal feature





• Anorexia

• Nausea

• Vomiting

• Fatigue

• Mental confusion

(Psychic moans)

• Polyuria &    


• Renal colic

from stones

• Bone pain

- Bone cysts

- Brown tumor

• Peptic ulceration

(abdominal groans)

• Constipation (LQ 2012)

• Short QT interval in ECG arrhythmias


• Ectopic calcification & chondrocalcinosis


Extra Edge:

Polyuria results from effect of hypercalcemia on renal tubules reducing their concentrating ability, a form of nephrogenic diabetes insipidus

Serum Abnormality In Hyperparathyroid


Serum Ca

Serum phosphate

Alkaline phosphatase


Primary hyperparathyroidism

Secondary hyperparathyroidism

Tertiary hyperparathyroidism


Extra Edge:
  1. 24 hrs Ca excretion in urine is increased in hyperparathyroid.
  2. Serum calcitonin is not a marker of hyperparathyroid.
  3. In renal osteodystrophy (CRF) calcium is low but phosphate is high but in nutritional secondary hyperparathyroid both calcium and phosphate are low. (LQ 2012)

Pathology of Skeletal Changes In Hyperparathyroidism

  1. Diffuse bone resorption:
    1. The Howship lacunae are filled with large number of osteoclasts and the Haversian canals are enlarged.
  2. Brown tumours:
    1. The "tumour" is a well circumscribed dark brown area of soft consistency, situated where bone resorption has been severe.
  3. Osteitis fibrosa cystica:
    1. Healing in case of hyperparathyroidism occurs by fibrous tissue replacement or sometimes the centre may liquefy and a bone cyst remains. (LQ 2012)
  4. Deformities:
    1. Intervertebral disk becomes ballooned as they indent soft vertebral bodies forming the 'Cod Fish spine'.
      Note: Osteopetrosis is not a feature.
  5. X-Ray findings
    1. Osteoporosis:
      1. The early finding is that of generalized deossification.
    2. Subperiosteal resorption:
      1. Subperiosteal erosions are most frequently identified along the middle phalanges of the index and middle fingers is a characteristic feature. (Tufting of the phalanges.)
      2. This x-ray feature is virtually diagnostic of hyperparathyroidism.
      3. Pinhead stippling:
        1. The skull displays a diffuse osteoporosis described as pinhead stippling. (pepper pot appearance)
      4. Mandible x-ray = Demineralization of mandible
      5. Calciphylaxis = Metastatic calcification of blood vessel (secondary to hyperphosphatemia) may lead to ischemia damage to skin & other organs.
      6. Rugger Jersey spine is seen in CRF

Location of The Adenoma

99Tc sestamibi scan.
  1. After one hour of injection, uptake is done by both thyroid and parathyroid gland.
  2. After 3 hrs uptake evidence is there only in parathyroid. So by computer subtraction adenoma is located.   

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