Friday, February 8, 2013

Parathyroid Glands

Four in number : 2 superior & 2 inferior
6mm in length
30-50mg each

Location:
    a. Superior parathyroid- near the junction of inferior thyroid artery & rec. laryngeal nerve.
    b. Inferior parathyroid – situated in the lower pole

Blood Supply: 
  Branches of the inferior thyroid arteries.
  May also be supplied by: sup. thyroid artery
                                          thyroid ima artery
                                          laryngeal, tracheal & esophageal arteries.
Venous Drainage:
   Parathyroid veins drain into thyroid plexus of veins of the thyroid gland and trachea.


Lymphatic Drainage:
     Deep cervical & paratracheal L.N

Nerve Supply of parathyroid gland is derived from thyroid branches of cervical sympathetic ganglion.

DEVELOPMENT

  • Superior parathyroid from fourth pharyngeal pouch
  • Inferior parathyroid from third pharyngeal pouch
  • Parafollicular cells from ultimobranchial body ( 4th pharyngeal pouch)



HISTOLOGY
-capsule
-cells present are: chief cell ( contain lipid)
                             oxyphil cell
                             stromal, connective tissue and fat.
FUNCTION
-PTH secretion : Calcium homeostasis

Primary hyperparathyroidism



a.Etiology

Parathyroid adenoma (80%); may be associated with MEN I and II
Parathyroid hyperplasia (15%):
Diffuse enlargement of four glands
Usually composed of chief cells
Parathyroid carcinoma (very rare)
Paraneoplastic syndrome: lung and renal cell carcinomas

b. Pathogenesis: excess production of parathyroid hormone (PTH) leads to hypercalcemia
 c.Clinical features
 Often asymptomatic
 Kidney stones
 Osteoporosis and osteitis fibrosa cystica
 Metastatic calcifications
 Neurologic changes


Secondary hyperparathyroidism
a. Etiology
i. Chronic renal failure
 ii. Vitamin D deficiency
iii. Malabsorption
b. Pathogenesis: caused by any disease that results in hypocalcemia, leading to
increased secretion of PTH by the parathyroid glands

Hypoparathyroidism



a. Etiology
i. Surgical removal  of glands during thyroidectomy
ii. Di George syndrome
 iii. Idiopathic
b. Clinical features
i. Lab: hypocalcemia
 ii. Neuromuscular excitability and tetany: Chvostek's and Trousseau's signs
iii. Psychiatric disturbances
iv. Cardiac conduction defects (ECG: prolonged QT interval)
T/t: Vit D & Calcium

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