The parathyroid glands secrete parathyroid hormone (PTH) which regulates calcium levels in the blood. PTH acts on bone, kidney and intestine to increase blood calcium. It causes bone to release calcium, kidneys to reabsorb more calcium, and intestine to absorb more calcium. When calcium levels decrease, PTH secretion increases to restore normal levels. Calcitonin from the thyroid gland acts opposing PTH to decrease blood calcium and is released when calcium levels rise. Vitamin D aids in intestinal calcium absorption and works synergistically with PTH on bone. Calcium is essential for many bodily functions and maintaining normal blood levels of 10mg/dl is important.

1. PRESENTED BY-
Dr. FIRDOSH ROZY
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2. INTRESTINGFACT
Richard Owen,
(1804 – 1892) who
discovered the
parathyroid glands
in 1850 in a
rhinoceros
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3. The endocrine system regulates body activities by
releasing hormones (chemical messengers) into the
bloodstream, where they are carried throughout the entire
body.
 Glands secrete their products (hormones) into the
extracellular space around the secretory cells.The
secretions diffuse into capillaries and are carried
throughout the body by the circulatory system.
The specific cells which are affected by a hormone are
called target cells.
Circulating hormones may linger in the blood for minutes
to hours or exerting their effects for a prolonged period of
time
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4. Prathyroidgland
Parathyroids are two
paired endocrine
glands located on
the thyroid
glands.
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5. DEVELOPMENT
Endodermal proliferation of 3rd and 4th pharyngeal pouches.
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6. ANATOMY
Two pairs of glands 80 – 97%
>4 – 13%, 3 – 3%
Light yellowish to reddish brown
Oval or lentiform shaped
Bilobed 5%, multilobed 1%
5x3x2 mm
40 – 50 gms
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7. Superior parathyroids –
more consistent in location
Subcapsular
1cm above the intersection between
inferior thyroid artery and the recurrent
laryngeal nerve
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8. Inferior parathyroids
variable in location
 inferior, posterior or lateral to the lower pole 61%
Inferior to lower pole in close relation to the thyrothymic
ligament
26% within cervical part of thymus
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9. Positionofparathyroid
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10. 2% in the mediastinal portion of thymus
 0.2% in the mediastinum
 In some cases they fail of descent – located above
the position of superior parathyroid glands
surrounded by remnants of thymic tissue
 Superior parathyroids lie posterior and inferior
parathyroid lie anterior to recurrent laryngeal nerves
POSITIONS OF PARATHYROID –
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12. HISTOLOGY
Histology
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13. (Principal Cells): These cells release PTH and are more
numerous, smaller, with a slightly eosinophilic cytoplasm
CHIEF CELLS;
OXIPIL CELLS;
They are found individually, or clustered in groups. The
function of these cells is unknown.
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14. PHYSIOLOGY
Major function of the parathyroid gland is homeostasis of
calcium via Parathyroid hormone (PTH)
PTH is synthesized in the parathyroid gland as a precursor
hormone the preproparathyroid hormone 115amino acid
which is cleaved first to proparathyroid hormone 90 and finally
to the 84amino-acid
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15. Half-life of 2 to 4 minutes
Secretion mainly controlled by ionized calcium levels via
calcium sensing receptors ( CaSR)
CaSR are G protein coupled receptors present on the chief
cells
 and it is expressed on the surface of the parathyroid cell and
senses fluctuations in the concentration of extracellular calcium
Calcium binds on CaSR and reduces intracelular c AMP
decreases the PTH secretion
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16. PTH functions to regulate calcium levels via its
actions on three target organs; bone, kidney,
intestine.
PTH secretion is also controlled by catecholamine
levels and magnesium levels.
It is stored in secretory vesicles within the cells,
and released when required.
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17. TARGET ORGANS FOR PTH
Some effect on intestine also
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18. The Role of the Parathyroid Glands
PTH raises the blood calcium level by:
1. breaking down the BONE (where most of the body's
calcium is stored) and causing calcium release.
2. increase the GIT ability to absorb calcium from food.
3. increasing the KIDNEY's ability to retain calcium that
would otherwise be lost in the urine.
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21. PTH ACTION ON BONE FORMATION
•Increase osteoblastic number
• Increase collagen synthesis
• Increase alkaline phosphatase activity
• Increase local growth factors: IGF and transforming
factors
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22. PTH ACTIONS ON KIDNEY
• Increase calcium and magnesium reabsorption from
ascending loop and distal tubule
• Increase chloride reabsorption from proximal tubule
• Decrease phosphate,sodium and bicaronate
reabsorption from the proximal tubule
• Increase proximal tubule 1-alpha-hydroxalase activity
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23. PTH ACTIONS ON INTESTINE
Increases Ca absorbtion indirectly via 1,25-didroxcolecalciferol.
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25. CALCITONIN
• Polypeptide hormone
• Synthesized and secreted by the parafollicular C-cells of the
thyroid gland
Action:
•receptors for Calcitonin are found in the bones and the
kidneys.
• It inhibits the activity of osteoclasts and also increase
Ca++ in the urine
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26. Vitamin D-3 formed in the skin when a cholesterol precursor,
is exposed to ultraviolet light.
Activation occurs when the substance undergoes 25-
hydroxylation in the liver and 1-hydroxylation in the kidney.
The primary action of 1,25-(OH)2 D3 is to promote gut
absorption of calcium by stimulating formation of calcium-
binding protein within the intestinal epithelial cells.
VIT D
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27. Vitamin D also promotes intestinal absorption of phosphate
ion, although the exact mechanism is unclear. Negatively
charged phosphate ion may passively flow through the
intestinal cell because of flux of the positively charged
calcium ion.
In bone, vitamin D may play a synergistic role with
parathyroid hormone (PTH) in stimulating osteoclast
proliferation and bone resorption. Compared to parathyroid
hormone (PTH), vitamin D exerts a much slower regulatory
effect on calcium balance.
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28. Why Calcium is so Important?
A specific gland just to maintain Ca level !
It has a wide range of functions
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 Stimulate hormone secretion.
 Muscle contraction.
 Blood clotting.
 Nerve function- transmit nerve impulse.
 Necessary for the activation of some enzyme.
 Transport ion across membrane.
 Maintain regular heart beat (conduct electricity).
Normal level of Ca in the blood is around 10mg/dl.
(Ganong’s review of med. Phy.)

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