parathyroid gland hormone physiology.pdf

physio lecture

1. Calcitoninand
Parathyroid gland

2. The hormone produced by the parafollicular cells of the
thyroidgland is calcitonin (CT).
CT can decrease the level of calcium in the blood by inhibiting
the action of osteoclasts, the cells that break down bone
extracellular matrix.
secretion of CT is controlled by a negative feedback system
Calcitonin

3. Effect of calcitonin on calcium and phosphates
Whenitsbloodlevelishigh,calcitoninlowerstheamountof
bloodcalciumandphosphatesbyinhibitingboneresorption
(breakdownofboneextracellularmatrix)byosteoclastsandby
acceleratinguptakeofcalciumandphosphatesintobone
extracellularmatrix.
Effectiveroleinosteoporosisbecauseitincreasesbone
strengthbydepositingmorecalciumonbones.

4. Parathyroid Glands
Parathyroid glands are several small, round masses of tissues
partially embedded in the posterior surface of the lateral lobes
of the thyroid gland.
Parathyroid glands contain two kinds of epithelial cells
1.chief cells or principal cells, produce parathyroid hormone
(PTH), also called parathormone
2.oxyphilcell

5. Parathyroid hormone
Parathyroid hormone is the major regulator of the levels of
calcium, magnesium, and phosphate ions in the blood.
The specific action of PTH is to increase the number and
activity of osteoclasts..
The result is elevated bone resorption, which releases ionic
calcium and phosphates into the blood.

6. Effect of PHT on Kidney
➢In kidney it slows the rate at which Ca and Mg are lost from
blood into urine.
➢It increases loss of HPO4 from blood into the urine.
➢PTH decreases blood HPO4 level and increases blood Ca and
Mg levels.
➢It promote formation of the hormone calcitriol the active form
of vitamin D.
➢Calcitriol (D3) increases the rate of Ca+2, HPO4, and Mg+2
absorption from the gastrointestinal tract into the blood.

7. `

8. Control of Secretion of Calcitonin and
Parathyroid Hormone
The blood calcium level directly controls the secretion of both
calcitoninand parathyroid hormone via negative feedback
loops
1.A higher-than-normal level of calcium ions in the blood
stimulates parafollicularcells of the thyroid gland to release
more calcitonin.
2.Calcitonininhibits the activity of osteoclasts, thereby
decreasing the blood Ca level.
3.A lower-than-normal level of Ca2 in the blood stimulates
chief cells of the parathyroid gland to release more PTH.

9. 4.PTH promotes resorption of bone extracellular matrix,
which releases Ca2 into the blood and slows loss of Ca in
the urine, raising the blood level of Ca.
5.PTH also stimulates the kidneys to synthesize calcitriol, the
active form of vitamin D.
6.Calcitriol stimulates increased absorption of Ca2 from foods
in the gastrointestinal tract, which helps increase the blood
level of Ca.

10. Parathyroid hormone (PTH)stimulates both osteoblasts and
osteoclasts
Parathyroid hormone (PTH)stimulates both osteoblasts and osteoclasts, but in a
complex and indirect manner.PTH primarily acts on osteoblasts to increase
their expression of RANKL, which then stimulates osteoclast activity.In
addition to this, PTH can also directly stimulate osteoblast activity, leading to
bone formation.
Here's a more detailed explanation:
•PTH and Osteoblasts:
•PTH binds to receptors on osteoblasts, triggering them to release RANKL
(Receptor Activator of Nuclear factor-κBLigand) and inhibit the production
of osteoprotegerin(OPG).
•RANKL and Osteoclasts:
•RANKL is a signaling molecule that stimulates osteoclast precursors to mature
and differentiate into active osteoclasts.

11. •OPG and Osteoclast Differentiation:
•OPG normally acts as a decoy receptor for RANKL, preventing it from binding to
RANK and stimulating osteoclast differentiation.PTH's inhibition of OPG production
allows RANKL to more effectively stimulate osteoclast activity.
•PTH and Bone Resorption:
•The increased osteoclast activity leads to bone resorption, where osteoclasts break
down bone tissue, releasing calcium into the bloodstream.
•PTH and Bone Formation:
•In addition to its catabolic effects, PTH can also have anabolic effects on bone,
directly stimulating osteoblast activity and increasing bone formation, according to a
study on PubMed Central.This effect is particularly noticeable during intermittent
administration of PTH.
In summary, PTH indirectly stimulates osteoclasts through its effects on osteoblasts,
and it can also directly stimulate osteoblast activity, leading to both bone resorption
and formation.