Dr. K. Kharshiing · Surgical removal of the parathyroid glands (parathyroidectomy) Removal of...
Transcript of Dr. K. Kharshiing · Surgical removal of the parathyroid glands (parathyroidectomy) Removal of...
Dr. K. Kharshiing
Location
Hormone of the gland
Functions
Regulation
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The parathyroid glands are four
small glands, located on the
posterior surface of the thyroid
gland (Two on each lobe ).
The two parathyroid glands on each side
which are positioned higher (closer to the
head) are called the superior
parathyroid glands, while the lower two
are called the inferior parathyroid
glands.
In humans, the parathyroid glands are about
the size of a grain of rice and weigh between
25mg and 40mg and measuring about 6 mm
long, 3 mm wide and 2 mm thick.
Name Staining Quantity Size Function
Chief cells darker many smallermanufacture
Parathormone(PTH)
Oxyphilcells
lighter few largerfunction unknown.
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Rare chief cells
Abundant oxyphil cells
(unknown function)
Chief cells produce PTH
◦ Parathyroid hormone, or
parathormone
◦ A small protein hormone
PTH is secreted by the chief cells of the
parathyroid.
It is an 84 amino acid peptide with a
molecular weight of 9500 Da and a short
half‐life (2–3 min) in the circulation.
Parathyroid hormone (PTH)
PTH plays a central role in the
rapid control of calcium
homeostasis. PTH maintain the
blood calcium within the critical
range of 9.0 to 11 mg/dL.
The major physiological effect
of PTH is thus enhancement of
Ca2+ reabsorption from the bones,
kidney tubules and absorption of
Ca2+ from the GI tract
Calcium is essential to life, and is used primarily for three things:
• To provide the electrical energy for our nervoussystem. Calcium is what the nervous system of our body usesto conduct electricity.
• To provide the electrical energy for our muscularsystem. Our muscles use changes in calcium levels inside thecells to provide the energy to contract.
• To provide strength to our skeletal system. The bonesthemselves serve as the storage system that make sure we willalways have a good supply of calcium.
Thus, calcium is the most closely regulated element inour bodies. In fact, calcium is the ONLY element /mineral that has its own regulatory system
(the parathyroid glands).
• The Most important function of the parathyroid glands is to
regulate the calcium level in our bodies within a very narrow
range so that the nervous, muscular and skeletal systems can
function properly.
…….and if the calcium levels go down a little bit, the parathyroid
glands recognize it and make parathyroid hormone (PTH) which
goes to the bones and takes some calcium out (makes a
withdrawal from the calcium vault) and puts it into the blood.
When the calcium in the blood is high enough, then the
parathyroids shut down and stop making PTH.
Controls the blood phosphate level.
It stimulates resorption of phosphate from bones thereby
decreasing phosphate level in the blood.
PTH also helps in activation of vitamin D
Since vitamin D is very essential for calcium absorption
from the GI tract. But, vitamin D itself is not an active
substance. Instead, has to be converted to 1, 25-
dihydrocholecalciferol in the liver and kidney which
requires the presence of PTH
Other functions of PTH includes.......
Ca2+ ion regulates the hormone secretion through a
feedback mechanism
Plasma phosphate ion level may also contribute in the
regulation of the parathyroid secretion
Feedback Loop
A drop in blood Ca2+
causes
the parathyroid gland to
produce PTH, stimulating the
release of Ca2+
from bone.
PTH also promotes
reabsorption of Ca2+
in
kidneys and uptake of Ca2+
in intestines.
A rise in blood Ca2+
causes
release of calcitonin from the
thyroid gland, promoting
Ca2+
deposition in bone and
reducing reabsorption in
kidneys.
Disorder of the parathyroid Glands
Disorders of the parathyroid Glands
Hypoparathyroidism
o Decrease secretion of PTH. It leads to
hypocalcemia
Hyperparathyroidism
o Hypersecretion of PTH. It results in
hypercalcemia
Hypo-parathyroidismCauses:
Surgical removal of the parathyroid glands
(parathyroidectomy)
Removal of parathyroid glands during surgical
removal of the thyroid glands (thyroidectomy)
Autoimmune diseases
Deficiency of receptors for PTH in the target cells.
In this, the PTH secretion is normal or increase but
the hormone cannot act on the target cells. This
condition is called pseudohypoparathyroidism
Hypocalcemia and Tetany
Hypoparathyroidism causes hypocalcemia (decrease in
plasma calcium level) by decreasing the resorption of
calcium from bones. It causes neuromuscular
hyperexcitability resulting in hypocalcemia tetany.
Normaly. tetany occurs when plasma calcium level falls
below 6 mg/dL from its normal value of 9 mg/dL
Tetany is an abnormal condition characterized by
hyperexcitability of nerves and skeletal muscles resulting in painful
muscular spasm (involuntary contraction of muscle or group of
muscles) particularly of the hands and feet.
Hypocalcemia tetany
Signs and symptoms:
Hyper-reflexia (over active reflex action) and
convulsions (convulsive muscular contraction)
Carpopedal spasm (violent and painful contraction in
the hand and feet).
Laryngeal stridor (loud crowing sound during inspiration
which occurs mainly due to laryngospasm. Laryngeal
stridor is a common feature of hypocalcemic tetany)
Cardiovascular changes
• Dilation of the heart
• Arrhyrhmias
• Hypotension
• Heart failure
Other features
• rise in body temperature
• profuse sweating
Hyperparathyroidism
o Hypersecretion of PTH. It results in
hypercalcemia (higher than normal blood
calcium level)
Due to excess secretion of PTH a bone
disease called Osteitis fibrosa cystica is
caused and cyst like cavities make their
appearance in the bone. There is loss of
mucopolysaccharide from the bone matrix
The parathyroid functionTest
An intact PTH is the most frequently ordered parathyroid hormone
test. It is ordered to help diagnose the reason for a low or high
calcium level and to help distinguish between parathyroid-related
and non-parathyroid-related causes.
It may also be ordered to monitor the effectiveness of treatment
when a patient has a parathyroid-related condition.
A calcium test is almost always ordered along with a PTH test. It is
not just the levels in the blood that are important, but the balance
between them and the response of the parathyroid glands to
changing levels of calcium.
Let us recap……• There are 4 parathyroids glands. We all have 4 parathyroids
glands.
• Parathyroid glands are in the neck behind the thyroid.
• Parathyroids are NOT related to the thyroid (except they
are neighbors in the neck).
• The thyroid gland controls much of your body's
metabolism, but the parathyroid glands control body
calcium.
Parathyroid glands make a hormone, called "Parathyroid
Hormone“ (PTH).
All four parathyroid glands do the exact same thing.
Parathyroid glands control the amount of calcium in your
blood.
Parathyroid glands control the amount of calcium in your
bones.
Also maintains the Phosphate level in the blood
Usually doctors are concerned about either severe
imbalances in calcium regulation that may require
medical intervention or in persistent imbalances that
indicate an underlying problem.
PTH levels can be used to monitor people who
have conditions or diseases that cause chronic calcium
imbalances or to monitor those who have had surgery or
other treatment for parathyroid tumors.