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.