Parathyroid Hormones

and Calcitonin Habon, Cecille

Jove, Jessica

Lazo, Kareen

Parathyroid Hormone

• A mechanism for controlling extracellular

calcium and phosphate concentrations by

regulating intestinal reabsorption, renal

excretion, and exchange between the

extracellular fluid and bone of these ions.

Synthesis of PTH

• PTH is translated as a pre-prohormone.

• Cleavage of leader and pro-sequences

yield a biologically active peptide of 84 aa.

• Cleavage of C-terminal end yields a

biologically inactive peptide.

Regulation of PTH

• PTH secretion responds to small alterations in plasma Ca2+ within seconds.

• A unique calcium receptor within the parathyroid cell plasma membrane senses changes in the extracellular fluid concentration of Ca2+.

• This is a typical G-protein coupled receptor that activates phospholipase C and inhibits adenylate cyclase

Regulation of PTH

• When Ca2+ falls, cAMP rises and PTH is secreted.

• 1,25-(OH)2-D inhibits PTH gene expression, providing another level of feedback control of PTH.

Regulation of PTH

Calcium

regulates

PTH

secretion

PTH action

• Increases Calcium and Phosphate

Absorption from the Bone

• Decreases Calcium Excretion and

Increases Phosphate Excretion by the

Kidneys

• Increases Intestinal Absorption of Calcium

and Phosphate

Control of Parathyroid Secretion by Calcium Ion Concentration

• Slightest decrease in Ca++ ion concentration (in ECF)

causes the parathyroid glands to increase their rate of

secretion within minutes

• If a decreased calcium concentration persists, the glands

will hypertrophy, sometimes fivefold or more

• An increase calcium ion concentration (above normal)

cause decreased activity and reduced size of the

parathyroid glands

Conditions:

Excess quantities of calcium in the diet

Increased vitamin D in the diet

Bone absorption caused by factors other than PTH

Calcitonin • 32 amino acid peptide

• Molecular weight: 3400

• Primary stimulus: Increase calcium

concentrations

• Parafollicular cells of the thyroid glands

0.1 per cent of the human thyroid

gland

Remnants of the ultimobrachial glands

of lower animals (such as fish,

amphibians, reptiles, and birds)

• ANTAGOSNIST to PTH

Calcitonin Action

1. Decreases plasma calcium concentration

How to reduce plasma calcium?

Decrease the absorptive activities of the

osteoclasts

Decrease the formation of new

osteoclasts

Increase in osteoblastic activity

Calcitonin Action 2. Has a Weak Effect on Plasma Calcium

Concentration in the Adult Human

Twofolds:

First: Initial reduction of the calcium

ion concentration caused by calcitonin

Second: Daily rates of absorption and

deposition of Calcium [on the bone]

In adults: SLOW

In children: RAPID

Other Calcitonin Actions

• Inhibits resorption (bone)

• Increase secretion of water and

electrolytes (intestine)

• Increase Sodium, Calcium and

phosphate excretion in the urine

(kidneys)

• Decrease gastric acid secretion (GIT)

Hypoparathyroidism • Pathogenesis

– Heavier periods in

females

– Cataracts

– Tingling sensations

– Muscles spasms

– Dry hair and skin;

brittle nails

– Weakened tooth

enamel in kids

• Etiology

– Family History

– Autoimmune Disorder

– Excessive radiation

treatment

– Low levels of Mg in

blood

• Treatment

– Take vitamins with

Calcium and Vitamin D

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Hyperparathyroidism • Primary Hyperparathyroidism

Pathogenesis

– Tumor

– Bone Disease

– Hypercalcemia

– Parathyroid Poisoning and

Metastatic Calcification

– Formation of Kidney Stones

• Secondary

Hyperparathyroidism

Pathogenesis

– Rickets

• Etiology

– Overproduction of

the cells secreting

PTH

– Parathyroid

develops a tumor

• Treatment

– Remove the tumor

surgically

– Acidotic diets and

acidic drugs (for tx

of kidney stones)

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Osteoporosis

• Etiology

– Loss of Calcium

– Too much PTH

• Pathogenesis

– "Thin Bones"

– Malnutrition

– Lack of vitamin C

– Postmenopausal lack of estrogen secretion

– Old age

– Cushing’s syndrome

– Deficiency of protein metabolism

• Treatment

– Remove the bad parathyroid gland

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Parathyroid Cancer

• Pathogenesis

– Weakness

– Lump in neck

– Trouble swallowing

– Loss of appetite

– Unquenchable thirst

Etiology

Out of control PTH

production

Family history

Hyperparathyroidism

Treatment

Surgery

Radiation therapy

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