parathyroid hormones and calcitonin
TRANSCRIPT
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Parathyroid Hormones
and Calcitonin Habon, Cecille
Jove, Jessica
Lazo, Kareen
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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.
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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.
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Regulation of PTH
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• 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
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• 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
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Calcium
regulates
PTH
secretion
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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
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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
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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
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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
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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
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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)
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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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