parathyroid hormone
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Parathyroid Hormone. ENDO BLOCK 412. Dr. Shaikh Mujeeb Ahmed Assistant Professor AlMaarefa College. Lecture Objectives. At the end of this lecture the student should be able to Describe the role of calcium in the body Enumerate the factors affecting plasma calcium - PowerPoint PPT PresentationTRANSCRIPT
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Parathyroid Hormone
Dr. Shaikh Mujeeb AhmedAssistant ProfessorAlMaarefa College
ENDO BLOCK 412
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Lecture Objectives• At the end of this lecture the student should be able to • Describe the role of calcium in the body• Enumerate the factors affecting plasma calcium• Describe the mechanisms controlling plasma Ca++ concentration• Describe the chemical nature, source and actions of parathyroid
hormone• Describe the chemical nature, source and actions of calcitonin
hormone• Describe the role of vit.D in regulation of Ca++ conc.• Describe Pathophysiology of hypo & hyperparathyroidism• Describe the effects of Vit.D deficiency
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Calcium Distribution
Total Body Ca++
Body fluid (1%)
ECF (0.1%)
Free form (50%)
Bound to plasma
protein (50%)
ICF in soft tissues (0.9%)
Skeleton & teeth (99%)
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Vital role of Ca++
• Neuromuscular excitability• Excitation contraction coupling in cardiac,
smooth & skeletal muscle• Stimulus secretion coupling• Excitation secretion coupling• Maintenance of tight junctions between cells• Clotting of blood
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Endocrine Control of Calcium Metabolism
• Three hormones regulate plasma concentration of Ca2+ (and PO4
3-)– Parathyroid hormone (PTH)– Calcitonin– Vitamin D
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Ca++ homeostasis & Ca++ balance• Ca++ homeostasis
– Ca++ adjustment on Minute to minute basis • Exchange between bone and ECF
• Ca++ balance– Slowly responding adjustment
• Ca++ intake Vs Ca++ excretion
• Parathyroid hormone (PTH) the principal regulator of Ca++ metabolism , acts directly or indirectly on all three of these effector sites.
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Parathyroid hormone• secreted by the
parathyroid glands, • four rice grainsized
glands located on the back surface of the thyroid gland, one in each corner
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Cont…• PTH is essential for life• The overall effect is increase plasma Ca++
• Complete absence of PTH ensues death within few days.
• It acts on bone, kidneys and intestine• PTH acts to lower plasma PO4
3- conc.
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PTH raises plasma Ca2+ by withdrawing Ca2+
from the bone bank.
• induces a fast Ca2+ efflux into the plasma from the small labile pool of Ca2+ in the bone fluid.
• Second, by stimulating bone dissolution, it promotes a slow transfer into the plasma of both Ca2+ and PO4
3- from the stable pool of bone minerals in bone itself.
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PTH’s chronic effect is to promote localizeddissolution of bone to release Ca2+ into plasma.
• Stimulate osteoclast• Both Ca2+ & PO4
3- are released in plasma• PTH deals with PO4 by its action on kidneys
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PTH acts on the kidneys to conserve Ca2+
and eliminate PO43-
• Absorb more Ca++
• Decrease reabsorption of PO43-
• an inverse relationship exists between the plasma concentrations of Ca2+ and PO4
3-
• Activation of Vit. D• PTH indirectly promotes Ca++ & PO4
3-
absorption from the intestine by helping Vit.D
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Regulation of PTH secretion• PTH secretion increases
when plasma Ca2 falls and decreases when plasma Ca2 rises.
• this relationship forms a simple negative- feedback loop for controlling PTH secretion
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Calcitonin• Polypeptide hormone produced by C cells of thyroid
gland• Decreases plasma Ca ++ levels• on a short-term basis calcitonin decreases Ca ++
movement from the bone fluid into the plasma. • Second, on a long-term basis calcitonin decreases bone
resorption by inhibiting the activity of osteoclasts via the cAMP pathway.
• Calcitonin also inhibits Ca ++ and PO43- reabsorption from
the nephron
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ACTIONS OF CALCITONIN ON BONE
• Decresaed osteoclastic number• Decreased osteoclastic activity• Actions are proportional to baseline rate of
bone turnover
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VITAMIN D• cholecalciferol, or vitamin D, a steroid like
compound essential for Ca++ absorption in the intestine.
• Activated by the addition of two (-OH) groups.• The first reaction occurs in the liver & the
second in kidneys.• The active form of vit.D is 1,25-(OH)2- vitamin
D3 also known as calcitriol.
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Fig. 19-27, p. 736
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Disorder of parathyroid hormone• PTH hypersecretion – hyperparathyroidism
– Characterized by hypercalcemia & hypophosphatemia
– Clinical features: • Muscle weakness• Decrease alertness, poor memory & depression• Cardiac disturbances • Mobilization of Ca2+ & PO43- from skeletal store may
results in thinning of bone, fractures, skeletal deformities• Increase incidence of Kidney stones
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Hyperparathyroidism• Bones• Stones• Abdominal groans
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PTH hyposecretion• Hypoparathyroidism• Inadvertent removal of parathyroid gland
– Hypocalcemia and hyperphospatemia– Increased neuromuscular excitability– Muscle cramps twitches– Tingling and pins and needle sensation– Irritability & paranoia
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SIGNS AND SYMPTOMS OF HYPOPARATHYROIDISM
• Positive Chvostek’s (facial muscle twitch) sign• Positive Trousseau’s (carpal spasm) sign• Delayed cardiac repolarization with
prolongation of the QT interval• Paresthesia• Tetany
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Hypocalcemic tetany
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VITAMIN D DEFICIENCY• Decrease Ca++
absorption from intestine.
• PTH increases plasma Ca++ from bone
• Demineralization of bones - softening
• Rickets in children• Osteomalacia in adult.
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p. 730
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1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
2
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
3
2
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.
3
4 2
1
PTH also stimulatesthe kidneys to releaseCALCITRIOL.
High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.
3
4 25
1
CALCITRIOL stimulatesincreased absorption ofCa2+ from foods, whichincreases blood Ca2+ level.
PTH also stimulatesthe kidneys to releaseCALCITRIOL.
High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.
3
4 25
6
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30
References
Human physiology, Lauralee Sherwood, seventh edition.
Text book physiology by Guyton &Hall,11th edition.
Text book of physiology by Linda .S .Costanzo third edition