goiter physio (2)
TRANSCRIPT
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PHYSIOLOGY OFTHYROID GL ND
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THYROID GLAND SECRETIONS
Thyroid gland secretes thyroid hormones
Thyroxine or Tetraiodothyronine 93%
Triiodothyronine 7%
Calcitonin: polypeptide hormone.
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REGULATION OF THYROID HORMONE SECRETIONS
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METABOLIC EFFECTS OF THYROID HORMONES
A. Carbohydrate Metabolism Increase absorption of glucosefrom GIT
Enhance glycogenolysis, gluconeogenesis and enhances
diabetogenic effectsof glucagon, cortisol and growth hormone.
Enhancement of glucose utilizationof peripheral tissues.
PHYSIOLOGICAL EFFECTS OF THYROID HORMONES
EFFECT ON TRANSCRIPTION OF GENES
Activates the nuclear transcription of large numbers of genes.The net result is generalized increase in Metabolic activity
throughout the body.
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B. Protein Metabolism
T4 and T3 in physiological dosages stimulates proteinsynthesis, increasing anabolismof protein and causing
positive nitrogen balance .
C. Effect On fat metabolism
Accelerate the oxidationof free fatty acids by cells. Promote synthesisof cholesterol.
Also increase decompositionof cholesterol by liver cells.
Net effect of T3 and T4 is to decrease plasma
cholesterol concentration because the rate ofsynthesis is less than that of decomposition.
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Calorigenic action of thyroid hormones
Increase O2consumption .
Increase in number and activity of mitochondria.
Increasing heat production and BMR ( 60 to 100% above
normal).
Enhances Na+-K+ATPase activity.
Makes cell membrane of most cells to become leaky to Na+
ions, which farther activates Na+pump and increases heat
production.
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EFFECTS OF THE THYROID HORMONES
ON DIFFERENT BODY SYSTEMS
EFFECT ON THE CARDIOVASCULAR SYSTEM
Increased blood flow and cardiac output.
Increases heart rate. Increases heart strength.
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EFFECT ON RESPIRATORY SYSTEM
Increases rateand depthof respiration.
EFFECTS OF THYROID HORMONE ON NERVOUS
SYSTEM:
Increases excitabilityof central nervous system.
These hormones increases the rapidity of cerebration.
These can also stimulate the sympathetic nervous
system.
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EFFECT OF THYROID HORMONES ON GROWTH AND
DEVELOPMENT
Essential for normal growth and development especiallyskeletal growth and development.
Stimulate formation of dendrites, axons, myelin sheath and
neuroglia.
EFFECT ON GASTROINTESTINAL TRACT:
Increase the appetiteand food intake.
Increase both the rate of secretion of the digestive juices and
the motilityof the gastrointestinal tract.
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BIOCHEMISTRY OFTHYROID HORMONES
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CHEMISTRY OF THYROID HORMONESThyroid hormones are derivativesof the the amino acid
tyrosine bound covalently to iodine.
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MECHANISM OF ACTION OF THYROID HORMONES
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Transport & Protein Binding
Plasma proteins
Thyroxin-binding Globulin
Thyroxin-binding Prealbumin
Albumin
Free T3and T4is the physiologically activeform .
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EXCRETION
Both T3 and T4 also form
glucuronideconjugates in the liver
that are excreted via bile into feces.
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