Thyroid gland One of largest pure endocrine glands in the body ( 20gms). Its size depends on: 1....
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Transcript of Thyroid gland One of largest pure endocrine glands in the body ( 20gms). Its size depends on: 1....
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Thyroid gland
One of largest pure endocrine glands in the body ( 20gms).
Its size depends on: 1. age … age size. 2. sex … female > male. 3. physiological condition … (pregnancy, lactation)
Site: Located in the neck just below the larynx, on either side of & anterior to the trachea.
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Thyroid gland … (Continued)
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Thyroid and para
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Thyroid gland secretions
- Secreted by Parafollicular cells.
- Important hormone for Ca2+ metabolism & homeostasis.
● 2 important thyroid hormones: ● Thyroxine (T4) or tetraiodothyronine ● Triiodothyronine (T3)
- Secreted by Follicular cells.
- Can be stored in thyroid gland for couple of months (2-3 months). - Having significant effect on metabolic rate of the body.● Calcitonin
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Thyroxine and its precursors: Structure &
Synthesis
Figure 23-8: Thyroid hormones are made from tyrosine and iodine
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Thyroid Hormone:Transport
T3 & T4 leave the thyroid gland by diffusion
Both are transported in blood by three transport proteins, Thyroxine binding globulin (TBG), transthyretin and albumin
A majority (70%) of T4 & T3 is bound to TBG
Both enter their target cells by diffusion
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Thyroxine and its precursors: Activity
T4 mainly functions as a prohormone. T3 is the main active
thyroid hormone and has the highest binding affinity for thyroid hormone
receptor (TR).Thyroid hormone activity can be
increased in plasma without new synthesis by converting T4 to T3.
If too much thyroid activity is present T4 is converted to the
inactive metabolite rT3 to reduce activity.
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T3 & T4 Control Pathways & Diseases from Malfunction
HypothalamusAnterior PituitaryThyroidHypothyroidismGoiter (TSH )Grave's disease
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Abnormal thyroid
hormonessecretions
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Overview of Thyroid Disease States
Hypothyroidism
Hyperthyroidism
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Hypothyroidism
Hypothyroidism is a disorder with multiplecauses
in which the thyroid fails to secrete an adequate amount of thyroid
hormoneThe most common thyroid disorder Usually caused by primary thyroid
gland failureAlso may result from diminished
stimulation of the thyroid gland by TSH
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Hypothyroidism
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II: Hypothyroidism (myxedema) … cont.
Symptoms of Hypothyroidism:
- Decreased metabolic rate. - Slow heart rate & pulse. - Slow muscle contractions - appetite, weight gain, & constipation. - Prolonged sleep, & dizziness. - Coarse skin. - Slow thinking, lethargy, & mask face. .
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Hyperthyroidism
Hyperthyroidism refers to excess synthesis and secretion
of thyroid hormones by the thyroid gland, which results in
accelerated metabolism in peripheral tissues
90% of hyperthyoidism is due to “Grave’s disease
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“Grave’s disease
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Typical Thyroid Hormone Levels in Thyroid Disease
TSHT4 T3
Hypothyroidism HighLow LowHyperthyroidism LowHigh High
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Populations at Risk for Mild Thyroid Failure
WomenPrior history of Graves disease or
postpartum thyroid dysfunctionElderlyOther autoimmune diseaseFamily history of
Thyroid diseasePernicious anemiaType 1 Diabetes mellitus
Caraccio N, et al. J Clin Endocrinol Metab. 2002;87:1533-1538.
Carmel R, et al. Arch Intern Med. 1982;142:1465-1469.
Perros P, et al. Diabetes Med. 1995;12:622-627.
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function
A. Stimulates formation of proteins, which exert trophic effects on tissues
B. Is essential for normal brain development
D. Help regulating lipid & CHO metabolism
C. Essential for childhood growthE. important for reproductive functionF. T3 is an important regulator of
skeletal maturation at the growth plate
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by
Bader al-onazi