THE THYROID GLAND. Anatomical Structure Gross Anatomy Located in neck –lobes –isthmus Relations...
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Transcript of THE THYROID GLAND. Anatomical Structure Gross Anatomy Located in neck –lobes –isthmus Relations...
THE THYROID GLAND
Anatomical Structure
Gross Anatomy• Located in neck
– lobes– isthmus
• Relations– Larynx– Trachea– Recurrent laryngeal
nerves– Parathyroid glands– Carotid sheath
• Blood supply– Sup. thyroidal a.– Inf. thyroidal a.
Embryology
• Thyroglossal duct• Foramen caecum• Thyroid cysts
Histology
• Thyroid follicles– Simple cuboidal-
columnar
• Colloid– Thyroglobulin
• Rich vascularization
• Colloid– Thyroglobulin
• Rich vascularization
• Parafollicular cells• Parafollicular cells
Thyroid Hormone
• 3-Monoiodotyrosine (MIT)
• 3,5-Diiodotyrosine (DIT)• 3,5-Diiodotyrosine (DIT)
• 3,5,3’-Triiodothyronine (T3)• 3,5,3’-Triiodothyronine (T3)
• Tyrosine• Tyrosine
• 3,5,3’,5’-Tetraiodothyronine (T4)• 3,5,3’,5’-Tetraiodothyronine (T4)
• 3,3’,5’-Triiodothyronine (Reverse T3, rT3) • 3,3’,5’-Triiodothyronine (Reverse T3, rT3)
Thyroid Hormone Synthesis
• Tyrosine in Thyroglobulin
CH3CHCH3CH
NN
C=OC=O
RCRC
C=OC=O
RCRC
OH-OH-
Thyroid Hormone Synthesis
• Thyroperoxidase attaches Iodine to 3 position---MIT
CH3CHCH3CH
NN
C=OC=O
RCRC
C=OC=O
RCRC
II
OH-OH-
Thyroid Hormone Synthesis
• Thyroperoxidase attaches Iodine to 5 position---DIT
CH3CHCH3CH
NN
C=OC=O
RCRC
C=OC=O
RCRC
II
II
OH-OH-
Thyroid Hormone Synthesis
• Thyroperoxidase attaches ring from one DIT to adjacent DIT = Thyroxine (T4)
CH3CHCH3CH
NN
C=OC=O
RCRC
C=OC=O
RCRC
II
II
OO
II
II
OH-OH-
Thyroid Hormone Synthesis
• Thyroperoxidase attaches ring from one MIT to adjacent DIT = Triiodothyronine (T3)
CH3CHCH3CH
NN
C=OC=O
RCRC
C=OC=O
RCRC
II
II
OO
II
OH-OH-
Thyroid Hormone Synthesis
• Thyroperoxidase attaches ring from one DIT to adjacent MIT = Reverse T3
CH3CHCH3CH
NN
C=OC=O
RCRC
C=OC=O
RCRC
II
OO
II
II
OH-OH-
Thyroid Hormone Biosynthesis
• Iodine pump/trap• Thyroglobulin• Iodination• Thyronine• Thyroglobulin
pinocytosis• Hormone release
Thyroid hormone transport
• Thyroid binding globulin (TBG)– Highest affinity
• Thyroid binding prealbumin– Intermediate affinity
• Albumin– Low affinity, High capacity
Thyroid Hormone
• T3 is 3-8X more active than T4
• Thyroid Gland produces 10X T4 to T3
• 5’-deiodinase– Converts T4 to T3 in Target Tissues
– Primarily responsible for circulating levels of T3
• T4 probably a pro-hormone
• Thyroid hormone receptor– Nuclear
Physiological effects of thyroid hormone
• Increases oxygen consumption and heat production
• Positive chronotropic and inotropic effects on heart
• Increase sensitivity to adrenergic effectors– Up-regulates -adrenergic receptors
• Increase gut motility
• Increase bone turnover
Physiological effects of thyroid hormone
• Increases reflex response
• Increase hepatic glycogenolysis and gluconeogenesis
• Stimulates lipolysis
• Developmental effects– Growth– Brain development
REGULATION OF THE THYROID GLAND
THYROIDGLAND
THYROIDGLAND
ANTERIORPITUITARYANTERIORPITUITARY
HYPOTHALAMUSHYPOTHALAMUS
TRHTRH
TSHTSHT4T4
LONG-LOOPFEEDBACK
LONG-LOOPFEEDBACK
T3 & T4T3 & T4
TSHTSH
SHORT-LOOPFEEDBACK
SHORT-LOOPFEEDBACK
BODYTEMP.BODYTEMP.
EXPOSURETO COLD
EXPOSURETO COLD
STARVATIONSTARVATION
TSH-RECEPTOR
ANTIBODIES
TSH-RECEPTOR
ANTIBODIES
THYROID AUTOREGULATION
THYROID AUTOREGULATION
HIGHSERUM IODIDE
HIGHSERUM IODIDE
HIGHER BRAINCENTERS
HIGHER BRAINCENTERS
GOITROGENSGOITROGENS
Endocrinopathies
Hyperthyroidism
• Level of the defect (1, 2, 3)
• Thyrotoxicosis• Graves’ disease• Toxic Adenoma• Toxic Multinodular
Goiter• Chronic Thyroiditis
Hyperthyroidism Symptoms • Tachycardia/arrhythmia• Muscle tremors• Hyperreflexia• Increased core & skin
temp./ Heat Intolerant• Exophthalmos• Muscle wasting• Loose stool• Osteoporosis• Hair loss• Oligo-/amenorrhea• Irritability, Restlessness
Hypothyroidism
• 1, 2, 3 • Newborn
– Cretinism– Lack of myelination
• Children– Retarded Growth– Disproportionate
Hypothyroidism
• Adult– Muscle weakness– Mental slowness– Tired/fatigued– Cold– Slowed intestinal
peristalsis– Impaired renal
function– Anemia– Myxedema
Myxedema
Causes of Hypothyroidism
• Iodine deficiency
• Hashimoto’s Disease– Initially hyperthyroid
• Post-ablative
• 5’-Deiodinase Deficiency
Thyroid hormone resistance
• Mutation of the receptor.
• Characterized by high blood levels of both TSH and Thyroid hormones
Non-toxic goiter
• Iodine deficiency
Thyroiditis
• Subacute thyroiditis
• Chronic thyroiditis (Hashimoto’s Disease)– Autoimmune
Euthyroid Syndrome
• Patient presents and complains of hypothyroid type symptoms
• Levels of Thyroid hormones (free & total), & TSH in low normal range.
• May be due to a 5’-deiodinase deficiency
Allopathic treatments for thyroid disorders
• Hyperthyroidism– Goitrogens– Partial thyroidectomy– Radiothyroidectomy
• Hypothyroidism– Hormone Replacement