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THYROID GLANDBy: Kathleen Kaye A. Luceara
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THYROID GLAND
GOITER
Latin Guttur (Throat)
An enlargement of the
thyroid gland
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Embryology
Primitive foregut: 3 WEEKS AOG
Origin: Foramen Cecum
Endoderm cells (floor of pharyngeal anlage):Medial Thyroid Anlageto form (1) Hyoid and
(2) Larynx
Connection: Thyroglossal Duct Epithelial cells of anlage becomes the Thyroid
Follicular Cells
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Embryology
Paired lateral anlage are neurectodermal in
origin fuse with median anlage becomes
Parafollicularor C cells
Apparent by 8 WEEKS
Produce colloid by 11 WEEKS
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Developmental Abnormalities
(1) Thyroglossal Duct Cyst and Sinuses
Most commonly encountered
5 WEEKS gestation begins to becomeOBLITERATED
8 WEEKS completely OBLITERATED
Occurs anywhere in the path of the thyroid
80% in juxtaposition to the HYOID BONE
Asymptomatic but frequently become infected
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Developmental Abnormalities
Thyroglossal Duct Cyst and Sinuses
HISTOLOGY:
pseudostratified ciliated columnar epithelium and
squamous epithelium with heterotopic thyroid tissue(20% of the time)
DIAGNOSIS:
1 to 2 cm, smooth, well-defined MIDLINE neck mass
that moves upward with protrusion of the tongue Thyroid imagingnot done routinely, thyroid
scintigraphy and ultrasound done to detect thyroidtissue
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Developmental Abnormalities
Thyroglossal Duct Cyst and Sinuses
TREATMENT:
Sistrunk operation: en bloc cystectomy and excision ofthe central hyoid bone to prevent recurrence.
MALIGNANT TENDENCY:
1% found to have cancer most common type
PAPILLARY(85%) Medullary CANOT FOUND in Thyroglossal Duct Cysts
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Developmental Abnormalities
(2) Lingual Thyroid
Failure of the median thyroid anlage to descend
INTERVENTION needed with signs of obstruction:
Choking Dysphagia
Airway obstruction
MEDICAL TREATMENT:
Administer exogenous thyroid hormone to suppress TSH
Radioactive iodine (RAI) ablation followed by hormonereplacement
SURGICAL MANAGEMENT:
Rarely needed but if needed check for thyroid tissue in the neck
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Developmental Abnormalities
(3) Ectopic Thyroid
Normal thyroid tissue found anywhere in the neckcompartment
Aortic arch
Aortopulmonary window
Pericardium
Interventricular septum
Lateral Aberrant Thyroid: Lateral to carotid sheathand jugular veinMETASTATIC THYROID CANCERin lymph nodes (Papillary Thyroid Cancer)
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Developmental Abnormalities
(4) Pyramidal Lobe
Thyroglossal duct
atrophies
50%- distal end
persists connected to
isthmus
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THYROID ANATOMY
GROSSLY:
COLOR :Brown
CONSISTENCY :Firm
LOCATION :Behind strap muscles
WEIGHT :20 grams
LOBES :adjacent to thyroid cartilage
connect in midline to theisthmus, cc inferior to the
cricoid cartilageCAPSULE: :thin, adherent fibrous layer
condensed into a posteriorsuspensory (Berrys) ligament
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THYROID ANATOMY
DRAINAGE:1. Superior and middle thyroid
veindrain to the internal
jugular vein
2. inferior thyroid veindrains
into the brachiocephalic veins
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THYROID ANATOMY
BLOOD SUPPLY:1. Superior thyroid arteries from
the external carotid arteries
divide to Anterior andPosterior Branches
2. Inferior thyroid arteries fromthyrocervical trunktravelupward POSTERIOR to carotid
sheath enter at the midpoint
3. Thyroidea Imaaorta orinnominate artery (14%)0
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THYROID ANATOMY
NERVES:1. LEFT RLNfrom vagus nerve
at its intersection with the
aortic arch, ascends at thetracheoesophageal groove
2. RIGHT RLNfrom vagusnerve at its intersection withthe right subclavian artery,
more oblique the left.
***Terminate at the larynx postto cricothyroid muscle
NERVES: Innervate all INTRINSIC
muscles except Cricothyroid
Muscles INJURY
One RLNnormal but weak
voice
Both RLNairway obstruction Superior laryngeal Nerve
(external branch)cannot reach
high-pitched sounds
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THYROID ANATOMY
LYMPHATIC DRAINAGE:
Levels Regions
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THYROID HISTOLOGY
FOLLICLESNumber : 2040 per lobule
Size : 30m in diameter
Lining : Simple cuboidal epithelial cellsContent : Colloid under the inf. of TSH
C CELLS
Hormone : Calcitonin
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THYROID PHYSIOLOGY
IODINE METABOLISMaverage daily iodine requirement 0.1mg from:
1. Fish
2. Milk
3. Eggs4. Additives in bread or salt
Absorbed in STOMACH and JEJUNUM
Converted to Iodide
Active transport into the THYROID FOLLICLES
THYROID: 90% of iodine in the body; 1/3 of plasma
iodine loss
CLERANCE: Renal
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THYROID PHYSIOLOGY
THYROID HORMONE SYNTHESIS, SECRETION andTRANSPORT
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THYROID PHYSIOLOGY
THYROID HORMONE SYNTHESIS, SECRETION andTRANSPORT
1. Iodide trappingNIS, TSH
2. Oxidation of iodide to iodine and iodination of tyrosine
residues
3. Coupling of two DIT (form T4) or a DIT and a MIT (form T3)
(Thyroid Peroxidase)
4. Thyroglobulins are hydrolyze to form Free T3 andT4
5. Deiodination of T4recycle iodide and reused in the
thyrocyte
6. Deiodination at periphery via 5-mono-deiodinase
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THYROID PHYSIOLOGY
THYROID HORMONE SYNTHESIS, SECRETION andTRANSPORT
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THYROID PHYSIOLOGY
HYPOTHALAMIC, PITUITARY, THYROID AXIS
NOTE:
- Pituitary has the ability to
convert T4 to T3
- T3 is more important in the
feedback control
- T3 can also inhibit TRH
release
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THYROID PHYSIOLOGY
HYPOTHALAMIC, PITUITARY, THYROID AXIS
Thyroid Autoregulation:
- With LOW IODINE INTAKEproduces more T3 than T4- Iodine Excessthyroid hormone secretion is inhibited
- Excessively large doses of IODIDEincreased
organification, suppression Wolffe-Chaikoff Effect
- Epinephrine and HCG - stimulate Thyroid Hormone
Production
- Glucocorticoids- inhibit thyroid hormone production
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THYROID PHYSIOLOGY
THYROID HORMONE FUNCTION
Other functions:
Maintain normal hypoxic and hypercapnic drive in the
respiratory center
Increase GI motility
Increase bone and protein turnover
Increased speed of muscle contraction and relaxation
Increased glycogenolysis, gluconeogenesis, intestinal
glucose absorption, cholesterol synthesis and degradation