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Thyroid Gland Slides

Jun 03, 2018

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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