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Thyroid gland

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Thyroid gland Position: It lies in the front of the neck in relation to the larynx, pharynx trachea and esophagus. Shape: The gland consists of right and left lobes ... – PowerPoint PPT presentation

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Title: Thyroid gland


1
Thyroid gland
  • Position It lies in the front of the neck in
    relation to the larynx, pharynx trachea and
    esophagus.
  • Shape The gland consists of right and left lobes
    connected by a narrow isthmus.
  • - It is very vascular gland, surrounded by a
    sheath derived from the pretracheal fascia.
  • - The fascia attaches the gland to the larynx and
    trachea, so the gland moves up and down with the
    larynx during deglutition.

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Fascial layers of Neck
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Thyroid gland (cont.)
  • - Each lobe is pear-shaped with its apex directed
    upward reaching the oblique line on the lamina of
    the thyroid cartilage its base lies below at the
    level of the fifth tracheal ring.
  • - The isthmus extends across the midline in front
    of the second, third, and fourth tracheal rings.
  • - A pyramidal lobe usually presents extending
    upwards from the isthmus, to the left of the
    midline.
  • - A fibromuscular band connects the pyramidal
    lobe to the hyoid bone called levator glandulae
    thyroideae.

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Relations of the lobes
  • 1. Anterolaterally (superficial)
  • - It is covered by the skin, superficial fascia
    and deep fascia.
  • - It is overlapped by the sternothyoid,
    sternohyoid, omohyoid and anterior border of
    sternomastoid muscles.

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Relations of the lobes (cont.)
  • 2. Medially
  • - It is related to the larynx and pharynx
    above.
  • - It is related to the trachea and esophagus
    below.
  • - Cricothyroid muscle and its nerve supply, the
    external laryngeal nerve.
  • - It is related to the recurrent laryngeal
    nerve (very important) in the groove between the
    trachea and esophagus.

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Relations of the lobes
  • 3. Posterolaterally
  • - It is related to the carotid sheath with the
    common carotid artery, internal jugular vein, and
    vagus nerve.
  • - The posterior border of the lobe is related
    posteriorly to the superior and inferior
    parathyroid glands and the anastomosis between
    the superior and inferior thyroid arteries.

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Relations of the isthmus
  • Anteriorly The sternothyroids, sternohyoids,
    anterior jugular veins fascia and skin.
  • Posteriorly The second, third, and fourth rings
    of the trachea.
  • The terminal branches of the superior thyroid
    arteries anastomose along its upper border.

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Blood supplyA. Arterial supply
  • 1. Superior thyroid artery
  • - It is a branch of the external carotid artery.
  • - It descends to the upper pole of each lobe,
    accompanied by the external laryngeal nerve.

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A. Arterial supply (cont.)
  • 2. Inferior thyroid artery
  • - It is a branch of the thyrocervical trunk.
  • - It ascends behind the gland to the level of the
    cricoid cartilage.
  • - It then turns medially and downward, to reach
    the posterior border of the gland.
  • - the recurrent laryngeal nerve crosses either in
    front of or behind the artery or may passes
    between its branches.
  • 3. Thyroidea ima artery
  • - It is an occasional branch may be present.
  • - If present it may arise from the
    brachiocephalic artery or the arch of aorta.
  • - It ascends in front of the trachea to the
    isthmus.

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B. Venous Lymph drainage
  • 1. Superior thyroid vein
  • - It drains into the internal jugular vein.
  • 2. Middle thyroid vein
  • - It drains also into internal jugular vein.
  • 3. Inferior thyroid vein
  • - It receives its tributaries from the isthmus
    and the lower poles of the gland.
  • - The inferior thyroid veins of the two sides
    unite with each other and drain into the left
    brachiocephalic vein.
  • Lymph drainage
  • The lymph from the thyroid gland drains mainly
    into the deep cervical lymph nodes.
  • A few lymph vessels descend to the paratrachial
    nodes.

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Clinical notes
  • 1- Movement of the thyroid gland on swallowing
  • The gland moves up and down with larynx during
    swallowing because it is enveloped in the
    pretracheal fascia.
  • 2- Thyroid gland and the airway
  • In enlargement of thyroid gland it compresses the
    trachea because of its intimate relation.
  • 3- Retrosternal goiter
  • In enlargement of the thyroid gland it descends
    downwards behind the sternum (compressing the
    trachea or veins).
  • This is because the attachment of the
    sternothyroids muscles to the thyroid cartilage
    prevents its ascent.
  • 4- Thyroid arteries and important nerves
  • The superior thyroid artery is related to the
    external laryngeal nerve.
  • The terminal branches of the inferior thyroid
    artery are related to the recurrent laryngeal
    nerve.
  • In thyroidectomy operations damage to either
    nerve may happen.
  • 5- Injury of external laryngeal nerve results in
    paralysis of Cricothyroid muscle and this leads
    to hoarseness of voice and inability to tense
    voice.

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Clinical notes (cont.)
  • 6- Injury to recurrent laryngeal nerve produces
  • - Unilateral complete injury
  • Voice is not greatly affected because of
    compensation of the other normal side.
  • -Bilateral complete injury
  • Speech is lost (aphonia) and breathing is
    impaired, since the rima glottidis is partially
    closed.
  • - Unilateral partial injury
  • The abductors of vocal cord are more affected
    resulting in adduction of vocal cords.
  • - Bilateral partial injury
  • This leads to dyspnea (acute breathlessness) and
    stidor, and cricothyroidotomy or tracheostomy is
    necessary.
  • This is because of paralysis of abductors of
    vocal cords on both sides.
  • 7- The parathyroid glands and thyroidectomy
  • In partial thyroidectomy the posterior part of
    the thyroid gland is left to avoid removal of the
    parathyroid glands which lie on the posterior
    surface of the thyroid gland.

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Nerves related to Thyroid gland
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Parathyroid glands
  • - They are four yellowish-brown, ovoid bodies.
  • - They are embedded in the fascial capsule of the
    thyroid gland related to its posterior border.
  • - They receive blood supply from the superior and
    inferior thyroid arteries.
  • The two superior parathyroid glands
  • - These are more constant in position.
  • - They lie at the level of the middle of the
    posterior border of the thyroid gland.
  • The two inferior parathyroid glands
  • - They lie close to the inferior poles of the
    thyroid gland.

24
Trachea
  • It is a cartilaginous and membranous tube. It
    conveys air to and from the lungs. It is about
    10cm in length and is formed of incomplete
    cartilaginous rings completed posteriorly by
    smooth muscles.
  • It begins at the lower border of the cricoid
    cartilage opposite the 6th cervical vertebra.
  • It ends by dividing into two bronchi opposite the
    lower border of the 4th cervical vertebra.
  • Course Its upper half lies in the neck and lower
    half in the thorax. It descends in the midline,
    but at its bifurcation it lies slightly to the
    right.

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Trachea
  • Relations in the neck
  • Anteriorly skin, fascia, isthmus of the thyroid
    gland (in front of second, third, and fourth
    tracheal rings), inferior thyroid veins, jugular
    arch, hyroidea ima artery (if present), and the
    left brachiocephalic vein in children. It is
    overlapped by the sternomastoid and sternohyoid
    muscles.
  • Posteriorly The right and left recurrent
    laryngeal nerves, the esophagus and the vertebral
    column.
  • Laterally On each side the trachea is related to
    a lobe of thyroid gland, carotid sheath, and
    inferior thyroid artery.
  • Blood supply The trachea is supplied by the
    inferior thyroid arteries in the neck.
  • Lymph drainage The lymph vessels drain into the
    pretracheal and paratrachial lymph nodes in the
    neck.
  • Nerve supply The vagi, recurrent laryngeal
    nerves and sympathetic trunks.

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Esophagus
  • It is a muscular tube about 25cm (10 inches)
    long.
  • It begins as a continuation of pharynx at the
    level of cricoid cartilage, opposite the sixth
    cervical vertebrae.
  • It ends by joining the cardiac end of the stomach
    opposite the 10th thoracic vertebra.
  • Course It descends in the midline then it
    inclines to the left and leaves the neck to the
    thorax.

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Esophagus (cont.)
  • Relations in the neck
  • Anteriorly The trachea, the recurrent laryngeal
    nerves in the groove between the trachea and
    esophagus.
  • Posteriorly The prevertebral fascia, the longus
    colli muscle, and the vertebral column.
  • Laterally On each side the trachea is related to
    a lobe of thyroid gland, carotid sheath, and
    inferior thyroid artery. The thoracic duct
    ascends along the left margin for a short
    distance.
  • Blood supply The esophagus is supplied by the
    inferior thyroid arteries in the neck.
  • Lymph drainage The lymph vessels drain into the
    deep cervical lymph nodes.
  • Nerve supply The vagi, recurrent laryngeal
    nerves and sympathetic trunks.

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