3. Right Lobe of The Thyroid GlandLeft Lobe of The Thyroid Gland
Isthmus
True Capsule
False Capsule
Fascia of the Thyroid Gland (Capsules)
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4. Thyroid Gland
Site : in the lower part of the front and sides of the neck.
Shape : It is roughly H-shaped; the vertical limbs represent the two lobes and the
horizontal limb, the isthmus.
Extent:
1.Lies opposite 5th, 6th, 7th, cervical and 1st thoracic vertebrae.
2.Each lobe extends from the middle of the thyroid cartilage to the fourth or
3.fifth tracheal rings.
4.The isthmus lies opposite the second, third and fourth tracheal rings.
Parts : The gland has :
1. Two lobes (right and left).
2. Isthmus: connecting the two lobes. 3. Pyramidal lobe : is often present.
Lobes
Each lobe is conical in shape having :
(a) apex ; (b) base ; (c) three surfaces , lateral , medial and posterior and
(d) two borders , anterior and posterior.
(a) Apex :
• directed upwards
• limited superiorly by the attachment of the sternothyroid muscle to the oblique
line of the thyroid cartilage. Mohamed el fiky
5. (B) Base : is on the level with the 4th or 5th tracheal rings.
(C) lateral (superficial) surface : is convex and is covered by :
1.Sternothyroid
2. Sternohyoid.
3. Superior belly of omohyoid
4. Anterior border of the sternomastoid
(D) Medial surface : related to :
a.Two tubes : trachea and oesophagus
b. The upwards continuation of the two tubes : larynx and pharynx.
c. Two muscles : inferior constrictor and cricothyroid.
d. Two nerves : external laryngeal and recurrent laryngeal.
(E) Posterior surface: is related to the carotid sheath and parathyroid glands.
(F) Anterior border : is thin and related to the anterior branch of superior thyroid
artery.
(G) Posterior border : is thick and rounded and separates the the medial and
posterior branch between the superior and inferior thyroid arteries ; and prathyroid
glands.
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6. q Connects the lower parts to the lobes
q Has (a) two surfaces, anterior and posterior; and (b)two borders superior and
inferior.
Anterior surface : is covered by : (a) strenothyroids;
(b)strenohyoids;
(c) anterior jugular veins and (d) fascia and skin.
Posterior surface: related to 2nd , 3rd and 4th tracheal rings.
Upper border : is related to the anastomosing branches between the two
superior thyroid arteries.
Lower border :
• The inferior thyoid veins leave the gland at this border.
• Related to the anastomosing branches between the two inferior thyroid
arteries.
Pyramidal lobe
q Is a small conical process which extends from the upper border of the isthmus.
q Is usuall connected to the hyoid bone by a fibromuscular band called levator
glandulae thyroideae which is remnant of thyroglossal duct.
The Isthmus
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7. Right Lobe Left Lobe
Isthmus
Pyramidal Lobe
Apex
Base
Oblique line of
Thyroid cartilage
Divisions of the Thyroid Gland
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8. Relations of the Thyroid Gland
A- Relations of The Lobes
T1
C7
C6
C5
T1
C7
C6
C5
Oblique Line of Thyroid
Cartilage
5TH or 6TH Tracheal Ring
a- Relations of Apex
b- Relations of The Base
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9. Superior Belly of Omohyoid
Sternohyoid
Sternothyroid
c- Relations of The Surfaces
1- Relations of Lateral (Superficial) surface
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10. Anteriorly
Thyroid cartilage
Cricoid cartilage
Cricothyroid muscle
Inferior constrictor
of pharynx
External laryngeal nerve
(In the middle)
a- Anteriorly
1- Upper part b- Posteriorly
2- Lower part
a- Anteriorly
b- Posteriorly
Trachea
Esophagus
Recurrent laryngeal nerve
(in the middle)
2- Relations of Medial surface
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12. Anterior border related to
Anterior division of superior thyroid artery
Posterior border related to
Posterior division of superior thyroid artery
Inferior thyroid artery,
Parathyroid glands
D- Relations of The Borders
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13. Isthmus of Thyroid Gland
Skin and Fascia
Sternothyroid
and
Sternohyoid Muscles
Anterior Jugular Veins
a- Anterior Relations of the Isthmus
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14. The Isthmus of The Thyroid Gland is Related Posteriorly to
2nd ,3rd and 4TH Tracheal Rings
b- Posterior Relations of The Isthmus
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15. Anastomotic Branches
between
Superior Thyroid Arteries Pyramidal Lobe
and
Levator
Glandulae
Thyroidae
(If Present)
Inferior Thyroid Veins
c- Relations of Upper and Lower Borders
Of the Isthmus
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17. Blood Supply of the Thyroid Gland
1. Superior thyroid artery:
q is a branch of external carotid artery.
q Runs downwards and forwards with intimate
relation to the external laryngeal nerve.
q Divides into anterior and posterior branches
(2) Inferior thyroid artery:
q Is a branch of the thyrocervical trunk
from the subclavian artery
q Runs first upwards , then medially and
finally downwards to reach the lower
pole of the thyroid lobe.
q Its terminal part is intimately related to
the recurrent laryngeal nerve
(3) Thyroidea ima artery (in 3% individuals):
q Arises from the brachiocephalic artery or the aortic arch Ascends in
front of the trachea to reach the isthmus.
(4) Accessory thyroid arteries : come from the tracheal and esophageal
vessels.
Arterial supply
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18. Infrahyoid artery
Superior Laryngeal artery
Sternomastoid artery
Cricothyroid artery
Glandular arteries
Thyroidae ima artery
The Superior Thyroid Artery
The Inferior
Thyroid Artery
Arteries from Trachea
and Esophagus
to
The Thyroid Gland
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19. Venous Drainage of Thyroid Gland
1) Superior thyroid vein:
q Emerges at the upper pol
q Accompanies the superior
thyroid artery
q Ends in the internal jugular vein
2) Middle thyroid vein:
q Emerges at the middle of the
lobe.
q Ends in the internal jugular
vein
3) Inferior thyroid veins:
q Emerge at the lower border of
the isthmus
q Descend in front of the trachea
and drain into the left
brachiocephalic vein.
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20. Upper deep cervical
Lymph nodes
Lower deep cervical
Lymph nodes
Pretracheal
Lymph nodes
Lymph Drainage of Thyroid Gland
1.The upper part :
drains into the upper
deep cervical lymph
nodes
2.The lower part :
drains into the lower
deep cervical lymph
nodes
3.The isthmus :
drains into the
brachiocephalic
lymph nodes
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21. Superior Parathyroid
Gland
Inferior Parathyroid
Gland
Parathyroid Gland
The superior parathyroid : lies at the middle of
the posterior border of the lobe of the thyroid
gland within the capsule of the thyroid gland.
The inferior parathyroid : is variable in position
. it may lie
(1) within the thyroid capsule , below the inferior
thyroid artery and near the lower pole of the
thyroid lobe;
(2) (2) behind and outside the thyroid capsule,
immediately above the inferior thyroid artery ;
or
(3) (3) within the substance of the lobe near its
posterior border
Shape and size : oval or lentiform in shape ,
measures 6x4x2 mm . each one weighs 50 mg.
Arterial supply : from the inferior thyroid arteries
and the anastomosis between the superior and
inferior thyroid arteries. Mohamed el fiky
