surgical anatomy of the thyroid gland

1. B

2. EMBRYOLOGY
 AT 3rd WEEK OF INTRA UTERINE LIFE
 DEVELOPS AS A ENDODERMAL THICKENING JUST BEHIND
THE TUBERCULUM IMPAR @ FORAMEN CAECUM
 THIS THICKENING FORMS A DIVERTICULUM CALLED
THYROGLOSSAL DUCT.
 THIS DESCENDS SLIGHTLY TO THE LEFT OF MIDLINE AND
INFRONT OF THYROID CARTILAGE, IT BIFURCATES INTO
TWO LOBES OF THYROID & CENTRAL PORTION FORMS
THE ISTHMUS.
 THE PORTION OF THYROGLOSSAL DUCT NEAR THE
ISTHMUS FORMS THE PYRAMIDAL LOBE.

3.  IT IS THE FIRST GLAND TO BECOME FUNCTIONAL ,
ie., BY 7th WEEK OF INTRAUTERINE LIFE.
 SOMETIMES, THE PYRAMIDAL LOBE MAY BE
ATTACHED TO BODY OF THE HYOID BONE BY A
FIBROUS OR FIBROMUSCULAR BAND CALLED
LEVATOR GLANDULAE THYROIDEAE.
 THE NEURAL CREST CELLS & CELLS FROM
ULTIMOBRANCHIAL BODIES BECOME
INCORPORATED INTO THE THYROID AND THEY
FORM C –CELLS OR PARAFOLLICULAR CELLS.

4. EMBRYOLOGY

6. ANATOMY

7. ANATOMY
 THE LARGEST ENDOCRINE GLAND.
 EXTENDS FROM C5 TO T1
SPECIAL FEATURES
 ONLY ENDOCRINE GLAND LOCATED
SUPERFICIALLY.
 ONLY ENDOCRINE GLAND WHICH DEPEND ON
THE EXTERNAL ENVIRONMENT FOR RAW
MATERIAL, IODINE, TO SYNTHESISE
HORMONES.
 ONLY ENDOCRINE GLAND WHICH HAS THE
ABILITY TO STORE THE HORMONES &
RELEASE IT WHEN REQUIRED

8.  WEIGHT OF THE GLAND – 25 gms.
 DIMENSION 5x3x2 cm
 LATERAL LOBE EXTENDS FROM OBLIQUE LINE OF THYROID
CARTILAGE TO 5th OR 6th TRACHEAL RING
 THE ISTHMUS LIES INFRONT OF 2nd & 3rd TRACHEAL RINGS.
IT HAS TWO CAPSULES.
 INNER TRUE CAPSULE
FORMED BY PERIPHERAL CONDENSATION OF
FIBROUS STROMA OF THE GLAND.
 OUTER FALSE CAPSULE
FORMED BY THE PRETRACHEAL FASCIA.
THE FIBROUS SEPTA ARISING FROM THE TRUE
CAPSULE DIVIDE THE GLAND INTO MANY
LOBULES.

9. MOVEMENT OF THE GLAND
WITH DEGLUTITION
REASONS:
 BERRY’S LIGAMENT
IT CONNECTS THE LOBE OF THYROID TO THE
CRICOID CARTILAGE.
 ISTHMUS IS ATTACHED TO THE TRACHEA.
 INVESTING PRETRACHEAL FASCIA
SURROUNDING THE GLAND IS ATTACHED TO THE
LARYNX & HYOID BONE.

10. RELATIONS F THYROID
 APEX
EXTENDS ABOVE UPTO OBLIQUE LINE OF
THYROID CARTILAGE
SANDWICHED BETWEEN INF. CONSTRICTOR
MEDIALLY AND STERNOTHYROID LATERALLY.
 BASE
EXTENDS UPTO THE 5th OR 6th TRACHEAL RING.
 LATERAL SURFACE
CONVEX SHAPED
COVERED BY
 THREE STRAP MUSCLES ( sternothyroid ,
sternohyoid , superior belly of omohyoid)
 ANTERIOR BORDER OF SCM

11.  MEDIAL SURFACE
2 TUBES: Trachea & Esophagus
2 MUSCLES: Inferior cnstrictor & Cricothyroid
2 CARTILAGES: Cricoid & Thyroid
 POSTEROLATERAL SURFACE
CAROTID SHEATH
ANSA CERVICALIS
CERVICAL SYMPATHETIC CHAIN
 ANTERIOR BORDER
ANTERIOR BRANCH OF SUPERIOR THYROID ARTERY
 POSTERIOR BORDER
PARATHYROID GLAND
THIS BORDER CAN A PYRAMIDAL SHAPED
EXTENSION CALLED TUBERCLE OF ZUCKERKANDL

13. ARTERIAL SUPPLY
 SUPERIOR THYROID ARTERY
A BRANCH OF EXTERNAL CAROTIC ARTERY.
SUPPLIES THE UPPER 1/3rd OF LOBE & UPPER HALF OF
ISTHMUS.
 INFERIOR THYROID ARTERY
A BRANCH OF THYROCERVICAL TRUNK OF FIRST PART
OF SUBCLAVIAN ARTERY.
SUPPLIES LOWER 2/3rd OF LOBE & LOWER HALF OF
ISTHMUS.
 THYROIDEA IMA ARTERY
A BRANCH FROM BRACHIOCEPHALIC TRUNK OR ARCH OF
AORTA.
 ACCESSORY THYROID ARTERIES
FROM TRACHEAL & ESOPHAGEAL ARTERIES.

14. ARTERIAL SUPPLY

15.  THE SUPERIOR THYROID ARTERY IS CLOSELY
RALATED TO THE EXTERNAL LARYNGEAL NERVE.
THEY DIVERGE ONLY NEAR THE APEX OF THE
GLAND, THE ARTERY LIES SUPERFICIAL & THE
NERVE LIES DEEP TO THE APEX. HENCE, SUPERIOR
THYROID ARTERY IS LIGATED AS CLOSE TO THE
GLAND TO AVOID INJURY TO THE NERVE.
 THE RECURRENT LARYNGEAL NERVE LIES CLOSE
TO THE INFERIOR THYROID ARTERY NEAR THE
BASE OF THE GLAND. HENCE, THE ITA IS LIGATED
AS AWAY FROM THE GLAND AS POSSIBLE TO
AVOID INJURY TO THE RLN.

16. VARIOUS RELATIONSHIPS OF RLN WITH
THE INFERIOR THYROID ARTERY

17. VENOUS DRAINAGE
 SUPERIOR THYROID VEIN
DRAINS INTO THE INTERNAL JUGULAR VEIN
 MIDDLE THYROID VEIN
SHORT, STOUT
DRAINS INTO THE INTERNAL JUGULAR VEIN
 INFERIOR THYROID VEIN
FORM PLEXUS INFRONT OF TRACHEA &
DRAINS INTO THE LEFT BRACHIOCEPHALIC
VEIN
 KOCHER’S VEIN
EMERGE BETWEEN MIDDLE & INFERIOR
THYROID VEIN TO DRAIN INTO THE INTERNAL
JUGULAR VEIN

18. VENOUS DRAINAGE

19. RELATION B/W CAPSULE & VESSELS
 THE DENSE VENOUS
PLEXUS LIES DEEP
TO THE TRUE CAPSULE.
 THEREFORE,DURING
THYROIDECTOMY, THE GLAND
IS REMOVED ALONG
WITH THE TRUE CAPSULE TO
AVOID HEMORRHAGE.

20. LYMPHATIC DRAINAGE
 PRIMARY NODES
 PRE LARYNGEAL (DELPHIAN) NODE- LEVEL
VI
SINGLE NODE LOCATED ANTERIOR TO THE
CRICOTHYROID MEMBRANE B/W CRICOTHYRID
MUSCLES.
 PRE TRACHEAL & PARA TRACHEAL NODES
 PERITHYROID NODES
 MEDIASTINAL NODES
 SECONDARY NODES
 DEEP CERVICAL NODES
 SUPRA CLAVICULAR & OCCIPITAL NODES

21. LYMPHATIC DRAINAGE

22. NERVE SUPPLY
 PARASYMPATHETIC NERVE SUPPLY
VAGUS & RECURRENT LARYNGEAL NERVE
 SYMPATHETIC NERVE SUPPLY
SUPERIOR , MIDDLE & INFERIOR CERVICAL
SYMPATHETIC GANGLION, MAINLY FROM
MIDDLE.

23. MICRSCOPIC STRUCTURE

24. MICROSCOPIC STRUCTURE
 FOLLICULAR CELLS
CUBOIDAL EPITHELIAL CELLS FORMING THE
WALL OF SPHERICAL THYROID FOLLICLES.
SECRETE
THYROXINE – T4
TRIIODOTHYRONINE – T3
 PARAFOLLICULAR OR C – CELLS
PRESENT B/W THE FOLLICULAR CELLS
SECRETE CALCITONIN

26.  SECRETION OF THYROID HORMONES
THYROXINE – 93%
TRIIODOTHYRONINE – 7%
 FUNCTIONAL ANATOMY OF THYROID
 EACH FOLLICLE CONSISTS WHICH IS
COMPOSED OF THYROGLOBULIN
 THE THYROGLOBULIN IS SECRETED INTO THE
FOLLICLE BY THE CUBOIDAL EPITHELIAL CELLS
 THE BLOOD SUPPLY IS FIVE TIMES THE WEIGHT
OF GLAND EACH MINUTE.
 SECRETION OF PARAFOLLICULAR CELLS
C CELL SECRETE CALCITONIN

27.  REQUIREMENT OF IODINE
 50 mg/year OR 1 mg/Week
 TABLE SALT IS IODISED WITH 1 PART OF NaI IN
1,00,000 PARTS 0F NaCl.
 FATE OF IODINE
 MOST OF THE ABSORBED IODINE IS EXCRETED
SPONTANEOUSLY BY KIDNEYS.
 ONLY 1/5th OF CIRCULATING IODINE IS TAKEN
UP BY THE GLAND.

28. STEPS OF THYROID HORMONE
FORMATION
 IODIDE TRAPPING
BY THE SODIUM-IODIDE SYMPORTER INTO THYROID
CELL
BY PENDRIN, FROM THYROID CELL INTO
FOLLICULAR CELL.
 OXIDATION OF IODIDE ION INTO IODINE
 CATALYSED BY THE ENZYME PEROXIDASE
 ORGANIFICATION OF THYRGLOBULIN
BINDING OF IODINE WITH THYROGLOBULIN WITH
THE HELP OF THYROID PEROXIDASE.

29.  COUPLING OF IODOTYROSINE RESIDUES
DIT + DIT ------- T4(THYROXINE)
MIT + DIT ------T3(TRIIODOTHYRONINE)
DIT + MIT ------ RT3(REVERSE T3)
 RELEASE OF T3 & T4 INTO THE BLOOD
T3 & T4 ARE CLEAVED FROM THE THYROGLOBULIN
TO GET RELEASED INTO THE CIRCULATING BLOOD.
FIRSTLY THE THYROGLOBULIN IS ENDOCYTOSED
INTO THE FOLLICULAR CELLS.
THEN, THE PROTEOLYSIS TAKES PLACE TO
RELEASE T3 & T4 INTO THE BLOOD.
STORAGE OF THYROGLOBULIN
EACH THYROGLOBULIN MOLECULE CAN CONTAIN
UPTO 30 THYROXINE & FEW T3 MOLECULES.

30. CR

31.  IODINE RECYCLING
 ALMOST 3/4th OF THE IODINATED THYROID
HORMONES ARE MIT & DIT.
 SO, DURING DIGESTION OF THYROGLOBULIN, IODINE
IS CLEAVED FROM THEM BY DEIODINASE ENZYME.
 TRANSPORT OF T3 & T4
COMBINED WITH
TBG – THYRID BINDING GLOBULIN
TBPA – THYROID BINDING PRE ALBUMIN
ALBUMIN
 AFTER ENTERING THE CELL T3 & T4 GET
INCORPORATED INTO THE INTRACELLULAR PROTEINS.
 OF THESE TWO, T4 HAS MORE AFFINITY FOR TG &
BIND STRONGLY WITH INTRACELLULAR PROTEINS.
HENCE IT HAS LONG DURATION OF ACTION.

32. FUNCTIONS OF THYROID HORMONES
 REGULATION OF BASAL METABOLIC RATE
 REQUIRED FOR NORMAL PSYCHOSOMATIC
GROWTH
 HAS CHRONOTROPIC & IONOTROPIC EFFECT
ON HEART
 INCREASES THE SENSITIVITY OF RECEPTORS
TO CATECHOLAMINES & ALSO INCREASES
THE NO. OF RECEPTORS
 REQUIRED FOR NORMAL RESPIRATORY DRIVE
 REQUIRED FOR NORMAL HEMATOPOIESIS
 THYROXINE HAS OPPOSITE EFFECT OF
INSULIN
 INCREASES THE BONE TURNOVER

33.  FUNCTIONS OF CALCITONIN
 IT DECREASES THE SERUM CALCIUM LEVEL BY
REDUCING THE BONE RESORPTION
REGULATION OF THYROID
HORMONE SYNTHESIS
 BY TSH
 ACTIVATION OF CYCLIC AMP
 BY TRH
 EXPOSURE TO COLD
 NEGATIVE FEEDBACK MECHANISM