Thyroid Gland

INTRODUCTION:-

1. It is the largest endocrine gland.
2. It’s functions are as follows:-
   a. Secretes hormones –
   i. Triiodothyronine
   ii. Tetraiodothyronine
   iii. Calcitonin
3. Weight – 25g
4. It is a organ in the body which is having rich blood flow.
5. Dimensions – 5cmx2.5cmx2.5cm of each lobe.
6. Location
   a. It is present in the anterior aspect of the neck and both sides of the midline.
   b. It is present against the vertebrae c5-c7 and t1
   c. Each lobe extends from the middle part of the thyroid cartilage to the 4th/5th tracheal ring.
   d. Isthmus extends from the 2nd tracheal ring to the 4th tracheal ring.

Capsules of thyroid gland:-

1. True capsule :
   a. It is the peripheral condensation of the connective tissues of the thyroid gland.
   b. It contains the dense capillary plexus.
2. False capsule:
   a. It is derived from the pretracheal layer of the deep cervical fascia.
   b. It is thin along the posterior border of the lobe.
   c. It is the thick along the inner surface of the gland. It forms the suspensory ligament of the berry which connects the lobe with the cricoid cartilage.
   PARTS AND RELATIONS:-
3. The each lobe of the thyroid gland are conical in shapeand have:
   a. An apex
   b. A base
   c. 3 surfaces
   i. Lateral
   ii. Medial
   iii. Posterolateral
   d. 2 borders
   i. Anterior border
   ii. Posterior border
   APEX:-
   ATTACHMENTS:
4. STERNOTHYROID MUSCLES
5. THYROID CARTILAGE
6. SUPERIOR THYROID ARTEY
7. EXTENAL LARYNGEAL ARTERY
   BASE:-
8. 4TH/5TH TRACHEAL RING
9. INFERIOR THYROID ARTERY
10. RECURRENT LARYNGEAL NERVE
    3 SURFACES:-
    LATERAL BORDER:-
11. ANTERIOR BORDER OF THE STERNOCLEIDOMASTOID MUSCLE
12. STERNOHYOID MUSCLE
13. SUPERIOR BELLY OF THE OMOHYOID MUSCLES
14. STERNOTHYROID MUSCLES
    MEDIAL SURFACES:-
15. 2 TUBES
    A. TRACHEA
    B. OESOPHAGUS
16. 2 MUSCLES :-
    A. INFERIOR CONSTRICTOR MUSCLE
    B. CRICOTHYROID MUSCLES
17. 2 NERVES
    A. EXTERNAL LARYNGEAL NERVE
    B. RECURRENT LARYNGEAL NERVE
    POSTEROLATERAL SURFACE:-
18. CAROTID SHEATH
19. COMMON CAROTID ARTERY
    2 BORDERS:-
    ANTERIOR BORDER
20. ANTERIOR BRANCH OF THE SUPERIOR THYROID ARTERY
    POSTERIOR BORDER
21. INFERIOR THYROID ARTERY
22. CONNECTING LINK BETWEEN THE POSTERIOR BRANCH OF THE SUPERIOR THYROID AND THE ASCENDING LINK OF THE INFERIOR THYROID ARTERY.
23. PARATHYROID BONE
24. THORACIC DUCT PRESENT ON THE LEFT SIDE.
    ISTHMUS – BOTH THE LOBES OF THE THYROID GLAND ARE CONNECTED TO EACH OTHER BY THE HELP OF THE ISTHMUS.
    IT HAS 2 SURFACES.THESE ARE :-
25. ANTERIOR SURFACE
26. POSTERIOR SURFACE
    IT HAS 2 BORDERS.THESE ARE:-
27. SUPERIOR BORDER
28. INFERIOR BORDER
    ANTERIOR SURFACE:-
29. RIGHT AND LEFT STERNOTHYROID AND THE STERNOHYOID MUSCLES.
30. ANTERIOR JUGULAR VEINS
31. FASCIA AND THE SKIN
    POSTERIOR SURFACE :-
32. 2ND TO 4TH TRACHEAL RING
    SUPERIOR BORDER:-
    ANTERIOR BRANCHES OF THE LEFT AND THE RIGHT SIDE OF THE SUPERIOR THYROID ARTERIES.
    INFERIOR BORDER:-
    INFERIOR THYROID VEINS WHICH LEAVES THE GLAND AT THIS BORDER.

ARTERIAL SUPPLY:- {SILA – PNEUMONIC}

1. S- SUPERIOR THYROID ARTERY- BRANCH OF THE EXTERNAL THYROID ARTERY
2. I- INFERIOR THYROID ARTERY- BRANCH OF THE THYROCERVICAL ARTERY WHICH ENTERS INTO THE SUBCLAVIAN ARTERY.
3. L – LOWEST THYROID ARTERY- BRANCH OF THE BRACHIOCEPHALIC TRUNK
4. A- ACCESSORY THYROID ARTERY- BRANCH OF THE TRACHEAL AND THE OESOPHAGEAL ARTERIES
   VENOUS DRAINAGE:-{SMIF – PNEUMONIC}
5. SUPERIOR THYROID VEIN – BRANCH OF THE INTERNAL JUGULAR VEIN
6. MIDDLE THYROID VEIN – BRANCH OF THE INTERNAL JUGULAR VEIN
7. INFERIOR THYROID VEIN – BRANCH OF THE LEFT BRACHIOCEPHALIC VEIN
8. FOURTH THYROID VEIN – IT EMERGES FROM THE MIDDLE AND THE INFERIOR VEINS. WHICH IS BRANCH OF THE INTERNAL JUGULAR VEIN.
   LYMPHATIC DRAINAGE :-
9. LYMPH WHICH IS PRESENT IN THE UPPER PART OF THE THYROID GLAND IS THE UPEER DEEP CERVICAL LYMPH NODE WHICH PASSES THROUGH THE PHARYNGEAL LYMPH NODE.
10. LYMPH WHICH IS PRESENT IN THE LOWER PART OF THE THYROID GLAN ISS THE LOWER DEEP CERVICAL LYMPH NODE WHICH PASSES THROUGH THE PRETRACHEAL LYMPH NODE.
    NERVE SUPPLY:-
11. APEX – EXTERNAL LARYNGEAL NERVE
12. BASE – RECURRENT LARYNGEAL NERVE
13. NERVES – DERIVED FROM THE MIDDLE CERVICAL GANGLION AND PARTLY FROM THE SUPERIOR AND THE INFERIOR CERVICAL GANGLIA.
    CLINICAL ANATOMY :-
14. SWELLING OF THE THYROID GLAND LEADS TO GOITRE WHICH CAN BE PALPATED FROM BEHIND
15. REMOVAL OF THE THYROID KNOWN AS THE THYROIDECTOMY WHICH TAKES PLACE IN THE CASE OF HYPERTHYROIDISM.
16. HYPOTHYROIDISM WHICH LEADS TO CRETINISM IN INFANTS AND MYXOEDEMA IN THE ADULTS.
    HISTOLOGY:-
    THE THYROID GLAND IS MADE UP OF THE TWO SECRETORY CELLS THAT IS FOLLICULAR CELLS AND THE PARAFOLLICULAR CELLS.
    DEVELOPMENT:-
    THE THYROID GLAND DEVELOPS FROM THE MEDIAN ENDODERMAL THYROID DIVERTICULUM WHICH GROWS DOWN IN FRONT OF THE NECK FROM THE FLOOR OF THE PHARYNX.

Contributor- Medico Abinash Jena