Thyroid anatomy and physiology dr syed ubaid associate professor of surgery

1. THYROID GLAND
DR SYED UBAID
Associate professor of surgery

2. SURGICAL ANATOMY
FROM GREEK thyreoeides= SHIELD SHAPE

3. Thyroid Gland, Anterior and Posterior
Views

4. SURGICAL ANATOMY
• TWO LOBES JOINED BY ISTHMUS
• PYRAMIDAL LOBE (80%)PROJECT UPWARDS
FROM ISTHMUS OR EITHER OF THE LOBES
• A FIBROMUSCULAR BAND levator glandulae
thyroideae DESCEND FROM THE BODY OF THE
HYOID BONE TO ISTHMUS OR TO PYRAMIDAL
LOBE

6. SURGICAL ANATOMY

7. SURGICAL ANATOMY
• GLAND LIES AGAINST C5,6,7 &T1 VERTEBRAE
• EACH LOBE EXTENDS FROM MIDDLE OF
THYROID CARTILAGE TO 4TH OR 5TH
TRACHEAL RING.
• ISTHMUS EXTENDS FROM 2ND TO THE 3RD
TRACHEAL

8. SURGICAL ANATOMY

9. SURGICAL ANATOMY
• EACH LOBE MEASURES 5cmX2.5cmX2.5cm
• ISTHMUS MEASURES 1.2cmX1.2cm
• GLAND MEASURES 25gms
• LARGER IN FEMALES THAN MALES
• INCREASES IN SIZE DURING PREGNANCY AND
MENSTRUATION

10. SURGICAL ANATOMY

11. SURGICAL ANATOMY
CAPSULES
• TRUE‐PERIPHERAL CONDENSATION OF
CONNECTIVE TISSUE OF GLAND
• FALSE/SURGICAL‐FROM PRETRACHEAL LAYER
OF DEEP CERVICAL FASCIA

12. SURGICAL ANATOMY
• CAPSULES

13. SURGICAL ANATOMY
SUSPENSORY LIGAMENT OF BERRY :
THE PRETRACHEAL LAYER IS THIN ALONG THE
POSTERIOR BORDER OF THE LOBES, BUT
THICK ON THE INNER SURFACE OF THE GLAND
WHERE IT FORMS A SUSPENSORY LIGAMENT
OF BERRY WHICH CONNECTS THE GLAND TO
THE CRICOID CARTILAGE

14. SURGICAL ANATOMY
WHY THYROID MOVES WITH DEGLUTITION
• DURING 1ST STAGE OF DEGLUTITION
• HYOID BONE MOVES UP
• PULLS PRETRACHEAL FASCIA UP
• THIS PULLS LIGAMENT OF BERRY UP
• THIS PULLS THYROID UP

15. SURGICAL ANATOMY
• ALL STRUCTURES ENCLOSED IN THE
PRETRACHEAL FASCIA MOVES UP WITH
DEGLUTITION
• THYROGLOSSAL CYST
-SUBHYOID BURSITIS
-PRE TRACHEAL LYMPH NODES
-PRE LARYNGEAL LYMPH NODES

16. SURGICAL ANATOMY
VASCULAR ANATOMY
• HIGHLY VASCULAR
• TWO ARTERIES
• SUPERIOR THYROID ARTERY
• INFERIOR THYROID ARTERY

17. SURGICAL ANATOMY
• 3 VEINS
• SUP THYROID VEIN
DRAINS INTO IJV OR COMMON FACIAL V.
• MIDDLE THYROID VEIN DRAINS TO IJV
• INFERIOR THYROID VEIN
INTO LEFT BRACHICEPHALIC V.
• A 4TH VEIN OF KOCHER’S EMERGE B/W MIDDLE
AND INFERIOR VEINAND DRAIN INTO IJV

18. SURGICAL ANATOMY

19. SURGICAL ANATOMY
LYMPHATICS
• PRIMARILY TO INTERNAL JUGULAR NODES
• SUPERIOR POLE & MEDIAL ISTHMUS TO
SUPERIOR GROUP
• LOWER POLE OF THYROID TO INFERIOR
GROUP
• EMPTY INTO PRETRACHEAL & PARATRACHEAL
NODES

20. SURGICAL ANATOMY

21. SURGICAL ANATOMY
Innervation
• Principally from ANS
• Parasympatheticfibers –from vagus
• Sympatheticfibers –from superior, middle, and
inferior ganglia of the sympathetic trunk
• Enter the gland along with the blood vessels.

22. SURGICAL ANATOMY
• RECURRENT LARYNGEAL NERVE SUPPLIES THE
INTRINSIC MUSCLE OF LARYNX EXCEPT
CRICOTHYROID WHICH IS SUPPLIED BY
EXTERNAL LARYNGEAL NERVE
• ACIDENTAL DAMAGE TO THIS NERVE DURING
SURGERY CAUSES IPSILATERAL VOCAL CORD
PARALYSIS & DIFFICULTY IN PHONATION

23. SURGICAL ANATOMY
• RT SIDE IT ORIGINATES FROM VAGUS CROSSES
FIRST PART OF SUBCLAVIAN.A LOOPS UNDER
IT RUNS OBLIQUE TO ENTER LARYNX AT LEVEL
OF CRICOID

24. SURGICAL ANATOMY
• LEFT SIDE AFTER ORIGIN FROM VAGUS
CROSSES AORTIC ARCH LOOPS POSTERIORLY
AROUND LIGAMENTUM ARTERIOSUS
ASCENDS MEDIALLY IN TRACHEO
ESOPHAGEAL GROOVE

25. SURGICAL ANATOMY

26. SURGICAL ANATOMY
• SUPERIOR LARYNGEAL NERVE HAS INTERNAL
BRANCH(SENSORY) & EXTERNAL
BRANCH(MOTOR)HELPS IN VOCAL CORD
TENSION AND PITCH OF VOICE

27. SURGICAL ANATOMY
• SUPERIOR LARYNGEAL NERVE RUNS IN
CLLOSE PROXIMITY TO SUPERIOR POLE
VESSELS, TO AVOID INJURY SUPERIOR POLE
VESSELS SHOULD BE INDIVIDUALLY LIGATED &
DIVIDED LOW ON THYROID GLAND AND
DISSECTED LATERALLY TO CRICOTHYROID
MUSCLE

28. SURGICAL ANATOMY
HISTOLOGY
The functioning unit is the lobule supplied by a
single arteriole and consists of 24–40
follicles lined with cuboidal epithelium. The
follicle contains colloid in which thyroglobulin
is stored.

29. SURGICAL ANATOMY
HISTOLOGY
• PARAFOLLICULAR CELLS(C CELLS)-
LOCATED UTSIDE FOLLICLES SECRETE
CALCITONIN .
– MEDULLARY CA ARISES FROM C CELLS

30. SURGICAL ANATOMY

31. EMBRYOLOGY
• The thyroglossal duct develops from the
median bud of the pharynx. The foramen
caecum at the base of the tongue is the
vestigial remnant of the duct. This initially
hollow structure migrates caudally and passes
in close continuity with, and sometimes
through, the developing hyoid cartilage.

32. EMBRYOLOGY
• The parathyroid glands develop from the third
and fourth pharyngeal pouches
• The thymus also develops from the third
pouch.
• As it descends it takes the associated
parathyroid gland with it which explains why
the inferior parathyroid which arises from the
third pharyngeal pouch normally lies inferior
to the superior gland.

33. EMBRYOLOGY
• However, the inferior parathyroid may be found
anywhere along this line of descent.
• The developing thyroid lobes amalgamate
• with the structures that arise in the fourth
pharyngeal pouch, i.e. the superior parathyroid
gland and the ultimobranchial body.
• Parafollicular cells (C cells) from the neural crest
reach the thyroid via the ultimobranchial body.

34. EMBRYOLOGY

35. Physiology
 The thyroid follicles secretes tri-iodothyronine(T3)and
thyroxin(T4)
 synthesis involves combination of iodine with tyrosine group
to form mono and di-iodotyrosine which are coupled to form
T3 andT4.
 The hormones are stored in follicles bound to thyrogobulin
 When hormones released in the blood they are bound to
plasma proteins and small amount remain free in the plasma .
 The metabolic effect of thyroid hormones are due to free
(unbound)T3 and T4.
 90%of secreted hormones is T4 but T3is the active hormone
so, T4is converted to T3 peripherally.

36. Physiological control of secretion
Synthesis and libration of T3 and T4 is controlled by thyroid
stimulating hormone(TSH)secreted by anterior pituitary gland.
TSH release is in turn controlled by thyrotropin releasing
hormone (TRH)from hypothalamus .
Circulating T3and T4 exert –ve feedback mechanism on
hypothalamus and anterior pituitary gland .
So, in hyperthyroidism where hormone level in blood is high ,TSH
production is suppressed and vice versa.

37. PHYSIOLOGY
• IODINE –RAW MATERIAL FOR THYROID
HORMONE SYNTHESIS
• INGESTED IODINE CONVERTED TO IODIDE
BEFORE ABSORPTION
• 15O μg OF IODINE MINIMUM REQD FOR
NORMAL THYROID FUNCTION OF WHICH
120μg ENTER THYROID AT NORMAL RATES OF
HORMONE SYNTHESIS AND SECRETION

38. PHYSIOLOGY
• THYROGLOBULIN IS A GLYCOPROTEIN SYNTHESIZED
IN THYROID CELLS AND SECRETED INTO THE COLLOID
BY EXOCYTOSIS
• THYROGLOBULIN IS BOUND TO THYROID HORMONES
TILL IT IS SECTRETED INTO BLOOD, AFTER WHICH IT
IS INGESTED BACK INTO THE COLLOID

39. PHYSIOLOGY
• STEPS OF THYROID HORMONE SYNTHESIS
1. IODINE TRAPPING
2. OXIDATION
3. IODINATION
4. COUPLING
5. STORAGE
6. RELEASE

40. PHYSIOLOGY
IODINE TRAPPING
• IODINEAVAILABLE THROUGH CERTAIN FOODS (EG,
SEAFOOD, BREAD, DAIRY PRODUCTS), IODIZED SALT,
OR DIETARY SUPPLEMENTS ETC
• THYROID CELL MEMBRANES FACING THE
CAPILLARIES CONTAIN A SYMPORTER OR IODINE
PUMP THAT TRANSPORTS Na+/I‐AGAINST
ELECTROCHEMICAL GRADIENT

41. Biosynthesis of T4 and T3
The process includes
• Dietary iodine (I) ingestion
• Active transport and uptake of iodide (I-) by
thyroid gland
• Oxidation of I- andiodination of thyroglobulin (Tg)
tyrosine residues
• Coupling of iodotyrosine residues (MIT and DIT)
to form T4 and T3
• Proteolysis of Tg with release of T4 and T3 into the
circulation
41

42. Regulation of TH synthesis/secretion

43. Normal circulatory concentrations
– T4 4.5-11 g/dL
– T3 60-180 ng/dL (~100-fold less than T4)
43

44. Carriers for Circulating Thyroid
Hormones
• More than 99% of circulating T4 and T3 is bound to
plasma carrier proteins
– Thyroxine-binding globulin (TBG), binds about
75%
– Transthyretin (TTR), also called thyroxine-binding
prealbumin (TBPA), binds about 10%-15%
– Albumin binds about 7%
– High-density lipoproteins (HDL), binds about 3%
• Carrier proteins can be affected by physiologic
changes, drugs, and disease
44

45. PHYSIOLOGY
• PHYSIOLOGICAL ACTIONS
• HEART
INCREASE CARDIAC
OUTPUT,HEART RATE
• ADIPOSE TISSUE
STIMULATE LIPOLYSIS

46. PHYSIOLOGY
• MUSCLE INCREASES PROTEIN
BREAKDOWN
• BONE
PROMOTES NORMAL
GROWTH AND SKELETAL
DEVELOPMENT

47. PHYSIOLOGY
• NERVOUS SYSTEM
PROMOTE NORMAL BRAIN
DEVELOPMENT
• GUT
INCREASESRATE OF CHO
ABSORPTION

48. Thyroid Hormone Plays a Major Role in
Growth and Development
• Thyroid hormone initiates or sustains differentiation
and growth
– Stimulates formation of proteins
– Is essential for normal brain development
• Essential for childhood growth
– Untreated congenital hypothyroidism or chronic
hypothyroidism during childhood can result in
incomplete development and mental retardation
48

49. Thyroid Hormones and the Central
Nervous System (CNS)
• Thyroid hormones are essential for neural
development and maturation and function of the
CNS
• Decreased thyroid hormone concentrations may lead
to alterations in cognitive function
– Patients with hypothyroidism may develop
impairment of attention, slowed motor function,
and poor memory
– Thyroid-replacement therapy may improve
cognitive function when hypothyroidism is present
49

50. Thyroid Hormone Influences the
Female Reproductive System
• Normal thyroid hormone function is important
for reproductive function
– Hypothyroidism may be associated with menstrual
disorders, infertility, risk of miscarriage, and other
complications of pregnancy
50

51. Thyroid Hormone is Critical for Normal
Bone Growth
– T3 also may participate in osteoblast
differentiation and proliferation, and chondrocyte
maturation leading to bone ossification
51

52. Thyroid Hormone Regulates
Mitochondrial Activity
• T3 is considered the major regulator of mitochondrial
activity
– A potent T3-dependent transcription factor of the
mitochondrial genome induces early stimulation
of transcription and increases transcription factor
(TFA) expression
– T3 stimulates oxygen consumption by the
mitochondria
52

53. Thyroid Hormones Stimulate
Metabolic Activities in Most Tissues
• Thyroid hormones (specifically T3) regulate rate of
overall body metabolism
– T3 increases basal metabolic rate
• Calorigenic effects
– T3 increases oxygen consumption by most
peripheral tissues
– Increases body heat production
53

54. Investigation
Laboratory investigation:
-serum T3, T4.
-serum TSH.
-thyroid antibodies:
in hashimoto’s disease.

55. Investigation
-chest and neck x-ray:
Show descend of thyroid gland to thorax and
mediastanal shifting in retrosternal goitre.
-iodine isotopes
By i.v injection of I131. Then, use gama rays to show
hot and cold nodules.
-CT scan
Show thyroid size and if there is compression to
trachea

56. Investigation
-Endoscopic investigation:
-bronchoscopy: show compression and
infiltration of trachea by tumer
Biopsy:
-fine needle aspiration biopsy.
-true-cut biopsy.

57. MIDLINE SWELLINGS
• Thyroid enlargement
• Thyroglossal cyst
• Dermoid cyst

58. THANK YOU 