Anatomy and physiology of thyroid and parathyroid glands.pptx

Anatomy of thyroid
Anatomy of Parathyroid
Physiology of thyroid hormone
Physiology of Parathyroid hormone

1. ANATOMY & PHYSIOLOGY OF THYROID & PARATHYROID GLANDS DR. SUDIN KAYASTHA RESIDENT ORL HNS BIR HOSPITAL, NAMS

2. INTRODUCTION A butterfly shaped gland Lower anterior neck 2 primary endocrine functions 1) Secretions of thyroid hormones: T3 and T4 > ensures metabolic demands of body is met > Regulates carbohydrate and lipid metabolism 2) Secretion of Calcitonin

3. HISTORY

4. EMBRYOLOGY Thyroid develops from fusion median a nlage two lateral anlagen , Originating from two distinct regions of endodermal pharynx. Colloid production starts at 13-14 weeks of gestation Thyroxine detected in foetal serum at 11-13 weeks . Structural Maturity of fetal thyroid gland achieved at 17.5 weeks

5. Embryology MEDIAN ANLAGE Mid line thickening of ventral surface of primitive pharynx Between 1 st and 2 nd branchial arches 16 th / 17 th gestational day : a diverticulum formed Recognized as a small blind pit in midline between anterior two thirds and posterior third of tongue Known as Foramen Caecum

6. Diverticulum expands at its distal tip ----  bilobed structure Migrates to the lower neck, anterior to hyoid, laryngeal cartilages and pharyngeal gut. Pulled into position by the descent of heart Reaches final location ( anterior to the trachea) : 7 th gestational week

7. The stalk eventually fragments and disappears Persistence of the stalk , anywhere between the foramen cecum and thyroid isthmus Thyroglossal duct cyst

8. Rarely : thyroid descent may become arrested anywhere along the tract lingual thyroid ectopic thyroid tissues in the sublingual, high cervical, mediastinal region, cardiac endothelium

9. LATERAL ANLAGEN Ultimobranchial bodies Caudal end of fourth or fifth pharyngeal pouches Supplemented by migratory neural crest elements Fuse with median enlage as the gland descents 6 th week of development Contributes 10% of the mass of thyroid gland

10. Lateral anlagen Failure of fusion: lateral thyroid lobe Responsible for production of Parafollicular (C cells) Para follicular cells migrate to be distributed throughout the gland Lateral thyroid lobe : greater than normal amount of parafollicular tissue  increased tendency to become neoplastic

11. ANATOMY MACROSCOPIC ANATOMY Largest endocrine gland Weighs : 15-20 grams (0.4% of body mass) Slightly heavier in females Enlarges during pregnancy and menstruation

12. Location : Anteriorly in the lower neck level C5- T1 Colour : Reddish brown Parts: T wo large lobes : situated on either side of trachea Isthmus : joins the lobes and straddles the midline. Pyramidal lobe ANATOMY

13. RELATIONS OF THYROID GLAND Anteriorly : Skin superficial fascia Investing fascia Strap muscles and pretracheal fascia Posteromedially : Larynx, trachea, pharynx, esophagus Recurrent laryngeal nerve Posterolaterally Carotid sheath Cervical Sympathetic trunk

14. Anatomy: THYROID LOBE Pear shaped /conical in shape Measures : 5cm x 3cm x 1.5cm Extensions: Apex: narrow and conical in shape extends beneath sterno thyroid up to its insertion on oblique line of thyroid cartilage . L ower pole: more rounded extends to level of 4 th or 5 th tracheal ring Lies medial to carotid sheath & lateral to trachea and oesophagus

15. THYROID ISTHMUS Immediately caudal to inferior border of cricoid cartilage Covers 2 nd and 3 rd ring of trachea Joins two lobes together Anterior Jugular vein cross over isthmus.

16. PYRAMIDAL LOBE Conical protrusion of varying size Present in 12-81% of cases Represents distant remnant of thyro glossal duct Originates from any part of the isthmus or adjacent lobe (L>R) Extends superiorly : thyroid cartilage or hyoid bone 3 mm to 63 mm in length

17. Usually situated on the left side May arise from right side of isthmus or close to midline Occasionally detached or in two parts Removal: part of routine thyroid lobectomy Apex may be replaced by fibrous or fibromuscular tissue  Levator of thyroid gland PYRAMIDAL LOBE contd …

18. TUBERCLE OF ZUCKERKANDL Lateral or posterior projection of thyroid lobe Posterior horn of thyroid 60% of surgical dissections Represents point of embryological fusion of lateral anlagen & median anlage

19. TUBERCLE OF ZUCKERKANDL: Surgical importance Recurrent Laryngeal nerve most often runs medial to it Superior parathyroid gland usually attached to its cranial aspect When enlarged as part of goiter, can be left behind during subtotal thyroidectomy

20. CAPSULES OF THYROID Enclosed by fibrous capsule (true capsule). Invested by pre tracheal layer of cervical fascia ( false capsule ). True capsule : Tightly adherent to gland Into parenchyma to form septa  lobules During surgeries : thyroid removed along with true capsule: presence of dense capillary plexus deep to capsule  avoid hemorrhage

21. Pre tracheal Fascia Visceral layer of deep cervical fascia Superiorly : to hyoid bone Inferiorly: into mediastinum , fusing with fascia surrounding aorta, pericardium and parietal pleura at level of carina Laterally : Blends with carotid sheath Posteriorly : merges with prevertebral fascia Anteriorly : forms distinct layer separating thyroid from strap muscles

22. On posterior aspect of isthmus, fascia sometimes perforated by small tracheal vessels  anterior tracheal ligament Upper part on each side  much thicker and binds gland firmly to sides of cricoid cartilage and 1 st tracheal ring  L ateral ligament of thyroid or ‘ suspensory ligament of Berry ’. Fixation to the trachea  thyroid gland move on swallowing. Recurrent laryngeal nerve may lie lateral, medial or within ligament just before it enters larynx

23. ARTERIAL SUPPLY Main blood supply Superior thyroid arteries Inferior thyroid arteries Thyroid ima artery (12%)

24. Superior thyroid artery Origin: anterior surface of External carotid artery, below the level of greater cornu of hyoid bone Passes antero -inferiorly Pierces the thyroid fascia Divides into anterior and posterior branches

25. SUPERIOR THYROID ARTERY ANTERIOR BRANCH Follows medial margin of superior lobe to the isthmus Anastomoses with its opposite artery Several descending arteries from this arcade anastomose with branches of Inferior thyroid artery Supplies the anterior surface of the gland

26. POSTERIOR BRANCH : Descends on the posterior surface of gland Joins ascending branch of inferior thyroid artery( 45%) Supplies the lateral and medial surface SUPERIOR THYROID ARTERY

27. INFERIOR THYROID ARTERY Arises from the Thyrocervical trunk , branch from the first part of Subclavian artery. 15% : may come off directly from the subclavian artery.

28. Ascends infront of Ant.Scalene muscle Turns medially, infront of vertebral artery Goes behind carotid sheath and sympathetic trunk Descends on anterior surface of longus colli Reaches lower border of thyroid Divides into Ascending and descending branches on the posterior surface of gland INFERIOR THYROID ARTERY Course

29. Supplies inferior and posterior surfaces of gland Gives of branches to Superior and Inferior parathyroid glands superior parathyroid : receives a terminal blood supply, either from its anastomoses with post branch of STA or directly from STA Inferior parathyroid : supplied by a terminal branch of descending branch Gives of branches to trachea, oesophagus , lower part of the pharynx INFERIOR THYROID ARTERY

30. Acts as an important Surgical landmark for RLN and Parathyroid glands RLN passes immediately superficial to the artery , deep to it or between its two terminal branches INFERIOR THYROID ARTERY

31. INFERIOR THYROID A. Location of parathyroid glands : glands supplied by the terminal branches tracing of the artery to its destination  identification of parathyroid glands

32. THYROID IMA ARTERY A miniscule vessel Present in 12% of cases Arises from : Brachiocephalic artery ( most common), Aorta, Rt common carotid a., Subclavian a., internal thoracic a. ascends infront of the trachea to end at the isthmus

33. VENOUS DRAINAGE The veins form a venous plexus Drain via 3 main groups 1: Superior thyroid veins 2: Middle thyroid veins 3: Inferior thyroid veins

34. Superior thyroid veins Emerges from upper part of the gland Accompanies the corresponding artery Drains into Internal Jugular vein or Facial vein ( occasionally )

35. Middle Thyroid veins Arises from lateral surface of the gland at junction of middle and lower thirds of gland Maybe double or absent Receives blood from inferior and antero -lateral part of the gland larynx and trachea Drains into the internal Jugular vein

36. Inferior thyroid veins Arises in a glandular venous plexus Connects with Middle and superior veins Forms a venous plexus Drains into right and left inferior veins which then drains into their respective Brachiocephalic veins Drains via a common trunk into superior vena cava or left brachiocephalic vein

37. LYMPHATIC DRAINAGE Contains rich network of lymphatics Level II /III : upper poles of the gland, isthmus and pyramidal lobe Level III/IV : Lateral aspect of each lobe Lower pole of the gland : drains into peri and paratracheal nodes in VI, then on to both Level IV and VII nodes

38. Lymphatic drainage may also pass to nodes in parapharyngeal and retropharyngeal spaces Level I and II : rarely involved in metastatic thyroid Ca Extensive communication : level II, III , IV and superior mediastinum via VI

39. NERVE SUPPLY Under the influence of autonomic system as well as hormonal control Sympathetic fibers : originate from Superior cervical and stellate ganglia Enter gland along with the main arteries Parasympathetic fibers : come from vagus

40. NERVE SUPPLY Recurrent laryngeal nerve and External branch of Superior laryngeal nerve: Donot supply the gland Lies in close proximity to the gland Renders them extremely important in assessment of thyroid conditions and surgeries.

41. RECURRENT LARYNGEAL N . Branch of vagus nerve Supplies all intrinsic muscles of the larynx except cricothyroid muscle. Supplies sensory fibres to the mucus membrane below the level of vocal fold.

42. RECURRENT LN RLN variable in size : 1.5- 4 mm in diameter Identified : whitish appearance Characteristic longitudinal vessel running along its length Flattened, rounded surface Nerve divides into 2 or occasionally upto six terminal branches : 39%

43. LEFT RLN Leaves vagus in the mediastinum Anterior to arch of the aorta Passes behind the ligamentum arteriosum Posteriorly under concavity of arch Superiorly to lie in trachea- oesophageal groove Behind ITA, posterior to Ligament of Berry, Under or between fibres of cricopharyngeal part of inferior constrictor m. Lies immediately behind the capsule of cricothyroid joint.

44. RIGHT RLN The nerve passes posteriorly Loops under the first part of Subclavian artery Via an oblique course reaches the Tracheo-oesophageal groove It then enters the larynx in the similar fashion to LRLN.

45. Relationship RLN with the inferior thyroid artery is variable In order of decreasing frequency: it lies behind, Between the terminal branches Occasionally superficial to the artery . Used in the past to identify the nerves during surgeries : not reliable now

46. BEAHRS’ TRIANGLE Best and safest way to identify RLN third side of the triangle formed by RLN Other two sides : common carotid artery inferior thyroid artery

47. NON RECURRENT LARYNGEAL N. Found in 0.2- 0.4 % pt Tends to be thicker Usually associated with : RT side : vascular anomaly of Subclavian a. Left side : transposition of great vessels Commonly found on the right side ( 2%)

48. Comes off vagus nerve directly passing medialy to reach trachea- oesophageal groove, then it follows the usual route to larynx.

49. EXTERNAL BRANCH OF SUPERIOR LARYNGEAL NERVE Lies deep to upper pole of the thyroid gland Supplies Cricothyroid muscle Runs parallel to Superior thyroid vessels : 85% Most often runs medial to the vessels

50. Variations of EBSLN Various classification systems have been used to describe the course of the EBSLN. The Friedman classification system describes three anatomic variants of the nerve(cadaveric dissection) The other classification systems for the EBSLN are the Cernea classification the Kierner classification

51. Friedman’s classification

52. JOLL’S TRIANGLE Used for the identification of EBSLN Sternothyrolaryngeal triangle Boundaries : Superiorly : Attachment of the Strap muscles Deep investing fascia to hyoid bone Laterally : Upper pole of thyroid gland and superior thyroid veins Medially : mid line Floor : Cricothyroid muscle Roof : Strap muscles Contents: External Laryngeal nerve.

53. Importance of EBSLN : important for voice quality Injury to the nerve result in limitation of voice range pt would have difficulty reaching high notes Breathy voice.

54. Others: Cutaneous nerves C2 and C3 run superficial to the deep investing layer of cervical fascia Can be damaged during thyroid surgeries Anaesthesia of anterior neck skin

55. MICROSCOPIC ANATOMY Thyroid gland consists mainly of follicular cells A rranged in one cell thick aggregates around a central pool of colloid to form follicles A thyroid Lobule : 20-40 follicles

56. Follicular Cells : ~ spherical in shape 0.02 – 0.9 mm in diameter Have characteristic cytoplasmic features : long segments of RER, Golgi Apparatus: synthesizing and packaging proteins Plasma membranes of apical and basal layers kept separate by tight junctions: control storage of TH in the colloid and their release into circulation

57. When gland is inactive : cells are flattened , colloid is abundant, dense and homogenous in appearance Prolonged excessive TSH stimulation : cells become hypertrophied and hyperplastic : adopt a columnar shape Increase in prominence of intacellular organelles and microvilli development Overall increase in vascularity in the gland.

58. Each follicle interlaced with LCT ( stroma ) containing fenestrated capillaries and expanded lymphatics Interfollicle Connective Tissue spaces : Large Contain collagenous matrix ,fibroblasts , unmyelinated nerve fibres , fat cells, macrophages and lymphocytes

59. Para follicular cells : single or in small clumps adjacent to the stromal aspect of the follicular cells Recognized : spindle or polygonal shape large “light” cytoplasm

60. Tyrosine and iodine are essential for synthesis of thyroid hormones. Both are taken up by the blood Tyrosine is synthesised by the body (in the thyroglobulin ). Iodine is a dietary essential. Hormone synthesis occurs on the thyroglobulin . Physiology of Thyroid

61. Following steps are involved synthesis, storage and secretion: Thyroglobulin production by follicular cell and released into colloid by exocytosis Iodine uptake by follicular cell from the blood and transferred to colloid Attachments of iodine to tyrosine on thyroglobulin in colloid Coupling processes between the iodinated tyrosine molecules to form T4 and T3 . Secretion (upon stimulation) of T4 and T3 occurs by endocytosis a piece of colloid, uncouplingof T4 and T3 and diffusion out of the follicular cell into the blood

62. Approximately, 90% of the hormones released from the thyroid gland initially appear in the form of T4. However, a majority of the T4 that is secreted from the thyroid gland is subsequently converted to T3. T3 is 4times more potent in its biologic form than T4 and is the major hormone that interacts with the target cells.

63. Both the hormones are highly lipophilic and once in the blood, immediately bind to proteins: Thyroid hormone specific protein- thyroxine binding globulin (70-80%) Other non-specific proteins Less than 0.1% of T4 and 1% of T3 are in unbound form. These free T4 and T3 compounds are biologically active, and it is these components that produce the effects of the thyroid hormones on peripheral tissues and on the pituitary feedback mechanism.

64. REGULATION OF THYROID HORMONE SECRETION

65. Actions of thyroid hormone Metabolic rate and heat production: ↑ metabolic activities ↑ O₂ consumption to most metabolically active tissues BMR can ↑ by 60 – 100% Since ↑ metabolism results in ↑ heat production → thyroid hormone effects is calorigenic Intermediary metabolism:  Modulates rates of many specific reactions involved in fuel metabolism

66. Effects of throid hormone

67. PARATHYROID GLANDS

68. PARATHYROID GLANDS Embryology 1) The parathyroid primordia first appears at 32 days of embryonic development 2) develop from endodermal cell proliferation of 3 rd & 4 th pharyngeal pouch 3) Dorsal aspect of third pharyngeal pouch forms inferior parathyroid gland and ventral aspect forms thymus 4) 4 th pharyngeal pouch dorsal aspect forms superior parathyroid glands and ventral aspect along with remnants of 5 th pharyngeal pouch form ultimobranchial bodies

69. Superior Parathyroid Endoderm of dorsal part of fourth pharyngeal pouch The superior parathyroid gland migratecaudally and medially At the end of the fifth week of gestation reaches its final anatomical position which is posterior to lateral thyroid lobes

70. Inferior Parathyroid Gland Endodermal cells from parathyroid/thymus primordium in third pharyngeal pouch At 5 weeks of gestation – thymus migrates caudally and medially (pulls inferior parathyroid gland with it) At 7 weeks of gestation – reach it’s normal position

71. At 5 weeks of gestation End of 7 weeks of gestation

72. NUMBER Four parathyroid glands - 84% Gilmour - 527 autopsy cases, four glands - 80% three - 13% five - 6.1% two - 0.2% Akerström dissected 503 autopsy cases, four glands- 84% more than four - 13% three - 3%

73. SIZE & WEIGHT Size : 5mm x 3mm x 1-2mm Weight : 30-40 mg Inferior parathyroid gland heavier Vary with : *Age and gender *Body weight * Race -Depends on vascularity

74. SHAPE Akerström documented, 83% - oval, bean shaped or spherical 11% - elongated 5% - bilobed 1% - multilobed Thyroid gland (back view)

75. MACROSCOPIC APPEARANCE Color - light yellow to reddish-brown (In children - salmon-pink) Inferior parathyroid gland Superior parathyroid gland Recurrent laryngeal nerve

76. Parathyroid gland Lymph node Fat lobule Thyroid nodule Color Yellow or reddish brown More translucent Yellow Reddish Consistency Soft, mobile Hard Soft Hard Form Distinct edge/capsule Indistinct Less well demarcated from surrounding fat Not separable from thyroid gland Vascularity Vascular Less vascular Less vascular Less vascular

77. Gross appearance of (a) a lymph node, (b) a parathyroid gland and (c) a fat lobule in a surgical field

78. LOCATION: Superior parathyroid gland more constant in location compared to the inferior parathyroid gland Posterior- recurrent laryngeal nerve Above - inferior thyroid artery Middle of posterior border - thyroid lobes Within 1cm - cricothyroid joint In 85% of the cases it is found within a 2cm diameter of a point 1 cm above the crossing of the inferior thyroid artery and recurrent laryngeal nerve 7) The RLN is a good constant landmark for identification of the superior parathyroid position

79. Cricothyroid joint Inferior thyroid artery Recurrent laryngeal nerve Thyroid cartilage Thyroid lobe Trachea

80. Ectopic Locations Posterior neck Retropharyngeal– oesophageal space Carotid sheath Posterior mediastinum Intra- thyroid

81. LOCATION: Inferior parathyroid gland Location of Inferior parathyroid glands are not constant but frequently found Below ITA Infront of RLN Within 1 cm of the lower pole of the thyroid gland

82. Inferior thyroid artery Esophagus Recurrent laryngeal nerve Thyroid lobe Thyroid cartilage Trachea

83. Ectopic Locations Cervical thymus (39%) Mediastinal thymus (6%)

84. ARTERIAL SUPPLY Superior and inferior parathyroid glands Inferior thyroid arteries Superior parathyroid -Superior thyroid artery - Anastomoses between the superior and inferior thyroid arteries (10–15% cases)

85. VENOUS DRAINAGE Upper and central parts of the ipsilateral parathyroid glands Superior and middle thyroid veins

86. INNERVATION Adrenergic from sympathetic system Superior cervical ganglia Middle cervical ganglia gland activity controlled by changes in plasma calcium levels Vasomotor nerves

87. MICROSCOPIC APPEARANCE Capsule and septae divides gland into lobules Perenchymal cells – in clusters Within the fibrovascular stroma : -Adipocytes -Macrophages -Mast cells Intrathyroidal parathyroid gland ( H&E stain, low magnification )

88. Chief cells Dominant cell type Scanty, slightly eosinophilic cytoplasm Function: Synthesize and secrete parathyroid hormone Nests and trabecula of chief cells ( H&E stain, high magnification)

89. Oxyphil cells Hallmark: Copious, granular and densely eosinophilic cytoplasm Function : Unknown Nodular sheets of oxyphil ( H&E stain, high magnification ).

90. PHYSIOLOGY

91. E ncoded by a gene in chromosome 11 Pre-pro-PTH (115 amino acids) Pro-PTH (90 amino acids) Active peptide hormone (84 amino acids) Stored in - secretory vesicles Biosynthesis Parathyroid Hormone

92. In response to hypocalcaemia , -PTH concentrations change within 1 min -Peak in 4–10min -Decline within 60min Once released, broken down in the liver & kidney into three smaller fragments (1 to 36 amino-terminal chain has biologic activity) Half-life : 3mins

93. Actions of parathyroid hormone :

94. Bone Enhances resorption of calcium from bones by acting on osteoblasts and osteoclasts Resorption occurs in two phases: Rapid phase Slow phase

95. Slow phase - Activation of osteoclasts

96. Rapid phase Within minutes Activate the calcium pump Increase permeability of osteoblast and osteoclast

97. Increases calcium reabsorption (ascending loops of Henle , distal convoluted tubule and proximal part of collecting duct) Blocks renal reabsorption of phosphate (proximal tubule) Activates 1α-hydroxylase enzyme (proximal renal tubules) Which has a role in vitamin D activation

98. Gastrointestinal tract

99. Role of PTH in the activation of vitamin D PTH 7 dehydroxycholesterol

100. In the skin, when 7-dehydroxycholesterol is exposed to UV light vitamin D3 is formed ‘Active’ vitamin D (1, 25-(OH)2 vitamin D3) occurs after: 25-hydroxylation in the liver 1-hydroxylation in the kidney Vitamin D3: Promotes absorption of calcium and phosphate in intestine Increases bone resorption of calcium Increases renal calcium reabsorption

101. Normal reference range: 2.20–2.60mmol/L Calcium

102. Phosphate Normal range: 0.8-1.4mmolL

103. REFERENCES Scott brown’ otorhinolaryngology head and neck surgery, 8th edition Scott brown’ otorhinolaryngology head and neck surgery, 7th edition Stell and Maran’s Textbook of head and neck surgery and oncology 5 th edition Bellenger’s otorhinolaryngology head and neck surgery 16th edition BD Chaurasia’s human anatomy 6 th edition Volume 3 Guyton and Hall textbook of medical physiology 13 th edition

104. THANK YOU