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The thyroid gland is the biggest gland in the neck. It is situated in the anterior part of the neck below the skin and muscle layers. The thyroid gland takes the shape of a butterfly with the two wings being represented by the left and right thyroid lobes which wrap around the trachea. The sole function of the thyroid is to make thyroid hormone. This hormone has an effect on nearly all tissues of the body where it increases cellular activity. The function of the thyroid, therefore, is to regulate the body's metabolism

Publicada em: Saúde e medicina


  1. 1. UNDERSTANDING THYROID GLAND By Dr Bashir Ahmed Dar Associate Professor Medicine Chinkipora Sopore Kashmir Email: drbashir123@gmai| .com
  2. 2. ‘*3 In
  3. 3. The presentation on thyroid is divided into three parts Part one deals with thyroid basics Part two on anti thyroid drugs and part three is on thyroid disorders a It therefore becomes important to read all the three parts to have better understanding of thyroid diseases and their management. Most of these slides are onJ, ~y slideshare and other websites ‘ ‘ 1.3 ll; 5’
  4. 4. * The purpose of this presentation is to explain the following diagram A and B. lf you understand the following diagram nicely then you may not need to read the whole slide presentation. ° Ifyou feel any difficulty in understanding the diagram A and B then you better read whole slide presentation. * Don't ignore Deiodinase enzyme that cuts iodide from thyroglobulin so that iodide can be , recycled in the process l‘}If'. . ’%; :3
  5. 5. g / .,, Thyroglobulin "'°e'°"“‘a5° , ', -'; ,'-/ - precursor (TG) 4- lodination at — 0 —; —— we and _<_> , Peroxidase I coupling 3 t s--%. ' . - /1 MIT. PIT Mn- DIT Secretion "' ' T3 RTE ' T" E’ ’/ Pinocytosis RT3 T4 Proteases Colloid T4 droplet Hrs ‘ Guyton Ha Ha‘ Textbook of Mrmcnl Pnyvc Ody. 12th Edition Copyng'~v. < Ion Dy Samdevs. on l'v‘pM“. or Ha. -wet, Inc All ngt~Ls veyzvcc
  6. 6. £3. ‘J Surnrnary scheme of thyroid hormone bicsynthesis and secmedon. ‘-1 fr , Ta Blood Vessel V’ ; :;: r‘ > VA Pnunary Tar 0t ‘'4, " ‘5"‘ D “’ _ Ti= £='-tgJ<vs‘-L’; 7 ‘_I, "T-3—v— it ’ *’"~— T ¢ 7 (TG) X "T7 i], __f ' —~‘_ Glucose / /3‘ “'/ V AATP 1” . VJ I? < . ¢AMp 7;. $ Fglodado : Exocylosls (.7; 1/ l, N ‘- .5 ~. /‘7 T-s-T3 Deiodinase G5‘, ‘_/ -—: > Iodotyroslnes e—> Iodide pamose Cycle G6P Lysosomc (RGCYC/45‘) NADFf“H Secondary 5‘. __ ————~ _ Lysosomo ’/ / ‘ Nucleus '-V O '‘T''/ ‘ Peroxld3‘—? NADP l DNA A’ GODQFEUFIQ System , Ri*’, I ¢ 02/1 __ Thyroglobulin H o C DrobletmRNAE7-G)/ synflwsis K‘; 2 Z/ X5 Peroxidase ( t§sis) ®> Q9 $ / _ x by Trapping Mechanism (Iodide Pump _‘(f? haz_-; ocyro_: «’<)' M K ’» . A Thyroglobulin " Tn! ” _ . "]'fi 7 —/ —, —~~‘' . / ' / - ,1 1} / _ , / __ y ‘ _ / .v’ x ‘-. J DIT DIT MIT DIT -; (L)x: daI/ vu (. oupI: n_q) ‘ ’ -- I N’ 'frL/ ‘NT "'/ Follicular Lurne-n"». ’ Re: x!)s, o.rption -1 J (cgumd Spaca) ’ L: ar. un5c~
  7. 7. * Thyroid gland is highly vascular Thymld 9'3"“ tr. l»(n. «.‘ c. vow may m‘”wu' Cwohd ‘-‘lay MD id ban" : .uPMol L, *.'Y"Q"~1I nv/ we / “ / supurlof ttrymd ‘V xlory and van ‘§ . . mu-rm: yugular ‘ A thy-3a: l cartilage van N -' / ,// tum-was oon"noncxrclld«—‘_‘_ / ” my K l i_ Dvramldal lobe naht lobe cl , _, ;~‘” 01 myro-J gland myn: u1gl. md xi ’ y/ _/" lv~! l lobr of "‘‘’3°’‘' "'Y'°"’ ~ ‘ - ‘ . // in~, m.. | gland vein R} ' __, ’—‘ ‘ lnfma lhylold 'T‘-- VI__ _ ‘~-__‘ isthmus oi ‘ ‘"'V k _ , tlmu-dflkmd , .. ~-5'-fl vwgu-5 , /‘ . _. . / , ’ right vague ntrvc / /" ' . tn! -not thyroid vr, -vns br. «cfw: )capn, : .4: (run, »'/ ,. r’ ‘FY’. brachlocntwpr. «‘lc / y. —. r1’. / pvscracns-av lymph node-: . sup. ¢iorv- ri. ac. v..1 ; _Q". ; _. »L; y, 9 :00 : .., ..-. .pu. s.. cr. um. ..~a, 'w. .
  8. 8. 5 brownish-red gland located anteriorly in the lower part of neck xv" ll l. ‘ v _ l, 25. ,3’ , j., «_ 1”, ‘ flit)“ u---. . . . ‘ : 3 E Body of an o-you hone or--in ham unm hyoid ham | -lfwfifll P'I"tl"'lW= * Llmiu at an thyroid caning. Cocoa clmloqo L550 0"? ! lhynid gland Fm trnclwul mg Isthmus of the thyvo-d gum!
  9. 9. THYROID GLAND - The gland is U shape shaped and is formed by 2 elongated lateral lobes connected by a median isthmus
  10. 10. THYROID GLAND - Each lobe around 5 cm long, 3 cm wide and 2 cm thick. overlying the second to fourth tracheal rings.
  11. 11. THYROID GLAND weight of the gland averages 25-30 g in aduhs it is slightly heavier in women. The gland enlarges during menstruation and pregnancy
  12. 12. THYROID GLAND ° A conical pyramidal lobe often ascends from the isthmus toward the hyoid bone, to which it may be attached by a fibrous or fibromuscular band, the levator of the thyroid gland - The pyramidal lobe is a remnant of-the fetal thyroid stalk _
  13. 13. THYROID GLAND - Principal innervation of the thyroid gland derives from the autonomic nervous system.
  14. 14. ‘ * Parasym pathetic fibers come from the vagus as superior laryngeal and recurrent laryngeal nerves, if’ ‘R . ‘ T ’ ii if I T fl. 4;: ' lg, vi 2;’ r‘i‘rw ll “( ' | Right st. pv: no'___ . ' i Lclt s: ;)cr': r larywml rme ‘ ' " "l{£V)'l‘? _l. ‘6l . rem‘- Lon, -nx~~ I". Right }' xmzrrent '<‘. _ l. :ryi', t:ml . _CZ“ . ‘° l‘ l. t'. ‘.'l - A’; rm. -iron: , . ’_". lawnaeel i'i‘l". ‘ )-T. nmc . .~- ll . v'_. ‘. . _i. " . ;,if°'“', «,-,4‘ KL}
  15. 15. g. and sympathetic fibers are distributed from the superior, middle, and inferior ganglia of the sympathetic trunk. right thyroid gland trachm - Sympatiafr. Nerve
  16. 16. * These small nerves Supenor enter the gland along laryngeal 333;" with the blood "°"’°$‘. ..; ' Thymd V€$S€lS- Vagus nerve~"‘~ ~ / cartilage, Carofid , ‘ _/ ,// ’’/ /// / artery—”"" / Thyroid ghnd Recurrent N laryngeaL”’__, ,,. ‘ nerve . /~‘ ‘K Jugular -""'T"3°h°3 '; k_ vem
  17. 17. THYROI D GLAND - Branches of vagus nerve ‘""°"°"‘*"“%"'"*‘“° Internal branch External brancli lnlenor constrictor muscle Ansa galem Recurrent laryngeal nerve -zopwigimazorle by The M<'3vov~H-H Corn; -Irwin! In: All right: .. -.. .». a
  18. 18. * The thyroid gland is ensheathed by the visceral fascia, a division of the middle layer of deep cervical fascia Under middle layer of deep cervical fascia thyroid has an inner true _ capsule which is thin and . . adheres closely to the gland V“ ~ A ‘i. ill V V - / ,
  19. 19. THYROID GLAND ° The capsule is composed of an internal and external layer. The external layer is anteriorly continuous with the pretracheal fascia and posteriorolaterally continuous with the carotid sheath.
  20. 20. THYROID GLAND ° Anterior suspensory ligament extends from superior~media| aspect of each thyroid lobe to cricoid & thyroid cartilage ° Posteromedial aspect of gland is attached to side of cricoid cartilage, 15‘ & 2”“ tracheal ring by posterior suspensory (Berry) ligament 0 This firm attachment to the laryngoskeleton is responsiblefor its movement during wallowing
  22. 22. THYROI D GLAND ° This firm attachment of the gland by ligaments and fascia to the laryngoskeleton is responsible for movement of the thyroid gland and related structures . _cluring. .swa‘| lowing-. . I . I‘. I"; l we 3‘ . 3‘. _4§liF~r-07KlRQ€° Lilac‘. _ 2-“ 3 . . up '-H . ._ ‘ ‘; .. -J.
  23. 23. THYROID GLAND Muscles of the neck digs“ W”, - The lateral “Y‘°"*‘”"""°°‘° surface ofthe V stwohvovdmusde thyroid is ‘" e e “m; j:f~: j_: '°m covered by the °*‘°"W°“°**°'v tnyrohyordmuscle sternothyroid '‘’‘’‘‘"’°'” *7 . V. ..“ m'i°5.a°? 'n'l. ;'l. muscle "W °‘""”"° i L’ Ti myfyziusde scalane muscles manutanum oi sternun stamocloidomastoid muscle my! ” muse” 0 2000 Encyclopedia Britannica, ho.
  24. 24. THYROID GLAND - More anteriorly are the sternohyoid and superior belly of the omohyoid muscle, overlapped inferiorly by the anterior border of the sternocleidomastoid rriuscle. M"-35595 °' me “ck csgastvi: mscie «, ,ign, .ga mggie s’-. id'= ,t+d ri-»-use‘-e f, — ¥ / clqagiric n*. iS*: !E . ‘ / intemal iugular uiri‘ . , ' "5 emvoriycec muscse I S: J()e! l0' Delv Oi ‘ orzcrii, -3-r. ‘ muscie 1‘. V‘ external caiotici aneri f'i‘y". .'Jl] tore — trimc: ;artiIaQ9 , , . _.. _’: _'-———-— 5?? -'i"°"": W "-NSC‘? /[A imarior near; cl l scalane pussies i’ ‘K ‘>"“~""i‘°5 "‘U5Cl9 # ’ ’_ 1 l dell: -U mus: le . ‘Z . > ' ' ‘ m)5C: g rraoezius rmsce manubnurr at stevnurr Slél"Oll"_vlC)'d Muscle 0 20% Encyclopedia Bri1mmca, hc ‘3Y9'DC'ZlE'l'fl(‘/ "'ia5lOl3 muse e
  25. 25. THYROID GLAND The arterial supply to the thyroid gland comes from the superior thyroid artery a branch of the external carotid artery Internal pgular vein Common carotid artery Superior thyroid arte'y Superior thyroid vein Thyroid cartilage Pyramidal lobe Rlgm “)9 isthmus of Middle the thyroid thyroid vein Inferior thyroid Len '°be MEN Thyroid ima artery Inferior thyroid vein Bradiiocephalic ‘ van
  26. 26. THYROID GLAND - and inferior thyroid arteries that arise from the thyrocervical trunk, a branch of the subclavian artery and, occasionally, from the thyroidea ima. These arteries have abundant collateral anastomoses _with‘ each oth-er internal jiqda vein Supuior thyroid artsy Supeior thyroid vein Pyramidal lobe Isthmus of the thyroid mfaia myrmd LON ltbe Thyroid ima artery Inferior thyroid vein
  27. 27. * The thyroid ima is a single vessel that, when present, originates from the aortic arch or the innominate artery and enters the thyroid gland at the inferior border of the isthmus. L'ovmnon L -rmd all! -ry ' lhyrma cart lace Rig"! !w:1)(- ~- - iv Ll)y. 'O1d Vt-,1 — - Ir! h<. f)l (riyrcid 4 art. -‘fly §‘ lradw-=3 —u/ “ ~ " ’ Irnvr‘ “ 1,-9.1‘ 1' van ’——e -? -_ L‘ “ superior ‘. '~y. ro-O £: ‘V. (!7V “S<. pu1iu lhylunj my l I , ‘.’. > WEN Lvw -- s>yv. mm. -J «cup _7 l<': wr-us or _ . 1'»: vwod , ‘Z 1 . r “ ‘/ ,"“V’ j -- ‘wit um. - }I-—-—-— 4- ihyrc-A ~~n mo-y yen ‘ B‘ If, " iKr; l>. - , y. ~ri (‘———— «- —-—In'»—u9: myvo-J . .
  28. 28. THYROID GLAND - The superior thyroid vein ascends along the superior thyroid artery into internal jugular vein.
  29. 29. THYROI D GLAND - The middle thyroid vein follows a direct course laterally to the internal jugular vein.
  30. 30. THYROID GLAND - The inferior thyroid veins follow different paths on each side. The right passes to the right brachiocephalic . - On the left side, drainage is to the left brachiocephalic vein.
  31. 31. THYROID GLAND - Lymphatic drainage of the thyroid gland is extensive and flows multi directionally ; ’MY’| -i-III-I-ii-v-ulnllrt-htpdtnlr-Ii-llunlbntst-nun‘
  32. 32. THYROI D GLAND Cnnccrniltcfbyunflnvvdfunfinuldfilumdu an ° Lymphatic drainage courses to the peri glandular nodes to the pre laryngeal (Delphian), pre tracheal, and paratracheal nodes along the recurrent laryngeal nerve; and then to mediastijnal lymph nodes N7?"-‘villi! -I-rt‘-dnlnlilllitiuldl-Ililvlillfludho-tdcalbu‘
  33. 33. ° The thyroid gland controls how quickly the body uses energy, makes proteins and how sensitive the body is to adrenergic and other hormones Mich Atop . , . Thyroid ’ Canila-,5‘ V ' ' (‘irco-11I_'miil i Membrane '_I. ':I> _(‘ll: :« Hiyroid Carlilaur. ‘
  35. 35. ). . . . 1 . . , — _u: :::7 . —-e—-_. ———uT we "+: ~+ A —+— 4 l These foil‘ les are lined by cuboidalcells andlumenk ofthese follicles is filled up by glue like colloid substance.20-30 follicles form thyroid lobule
  36. 36. Between these follicles is interstitial A tissue inwhich run the blood vessels .
  37. 37. These cuboidal thyroid fcellsor thyrocytes secrete thyroid hormones T4 & T3
  38. 38. Thyroid hormones ° Thyroid hormones are needed for ° Mental maturation and development ° Physical maturation and development ° To raise basal metabolic rate ° And to make all cells of body sensitive to adrenergic and other hormones
  39. 39. Thyroid hormones ° Thyroid also secretes Calcitonin from cluster of cells called parathyroid glands located posteriorly by the side of thyroid gland that lowers calcium levels
  40. 40. Thyroid hormones - Thyroid hormone is controlled by hypothalamus that secretes thyroid releasing hormone and passes it on to pituitary gland through blood vessels called hypothamo pituitary
  41. 41. Thyroid hormones - Anterior pituitary thus under influence of thyroid releasing hormone secretes TSH that is passed on to the thyroid gland
  42. 42. Thyroid hormones ° TSH stimulates production of thyroid hormones by follicular cells. ° But there is a feedback mechanism here as too much of thyroid hormone secretion can suppress the hypothalamus so as to decrease production of thyroid releasing hormone
  43. 43. Thyroid hormones ° Presuming here we see thyroid follicular cell membrane and G proein I receptor which get -av. activated once binding with TSH converting GDP to GTP which increases cyclic AMP level ° Cyclic AMP then increases production of thyroid _ hormones
  44. 44. Now let us see how actually it stimulates thyroid cells, A surrounding around thyroid follicular cells we see blood vessels in interstitial tissue
  45. 45. There are many cations and anions in blood stream such as sodium , iodide and potassium
  46. 46. Insidefollicular cells we have endoplasmic reticulum which synthesises thyroglobulin
  47. 47. Thyroglobulin is sent and get packaged up in Golgi j apparatus and then released into the lumen of follicular . T, cells till all lumen is filled up and thus thyroglobulin is A stored here as colloid x A M4 g ; ,, ,
  48. 48. Thyroglobulin is actually a polypeptide chain made of many aminoacids. These chains also contain some special aminoacids called tyrosines which are tyre or wheel in shape
  49. 49. To synthesize thyroid hormones we need iodides so what happens here is that there is a transporter on the ‘ basal membrane of cuboidal cells facing the arteries ; called as sodium iodide symporter
  50. 50. Na and iodide are pumped in to the follicular cells and then Na goes out again in blood stream in exchange of K that moves into the cell as TSH stimulatesthis s morter
  51. 51. Now the iodide in follicular cells needs to be transported into the colloid of lumen of follicle. How it does it there is a transporter called pendrin on the membrane of follicular cell facing the lumen
  52. 52. This pendrin transporter transports iodide which is negatively charged chemical into the lumen of follicle where thyroglobulin colloid is stored in exchane of chloride 69 ‘E9 ’
  53. 53. l Now the iodide is in the lumen but before it be l utilized it has to be converted to iodine by a l enzyme called thyroid peroxidase present in the l lumen which actually oxidizes iodide to iodine ‘. «.7 - 7 . _i- . ‘’-‘-. -L-- 1 _ .
  54. 54. Formation of Mono and Diiodotyrosine Once iodine is formed it unites with tyrosine of thyroglobulin if one iodine unites with tyrosine we call it monoiodotyrosine if two iodine combine with tyrosine we call it diiodotyrosine The whole process is called organification
  55. 55. Formation of Mono and Diiodotyrosine ° So now the thyroglobulin will have monoiodotyrosine and diiodotyrosine on them as well as other amino acids on the chain in between these tryrosines
  56. 56. Formation of Mono and Diiodotyrosine W - / /// //“/ / ID°10€ . EE; ”“g§; .E§§. _§5&‘T 0 lg . ' cow 9“ N oi! oi fle (9 100m; 03 J /1 ~. I W A -"' I/ l ’ / we 6 °" 609 W s”‘-’. ’.‘ . ’ 017 ll. ’ C1
  57. 57. Coupling of mono and di iodotyrosine forms tri- iodotyrosine or Thyronine, while as coupling of di iodotyrosine form tetra iodotyrosine or Thyroxine. All these steps stimulated by thyroid peroxidase
  58. 58. Thyroid hormones ° I mean to say that all steps like conversion of iodide to iodine —organification - And uniting of iodine to tyrosine rings ° And coupling of mono and di iodotyrosine are all stimulated by thyroid peroxidase enzyme
  59. 59. 4 But the process is not ended up yet there are still mono—iodotyrosines and di-iodotyrosines on yr thyroglobulin chain that may not have coupled plus on ll the chain will be T3 and T4 that was due to coupling I
  60. 60. So all these molecules will be part of thyroglobulinlcolloid) . These molecules are then packaged up by pinocytosis by follicular cells and pulled inside the cells from lumen
  61. 61. In the follicular cells there are lysosomes that will bind together with endosomes containing thyroglobulin (colloid) and will cut and release T3 and T4 into the follicular cell
  62. 62. The MIT and OIT if presehtis De ionizedto release iodide by Deiodinase enzyme so that these iodides , are usd again in the process 5; . z _. ,. ~ “<-. :?= -—*- .5‘-T '7 * aw-r l l l I l
  63. 63. The T3 and T4 are then released into the blood stream where they combine with thyroxine binding globulin (proteins) which allow them to be transorted to taret or ans or taret cells
  64. 64. However once they reach target cells or organs the T4 is converted to T3 since T3 is 10 times more potent than T4 and also because T3 can easily pass through membranes
  65. 65. L After entering the target cell there is nucleaus in the cell so these lipid soluble hormones T3 and T 4 enter , into the nucleaus
  66. 66. In the nucleaus there are two thyroid hormone receptors that binds with these hormones and initiate gene transcription for various specific messenger RNAs that will promote thyroid induced response. _-. _¢—. ... _ ~, any, -.{ _ 1 _ fiuotvt II v <-. *.; :,, V, ’ , eE~F, = __ fa / aux I l “ . ' / ,
  67. 67. 3, _; , . .. . _~, m‘eése‘FIgeEinn‘/ imlii iéavé the n13&‘i’é’ia’iIsariai enter int cytoplasm of cell and synthesize new proteins or enzymes which will again promote functions of F thyroid hormone which is increasing the basal meta bolic ratejof cells l l i 3,. ’ l
  68. 68. Increase in metabolic rate can have many effects on growth, CNS development, meta bo| ism, ca rdiovascular 1 effects etc ‘I
  69. 69. ACTIONS OF THYROID HORMONES rOThyroid hormones are essential for normal growth of tissues, including the nervous system. OLack of thyroid hormone during development results in short stature and mental deficits (cretinism). OThyroid hormone stimulates or increase Basal i etabolic RTate(BM R).
  70. 70. ACTIONS OF THYROID HORMONES secretion - Required for GH action ° Increases intestinal glucose reabsorption (glucose transporter) ° Increases mitochondrial oxidative phosphorylation (ATP production) ° Required for GH and prolactin production and h
  71. 71. ACTIONS OF THYROID HORMONIES '° Increases activity of adrenal medulla (sympathetic; glucose production) ° Induces enzyme synthesis ° Result: stimulation of growth of tissues and increased metabolic rate. Increased heat production (calorigenic effect)
  72. 72. £tCTllOl_l'S OE THYROID HORMONES ON PROTEIN S -increased protein synthesis at low thyroid hormone levels (low metabolic rate; growth) -increased protein degradation at high thyroid hormone levels (high metabolic rate; energy)
  73. 73. ACTIONS OF THYROIIID HIORMONES ON CARBOHYDRATES -low doses of thyroid hormone increase 7 glycogen synthesis (low metabolic rate; storage of energy) - high doses increase glycogen breakdown (high metabolic rate; glucose production)
  74. 74. ACTIONS OF THYROID HIORMONES ON N1’: /K PIUMI? OPump_s sodium and potassium across cell membranes to maintain resting membrane potential OActivity of the Na*/ K* pump uses up energy, in the form of ATP OAbout 1/3rd of all ATP in the body is used by the Na*/ K* ATPase OT3 increases the synthesis of Na*/ Kt pumps, markedly increasing ATP consumption (BMR increases). OT3 also acts on mitochondria to_increase ATP _ synthesis(size and number of mitochondria will increase). OThe resulting increased metabolic rate increases thermo genesis (heat production).
  75. 75. ACITIIONS or THYROID HIORMONES ON N A/ K MUM? ° Increase mitochondrial size, number and key enzymes. ° Increase plasma membrane Na-K ATPase activity. - Increase futile(ineffective) thermogenic energy cycles. Decrease su peroxide dismutase activity.
  76. 76. ACTIONS Of’ THYROID IHIORMONES ON CA: RlDll. OVl1fi_. SCULA; R SYSTEM Increase heart rate Increase force of cardiac contractions Increase stroke volume Increase Cardiac output Up—regulate catecholamine receptors
  77. 77. ACTIONS OF THYROID HORMONES ON RESPERAWON - Increase resting respiratory rate ° Increase minute ventilation - Increase ventilatory response to hypercapnia and hypoxia
  78. 78. ACTIONS OLF THYROID ON BLOOD ° Increase blood flow l ° Increase glomerular filtration rate(GFR)
  79. 79. ACTIONS OF TIIYROID IIORMONIES ON BLOOD - Increase RBC mass ° Increase oxygen dissociation from hemoglobin
  80. 80. ACTIONS OI’ TI-IYROIID IIORMONES CN CIT Increase glucose absorption from the GI tract Increase carbohydrate, lipid and protein turnover Down-regulate insulin receptors Increase substrate availability
  81. 81. ACTIONS OE THYROID I-IIORMONES ON BONE Olncrease growth and maturation of bone. Olncrease tooth development and eruption. Olncrease growth and maturation of epidermis, hairfollicles and nails. Olncrease rate and force of skeletal muscle contraction. Olnhibits synthesis and increases degradation of mucopolysaccharides in subcutaneous U tissue.
  82. 82. ACTIONS OF THYROID IHIORMONIES ON CNS Critical for normal CNS neuronal development ° Enhances wakefulness and alertness ° Enhances memory and learning capacity ° Required for normal emotional tone 0 Increase speed and amplitude of peripheral nerve reflexes
  83. 83. ACTIONS CI‘ TIIYNCID IIIORMONES ON REPRODUCTIVE SYSTEM r° Required for normal follicular development and ovulation in the female ° Required for the normal maintenance of pregnancy ° Required for normal spermatogenesis in the male
  84. 84. The influence or a good teacher ,