Anatomy of Thyroid Gland
q Normal Thyroid gland weights – 20-25 Gms.
q 15 gm at birth – 16 yrs. maximum: 17 + 7 gms
q Weighs more in Female than male,
q More in summer than in winter
q More during pregnancy lactation than Otherwise
q More in Kulu- Manali than in Delhi.
Butterfly shaped gland..
Connected by isthmus
Pyramidal lobe as long narrow projection of thyroid tissue extending from isthmus upwards laying on surface of thyroid cartilage
Rt. lobe bigger than left
Convex anteriorly and concave posteriorly as it has to accommodate of anterolateral portion of trachea and Larynx.
Firmed fixed to them by fibrous tissue.
Bed between medially Larynx and Trachea
Laterally Sternomastaoid and Carotid sheath
Capsule:
v Enveloped by thick fibrous capsule, which sends septa into gland substance to produce pseudolobutation.
v No true capsule exists.
v Pretracheal fascia divides in to anterior and posterior layer to invest the gland - producing false capsule.
Blood Supply:.
Superior Thyroid Inferior Thyroid and some times Thyroid Ima artery
Abundant 5ml / gm / minute.
Innervation :
Sympathetic – cervical ganglion and enters through blood vessel.
Parasympathetic – Vagus via branches from laryngeal nerves.
Deep fascia of Neck
External occipital protuberances
(a) Invasting Layer Superior Neuolal line
Base of mastario process
Zygomatic arch
Lower border of mandible.
Spine of scapula and achromion process
Clavicle
Manubrium sterni.
Splits tochclose - Trapezius, Sternomastoid – 2 muscles.
2 Salivary gland - Submandibular, parotid.
Zoof of two
Post Anterior Space of Burn
Gives slip to Carotid Prewashead layer
Sheath investing layer
Carotid Buecopharyngeal
Sheath Fascia
Pretracheal Layer : Thyroid bone
Cricoid and Thyroid Cartilage.
Blends up with fibrous pericardium over the great vessels – sup. Mediastanum.
From, inner and back Ligament of Berry : condonsation of both layers
part of gland, it goes to above the Thyroid gland.
Cricoid Cartilage. Then invests the Thyroid gland.
Rt. & Left anchors the Postly, the fascia has attachment to Laryngeal Cartilage
gland preventing the Postly it is weakest.
taking away from Larynx. Enlargement of gland therefore occurs postly
Oesophagus
Br Trachea
It gives of one fascial process to Prevertibral fascia.
This process in front of sternochyoid, sterothyroid and
omdhyeid muscles.
Binds dor with intermidiate tendon of Omdhyoid.
Pre-Vertebral Fascia
1.)Horozontal extent : Starts from deep surface of SM
Post to cartotid system, to pharynx, larynx, oesophagus but
in front of prevertebral muscles,
]
2.) Vertical extent : Base of skull
Below it extends in Sup. Mediartumum along post. wall.
Surgical Anatomy :
* Skin : Several Transverse folds, deciding for incision
Group of folds just above sternum, clavicle
Collar incision.
* Muscles :
Platysmo : subcutaneous, sheet like muscle.
fan like, clavicle---- mandible. Leaving space in midtime.
Fascial plane between platysma and pre Thyroid – avascular
i.e. Skin, subcutaneous fat, platysma
reflected in one plane.
Sternomastaoid - 2. from lateral boundaries.
Sternotysis – anteriorly
Sternothyroid - Post. covers Thyroid capsule.
Nerve supply – Areas hypoglassi – enters low in neck.
It intrathyroid muscle to be cut – High transaction advised.
Fascia of sternomastoid along anteromedial border fuses with lateral border of sternothyroid.
Surgical Anatomy : Thyroid
Normal Thyroid Gland –: 20-25 gms in weight
Butterfly shaped biloboo, connected by Isthamus
Right lobe bigger than Left, Pyramidal lobe extending up from midline in adult
1.5 gm at birth --- 16 yr. Maximum 17 + 7 gm
Histology :
Unit is folida, 200 in dial
Lined by single layer of cuboidal epithalium
Colloid in center. Thyroglobulin
Microscopy”
Shape, sponginess, presence of colloid.
Arteries :
1.Sup. Thyroid Artery : 1st branch of Ext. car. of bifurcation of CCA
Runs downward and medially on the surface of Miodl
constrictor
Enters upper pole at antero sup. surface
Downward Course : It is just inferior and lateral to sup. laryngeal nerve.
1cm above sup; pole.
Applied : The artery to be ligated close to gland parenchyma
Enlarged gland – lingular of thyroid –above and lateral to anterior of artery-
Mistaken as sup. pole.- High ligation – injury to nerve.
(2) Inf. Thyroid Artery : Thyrocarvical Trunk : just after origin from subclavi ascorid up behind carotid and jugular vein above the level of Inf.. pole of thyroid.
Loop downward and medially enters the gland at mid portion
rotates to recurrent Laryngeal Nerve.
Ligated as far as possible.
(3) Thyroida ima : Unusual, aorta, innominate artery.
Passes directly upwards in front of Trachea.
Enters Lower border of Isthemus.
Veins : (1) External Jugular Vein : Lateral, cross over the belley of sternomastoid
(2) Anterior Jugular Vein : Lie on sternohyoid.
I)Superficial Just below the Platysma
A communicating plexus of these veins present.
Goitre : Those veins are Large.
Applied : Fascia between stermastoid and sternohyoid, it cu. comm. vein to be cut.
External jugular vein to be refracted lateraly.
II) Deep Veins : Superior, Middle, Inferior, Thyroida ima vein. accompany artery but less constant in number ,position and size.
a) superior : Leaves the gland at sup. pole ant. and lat. to artery – cricothyoid tributary of internal jugular vein.
b) Inferior : one or more trunks frequently plexus. not accompanied by artery
I.Jugu.ve or directly in to in nominate vein
c) Middle : from lateral border directly pass in to IJV. Large glands it is difficult.
Nerves : Left Right
Hooks around
(1) Recurrent Laryngeal Nerve aorta subdavian
ascends lateral to Trachea groove of
Then groove in between oesophagus, trachea
Enters larynx post to cricothyroid articulation.
Extra laryngeal branches are motor from a loop with internal branch of Sup. Laryngeal Nerve. Sensory branch of Rec. laryngeal Nerve. ) Loop of Galen
(2) Sup. Laryngeal Nerve :
Arises from vagus close tobase of skull.
descends medial to carotid vessels, up to corner of hysio bone. Rt Lb.
Where divides in to Internal, External branch. 64 77 TO
Tensor of vocal cord – Cricothyroid - 33 22 Lat.
6 4 Ant.
Recurrent Laryngeal Nerve :
7% Nerve penetrates the gland
32%Passes through area of graalist and hormone of gland with Larynx Through ligament of Bony
59% Tracheo Oesophagial Suleus
1 in 1000 Is not recurrent, given directly in Neck.
Recurrent Laryngeal Nerve Palsy : Paralysis on Ipsilateral side.
Semon-Rosonbach Law : abducted fibres more sensitive than adductor fibros.
Wagner-Irossman : Paramedian : Rec lay.
Intrermediate : Re + Sup.
Abductors : ( Internal arathhoid, Thyroaratenoid ) Recurrent
Adductors : (Lateral, post. ericoarahynoid ) )
Tensor )Sup. Lary.
Lymphatics:
Accompany Veins
Collecting Lamph channels --- draining intraglandular capillaires ---beneath Thyroid capsule ----- drain in to channels of capsule---communicate with isthasmus Sup. Lobe.
1) Sup. Lymph Vessels : Isthemus, medial sup. portion –Sub diagastric (I.T.L.)
2) Median Inf. Vessels : descend with Inf. veins --- Pre Tracheal Nodes.
3) Lat. Vessels : Ant. Inf. nodes of Int. Jugular Chain(Lateral )
Pretrachaec nodes – ant. sup. mediasternal nodes.
Recurrent laryngeal Nodes : Beyond Radical Neck Dissection.
( Macclintive – Trans sternol dissection of node with RND.
4.)Post sup. aspect : Leave post capsule – Retropharyngeal nodes
Rouviere found in 1/5th dissection – Beyond RND
5)Pyramidal Lobe of the upper part of Isthamus – Pre laryngeal
Inferior & Anterior group.
Sub digastrics Lymph node
Median Sup. Post Sup aspect
Isthemus
Retropharyngeal LN
Lat. vessels Ant. Sup. Chain
Lateral and Inferior Nodes of IJV
Pre tracheal
Auto sup. Mediastanal
Lymph Nodes.
HISTOLOGY :
Compared of follicles or acini
Spherical in outline diameter less than 0.1 mm
Tiny Sac enclosed by single layer of epithelial cells.
Filled with pink staining protein called Colloid.
Projecting in to colloid from apices of individual thyroid cells are numerous micro with
Basement membrane surrounds in each follicle and separates
Thyroid epithelium from Genestrated walls of rich capillary network.
Resting acini large , Hastened cells dense deeply stained colloid.
Secretory cuboidal epithen. does not stain sointons “ “ small acini
Resorptive phase : Columnar “ Lightly stained vacuolateo “ “ Reabsorption Lacunae.
Retropharyngeal nodes Superior Nodes - Sub. Diagastric
Pre Laryngeal
Lateral vessels Lateral nodes
Pre tracheal
Inferior nodes
anterior
Mediasternol.
Hyperplasia – Involution cycle.
Comparable to monthly endometrial changes.
No regularity
Hypoplasia : Tall Column When iodine conc. of
Nucleus central Thyroid falls down 0.1%
Numerous Mitosis Gland undergoes hyperplasia.
Acinar space increases
Papillary process
Colloid Thin, vacuolated
Vascularity increased
Lymphocyte Stroma increased
Involution : Natural complement
No pap. process
Wilksed branches of bu out. tree
Low tuboid epithelium
Regulation :
1) Hypothalamus : Pituitary Thyroid axis.
2) LATS : IgG
Acts as antibody to Thyroid antigen
Action like TSH but prolonged
1.5 to 3 hrs. 16-24 hrs.
Measured by mouse bioassay system.
Unique feature of Thyroid Metabolition is storage of of Hormone in extra cellular location ie colloid anchored to molecule of Thyroid.
Thyroglobulin which is also product of acini- mycoprotein of high molecular weight.
By means of protedyle enzyme which hydrolyses peptide bond, T3 and T4 are released into capillary network which surrounds the acini.
Active T3 and T4
1)Increase tissue metabolism
(by increasing the respiratory Increased appetite
enzymes in mitachondria ) Decreased weight
Increased heat production and
Oxygen consumption.
2.) Increased sensitivity of Tachycardia
Beta Adrenergic receptor Lid Lag
Tremors
Nervousness
3.) Increase tissue growth Increased growth
( By increasing metabolism and and tissue maturation
secretion of growth hormone )
Regulation
TSH Pituitary Hormone Excreted by
Single Gene 60 Kilobe
Binds to TSH Receptor ( TSH – R )
6 Protein
Coupled Receptor
Family
Activation of Extra cellular Domain :
Adenylate Cyclase ) 398 Amino Acid
Phospholipase C ) Pathway Membrane spanning Domain
266
Intracellular Carboxy Terminal
66
160 mg
Iodine in test
CLO4----------------------- 5000 mg
Active
GIT Absorption Plasma---------------------I Iodine Active Iodine Iodine
Transport
Faces 10 mg Kidney
Iodine is also concentrated in Salivary Glands,
Lactating breast tissue and in Gastric mucosa.
Inhibitors:
Ioding Transport SCN, CLOA
Oxidation Thio urea
Organic binding Thiocyanides
Coupling BAS
Gertrpgems
Proteolysis Iodine
Release
Benatogenation
Iodine inactivates both TSH and
Proteolysis which releases T4 from Thyroglobulin.
Hormone Synthesis:
Requirement I Receptor protein
TBG
Daily Intake : m 0.2mg/day now 1.0 mg /day.
Iodine is removed by Thyroid Salivary Gland,
Kidney GIT
GFR Reabsorber
Mechanism of action of Thyroid hormones.
Thyroid hormones enter cells and T3
joints to receptor in nuclei like steroids - Non histone protein in ribosome.
T4 also can bind but much of T4 DNA
is converted to T 3 in cytoplasm MRNA ribosonal RNA
Protein
Scheme developing normal pathways of Iodine metabolism in state of Iodine balance.
Note ; 90% store in Thyroid gland 10% at Iodine.
Physiology
Foetal Thyroid - can concentrate Iodine at 10 weeks
T4, TSH - second Trimester
detectable
Foetal Hypothalmus starts secreting
TBG appears
T4 up Maternal TRH
Foetal T 3 is low but V T3 is high
Foetal axis is differant
Peripheral Deiodination of T 4
- 5 ‘ de-iodenase
Fasting
Fetus
Systemic illness
Old age T 3 3’ 3 5 (I)
Liver diseases
Propylthionracil (Active)
Propranolon
Radiographic dye
In peripheral tissue
T4 T3 conversion occurs 5’ deiodinase - T3 or 5 dei – T3
T4 appears to be prehormone Reverse T3 is biologically inactive.
If T3 levels are decreased. T3 increases.
Energy dependent transport system -----T3 -------cell membrane-------cytoplasm
Diffuses to receptors in cytoplasm
Alters the production of Sp. MRNA
Physiological effects.
Thyroid Hormones:
4mg. 40 mg
T3, T4 Reverse T3 ( 3, 3’, 5’ Triido thyromine ( smg )
MIT
L-Thyroxine – D- Thyroxine ( small activity )
Thyroglobulin:
Molecular weight 660,000, 10% Carbohydrate
123, Tyrosine residue.
Synthetised in the thyroid cells--- secreted to colloid by exocytosis
When secreted
Peptide bond hydrolysed
Colloid back to acinar
T4, T3 in circulation.
Intra Thyroidal Iodide :
Inversely influences to T.S.H.
Small dose ---- increase the T4
Large doses ----- Biphasic response ) Blockade of
First increasing ) Org. binding.
Then decreasing.
Moderate or Repeatedly ---adaptation
Large doses
Decrease the rate of release of gla.
Iodine ------- T4 –
Vascularity decreased hyperplasia decreases.
