PPT

1. DR MANOHAR, RESIDENT
INHS ASVINI

2.  Embryology
 Macroscopic anatomy
 Microscopic anatomy
 Physiology

3.  Median anlage-midline thickening of ventral
surface between 1&2 Branchial arches
 Diverticulum at 16 or 17 day-Foramen caecum
 Bilobed structure
 Thyroglossal duct cyst-persistence of stalk
 most common between hyoid bone & isthmus

6.  Lateral anlagen-ultimobranchial bodies from
4 or 5 pouches
 fuse with median by 6th week
 Lateral thyroid lobe-tendency for neoplasia
 C-cells-numerous at point of fusion
 Medullary carcinoma

7.  Inferior parathyroid –dorsal wing of 3rd
pharyngeal pouch
 Superior parathyroid- dorsal wing of 4th
pharyngeal pouch

8.  15 to 25 gm
 rarely one lobe fails to develop-left
 Apex narrow upto oblique line of thyroid cart
 Rounded lower pole upto 4th or 5th tra. Ring
lateral to trachea and oesophagus, medial to
to carotid sheath
 Pyramidal lobe in 50%

10.  Tubercle of Zuckerkandl in 60%
point of fusion ultimobranchial bodies and
median anlage
 Surgical Imp:
1. recurrent laryngeal N runs medially
2. sup parathyroid gland attached cranially
3. when enlarged can be left behind

12. Thyroid gland Fascia
 Invested in pretracheal fascia
 Suspensory ligament of berry-small blood
vessels
 divided with care as recurrent Laryngeal N may
lie medially, laterally or in ligament
 Laterally fascia blends with carotid sheath
Inferiorly blends with adventitia of arch of
aorta

15. Arterial Supply
 Superior thyroid artery-external carotid A
(a) Anterior and (b) posterior branch
at superior pole
 Posterior branch descends on posterior surface
 In 45% joins with ascending branch of inferior
thyroid artery

16.  Inferior thyroid artery
 thyrocervical trunk
 from subclavian artery in 15%
 divides in ascending and descending branch
 Inferior Laryngeal artery
 ascends with recurrent laryngeal N to enter
larynx deep to inferior constrictor ms
accompanied with plexus of veins in region
of ligament of berry
 Thyroidea ima art in 12% from brachiocephal
artery

18.  Superior thyroid vein-internal jagular vein
 Middle thyroid vein
 blood from inferior and anterolateral part &
larynx and trachea
 cross common carotid and drain in IJV
 Inferior thyroid vein
 plexus on trachea and drain into (R) & (L)
inferior veins-respective brachiocephalic vein
 In few paired inferior form common trunk- SVC

20.  Autonomic and Harmonal control
 Sympathetic from superior cervical and
stellate ganglion
 Parasympathetic from nodose and local vagal
ganglia
 Left recurrent laryngeal N
 passes behind inferior thyroid artery & then post
to ligament of berry before passing between
fibres of cricopharyngeal part of inferior
constrictor, it lies behind capsule of cricothyroid j
 (R) recurrent-loops 1st part of subclavian artery

24.  lateral aspect to level III, IV and V
 more medial into level VI in turn in upper
anterior mediastinum level VII
 level I& II rarely involved

26.  follicular cells around central pool of colloid
 follicles spherical 0.02 & 0.9mm in diameter
 thyroid lobule consist of 20-40 follicles
 follicular cells long rough endoplasmic
reticulum and large golgi apparatus,
prominent lysosomal bodies
 Inactive gland-cells flattened and abundant
colloid
 On stimulation with TSH-columnar shape

27.  Each follicle invested in loose connective tissue
consists of plexus of capillaries& lymphatics
 Interfollicular connective tissue consists of
fibroblasts, unmyelinated nerve fibres with
schwann cells,fat cells, plasma cells,macrophage
,lymphocytes
 Calcitonin producing C-cells singly or in
small clumps adjacent to stromal aspect of
follicular cells

29. Physiology of thyroid gland
 Regulation of thyroid gland metabolism

31.  The thyroid gland synthesizes and secretes
three hormones:
• Thyroxine (T4).
• Tri-iodothyronine (T3).
• Calcitonin

32. • Dietary iodine is absorbed in the GI tract
• 90% excreted in kidney
• The transport of iodide into follicular cells is
dependent upon a Na+/I- cotransport system.
• Iodide taken up by the thyroid gland is oxidized by
peroxide in the lumen of the follicle
• Oxidized iodine can then be used in production of
thyroid hormones.

34.  Daily iodine requirement-150 microgram/d
 Less than 50 microgram/day-goitre
 Selenium
 Iodine excess- inhibits iodide oxidation
organification and thyroglobulin proteolysis

35.  Pituitary produces TSH, which binds to follicle cell
receptors.
 The follicle cells of the thyroid produce
thyroglobulin.
 Thyroglobulin incorporated in apical vesicles
 At apical membrane thyroid peroxidase use H2O2
and iodide to oxidize and organify thyrogloulin
protein into MIT and DIT as well as some T4&T3.

37. • They are found in the circulation associated
with binding proteins:
- Thyroid Hormone-Binding Globulin (~70%
of hormone)
- Pre-albumin (transthyretin), (~15%)
- Albumin (~15%)
• Less than 1% of thyroid hormone is found
free in the circulation.
• Only free and albumin-bound thyroid
hormone is biologically available to tissues.

38.  Enter cell by diffusion, active transport, reach
endoplasmic reticulum where T4- T3
Intracellular T3 acts on specific nuclear receptors
(members of c-erbA superfamily)
 Thyroid hormones are essential for normal growth of
tissues, including the nervous system.
 Lack of thyroid hormone during development results in
short stature and mental deficits (cretinism).
 Thyroid hormone stimulates basal metabolic rate

39.  Required for GH and prolactin production and
secretion
 Increases intestinal glucose reabsorption
 Increases mitochondrial oxidative phosphorylation
(ATP production)
 Increases activity of adrenal medulla

40. • Effects on protein synthesis and
degradation:
-increased protein synthesis at low thyroid
hormone levels (low metabolic rate)
-increased protein degradation at high
thyroid hormone levels (high metabolic
rate)
• Effects on carbohydrates:
-low doses of thyroid hormone increase
glycogen synthesis (low metabolic rate)
- high doses increase glycogen breakdown
(high metabolic rate)

41.  Excess thyroid harmone secretion:-
1. Increased O2 consumption
2. Weight loss (protein, fat cataolism)
3. skeletal muscle catabolism-hypercalcemia
osteoporosis-mobilization of bone protein

42.  Increase heart rate
 Increase force of cardiac contractions
 Increase stroke volume
 Increase Cardiac output

43.  Increase resting respiratory rate
 Increase minute ventilation
 Increase ventilatory response to hypercapnia
and hypoxia

44.  Increase blood flow
 Increase glomerular filtration rate

45.  Increase growth and maturation of bone
 tooth development and eruption
 growth and maturation of epidermis,hair follicles
and nails
 Increase rate and force of skeletal muscle
contraction
 Inhibits synthesis and increases degradation of
mucopolysaccharides in subcutaneous tissue

46.  Critical for normal CNS neuronal development
 Enhances wakefulness and alertness
 Enhances memory and learning capacity
 Required for normal emotional tone
 Increase speed and amplitude of peripheral
nerve reflexes

47.  Required for normal follicular development
and ovulation in the female
 Required for the normal maintenance of
pregnancy
 Required for normal spermatogenesis in the
male

48.  Early onset: delayed/incomplete physical and
mental development
 Later onset (youth): Impaired physical growth
 Adult onset (myxedema) : gradual changes occur.
Tiredness, lethargy, decreased metabolic rate,
slowing of mental function and motor activity, cold
intolerance, weight gain, goiter, hair loss, dry skin.
Eventually may result in coma.

49.  Calcitonin in response to elevated levels of
calcium or gastrin.
 It lowers serum calcium and phosphate by
inhibiting osteoclastic resorption of bone &
enhance excretion by kidneys.