This document summarizes the anatomy, blood supply, innervation, development, histology, and functions of the thyroid gland. It describes the thyroid's location in the neck, its lobes and isthmus, and its descent from the foramen caecum. It also outlines the hormones produced by the thyroid (T4, T3, calcitonin), how they are synthesized and regulated, and their roles in metabolism, growth, and other bodily functions.

1. Dr Dipesh

2.  Lies against C5, C6, C7 and T1 vertebrae
 Claps the upper part of trachea
 Each lobe extend from middle of thyroid
cartilage to 4th or 5th tracheal ring
 Isthmus extends from 2nd to 3rd tracheal ring
 Two lateral lobes are joined by isthmus
 Pyramidal lobe (80%) projects upwards on
either sides of lobe

3.  A fibromuscular band (levater glandulae
thyroideae) descend from body of hyoid bone
to isthmus or pyramidal lobe

4.  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

5.  Midline thickening developed on ventral
surface between 1st and 2nd Branchial arches
forming median anlagen
 Diverticulum developed at 16 or 17 day from
Foramen caecum
 Ultimobranchial bodies from 4th and 5th
pouches form lateral anlagen that fuse with
median by 6th week produce calcitonin
 Tubercle of Zuckerkandl (60%): point of
fusion ultimobranchial bodies and median
anlage

6.  Inferior parathyroid –dorsal wing of 3rd
pharyngeal pouch
 Superior parathyroid- dorsal wing of 4th
pharyngeal pouch
 Pyramidal lobe in 50%

15.  Invested in pretracheal fascia
 Suspensory ligament of berry-small blood
vessels
 Laterally fascia blends with carotid sheath
 Inferiorly blends with adventitia of arch of
 aorta

17.  Superior thyroid artery branch of external
carotid artery
 Anterior
 Posterior branch
 Inferior thyroid artery branch of thyrocervical
trunk
 Ascending branch
 Descending branch
 Inferior Laryngeal artery
 Thyroidea ima art in 12% from brachiocephalic
artery

18.  Superior thyroid vein-internal jugular vein
 Middle thyroid vein
 blood from inferior and anterolateral part &
larynx and trachea drain into internal jugular
vein
 Inferior thyroid vein
 plexus on trachea and drain into (R) & (L)
respective brachiocephalic vein

21.  Sympathetic from superior cervical and
stellate ganglion
 Parasympathetic from vagus nerve
 Superior/external laryngeal nerve
 Recurrent laryngeal nerve

22.  Left recurrent laryngeal Nerve
 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
junction
 Right recurrent laryngeal nerve
 loops 1st part of subclavian artery

25.  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

27.  Each thyroid lobe contains multiple lobule
 Each thyroid lobule consist of 20-40 follicles
 Each follicles are spherical in shape 0.02 &
0.9mm in diameter
 Follicular cells surrounds central pool of colloid
 Follicular cells contains long rough endoplasmic
reticulum and large golgi apparatus, prominent
lysosomal bodies

28.  Inactive gland-cells flattened and containing
abundant colloid
 On stimulation with TSH- cells becomes
columnar shape with release of thyroid
hormones contained in colloid within follicles

29.  Each follicle invested in loose connective
tissue consisting 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

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

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

34.  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

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.

38.  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.

39.  Enter cell by diffusion, active transport, reach
endoplasmic reticulum where T4 is converted to
T3
 Intracellular T3 acts on specific nuclear receptors
(members of c-erbA superfamily)

40.  Thyroid hormones are essential for normal
growth of tissues, including the nervous
system.
 Required for GH and prolactin production
and secretion
 Thyroid hormone stimulates basal metabolic
rate

41.  Increases intestinal glucose reabsorption
 Increases mitochondrial oxidative
phosphorylation (ATP production)
 Increases activity of adrenal medulla

42.  Increased protein synthesis at low thyroid
hormone levels (low metabolic rate)
 Increased protein degradation at high thyroid
hormone levels (high metabolic rate)

43.  Low doses of thyroid hormone increase
glycogen synthesis (low metabolic rate)
 High doses increase glycogen breakdown
(high metabolic rate)

44.  Increased O2 consumption
 Weight loss (protein, fat cataolism)
 Skeletal muscle catabolism resulting
hypercalcemia
 Osteoporosis due to mobilization of bone
protein

45.  Increase heart rate
 Increase force of cardiac contractions
 Increase stroke volume
 Increase Cardiac output

46.  Increase resting respiratory rate
 Increase minute ventilation
 Increase ventilatory response to hypercapnia
and hypoxia

47.  Increase blood flow
 Increase glomerular filtration rate

48.  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

49.  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

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

51.  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.

52.  Calcitonin is released 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.

53. Thank
you