2. Thyroid Gland
Lower part of the front & sides of the neck.
Weight-25gm
Capsules—True capsule & false capsule
IMPORTANCE
3. Location & Extent
-C5-T1, embracing the upper part of
the trachea.
-Lobe =the middle of the thyroid
cartilage to 4th -5th tracheal
ring.
-Isthmus = 2nd -4th tracheal ring.
Suspensory Ligament of Berry
Pyramidal lobe-Levator of TG
4. Functions
A) Regulates the BMR
B) Stimulates somatic & psychic
growth.
C) Plays an important role in
calcium metabolism.
5. Development
Pharyngeal outgrowths that migrate caudally to their final position as
development continues.
Foramen caecum of the tongue indicates the site of origin and the
thyroglossal duct marks the path of migration of the thyroid gland to its
final adult location.
Thyroglossal duct usually disappears early in development, but remnants
may persist as a cyst or as a connection to the foramen caecum (i.e. a
fistula).
There may also be remains of the thyroid gland: associated with the
tongue (a lingual thyroid); along the path of migration; or, upward from
the gland along the path of the thyroglossal duct (a pyramidal lobe).
6. Lobes -Conical -- Apex, Base,
3 surfaces( Lat, Medial & Posterolateral),
2 borders( Ant & Post)
• Ant border—Ant. Branch of the Sup thyroid art.
• Post border—Inf. Thyroid art, parathyroid glands.
7. Relation
• Apex—Upwards & Laterally, attached
to the sternothyroid to the oblique
line of the thyroid cartilage.
• Base– 4th -5th tracheal ring.
• Lateral –Sternothyroid, Sup. Belly of
Omohyoid, Sternohyiod, Ant. Border
of SCM muscle.
• Medial – 2 tubes( Trachea &
Oesophagus), 2 muscles(
Inf.constrictor,Cricothyroid), 2 nerves(
External & Recurrent laryngeal)
• Posterolateral—Carotid sheath
8. Blood supply
Sup. & Inf thyroid artery
SIGNIFICANCE
STA- First branch of ECA
Descent passing along the lateral
margin of the thyrohyoid muscle,
to reach the superior pole of the
lateral lobe of the gland where it
divides into anterior and
posterior glandular branches:
9. • Inferior thyroid artery is a branch of
the thyrocervical trunk, which arises
from the first part of the subclavian
artery .
• It ascends along the medial edge of
the anterior scalene muscle, passes
posteriorly to the carotid sheath, and
reaches the inferior pole of the
lateral lobe of the thyroid gland.
• Two br- inferior and ascending
(parathyroid)
10. Thyroid ima artery
Occasionally(3%), a small thyroid ima artery
Arises from the brachiocephalic trunk or the arch of the aorta
Ascends on the anterior surface of the trachea to supply the
thyroid gland.
11. -Sup, middle ,inf thyroid vein ,4th Kocher
vein
-Nerve supply—mainly from the middle
cervical ganglion & partly from superior &
inferior cervical ganglion .
-Lymphatic – Deep cevical node.
12. Microanatomy
• Unique among the human endocrine glands in that it stores large
amounts of hormone in an inactive form within extracellular
compartments in the centre of follicles; in contrast, other endocrine
glands store only small quantities of hormones in intracellular sites.
• Thyroid follicles store thyroglobulin, an iodinated glycoprotein, the storage
form of thyroxine (T4) and tri-iodothyronine (T3).
13. • The follicles are lined by epithelial
cells which are initially responsible
for the synthesis of the glycoprotein
component of thyroglobulin and for
the conversion of iodide to iodine,
the iodine linking to the glycoprotein
in the follicle lumen.
• When active thyroid hormone is
required, the same thyroid epithelial
cells remove some of the stored
thyroid colloid and detach T3 and T4,
which then pass through the cell
into an adjacent capillary.
• When inactive, thyroid epithelial
cells are simple flat or cuboidal
cells, but when actively synthesising
or secreting thyroid hormone they
are tall and columnar.
14. Thyroid C cell
• Clear or light cell
• Ultrastructural characteristics of neuroendocrine cells,
the C cell or parafollicular cell C, is found in the thyroid
gland as individual scattered cells in the follicle lining, or
as small clumps in the interstices between follicles.
• These cells secrete calcitonin, which is a physiological
antagonist to parathormone and therefore lowers blood
calcium levels by suppressing the osteoclastic resorption
of bone.
15. Thyroid gland pathology
Diffusely or focally enlarged(numerous causes)
Thyroid gland may under- or oversecrete the hormone thyroxine.
• One of the commonest disorders of the thyroid gland is a multinodular goiter,
which is a diffuse irregular enlargement of the thyroid gland with areas of thyroid
hypertrophy and colloid cyst formation. Most patients are euthyroid (i.e. have
normal serum thyroxine levels).
• Immunological diseases may affect the thyroid gland and may overstimulate it to
produce excessive thyroxine.
• These diseases may be associated with other extrathyroid manifestations, which
include exophthalmos, pretibial myxedema, and nail changes.
• Other causes of diffuse thyroid stimulation include viral thyroiditis.
• Some diseases may cause atrophy of the thyroid gland, leading to undersecretion
of thyroxine (myxedema).
17. Thyroid gland
Thyroidectomy - For benign diseases such as multinodular goiter.
possibility of damaging other structures when carrying out a
thyroidectomy, namely
• The parathyroid glands (which may be excised en masse with the
thyroid gland),
• The recurrent laryngeal nerve,
• The sympathetic trunk, and
• Rarely, the nerves of the carotid sheath.
18. • Pair of important endocrine
glands situated on the
posterior abdominal wall
• Over the upper pole of the
kidneys behind the peritoneum
• lies in the Epigastrium, in front
of the crus of the diaphragm,
opposite the vertebral end of
the 11th intercostal space and
the 12th rib.
19. • 50 mm in height, 30mm in breadth, 10 mm in thickness, 5
gm in weight.
• They are made up of 2 parts
a) An outer cortex- mesodermal origin which secrets a
number of steriod hormones.
b) An inner medulla- neural crest origin, which is made up of
chromaffin cells and secrets adrenalin & noradrenallin
(catecholamines)
20. Right Left
Shape Pyramidal Semilunar
Parts Apex-bare area of liver Upper end-close to spleen
Base-upper pole of right liver Lower end – hilum left
vein
Anterior surface IVC, Bare area of liver Cardiac end of
stomach,pancreas with
splenic artery
Posterior Rt crus of diaphragm,rt kidney Left crus of diaphragm,left
surface kidney
Anterior border Hilum-right hilum --------
Medial border Coeliac ganglia Coeliac ganglia
Lateral border Liver stomach
22. • The vascular system of the cortex C
consists of an anastomosing
network of capillary sinusoids
supplied by branches of the
subcapsular plexus, known as short
cortical arteries.
• The medulla is supplied by long
cortical arteries which descend
from the subcapsular plexus
through the cortex into the medulla
where they ramify into a rich
network of dilated capillaries
surrounding the medullary
secretory cells.
24. • Adrenal cortex has a similar embryological origin to the gonads
and, like them, secretes a variety of steroid hormones all
structurally related to their common precursor, cholesterol. The
adrenal steroids may be divided into three functional classes,
mineralocorticoids, glucocorticoids and sex hormones.
The mineralocorticoids are concerned with electrolyte and fluid
homeostasis.
The glucocorticoids have a wide range of effects on carbohydrate,
protein and lipid metabolism.
Small quantities of sex hormones are secreted by the adrenal cortex
and supplement gonadal sex hormone secretion.
• Adrenal medulla secretes the catecholamine hormones, adrenaline
(epinephrine) and noradrenaline (norepinephrine).
26. • The zona glomerulosa
G(1/5th) is composed of cells
arranged in irregular ovoid
clusters separated by delicate
fibrous trabeculae T
continuous with the
fibrocollagenous capsule Cap;
both the trabeculae and inner
capsule contain prominent
capillaries.
• The cells have round nuclei
and less cytoplasm than the
cells in the adjacent zona
fasciculata.
• The cytoplasm contains
plentiful smooth endoplasmic
reticulum and numerous
mitochondria, but with only
scanty lipid droplets.
27. • The zona fasciculata(3/5 th) is the
middle and broadest of the three
cortical zones.
• It consists of narrow columns and
cords of cells, often only one cell
thick, separated by fine strands of
collagen and wide bore capillaries.
• The cell cytoplasm is abundant and
pale staining due to the large
number of lipid droplets present;
mitochondria and smooth
endoplasmic reticulum are also
abundant.
28. • The zona reticularis(1/5th) R is the thin
innermost layer of the adrenal cortex, and
lies next to the adrenal medulla M.
• It consists of an irregular network of
branching cords and clusters of glandular
cells separated by numerous wide diameter
capillaries.
• The zona reticularis cells are much smaller
than those of the adjacent zona fasciculata
with less cytoplasm.
• The cytoplasm is darker staining because it
contains considerably fewer lipid droplets.
Brown lipofuscin pigment is sometimes seen
in the cells of this layer.
• The zona reticularis secretes small quantities
of androgens and glucocorticoids.
29. Adrenal medulla
• The adrenal medulla secretes
the amines adrenaline
(epinephrine) and
noradrenaline
(norepinephrine) under the
control of the sympathetic
nervous system.
• When stained with the
standard H [amp ] E method
the adrenal medulla is
composed of clusters of cells
with granular, faintly
basophilic cytoplasm, with
numerous capillaries in their
fine supporting stroma.
• Venous channels V draining
blood from the sinusoids of
the cortex pass through the
medulla towards the central
medullary vein.
30. APPLIED ANATOMY
• The excess hormone may be produced by a benign tumour (adrenal cortical
adenoma) or a malignant tumour (adrenal cortical carcinoma), or by diffuse
hyperplasia of the adrenal cortex.
• Destruction of both adrenals (for example, by autoimmune adrenalitis or, in
former years, by tuberculosis) leads to failure of secretion of all adrenal cortical
hormones (hypoadrenalism), leading to the clinical syndrome called Addison's
disease (weakness, tiredness, skin pigmentation, postural hypotension,
hypovolaemia and low blood sodium).
31. • More common is hyperadrenalism where there is excess secretion of one or more
of the cortical hormones, mainly glucocorticoids (producing Cushing's syndrome-
obesity,hirustism diabetes and hypogonadism) or mineralocorticoids (producing
Conn's syndrome) or virilism(excessive androgens may cause masculinization) or
male excessive estrogen cause feminisation—breast enlargement
• Children-excessive sex hormones cause adrenogenital syndrome—
pseudohermaphroidism
• Tumor of medulla-Pheochromocytoma---HTN,Excessive sweating,pallor of skin
