2. Thyroid Gland: Introduction
The largest pure endocrine
gland (15-25 gm), located in
the anterior neck
Consists of two lateral lobes
connected by a median
tissue mass called the
isthmus.
2
3. Thyroid Gland: introduction
Blood supply
Arterial blood supply
Superior thyroid artery from
external carotid
Inferior thyroid artery from
subclavians
Blood flow 4-6 ml/min/gm
Venous blood supply
Three pairs of veins supply
blood to the gland
4. The thyroid gland is made up of closely packed sacs called
thyroid follicles.
The structural and functional unit of thyroid gland.
Cyst-like structure
0.2 – 0.9 mm in diameter
Simple cuboidal epithelial (follicular cells) surrounding a lumen
filled with colloid.
T4 and T3 present in colloid bound to a large protein called
thyroglobulin.
Thyroid Gland: introduction
6. Development
from the floor of the primitive pharynx during the third
week of gestation
developing gland migrates along the thyroglossal duct to
reach its final location in the neck
rare ectopic location of thyroid tissue at the base of the
tongue (lingual thyroid)
occurrence of thyroglossal duct cysts along this
developmental tract
7. Thyroid gland secret 3 hormones
Thyroxin or (T4)
Tri-iodotyronine or (T3)
Main hormones secreted by thyroid gland
Secreted by follicular cells
Amino acid derivatives (tyrosine)
Calcitonin
Produced by parafollicular cells – C cells
Thyroid Gland: Introduction
8. Regulation of Thyroid Axis
TSH –
Thyrotrope cells of ant. Pituitary
31 kDa hormone α and β subunits
α subunit similar to LH, FSH and hCG
Stimulated by TRH
TSH, TRH supressed by Thyroxine
9.
10. Actions of Thyroid Hormones
Increase the body’s overall basal metabolic rate
Increase oxygen consumption
Essential for normal growth
Mental development
Sexual maturation
Increase the sensitivity of CVS and CNS to
catecholamines (↑COP and HR)
13. 13
Hypothyroidism
Prevalence
It is a common disorder with prevalence
ranges from 2-15% population
♀ > ♂
Female to male ratio = 10:1
↑ with age; ♀ = ♂
Mean age at diagnosis is 60 years
14. Iodine deficiency remains the most common cause
of hypothyroidism worldwide
areas of iodine sufficiency, autoimmune disease
(Hashimoto's thyroiditis) and iatrogenic causes
(treatment of hyperthyroidism) are most common
15. Primary Hypothyroidism
Disease of the thyroid gland
Secondary Hypothyroidism
Hypothalamic-pituitary diseases (reduced
TSH)
Hypothyroidism
19. SECONDARY
Hypopituitarism: tumors, pituitary surgery or irradiation,
infiltrative disorders, Sheehan's syndrome, trauma,
genetic forms of combined pituitary hormone deficiencies
Isolated TSH deficiency or inactivity
Hypothalamic disease: tumors, trauma, infiltrative
disorders, idiopathic
20. HASHIMOTO THYROIDITIS
Most common cause of hypothyroidism
Autoimmune, non-Mendelian inheritance
45-65 years, F:M = 10-20:1
Painless symmetrical enlargement
Risk of developing
B-cell non-Hodgkin’s lymphoma
Other concomitant autoimmune diseases
Endocrine and non-endocrine
21. Hashimoto Thyroiditis
Pathogenesis
Immune systems reacts against a variety of thyroid
antigens
Progressive depletion of thyroid epithelial cells which
are gradually replaced by mononuclear cells →
fibrosis
Immune mechanisms may includes:
CD8+ cytotoxic T cell-mediated cell death
Cytokine-mediated cell death
Binding of antithyroid antibodies → antibody dependent
cell-mediated cytotoxicity
23. Investigation of primary hypothyroidism
Serum TSH
The investigation of choice.
A high TSH level confirms primary hypothyroidism.
Serum T4
low free T4 level confirms the hypothyroid state.
Thyroid and other organ-specific antibodies
TPO antibodies
24. Investigations of other abnormalities:
Anaemia.
Increased serum aspartate transferase levels, from
muscle and/or liver
Increased serum creatine kinase levels, with associated
myopathy
Hypercholesterolaemia
Hyponatraemia due to an increase in ADH and impaired
free water clearance.
25. Treatment
Replacement therapy with levothyroxine
(thyroxine, i.e. T4) is given for life.
In the young and fit, 100 - 150 μg daily is suitable.
thyroid function tests after at least 2 months on a
steady dose
the aim is to restore T4 and TSH to well within the
normal range
An annual thyroid function test is recommended .
26. Subclinical Hypothyroidism
biochemical evidence of thyroid hormone deficiency
in patients who have few or no apparent clinical
features of hypothyroidism
guidelines do not recommend routine treatment
when TSH levels are below 10 mU/L
low dose of levothyroxine (25–50 g/d) with the goal
of normalizing TSH
27.
28. Myxoedema coma
Severe hypothyroidism, associated with:
- confusion or even coma.
- hypothermia.
- severe cardiac failure.
- Hypoventilation.
- Hypoglycaemia.
- hyponatraemia.
patients require full intensive care.
29. occurs in the elderly
usually precipitated by factors that impair respiration
drugs (especially sedatives, anesthetics,
antidepressants)
pneumonia, congestive heart failure, myocardial
infarction
gastrointestinal bleeding
cerebrovascular accidents
Sepsis
30. Myxoedema coma
Treatment:
Levothyroxine as a single IV bolus of 500 g, which
serves as a loading dose-50–100 ug/d
oxygen (by ventilation if necessary)
monitoring of cardiac output and pressures
gradual rewarming
hydrocortisone 100 mg i.v. 8-hourly
glucose infusion to prevent hypoglycaemia.
31.
32. Thyrotoxicosis - as the state of thyroid hormone
excess
Hyperthyroidism - result of excessive thyroid function
major etiologies of thyrotoxicosis are hyperthyroidism
caused by Graves' disease, toxic MNG, and toxic
adenomas
37. Graves' disease
The most common cause of hyperthyrodism
It is an autoimmune disorder. where the thyroid is
overactive, producing an excessive amount of thyroid
hormones
More common in adults -between 20 and 50 years
Can be familial and associated with other autoimmune
diseases
Characterized by hyperthyroidism, ophthalmopathy with
exophthalmos and dermopathy (pretibial myxedema)
38. Graves’ Disease
Autoimmune disease with breakdown of helper-T-cell tolerance
Excessive production of thyroid autoantibodies:
Thyroid-stimulating antibody (TSI)
Antibodies bind to the TSH receptor of the follicular cell
Stimulation of the cell resulting in:
Increased levels of thyroid hormones &
Hyperplasia of the thyroid gland
Hyperthyroidism and Thyroid gland enlargement
44. Graves' Ophthalmopathy
earliest manifestations - sensation of grittiness, eye
discomfort, and excess tearing
most serious manifestation is compression of the
optic nerve at the apex of the orbit, leading to
papilledema; peripheral field defects; and, if left
untreated, permanent loss of vision
45. 0 = No signs or symptoms
1 = Only signs (lid retraction or lag), no symptoms
2 = Soft-tissue involvement (periorbital edema)
3 = Proptosis (>22 mm)
4 = Extraocular-muscle involvement (diplopia)
5 = Corneal involvement
6 = Sight loss
46. Thyroid dermopathy/pretibial myxedema - most
frequent over the anterior and lateral aspects of the
lower leg
Thyroid acropachy - clubbing found in <1% of
patients with Graves' disease
47.
48. Investigation
Thyroid function test:
Serum TSH is suppressed in hyperthyroidism .
Diagnosis is confirmed with a raised free T4 or T3
. Measurement of TPO antibodies or TBII may be
useful if the diagnosis is unclear clinically
49.
50. Treatment
Antithyroid drugs:
1. Carbimazole.
2. Propylthiouracil.
These drugs inhibit the formation of thyroid hormones
common side effects - rash, urticaria, fever, and
arthralgia
Rare but major side effects include hepatitis; an
SLE-like syndrome; and, most important,
agranulocytosis
51. Treatment
Radioactive iodine
RAI accumulates in the thyroid and destroys the gland
by local radiation.
It takes several months to be fully effective.
53. Goiter
Goiter refers to an enlarged thyroid gland
Biosynthetic defects, iodine deficiency, autoimmune
disease, and nodular diseases can each lead to
goiter
diffuse nontoxic goiter - diffuse enlargement of the
thyroid occurs in the absence of nodules and
hyperthyroidism
Worldwide, diffuse goiter is most commonly caused
by iodine deficiency and is termed endemic goiter
55. Thyroglossal Duct Cyst
A thyroglossal duct cyst is a neck mass or lump that
develops from cells and tissues remaining after the
formation of the thyroid gland during embryonic
development.
Children
Failure of regression
Neck, medial
Squamous or columnar lining
often appears after an upper respiratory infection when it
enlarges and becomes painful.
Complications: inflammation,
sinus tracts