2. Thyroid gland
• Largest gland in the body
• Location : in the neck inferior the larynx and
spanning over the ventral surface of trachea
• Function:
– Secretion of thyroxin and triiodothyronine
– Secretion of calcitonin
3. Thyroid Gland
Anterior surface of the trachea
just inferior to thyroid cartilage
(or Adam’s apple)
Two lobes connected by an
isthmus
Microscopic thyroid follicles
produce thyroid hormone
CCells - produce calcitonin
( Ca2+)
9. Synthesis of thyroid hormones
1. Iodide trapping
– By sodium iodide symporter
– Blocked by:
• Thiocyanate SCN-
• Perchlorate ClO4-
• Pertechnetate TcO4-
2. Oxidation of iodide
– By thyroid peroxidase
– Inhibited by:
3. large intake of iodide >150mcgday
4. Thioamides(refer to hyperthyroidism therapy)
10. Synthesis of thyroid hormones
3. Organification
– Tyrosine residues of thyroglobulin is iodinated
1. Inhibited by large intake of
iodide >150mcgday
2. Thioamides(refer to
hyperthyroidism therapy)
– Produce monoiodotyrosine residues MIT
and diiodotyrosine residues DIT
11. Synthesis of thyroid hormones
4. Coupling
– DIT+MIT=T3
– DIT+MIT=T4
5. Storage :
– Along with thyroglobulin
6. Exocytosis and proteolysis
– Release of T4 & T3
7. Conversion of T4 to T3 in peripheral tissue
12.
13. T4 vs T3
T4
• Thyroid gland synthesize
90%
• 0.04%free
• Not active
• Long T12
T3
• Thyroid gland synthesize 9%
• 0.4% fr
• active
15. Thyroid Gland
Thyroid hormones target almost every body cell
Can enter cells & bind to intracellular receptors on
mitochondria & in nucleus
Effects include:
increased ATP production
increased cellular metabolism, energy utilization &
oxygen consumption
increased body temperature
growth & development of skeletal, muscular &
nervous system in fetus & children
16. Effects Of Thyroid Hormones On The
Cardiovascular System
• Increase heart rate
• Increase force of cardiac contractions
• Increase stroke volume
• Increase Cardiac output
• Up-regulate catecholamine receptors
17. Effects Of Thyroid Hormones On The
Respiratory System
• Increase resting respiratory rate
• Increase minute ventilation
• Increase ventilatory response to hypercapnia
and hypoxia
18. Effects Of The Thyroid Hormones On
The Renal System
• Increase blood flow
• Increase glomerular filtration rate
19. Effects Of The Thyroid Hormones On
Oxygen Carrying Capacity
• Increase RBC mass
• Increase oxygen dissociation from hemoglobin
21. Effects Of The Thyroid Hormones On
Intermediary Metabolism
• Increase glucose absorption from the GI
tract
• Increase carbohydrate,lipid and protein
turnover
• Down-regulate insulin receptors
• Increase substrate availability
22. Effects Of The Thyroid Hormones In
Growth And Tissue Development
• Increase growth and maturation of bone
• Increase tooth development and eruption
• Increase 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
23. Effects Of The Thyroid Hormones On
The Nervous System
• 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
24. Effects Of The Thyroid Hormones On
The Reproductive System
• Required for normal follicular development
and ovulation in the female
• Required for the normal maintenance of
pregnancy
• Required for normal spermatogenesis in
the male
26. THYROID DISORDERS MAY BE CLASSIFIED AS:-
Hyperthyroidism (Thyrotoxicosis)
•Overproduction of Thyroid hormones
Hypothyroidism (Gland destruction)
Underproduction of Thyroid hormones
29. .
SIGNS AND SYMPTOMS
For Hyperthyroidism:-
• Tachycardia
• Palpitations
• Nervousness
• Tremors
• Increased BP
• Heat intolerance
30. For Hypothyroidism
• Weight gain despite poor appetite
• Cold intoleration
• Constipation
• Lethargy
• But, these symptoms are often non- specific and
makes diagnosis difficult.
31. LABORATORY EVALUATION
• Normal TSH levels practically excludes
abnormalities
• If TSH is abnormal, next steps:-
• Total and free T4 & T3 levels
• TSI( Thyroid Stimulating Ig)
• TPO(Thyroid Peroxidase Ab)
• Anti mitochondrial Ab
• Serum Tg (Thyroglobulin)
• Radioactive uptake and Thyroid scanning
33. GOITER
• A goiter is a swelling of the neck or the larynx
resulting from the enlargement of the thyroid gland
( Thyromegaly ).
• Worldwide over 90 % cases of goiter are caused by
iodine deficiency.
• It may be associated with both Hypothyroidism and
Hyperthyroidism.
34. .
CLASSIFICATION OF GOITERS
GROWTH PATTERN:-
• UNINODULAR
• MULTINODULAR
• DIFFUSE
SIZE:-
• CLASS I
• CLASS II
• CLASS III
35.
36. CAUSES:
• Iodine deficiency
• Congenital hypothyroidism
• Pituitary diseases
• Thyroid cancer
• Thyroid hormone insensitivity
TREATMENT:
• It is treated according to the cause, if thyroid gland
is producing too much T4 and T3,
• radioactive iodine is given to the patient to shrink the
gland.
• If the cause is iodine deficiency, it is supplemented
as lugol’s solution or KI
37. GRAVE’S DISEASE
• Also known as toxic diffuse goiter is an
autoimmune disease that affects the thyroid gland.
• It is the most common cause of hyperthyroidism.
• The exact cause of the disease is unclear.
• However, it is believed to involve a combination
of genetic and environmental factors.
38. SIGNS AND SYMPTOMS:
• Almost all of the signs of the disease is believed to be
a result of hyperthyroidism.
• These include insomnia, hand tremors, hyperactivity,
heat intolerance, excessive sweating, weight loss
despite increased appetite, etc.
• Exceptions are ophthalmopathy, goiter and pretibial
myxedema .
39. MECHANISM:
• Thyroid stimulating immunoglobins recognize and
bind to Thyrotropin receptor (TSH receptor) which
further stimulates the release of T3 & T4
• Thyroxine receptors in the pituitary gets activated
by surplus hormone suppressing further release of
TSH in a negative feedback loop.
• The result is very high levels of circulating thyroid
hormone and a low TSH level.
40.
41. TREATMENT
• Treatment of graves’ disease include antithyroid drugs
which reduces the production of thyroid hormones.
• Radioiodine is also used as a measure.
Thyroidectomy(surgical excision of gland) is also
used in many cases.
• Mild cases of ophthalmopathy could be treated by
lubricant eye drops or non-steroidal anti inflammatory
drops.
42. CRETINISM
• Cretinism is a condition of severely stunted
physical and mental growth due to untreated
congenital deficiency of thyroid hormone, usually
due to maternal hypothyroidism.
PATHOPHYSIOLOGY
• Cretinism can be endemic, genetic or sporadic.
• Poor growth is apparent as early as the first year
of life. It causes mental deterioration, swelling of
skin and loss of hair. Bone maturation and
puberty is severely delayed.
• Ovulation is impeded and infertility is common
43. CAUSE AND TREATMENT
• Most common cause is iodine deficiency.
• Populations living in areas with low soil iodine
• concentration are prone to this disease.
• Sporadic and genetic cretinism results from abnormal
development or function of the fetal thyroid gland.
• This type of cretinism has been almost completely eliminated in
developed countries by early diagnosis by newborn screening
schemes followed by lifelong treatment with T4.
• Frequent monitoring (every 2–3 weeks during the first months
of life) is recommended to ensure that infants with congenital
hypothyroidism remain within the high end of normal range.
44.
45. MYXEDEMA
• Myxedema is a term used synonymously with severe
hypothyroidism
• Myxedema develops in the patient with almost total lack
of thyroid hormone function
• It is generally characterized by bagginess under the eyes
and swelling of the face.
• In this condition, greatly increased quantities of
hyaluronic acid and chondroitin sulfate bound with
protein form excessive tissue gel in the interstitial
spaces, and this causes the total quantity of interstitial
fluid to increase.
46. Because of the gel nature of the excess fluid, it is
mainly immobile, and the edema is the nonpitting type.
CAUSES
• Myxedema can occur in:
• Hyperthyroidism, associated with pretibial
myxedema and exophthalmos.
• Pretibial myxedema can occur in 1–4% of patients
with Graves' disease, a cause of hyperthyroidism.
• Hypothyroidism, including Hashimoto's thyroiditis
47. PATHOPHYSIOLOGY
• Myxedema causes specific forms of dermal edema.
• The connective fibres is separated by an increased am
ount of mucosaccharides.
• This protein-mucosaccharide complex binds water, producing
non-pitting boggy edema.
• In particular around eyes, hands, and feet.
• Myxedema is also responsible for thickening of tongue and
laryngeal and pharyngeal mucous membranes.
50. HASHIMOTO'S THYROIDITIS
• It is an auto-immune disease in which the thyroid gland
is gradually destroyed.
• Over time the thyroid may enlarge and form painless
goiter.
• Some people eventually develop hypothyroidism.
• After many years the thyroid shrinks in size.
• It is thought to be caused due to a combination of
genetic and environmental factors.
51. SIGNS AND SYMPTOMS
• Fatigue
• Weight gain
• Pale or puffy face
Feeling cold
• Joint and muscle pain
• Constipation
• Dry and thinning hair
Irregular menstrual
cycles Depression etc
52. PATHOPHYSIOLOGY
• Various auto-antibodies may be present against
thyroid peroxidase, thyroglobulin and TSH
receptors.
• Gross morphological changes within the thyroid
are seen in the general enlargement which is far
more locally nodular and irregular than more
diffuse patterns
53. TREATMENT
• Managing hormone levels:
• Hypothyroidism caused by Hashimoto's thyroiditis is
treated with thyroid hormone replacement agents.
• E.g.: Levothyroxine, triiodothyronine.
