cretinsm

2. THYROID GLAND
 It is endocrine gland
which drain
secretion into blood
stream directly.
 It locates in the
neck
 Consists of two
lobes connected by
isthmus
 Secret t3 and t4
hormones

3. Thyroid
Gland
stroma
C.T capsule Trabeculae Reticular C.t
parenchyma
Thyroid
Follicles
Principle
follicular
cells
Para
follicular C
cells
Inter
follicular
cells
HISTOLOGY OF THYROID GLAND

4. THYROID FOLLICLE
 Spherical in shape.
 Lined by two types of cells:
1- principle follicular cells .
secret T3 and T4 hormones.
2- Para follicular C cells.
secret calcitonin.
 Contain acidophilic colloid in the center
which contain stored hormones.

13. REGULATION OF SECRETION

14. SYNTHESIS OF THYROID HORMONE

16. MECHANISM OF ACTION

17. FUNCTIONS OF THYROID HORMONES
 Metabolic effect: (generally increase BMR.)
 on CHO metabolism:
 - increase absorption of CHO from GIT .
 - enhance gluconeogenesis and glycolysis .
 on protein synthesis
 small dose of thyroid hormone increase rate of
formation of proteins
 Large dose of thyroid hormone lead to catabolism
of muscle protein
 On fat metabolism
 Accelerate lipolysis
 Lower the level of cholesterol , phospholipids and
TAG

18.  Thyroid hormone is necessary for hepatic
conversion of carotene to vitamin A
 Effect on skeletal growth and development
 required for production and action of growth
hormone and insulin like growth factor
 On nervous system
 Promotes growth and development of the brain
during the fetal life for the first few years
 Essential for normal myelination of nervous system
in infant
 On sexual functions
 Essential for normal menstrual cycles and fertility
 They increase milk secretion in lactating women

19. ON NERVOUS SYSTEM
 Thyroid hormone promoted growth and
development of the brain during fetal life & for the
first few years of life.
 The thyroid hormone are essential for normal
myelination & development of the nervous system.
 In infant. If there is a deficiency in thyroid hormone
growth & maturation of the brain is retarded,
myelination is defective, the reflex time is
prolonged.
 In adult, thyroid hormone causes an increased
response of the brain to catecholamine & increase
activation of reticular activating system.
 An excess of thyroid hormone leads to restlessness

20. ON SEXUAL FUNCTIONS
 For normal sexual function to act thyroid hormone
secretion needs to be approximately normal.
 Thyroid Hs. Are essential for normal menstrual cycles
and fertility.
 They increase milk secretion in lactating women.
ON GASTRO INTESTINAL TRACT
 They increase the rate of secretion of the digestive juice
and motility.This leads to increase appetite and food
intake.
On respiration
 Thyroid hormone increase respiration due to increase
rate of metabolism which increase the utilization of
oxygen & the formation of carbon dioxide.

21. THE CARDIOVASCULAR SYSTEM
 thyroid hormone increase the number & affinity of
beta-1, adrenergic receptors in the heart, also it
increase its sensitivity catecholamine (catecholamine
increases all properties of the heart).
 Increased metabolism in the tissues causes more rapid
utilization of oxygen & greater metabolic end products
to be released from the tissues.These effects cause
vasodilatation, thus increasing the rate of blood flow in
the skin for heat elimination.
 Increase blood flow leads to increase venous return
leading to increase in cardiac output so the systolic
blood pressure thus, pulse pressure is increased.
 The hormone slightly increase the blood volume, partly
from vasodilatation and partly secondary to its

22. CONGENITAL HYPOTHYROIDISM
 Definition: it is inadequate thyroid hormone
production in newborn infants.
 Causes:
1- iodine deficiency.
2- Thyroid gland is absent or
underdeveloped.
3-A hypoplastic gland may develop higher in
the neck or even
in the back of the tongue (lingual thyroid)
4- One common cause is the presence of

23. SYMPTOMS AND SIGNS
 Infants born with congenital hypothyroidism
may show no effects, or may display mild
effects that often go unrecognized as a
problem.
1- excessive sleeping
2- reduced interest in nursing
3-, poor muscle tone
4- low or hoarse cry
5- infrequent bowel movements
6- exaggerated jaundice

24. DIAGNOSIS
 In the developed world, nearly all cases of
congenital hypothyroidism are detected by
the newborn screening program.
 These are based on measurement of TSH or
thyroxine (T4) on the second or third day of
life( Heel prick).
 If the TSH is high, or the T4 low, the infant's
doctor and parents are called and a referral
to a pediatric endocrinologist is
recommended to confirm the diagnosis and

25. TREATMENT
 The goal of newborn screening programs is
to detect and start treatment within the first
1–2 weeks of life. Treatment consists of a
daily dose of thyroxine, available as a small
tablet. The generic name is levothyroxine
 The tablet is crushed and given to the infant
with a small amount of water or milk
 Within a few weeks, the T4 and TSH levels
are rechecked to confirm that they are being
normalized by treatment

27. CRETINISM
 is an old term for the state of mental and
physical retardation.
 Result from:
 untreated congenital hypothyroidism
 Iodine deficiency

28. CLINICAL PICTURE
1) Full picture of Hypothyroidism.
2) Growth Retardation.
A) PHYSICAL
 Skeletal growth is more affected than soft
tissue growth
 Long bones (linear growth) are more affected
than short bones
Disproportionate Dwarfism.
 Delayed motor mile stones of development
(sitting, walking)
 Delayed dentition + small teeth.
 Delayed closure of fontanels.

31. B) MENTAL
 Mental Retardation (permanent).
C) SEXUAL
 Sexual retardation.
TREATMENT:
 Replacement therapy (start very early).