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 HYPOTHYROIDISM 😩

Hypothyroidism is a hypometabolic clinical state resulting
from inadequate production of thyroid hormones for
prolonged periods, or rarely, from resistance of the peripheral
tissues to the effects of thyroid hormones. The clinical
manifestations of hypothyroidism, depending upon the age
at onset of disorder, are divided into 2 forms:
1. Cretinism or congenital hypothyroidism is the development
of severe hypothyroidism during infancy and childhood.
2. Myxoedema is the adulthood hypothyroidism.

Cretinism

A cretin is a child with severe hypothyroidism present at
birth or developing within first two years of postnatal life.
This is the period when brain development is taking place;
in the absence of treatment the child is both physically and
mentally retarded. The word ‘Cretin’ is derived from the
French, meaning Christ-like because these children are so
mentally retarded that they are incapable of committing sins.

ETIOPATHOGENESIS. 

The causes of congenital hypothyroidism are as follows:
1. Developmental anomalies e.g. thyroid agenesis and ectopic
thyroid.
2. Genetic defect in thyroid hormone synthesis e.g. defect in
iodine trapping, oxidation, iodination, coupling and
thyroglobulin synthesis.
3. Foetal exposure to iodides and antithyroid drugs.
4. Endemic cretinism in regions with endemic goitre due to
dietary lack of iodine (sporadic cretinism, on the other hand,
is due to developmental anomalies and genetic defects in
thyroid hormone synthesis described above).

CLINICAL FEATURES. 

The clinical manifestations usually become evident within a few weeks to months of birth. The
presenting features of a cretin are: slow to thrive, poor
feeding, constipation, dry scaly skin, hoarse cry and
bradycardia. As the child ages, clinical picture of fullydeveloped
cretinism emerges characterised by impaired skeletal growth and consequent dwarfism, round face, narrow forehead, widely-set eyes, flat and broad nose, big
protuberant tongue and protuberant abdomen. Neurological
features such as deaf-mutism, spasticity and mental
deficiency are more evident in sporadic cretinism due to
developmental anomalies and dyshormonogenetic defects.
Characteristic laboratory findings include a rise in TSH
level and fall in T3 and T4 levels.

Myxoedema

The adult-onset severe hypothyroidism causes myxoedema.
The term myxoedema connotes non-pitting oedema due to
accumulation of hydrophilic mucopolysaccharides in the
ground substance of dermis and other tissues.

ETIOPATHOGENESIS.

 There are several causes of myxoedema listed below but the first two are the most
common causes:
1. Ablation of the thyroid by surgery or radiation.
2. Autoimmune (lymphocytic) thyroiditis (termed primary idiopathic myxoedema).
3. Endemic or sporadic goitre.
4. Hypothalamic-pituitary lesions.
5. Thyroid cancer.
6. Prolonged administration of antithyroid drugs.
7. Mild developmental anomalies and dyshormonogenesis

CLINICAL FEATURES.

 The onset of myxoedema is slow

and a fully-developed clinical syndrome may appear after

several years of hypothyroidism. 

The striking features are

cold intolerance, mental and physical lethargy, constipation,

slowing of speech and intellectual function, puffiness of face,

loss of hair and altered texture of the skin.

The laboratory diagnosis in myxoedema is made by low

serum T3 and T4 levels and markedly elevated TSH levels as

in the case of cretinism but cases with suprathyroid lesions

(hypothalamic-pituitary disease) have low TSH levels.

The clinical appearance of these three major forms of

functional disorders of the thyroid gland is shown in

Fig. 27.6.