ABNORMALITIES OF THYROID FUNCTION

Dr. Shaikh Mujeeb AhmedAssistant ProfessorAlMaarefa College

ENDO BLOCK 412

Objectives

• The student should be able to:• Describe the etiology, symptoms and

treatment of thyrotoxicosis and hypothyroidism.

Abnormalities

• Hypothyroidism– Deficient thyroid hormone secretion

• Hyperthyroidism• Excess thyroid hormone secretion

Hypothyroidism

• Primary failure of thyroid gland itself• Secondary to deficiency of TRH, TSH or both.• From an inadequate dietary supply of iodine.

Clinical features• The symptoms of hypothyroidism are largely caused by a

reduction in overall metabolic activity. • Reduced BMR (less energy expenditure at rest); • Displays poor tolerance of cold (lack of the calorigenic effect); • Tendency to gain excessive weight (not burning fuels at a normal

rate); • Easily fatigued (lower energy production); • Slow, weak pulse (caused by a reduction in the rate and strength

of cardiac contraction and a lowered cardiac output); and• Exhibits slow reflexes and slow mental responsiveness (because

of the effect on the nervous system). The• Mental effects are characterized by diminished alertness, slow

speech, and poor memory.

Causes of congenital hypothyroidism

• Maternal iodine deficiency• Fetal thyroid dysgenesis• Inborn errors of thyroid hormone synthesis• Maternal antithyroid antibodies that cross the

placenta • Fetal hypopituitary hypothyroidism

MYXEDEMA (Adult Hypothyroidism)

Puffy appearance, primarily of face, hands, and feet

Caused by infiltration of skin with complex water retaining carbohydrate molecules.

Symptoms: The patient becomes sluggish both mentally and physically and often feels cold. The hair becomes dry and the skin becomes dry and waxy. The tissues of the face swell.

Treatment: – If diagnosed early, can be treated by

administrating of T4. – Exception, if hypothyroidism caused by

iodine deficiency; treated by dietary iodine.

Cretinism• Results from hypothyroidism from birth • Characterized by dwarfism & mental retardation as

well as other general symptoms of thyroid deficiency. • At birth, child appears normal because thyroxine is

received from mother through placenta • Symptoms: growth retardation, abnormal bone

development, low body temperature, lethargy, severely mentally retarded (short limbs, a large protruding tongue, coarse dry skin, poor abdominal muscle, tone and an umbilical hernia).

Cretinism

HYPERTHYROIDISM

• The most common cause of hyperthyroidism is Graves’ disease.• immune disease• thyroid-stimulating immunoglobulin (TSI), also known as long-acting thyroid

stimulator (LATS),• ↑ BMR • poor tolerance of heat• Increased appetite • body weight• muscle weakness • Muscle termers• Sleep• ↑ Heart rate• ↑COP• Irritable, tense, anxious• Exophthalmos (bulging eyes) (grave’s disease)

Fig. 19-4, p. 696

Fig. 19-5, p. 697

• Anti thyroid drugs• Surgical removal• Administration of radioactive iodine

GOITER

• A goiter is an enlarged thyroid gland.

• Occurs when either TSH or TSI excessively stimulates the thyroid gland.

• The most common cause of goiter worldwide is a lack of iodine in the diet.

Causes of Goiter

• Iodine deficiency• Graves' disease• Hashimoto's disease• Multinodular goiter• Solitary thyroid

nodules• Thyroid cancer• Pregnancy• Inflammation

Fig. 19-6, p. 697

Table 19-1, p. 696

Synthesis, storage, and secretion of thyroid hormone

Thiocynate

XX

Thiouracil

Antithyroid Substances

• Thiocyanate Ions – Decrease Iodide Trapping– inhibition of the iodide-trapping mechanism

• Propylthiouracil – Decreases Thyroid Hormone Formation

Propylthiouracil & similar compounds as– methimazole and carbimazole– block the peroxidase enzyme

• Iodides in high concentrations decrease thyroid activity and thyroid gland size

19

References

Human physiology, Lauralee Sherwood, seventh edition.

Text book physiology by Guyton &Hall,11th edition.

Text book of physiology by Linda .S .Costanzo third edition