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Chapter 11: Thyroid axis 429

Actions of the
Hypothyroidism Hyperthyroidism
Thyroid Hormones
↓ Basal Metabolic Rate ↑ O 2 consumption ↑ Basal Metabolic Rate
(BMR) (BMR)

Intolerance Intolerance to heat,
↑ Heat production
to cold Sweatiness
Stunted growth Tissue growth

Mental retardation Brain development

Cardiovascular ↑ Cardiac output
↓ Cardiac output
Bradycardia Inotropic Tachycardia
Chronotropic Atrial Arrhythmias

Respiratory
Slow, shallow breathing
Central respiratory drive

Gut
Constipation Diarrhoea
↑ motility

Kidney
Anaemia
↑ erythropoiesis
Liver
↑ gluconeogenesis Exacerbates concomitant
diabetes mellitus
↑ glycogenolysis

Muscle
↑ Turnover Muscle wasting

Bone
Osteopenia
Figure 11.7 Actions of thyroid ↑ Turnover
hormones in thyroid dysfunction.

Table 11.7 Causes of goitre
Hyperthyroid (toxic goitre) Euthyroid (nontoxic goitre) Hypothyroid
Graves’ disease (thyrotoxicosis) Pregnancy, puberty De Quervain’s thyroiditis
Toxic multinodular goitre Endemic goitre (iodine deficiency) Iodine deficiency
Solitary toxic nodule Nontoxic multinodular goitre Hashimoto’s (autoimmune) thyroiditis
Solitary thyroid nodule or cyst