Name the disorder caused by the deficiency of thyroxine in adult humans.

• When there is lack of TSH (thyroid stimulating hormone) production by anterior pituitary, iodine deficiency in the diet or failure of enzyme systems involved in thyroxine production, it results in hypothyroidism.
  
• If there is a deficiency of thyroxine at birth this will lead to poor growth and mental retardation, a condition known as cretinism. If the condition is diagnosed at an early stage thyroxine can be given to restore normal growth and development.
• Thyroxine deficiency in later life gives rise to a condition known as myxoedema and the symptoms are a reduction in metabolic rate and accompanied by decreased oxygen consumption, ventilation heart rate and body temperature. Mental activity and movement becomes slower and weight increases due to the formation and storage of a semi-fluid material under the skin.
• This causes the face and the eyelids to become puffy, the tongue swells, the skin becomes rough and hair is lost from the scalp and eyebrows. All of these symptoms can be eliminated and the condition treated by taking thyroxine tablets.