Page 294 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Effects and Symptoms of Hypothyroidism
For a description of the functions of the thyroid musculature leads to constipation. Impaired
hormones, see p. 282. Metabolism and heat function of the esophageal musculature and
production are reduced in hypothyroidism. of the gastroesophageal sphincter may cause
Basal metabolic rate may fall by half (→ A1), gastric reflux and esophagitis.
and the patients easily feel cold (cold intoler- The activity and effectiveness of the auto-
ance). Oxygen consumption, ventilation, and nomic nervous system is reduced in hypothy-
erythropoiesis are diminished. In addition, the roidism (→ A7). Neuromuscular excitability is
development of anemia is encouraged by the also reduced, resulting in abnormal sensory
impaired absorption in the gut of iron, folic functions, hyporeflexia, loss of appetite, loss
acid, and vitamin B 12 . Reduced lipolysis pro- of memory, depression, and clouding of con-
motes weight increase and hyperlipidemia sciousness progressing even to coma. These
(VLDL, LDL), while the reduced breakdown of defects are reversible in adults. However, a
cholesterol to bile acids quickly leads to hy- lack of thyroid hormone in fetuses and neo-
percholesterolemia, and thus favors the devel- nates will produce irreversible brain damage.
opment of atherosclerosis (→ A2). Impairment The thyroid hormones are necessary for the
of glycogenolysis and gluconeogenesis can re- full development of dendrites and axons, the
Hormones down of glycosaminoglycans (mucopolysac- formation—all processes that are absolutely
sult in hypoglycemia (→ A3). Reduced break-
formation of synapses, myelination, and glial
charides, mucin) causes them to be deposited
essential for brain development in the fetus
of the skin, which is why the disease has been
deficiency of thyroid hormones thus massively
9 in various tissues and a dough-like consistency and up to two years after birth. Intrauterine
called myxedema (→ A4). In addition, fibro- impairs this development. If substitution with
nectin, collagen, and plasma albumin are de- thyroid hormones after birth is omitted, brain
posited in the skin. Reduced transformation of damage occurs that cannot be reversed by lat-
carotene into vitamin A causes hyperkeratosis. er thyroid hormone administration. Affected
Also, because of reduced sweat and sebaceous children are often deaf.
secretion, the skin is dry and the reduced heat Furthermore, bone growth is delayed in
production makes it feel cold. The patient of- these children (→ A8). Retarded growth and
ten has a hoarse voice. impaired mental capacity lead to the typical
Reduced stimulation of the heart by thyroid feature of cretinism.
hormones decreases contractility, heart rate, The functional effects of thyroid hormone
stroke volume, cardiac output and occasionally deficiency are accentuated by a reduced ex-
also the systolic blood pressure (→ A5). In pression of T 3 and T 4 receptors.
marked thyroid hormone deficiency heart fail- A T 3 /T 4 deficiency disinhibits the formation
ure can develop. Pleural and pericardial effu- of TRH and TSH (→ p. 280). TSH not only stim-
sions are common. The rate of breathing is ulates the formation of TSH, but also of prolac-
slowed and the ventilatory reaction to hyper- tin, and can thus trigger hyperprolactinemia
capnia and hypoxia is impaired. (→ p. 260). TSH also promotes the growth of
The glomeruli and tubules in the kidneys the thyroid gland, causing goitre (→ p. 280).
are smaller. Glomerular filtration rate, renal Lastly, abnormal release of gonadotropins can
plasma flow, and tubular transport capacity impair fertility.
are reduced. Decreased renal elimination leads
to water and NaCl retention (→ A6). Due to the
accumulation of fat, glycosaminoglycans, NaCl,
and water, the patient may look somewhat
bloated.
In addition, protein synthesis in the liver is
impaired and the breakdown of steroid hor-
284 mones and drugs is delayed.
The reduced stimulation of the intestinal
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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