Page 292 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Effects and Symptoms of Hyperthyroidism
In many tissues the thyroid hormones (T 3 , T 4 ) more quickly and more markedly than in
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increase enzyme synthesis, Na /K -ATPase ac- healthy people; the rise is followed by a rapid
tivity and oxygen consumption, leading to an fall (abnormal glucose tolerance). Although
increase in basal metabolism and a rise in body the thyroid hormones promote protein syn-
temperature. By stimulating glycogenolysis thesis, hyperthyroidism increases proteolytic
and gluconeogenesis, the thyroid hormones enzymes, and thus causes excess proteolysis
cause an increase in blood glucose concentra- with an increase in urea formation and excre-
tion, while on the other hand also increasing tion. Muscle mass is reduced (→ A1). Break-
glycolysis. They stimulate lipolysis, the break- down in bone matrix can lead to osteoporosis,
down of VLDL and LDL as well the excretion of hypercalcemia, and hypercalciuria (→ A4). As
bile acids in the bile. They stimulate, via in- a result of the stimulating action on the heart,
creased oxygen consumption, the release of cardiac output (CO) and systolic blood pressure
erythropoietin and thus erythropoiesis. The are raised (→ A5). Atrial fibrillation may occa-
high 2,3-bisphosphoglycerate (DPG) content sionally occur. The peripheral vessels are dilat-
in newly formed erythrocytes decreases O 2 af- ed. The glomerular filtration rate (GFR), renal
finity and thus favors the peripheral release of plasma flow (RPF), and tubular transport are
Hormones gans to catecholamines (especially by an in- liver the breakdown of steroid hormones and
increased in the kidneys (→ A6), while in the
O 2 . Thyroid hormones sensitize the target or-
drugs is accelerated. Stimulation of the intes-
crease in β-receptors) and thus increase, for
In addition, they raise intestinal motility and
increase in neuromuscular excitability to hy-
9 example, cardiac contractility and heart rate. tinal musculature leads to diarrhea; the
stimulate the transport processes in the gut perreflexia, tremor, muscular weakness, and
and kidneys. They promote physical (e.g., lon- insomnia (→ A7). In children, accelerated
gitudinal growth) and mental (especially intel- growth may sometimes occur (→ A4). T 3 and
lectual) development. T 3 and T 4 stimulate the T 4 promote the expression of their receptors
restructuring of bone and muscle, the catabol- and thereby sensitize their target organs to
ic effect predominating and increase neuro- their actions, thus increasing the effects of hy-
muscular excitability. T 3 and T 4 act mainly perthyroidism.
through enhanced gene expression, which In immunogenic hyperthyroidism (Graves’
takes several days. Beyond this their prolonged disease; → p. 280) exophthalmos may be add-
action is due to the long half-life in blood ed to the increased effects of thyroid hormones
(→ A8); protrusion of the eyes with diplopia,
(T 3 = one day; T 4 = seven days). Maternal T 3
and T 4 are largely inactivated in the placenta excessive tear flow, and increased photopho-
and thus have only a slight effect on the fetus. bia also occur. Its cause lies in an immune re-
In hyperthyroidism metabolism and heat action against retrobulbar antigens that are
production are raised (→ A1). Basal metabo- apparently similar to the TSH receptors. The
lism can nearly double. The affected patients result is a retrobulbar inflammation with
prefer cold ambient temperature; in a hot en- swelling of the eye muscles, lymphocytic infil-
vironment they tend to break into a sweat tration, accumulation of acid mucopolysac-
(heat intolerance). The increased O 2 demand charides, and an increase in retrobulbar con-
requires hyperventilation and stimulates nective tissue. Sometimes similar changes can
erythropoiesis. The raised lipolysis leads to be found in the pretibial region.
weight loss, on the one hand, and to hyper-
lipidacidemia, on the other (→ A1). At the
same time, the concentrations of VLDL, LDL,
and cholesterol are diminished (→ A2). The ef-
fects on carbohydrate metabolism (→ A3) fa-
vor the development of (reversible) diabetes
282 mellitus. When glucose is given (glucose toler-
ance test), plasma glucose concentration rises
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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