TSH

definition

The abbreviation TSH refers to the so-called “thyroid stimulating hormone” (thyroid stimulating hormone), or “thyrotropin”. It consists of amino acids that are chained together as a protein. For this reason, it is also known as the peptide hormone.
TSH is released from the pituitary gland (pituitary gland). The corresponding hormone, which in turn activates the pituitary gland to produce TSH, is called "TRH", or "thyrotropin-releasing hormone". This name already contains the function, it is used for the formation / release of "thyrotropin", i.e. TSH.

The TSH then travels from the pituitary to the thyroid via the blood. There it binds to the TSH receptor and increases iodine uptake in the thyroid gland, the formation and release of thyroid hormones and the growth of the thyroid gland. Adequate iodine uptake in the thyroid is important because iodine is an important component of thyroid hormones. The thyroid hormones increase the metabolism and affect almost all organs and tissues in the body.

Function of TSH

After the effect of the TRH on the pituitary gland, the TSH is released. This is released into the blood and has the thyroid gland as its target organ. Here the TSH causes the release of the vital thyroid hormones T3 (triiodothyronine) and T4 (thyroxine). This finely regulated circuit is known as the thyrotropic control circuit. This control circuit ensures a balance of the thyroid hormones T3 and T4 in the blood and ensures that the body functions properly
The thyroid hormones that are now released cause, for example, an increase in the heart rate in the heart, increased blood flow to the lungs in the lungs and an increased build-up of muscle fibers in the skeleton. In the metabolism, they cause an increased basal metabolic rate through increased oxygen consumption and increased body temperature.

Read more on the subject at: Effect of the thyroid hormones

Decisive systems of the body are controlled by this regulation cycle "diencephalon-pituitary-thyroid-axis" (hypothalamus-pituitary-axis), which requires a sensitive feedback on the exact amount required. Here, the circulating hormones of the respective organs partly act on their upstream organ and, if the concentration increases, inhibit the release of their activating hormone.
T3 and T4 thus, for example, inhibit the release of TSH but also inhibit the release of TRH at a higher level (so-called negative feedback)
TSH is also inhibited by other important hormones such as cortisone or dopamine. In a nutshell: TSH acts on the release of thyroid hormones and thus controls their function.

Values ​​/ normal values

The TSH level can be determined with a simple sample of blood from the blood. This value is very sensitive to changes and disorders of the thyroid hormones. If the thyroid hormone levels are significantly too high, the TSH level can drop below the detection limit. This is explained by the regulation cycle mentioned above, i.e. the thyroid hormones are too high and thus cause the TSH value to drop.
If the thyroid hormone levels are too low, the TSH level can be significantly increased. This property underlines the TSH value as an important course parameter in thyroid disorders. The normal values ​​in the blood serum are stated differently by the various medical societies, but in a healthy adult they are between 0.4 and 4.5 milli-units per liter. Depending on the laboratory investigating, there are sometimes different reference values. If these are scientifically plausible and justified, these reference values ​​should be observed.

Read more on the subject under: Thyroid values

Why is my TSH level too high?

The TSH value is higher when too few thyroid hormones are produced by the thyroid gland or when there is no thyroid gland from birth. The thyroid values ​​are too low in the case of hypothyroidism, for example if there is chronic inflammation.
The most common form is autoimmune thyroiditis called Hashimoto's thyroiditis. Here are so-called antibodies which are directed against enzymes and other important components of the thyroid tissue.
This disease usually remains undetected at first, as it initially does not trigger any symptoms. The TSH value returns to normal when thyroid hormones are taken, for example in the form of tablets (L-thyroxine).

Read more on the topic: Symptoms of an underactive thyroid

Why is my TSH level too low?

If the thyroid is overactive, again due to the control circuit and the so-called "negative feedback" when there is too much thyroid hormones in the blood, the TSH value will drop. Thyroid hormones therefore lead to a decrease in their stimulating factor.
An overactive thyroid can be triggered by various causes. On the one hand, Graves' disease should be mentioned. So-called autoantibodies are formed against the TSH receptors on the thyroid. These antibodies cause an increased production of thyroid hormones and thus cause hyperfunction.
Individual areas of the thyroid gland can also encapsulate themselves as what is known as an autonomous adenoma. These areas then produce more thyroid hormones and also induce hyperfunction without being subject to the aforementioned control loop. In addition to all illnesses, the intake of thyroid hormones can also lead to a drop in the TSH value and also to an apparent hyperthyroidism.

Read more on the subject at: Symptoms of an overactive thyroid

How does the TSH value change during pregnancy?

Pregnancy is divided into three main parts. Since the child goes through various growth and development steps in the mother, the need for thyroid hormones is significantly increased and different in the three sections. A healthy thyroid is able to meet this requirement with sufficient iodine intake.

Read more on the topic: Pregnancy process

According to the recommendation of the World Health Organization, the iodine requirement of a non-pregnant woman is at least 150 µg per day. Due to the growth processes, pregnant women need around 250 µg of iodine per day. The iodine plays a role in the formation of thyroid hormones. Since the need for thyroid hormones is high and so many thyroid hormones are consumed, there is less feedback to the pituitary gland and thus the increased release of TSH, which in turn causes an increased release of thyroid hormones.

Read more on the topic: Iodine deficiency in pregnancy

In the three parts of the pregnancy to be subdivided (trimenomes), different reference values ​​are given for the TSH, which are also subject to the blood levels of the pregnancy hormones. In the first trimester, the first part of pregnancy, pregnancy hormones lower TSH levels, which is normal. In the other two parts, the value slowly normalizes again.

Read more on the subject at: Thyroid levels in pregnancy

TSH level and pregnancy

If there is an underactive thyroid in a woman who wishes to have children, close specialist care should take place in coordination with the attending gynecologist. This is due to the fact that there is a higher need for thyroid hormones.
If the dose of thyroid hormones is adjusted, laboratory checks should be carried out every four weeks. Close monitoring of the TSH is of course also necessary in the event of overfunction. A derailed thyroid function in underactive or overactive can be a hindrance to conception and ovulation and influence the desire to have children.
In rare cases, after years of unfulfilled desire to have children, a now optimally adjusted thyroid can fulfill the desire to have children, since ovulation now proceeds regularly and all female hormones harmonize well in their structure. The TSH value is therefore a good progress parameter in the detection of an under- or over-active thyroid.

Read more on the subject at: Thyroid levels in pregnancy

TSH receptor antibodies

TSH receptor antibodies are, as the name suggests, antibodies against the TSH receptor. These antibodies arise from defective activation of the immune system and bind to the TSH receptor - usually with a stimulating effect.
By binding, the antibodies mimic the effects of TSH and thus increase the production and release of the thyroid hormones T3 and T4. Ultimately, this leads to an overactive thyroid (hyperthyroidism), thyroid growth and the typical symptoms such as high blood pressure, increased sweating, heat intolerance, cardiac arrhythmias or even diarrhea and sleep disorders.
The disease in which the TSH receptor antibodies have a stimulating effect is called Graves' disease.
In rare cases, the antibodies also block the TSH receptor so that TSH can no longer work. This receptor blockade ultimately leads to an underactive thyroid through reduced production of thyroid hormones.