thyroid hormone metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving any of the compounds secreted by the thyroid gland, largely thyroxine and triiodothyronine. [GOC:jl, ISBN:0198506732]

The thyroid hormone metabolic process is a complex and tightly regulated process that involves the synthesis, secretion, transport, and degradation of thyroid hormones. These hormones, thyroxine (T4) and triiodothyronine (T3), are essential for normal growth, development, and metabolism.

**Synthesis:**
- The process begins in the thyroid gland, where thyroid follicular cells synthesize thyroid hormones from iodine and the amino acid tyrosine.
- Iodine is actively transported into the follicular cells, where it is incorporated into tyrosine molecules.
- Through a series of enzymatic reactions, these iodinated tyrosine molecules are coupled to form T4 and T3.
- T4 is the major hormone produced, but it is converted to T3 in peripheral tissues.

**Secretion:**
- T4 and T3 are stored within the thyroid gland in a colloid form.
- Upon stimulation by thyroid-stimulating hormone (TSH), these hormones are released from the gland and enter the bloodstream.

**Transport:**
- Thyroid hormones are transported in the blood bound to carrier proteins, primarily thyroxine-binding globulin (TBG).
- Only a small fraction of circulating thyroid hormones are free and biologically active.

**Action:**
- T3 binds to nuclear receptors in target tissues, initiating a cascade of gene expression changes.
- These changes affect a wide range of metabolic processes, including:
- Increased basal metabolic rate
- Stimulation of protein synthesis
- Regulation of carbohydrate metabolism
- Promotion of growth and development
- Influence on heart rate and blood pressure

**Degradation:**
- Thyroid hormones are inactivated through deiodination, a process that removes iodine from the molecule.
- This process occurs primarily in the liver and kidneys.
- The breakdown products of thyroid hormones are excreted in the urine and feces.

**Regulation:**
- The production and release of thyroid hormones are tightly regulated by a feedback loop involving the hypothalamus, pituitary gland, and thyroid gland.
- The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to secrete TSH.
- TSH acts on the thyroid gland to promote thyroid hormone synthesis and secretion.
- When thyroid hormone levels in the blood rise, they inhibit the release of TRH and TSH, creating a negative feedback loop that maintains hormone homeostasis.

**Disorders:**
- Dysregulation of thyroid hormone metabolism can lead to various disorders, including:
- Hypothyroidism: Deficiency of thyroid hormone
- Hyperthyroidism: Excess of thyroid hormone
- These disorders can manifest with a wide range of symptoms affecting different systems of the body.

In summary, the thyroid hormone metabolic process is a complex and essential process that involves multiple steps, including synthesis, secretion, transport, action, and degradation. This process is tightly regulated to ensure appropriate levels of thyroid hormones in the body, which are crucial for normal growth, development, and metabolism.'
"

Proteins (2)

Compounds (5)