Gastrointestinal absorption sites for thyroxine

Gastrointestinal absorption sites for thyroxine refer to the physiological regions of the digestive tract, primarily the duodenum, jejunum, and ileum, where exogenous and endogenous thyroxine (T4) is transported into the systemic circulation (StatPearls, 2023). This process is critical for the management of hypothyroidism, as oral levothyroxine must be efficiently absorbed to maintain euthyroidism. Absorption is complex, involving both passive diffusion and carrier-mediated transport via proteins like monocarboxylate transporters (MCT8, MCT10) and organic anion transporting polypeptides (OATPs) located in the intestinal epithelium (PubMed, PMID: 21659471). The efficiency of this process is highly sensitive to gastric pH and the presence of interfering substances such as food, fiber, or coffee (NIH, 2022). Clinical conditions such as celiac disease, atrophic gastritis, or Helicobacter pylori infection can significantly impair absorption at these sites (NEJM, 2006). Additionally, the co-administration of certain medications, including proton pump inhibitors, calcium supplements, and iron salts, often leads to therapeutic failure due to reduced bioavailability (PubMed, PMID: 24793952). Understanding these sites is essential for optimizing dosing schedules and ensuring therapeutic efficacy in patients requiring thyroid hormone replacement therapy.

Other names

Intestinal thyroxine transportThyroxine absorption siteSmall intestine T4 absorptionLevothyroxine absorption sites

Thyroxine is absorbed through the intestinal mucosa via a combination of passive diffusion and active transport mediated by specific carrier proteins such as MCT8 (SLC16A2), MCT10 (SLC16A10), and OATPs; drugs interacting with this site typically inhibit absorption by binding the hormone in the lumen or altering the necessary acidic environment.