APUD cell

APUD cells are a group of cells characterized by their ability to amine precursor uptake and decarboxylation. These cells are found throughout the body and are involved in various physiological processes. The term APUD was coined by Pearse in 1969, who identified these cells as part of a system that could take up precursors of amines and then decarboxylate them to produce biologically active amines. This system was later named the APUD system and is considered an integral part of the neuroendocrine system.

Characteristics

APUD cells share several common characteristics, including the uptake of amine precursors, the decarboxylation of these precursors to form amines, and the presence of secretory granules. These cells are also known for their high levels of enzymes such as dopamine beta-hydroxylase and chromogranins, which are involved in the synthesis and storage of amines.

Location and Function

APUD cells are distributed throughout the body, with significant populations found in the gastrointestinal tract, pancreas, thyroid gland, adrenal medulla, and lung. In the gastrointestinal tract, they play a crucial role in controlling digestive functions by secreting various hormones and neurotransmitters. In the pancreas, APUD cells, specifically the islets of Langerhans, are involved in the regulation of blood sugar levels through the secretion of insulin and glucagon. In the thyroid gland, they contribute to the production of calcitonin, which is involved in calcium homeostasis. The adrenal medulla contains APUD cells that produce adrenaline and noradrenaline, which are critical for the body's response to stress. In the lung, these cells can influence respiratory function through the secretion of peptides and amines.

Clinical Significance

APUD cells are of clinical significance because they can give rise to a variety of tumors known as neuroendocrine tumors (NETs). These tumors can be benign or malignant and may arise in any part of the body where APUD cells are located. The most common sites for NETs include the gastrointestinal tract, pancreas, and lung. Symptoms of NETs vary depending on the location of the tumor and the types of hormones produced. Diagnosis often involves imaging studies, biochemical tests to measure hormone levels, and histological examination of tumor tissue.

Treatment

Treatment of NETs depends on the type, size, and location of the tumor, as well as whether it has spread to other parts of the body. Options may include surgery to remove the tumor, chemotherapy, radiation therapy, and targeted therapy to block the growth and spread of cancer cells. In some cases, treatment also involves managing the symptoms caused by hormone overproduction.

Conclusion

APUD cells play a vital role in the neuroendocrine system, influencing various physiological processes through the production of biologically active amines. While these cells are essential for normal body functions, their abnormal proliferation can lead to the development of neuroendocrine tumors, highlighting the importance of understanding APUD cell biology in the context of both health and disease.