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Brockmann body
Brockmann body is an endocrine organ in some teleost fish, and is composed of a collection of islet tissues. The islet tissues are in turn composed of endocrine cells which are the principal sites of insulin synthesis. They are distributed around the spleen and the large intestine. They also secrete other hormones such as glucagon and somatostatin. Hence, Brochmann body is the centre of control of blood glucose level in these fishes. Glucagon is also produced from the intestine, but Brockmann body is the major source. Increased level of glucose stimulate the Brockmann body to release insulin, while inhibiting glucagon. Somatostatin released from Brockmann body inhibits cells to produce insulin and glucagon. In addition it inhibits release of growth hormone from the pituitary. It is named after a German physician Heinrich Brochmann who discovered it in 1848.
Brochmann body has become a new attention in medical research, specifically in the management of type I diabetes mellitus. This is because the tissue is easy to harvest, and its insulin can be easily extracted. In addition, the teleost fishes can regenerate their endocrine tissues after harvest, the property of which has challenging implication in human diabetes.
==Structure==
A typical Brochmann body is mass of whitish nodules of variable sizes, ranging from 1 to 8 mm in diameter. The nodules are composed of polygonal and elongated cells. The cells are enveloped with connective tissues. They are separated into two major islets: one is found near the spleen and the other is located inside the wall of the duodenum, at the pyloric junction. Both islet groups contain insulin, glucagon, peptide YY and somatostatin, but these proteins are secreted only in the pyloric Brockmann bodies. The amino acid sequence and primary structure of the hormones are slightly different from their counterparts in higher vertebrates. For example, tilapia and human insulin differs by 17 amino acids. There are also amino acid variation among different species; for example, glutamine residue, at position 5 in the A-chain of insulin in most teleosts, is replaced by glutamic acid in tilapia.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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