Sinoatrial node is influenced by nerves that supply it. The sinoatrial node is a banana-shaped structure that varies in size, usually between 10-30 millimeters (mm) long, 5–7 mm wide, and 1–2 mm deep. The SA node is located in the wall (myocardium) of the right atrium, laterally to the entrance of the superior vena cava in a region called the sinus venarum (hence "sino-" + "atrial)". It is positioned roughly between a groove called the crista terminalis located on the internal surface of the heart and the corresponding sulcus terminalis, on the external surface. These grooves run between the entrance of the
Lymph node stromal cell travel from the bone marrow or high endothelial venules of the thymus where they develop as lymphoblasts, to lymph nodes, where they mature. The primary role of lymph node stromal cells is structural. They form a scaffold for hematopoietic cells and assist their movement along it. The molecular signaling systems (chemokines) that distribute lymphocytes to appropriate localities within the lymph node (T and B cell segregation) are also created by lymph node stromal cells. Lymphocytes have receptors for such chemokines. For example, Naive T cells express the CCR7 receptor for the chemokine CCL21. and B cells exhibit CXCR5 receptors for