Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In eudicots, pith is located in the center of the stem. In monocots, it extends also into flowering stems and roots. The pith is encircled by a ring of xylem; the xylem, in turn, is encircled by a ring of phloem.
Throughout the lymph node's interior are a series of street-like channels called sinuses that help guide the flow of lymph from the afferent lymphatic vessels, through the cortex and medulla, and finally to the efferent lymphatic vessels at the hilum.ach lymph node chain is responsible for draining a particular body region or structure. For example, the lymph node chains in your armpits drain your arms and upper chest, while the chains in your groin are responsible for filtering lymph from your feet, legs, genitals, and lower abdominal wall.
About.com states that lymph nodes are found in each part of the body except for the central nervous system. The lymph filtered by these specialized tissues refers to the clear fluid that surrounds the cells. According to About.com, the lymph nodes have an important function of filtering the lymph of pathogens, such as bacteria and viruses, dead cells, wastes and cancerous cells. The lymph that is filtered is then returned to the blood to prevent edema or the excess fluid buildup in the tissues. About.com also explains that lymph nodes contain lymphocytes, which are immune system cells that are responsible for identifying and battling pathogens.