<span>True i am not sure .......</span>
Primary lymphoid organs: These organs include the bone marrow and the thymus. They create special immune system cells called lymphocytes. Secondary lymphoid organs: These organs include the lymph nodes, the spleen, the tonsils and certain tissue in various mucous membrane layers in the body (for instance in the bowel).
In sports, you put your body into so much action and your body uses up so much oxygen. As a result, more of the blood are circulated back to the heart to be oxygenated back again. Thus, playing sports improves your cardiovascular system. Moreover, your metabolism also increases. This includes the production of your hormones that are the main cause of emotions. Specific hormones are secreted that give a feeling of calmness and satisfaction. Over time, your body would be more synchronized and you will have better sleep.
