FactsA dog’s lymph system is a network of lymph nodes and lymphatic vessels that are used to process and circulate disease organisms and foreign substances so that they may be presented to and destroyed by the immune system. Lymphocytes, which are a type of white...

Hormones are chemical messengers that influence the activity of cells and tissues all round the body. The first hormones to be identified were those produced by discrete, visible glands, such as the thyroid and the pituitary. Later, scientists discovered other messengers, including the brain biochemicals...