Circulatory system of the horse capacity of the muscular system far exceeds the capacity of the cardiovascular system to deliver oxygen. Blood is made up of red blood cells (erythrocytes) and white blood cells (leukocytes), as well as plasma. Produced in bone marrow, red blood cells are responsible for carrying oxygen to tissue and removing carbon dioxide, all via hemoglobin. White blood cells are used for defense against pathogens in the immune system. Plasma suspends the blood cells, contains clotting factors, and contributes to the greatest volume of blood. The heart and blood vessels contain approximately of blood in a horse, which equates to about
Milky spots Milky spots Milky spots are very small white-coloured areas of lymphoid tissue, found in the peritoneal, pleural and pericardial cavities. These are the three coelomic cavities that form as separate compartments from the intraembryonic coelom. More milky spots are found on the greater omentum in the peritoneal cavity than anywhere else. The milky spots are made up of mesenchymal cells and are covered in a layer of mesothelium. These structures surround the small blood vessels. The enclosing mesothelium contains macrophages, lymphocytes and mast cells. They are also known as secondary lymphoid organs. Most milky spots contain extremely thin-walled lymphatic capillaries.