In this sub-unit of human physiology we will explore contents of: Arteries convey blood at high pressure from the ventricles to the tissues of the body Arteries have muscle cells and elastic fibres in their walls The muscle and elastic fibres assist in maintaining blood pressure between pump cycles Blood flows through tissues in capillaries Capillaries have permeable walls that allow exchange of material between cells in the tissue and the blood in the capillary Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart Valves in veins and the heart ensure circulation of blood by preventing backflow