Flow of blood along the vessels
Blood pressure is the pressure of blood on vessel walls; it is highest in the aorta, falls with distance from the heart and is lowest in the venae cavae. This pressure difference makes blood flow. In a healthy adult at rest it is around 120/80 mmHg (the higher number when the heart contracts, the lower when it relaxes); it is measured with a tonometer, and a doctor interprets it. The pulse is the rhythmic vibration of an artery wall when the ventricle contracts; it can be felt and counted with a finger at the wrist or neck, each pulse matching one heartbeat. Blood moves fast in the aorta (about 40 cm/s) and slowest in capillaries (about 0.1 cm/s), which gives time for exchange. In veins blood returns to the heart by contraction of skeletal muscles, valves and the heart’s suction. The lymphatic system collects tissue fluid through lymph capillaries and returns it via lymph nodes (filters, where lymphocytes are made) to large veins. The spleen is a blood reservoir that removes old cells and takes part in immunity.
Find your pulse in the wrist artery (near the thumb) with two fingers, count for 15 seconds and multiply by 4. Use two fingers, not the thumb; do not press hard.