Final answer:
Blood pressure starts at around 120 mm Hg when the heart contracts and pushes blood into the aorta but decreases as blood travels through arteries, arterioles, and veins, approaching almost 0 by the time it returns to the heart. Hydrostatic pressure, dictated by the cardiac cycle of systole and diastole, as well as gravity when standing, affects blood pressure throughout the circulatory system.
Step-by-step explanation:
Changes in Blood Pressure Through the Body
After blood leaves the heart, it travels at a high pressure, with systolic blood pressure typically around 120 mm Hg. This pressure diminishes as blood moves through the arterial system into increasingly narrower vessels, from the aorta to arterioles and capillaries. The speed of blood flow decreases drastically, which is one of the factors reducing the blood pressure. Eventually, as blood returns to the heart through the veins, the pressure approaches almost 0. Gravity also affects blood pressure, causing an increase in pressure in the feet for a person standing up, due to the weight of the static column of blood above.
The heart's systolic contraction leads to high hydrostatic pressure in the arteries near the heart, propelling blood into narrower arterioles and further reducing the rate of flow. The elasticity of the artery walls helps to accommodate changes in pressure during the cardiac cycle, which consists of systole and diastole. As blood flows throughout the body, it passes through the capillaries and into the venous system, where blood pressure continues to decrease due to the lower pressure conditions required to return the blood to the heart.