From the Guidelines
Blood pressure gets lower due to the increased number of arterioles and capillaries as blood moves through the circulatory system from arteries to veins. When considering the impact of blood flow through the circulatory system on blood pressure, it's essential to understand the structural changes in blood vessels and their effects on pressure. As described by Segers et al. 1, the composition of the arterial wall changes from the central aorta towards the periphery, with a decrease in elastic lamellae and an increase in smooth muscle cells in smaller vessels like arterioles. This change affects the distensibility and stiffness of the vessels.
Key factors influencing blood pressure as blood moves from arteries to veins include:
- The increase in total cross-sectional area due to the branching of smaller vessels (arterioles and capillaries), which reduces the velocity and pressure of blood flow.
- The friction between blood and vessel walls, causing energy loss in the form of heat and further decreasing pressure.
- The structural changes in the arterial wall, such as the decrease in elastin and the increase in collagen, which affect the vessel's ability to distend and store elastic energy.
By the time blood reaches the veins, the pressure has dropped significantly, from about 120/80 mmHg in arteries to approximately 5-10 mmHg in veins, as a result of these factors 1. This pressure gradient is crucial for ensuring blood flows continuously from areas of high pressure (arteries) to areas of low pressure (veins), facilitating efficient circulation throughout the body. The decrease in blood pressure as blood moves through the circulatory system is a critical aspect of maintaining optimal blood flow and overall cardiovascular health.
From the Research
Blood Pressure Changes in the Circulatory System
- Blood pressure decreases as blood moves from arteries to veins due to the increased diameter and number of arterioles and capillaries, which increases the cross-sectional area and reduces resistance to blood flow 2.
- The structure and function of the vasculature, including large conduit arteries and the microcirculation, contribute to blood pressure elevation in hypertension 2.
- As blood flows through the circulatory system, the pressure decreases due to the increased diameter of the arterioles and capillaries, which reduces the velocity of blood flow and increases the cross-sectional area 3, 2.
Factors Affecting Blood Pressure
- The media/lumen ratio of small blood vessels is increased in hypertensive individuals, leading to a narrowed lumen and increased peripheral resistance 3.
- The renin-angiotensin-aldosterone and sympathetic nervous systems play a role in regulating blood pressure, and excessive activation of these systems can contribute to hypertension 2, 4.
- Lifestyle factors, such as diet and physical activity, can also affect blood pressure, with a healthy lifestyle helping to lower blood pressure and prevent hypertension 5, 6.
Blood Pressure Regulation
- The kidneys play a central role in the long-term regulation of blood pressure, and abnormal renal-pressure natriuresis is present in all forms of chronic hypertension 4.
- The integrated actions of multiple cardiovascular, renal, neural, endocrine, and local tissue control systems are involved in short-term and long-term blood pressure regulation 4.