The cardiovascular system is an intricately woven network of structures that form a closed circuit for nutrient and oxygen delivery and waste removal for the entire human body. One of the most efficient and adaptable systems, a major function of the cardiovascular system is to respond instantaneously to the changing demands of the body. To carry out this task, the structures of the cardiovascular system must work seamlessly.
Closed-Loop System
Blood flow enters the heart at the upper right chamber, called the right atrium, via the inferior and superior vena cava, or the great veins. From there it travels through the valve that separates the right atrium from the lower right chamber, the right ventricle. During a heartbeat, contraction of the right ventricle will cause blood to be ejected into the pulmonary circulation. While in pulmonary circulation, the blood will be taken to the lungs to receive oxygen and will then travel back to the heart and re-enter at the left atrium. Traveling through the valve that separates the left atrium and the left ventricle, the blood will await the next ventricular contraction which will force it out of the left ventricle and into systemic circulation.
Cardiac Contraction
The driving force for cardiac contractions is an electrical impulse. As described in the text "Cardiovascular Physiology," the impulse originates in the right atrium initiating a contraction of both the right and left atria, and is passed to the ventricles allowing for ventricular contraction. It is essential for the impulse to follow this pathway in order for the most efficient contraction to occur. During ventricular contraction, the heart simultaneously twists, squeezes and shortens. Without this sequence, the amount of blood pumped during each contraction is lessened and the efficiency of the heart is diminished.
Blood Vessels
The blood vessels serve as conduits used to carry blood between the heart and the various organ systems of the body. The blood vessels assist the heart in regulating pressure throughout the closed circulatory system by constricting or enlarging as necessary to regulate the amount of blood flow traveling through each vessel. If a greater amount of blood needs to be delivered to a specific area of the body, the vessels leading to that area will enlarge in diameter, or dilate, and vessels leading to areas of less nutrient demand will constrict. This creates a shunt to provide more blood flow to working areas of the body.
Pressure System
In his book "Human Cardiovascular Control," Loring B. Rowell explains the delicately balanced pressure scheme that controls cardiovascular function. Within the closed circulatory system, blood flows from areas of high pressure to areas of low pressure. Because of this it is imperative that the left ventricle generate the greatest amount of pressure and the right atrium be held at the lowest pressure. In essence, this circuitry provides for the continuous flow of blood from the left ventricle, through the blood vessels of the body and returning the blood to the right atrium. Significant disruptions in the pressure differences between the right atrium and left ventricle will affect blood flow throughout the entire cardiovascular system.
Regulation
The cardiovascular system is regulated by chemical and pressure gauges located in the aorta and in the arteries leading to the brain. These gauges, or receptors, provide feedback regarding the blood pressure in the system and the amount of wastes such as carbon dioxide that have built up in the system. In response to the information received from these receptors, the heart and blood vessels can make minute adjustments and maintain the body in a relatively stable condition.
References
- "Cardiovascular Physiology"; David E. Morhman, Ph.D.; 2003
- "Human Cardiovascular Control"; Loring B. Rowell, Ph.D.; 1993
