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Elastic properties of blood vessels

As stated previously, the arteries and veins make a negligible contribution to the total resistance to blood flow, which is carried through the bloodstream. Therefore, we usually do not attach much importance to the impact that a change in their diameter on blood flow through the systemic organs. At the same time, the elastic properties of the arteries and veins are a very important factor influencing the activity of the cardiovascular system, as these vessels can function as reservoirs, and they may have accumulated substantial amounts of blood.

Elastic properties of blood vessels or vascular system of departments are often characterized by such a quantity as elongation (C), which reflects how changes their volume (L V) in response to a specific change in transmural pressure (AP)

Transmural pressure represents the difference between the internal and external pressures on the vascular wall.

Elastic properties of veins are important for their function Escrow blood. As can be seen from the curves of pressure versus volume in Fig. 7-7, the veins more extensible than the artery. Since veins extensible so that even small changes in the peripheral venous pressure can cause significant movement of the circulating blood volume in a peripheral vein or a pool thereof. The transition to the vertical - the nose position of the body, for example, increases the venous pressure in the lower extremities, and contributes to the accumulation of blood (pooling) in these vessels, which corresponds to the movement from point A to point B in Fig. 7-7.

Fortunately, this process can be balanced by an active constriction of the veins. The dotted line in Fig. 7-7 reflects the relationship between venous pressure and volume, which is marked by narrowing of veins as a result of contraction of the smooth muscle of the veins. In the narrowed veins blood volume can match the rate (point C), or even be lower than normal (point D), despite the higher than venous pressure. Constriction of peripheral veins can in itself increase the peripheral venous pressure and move blood from the venous reservoir.

The elastic properties of the arteries allow them to function as a reservoir between heartbeats. Artery play an important role in the transformation of a pulsating flow of blood ejected from the heart, in a steady stream through the vascular system organ. From this viewpoint, the artery is performed as a buffer. In the early phase of rapid expulsion of the volume of arterial blood increases as the blood flows into the aorta 1 faster than it passes into the lumen of systemic arterioles. Thus, some of the work that the heart performs with the release of blood out of the tensile elastic walls of the arteries. Toward the end of systole and diastole during, arterial volume decreases because the blood flow exiting from artery exceeds the bloodstream flowing into the aorta. Located in a stretched state arterial wall is reduced and thus loses the stored potential energy. This energy is converted from one form to another, and provides work to promote blood through the peripheral vascular bed during diastole. If the artery is a rigid tube, are not able to accumulate energy by elastic stretching, blood pressure immediately dropped to zero at the end of each process in cardiac output.



Mechanicle in lung

When discussing the elastic properties of the lung, there are three basic components that are involved with respiration. These include elastic recoil, stiffness, and lung distensibility. Distensibility is the term applied to the ease with which the lungs can be stretched or inflated. Stiffness is defined as resistance to stretch or to inflation. Elastic recoil is defined as the ability of a stretched or inflated lung to return to its resting volume (FRC). Elastic recoil of the lung is directly related to lung stiffness, that is, the stiffer the lung, the greater the elastic recoil. An analogy of this relationship is a coiled spring—the more difficult it is to stretch the spring (greater stiffness), the greater the ability to snap back (greater elastic recoil); similarly, a lung that is stiff is more difficult to stretch (inflate), but the inflated lung has a greater ability to recoil back.


Date: 2016-01-03; view: 909


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