The Law of LaPlace states that the tension or stress within a vessel wall is directly proportional to the amount of pressure within the vessel and the radius of the vessel. Therefore, when the heart is stretched due to increased blood volume, the tension within the heart wall increases, which in turn increases the force of contraction and stroke volume.
Resistance to fluid flow is affected by factors such as the diameter of the vessel, viscosity of the fluid, and length of the vessel. Resistance is the opposition to flow, while compliance is the ability of a vessel to expand or contract in response to changes in pressure.
An enlarged section of a blood vessel has a greater radius and therefore more tension within the vessel wall. This increased tension can cause weakness and ultimately rupture, whereas a narrow section has less tension and is less likely to burst.
Stretching of the heart does not increase heart rate. However, it can increase contractility and stroke volume, which may initially lead to an increased heart rate as the body compensates for the new flow demands.
The Law of LaPlace explains
O why stretching of the heart increase the stroke volume
• the different factors that add to resistance of fluid flow
• the difference between resistance and compliance in small arterioles
• why an enlarged section of a blood vessel is more likely to burst than a narrow section of the same vessel
• why stretching of the heart increases heart rate
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