1. Hydrostatic pressure is refers to the pressure exerted by any fluids in a confined space. It is the pressure of fluid on the capillary walls either by the blood plasma or interstitial fluid .It is very important for the arteries to be elastic because arteries carries blood from the heart to all the parts of the body in high pressure and the elastic property of the arteries helps in maintaining a relatively constant pressure gradient which allows normal flow of blood. 2.The entry of calcium through the ion channels helps in activating the ryanodine receptors which helps in releasing enough calcium from the sarcoplasmic reticulum to initiate a heart muscle contractions . 3.If the atria do not contract , ventricles are still filling with blood . The heart is still capable of pumping blood regardless of atrial contractions. It is very important for the atrial contraction of blood because the heart rate is maintained by atrial contractions.