MICROANATOMY

Detailed explanation-1: -The three most important factors affecting resistance are blood viscosity, vessel length and vessel diameter and are each considered below.

Detailed explanation-2: -There are three primary factors that determine the resistance to blood flow within a single vessel: vessel diameter (or radius), vessel length, and viscosity of the blood. Of these three factors, the most important quantitatively and physiologically is vessel diameter.

Detailed explanation-3: -Four major factors interact to affect blood pressure: cardiac output, blood volume, peripheral resistance, and viscosity. When these factors increase, blood pressure also increases. Arterial blood pressure is maintained within normal ranges by changes in cardiac output and peripheral resistance.

Detailed explanation-4: -Although SVR is primarily determined by changes in blood vessel diameters, changes in blood viscosity also affect SVR. SVR can be calculated if cardiac output (CO), mean arterial pressure (MAP), and central venous pressure (CVP) are known.

Detailed explanation-5: -The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood.