Final answer:
Low blood viscosity leads to decreased resistance in blood vessels (option 1), increasing blood flow. Blood viscosity directly impacts resistance, with greater thickness causing more resistance. Vessel traits, such as length and diameter, as well as conditions affecting red blood cells and plasma proteins, also play a role.
Step-by-step explanation:
The question asks about factors that would cause decreased resistance in blood vessels, leading to an increase in blood flow. Low blood viscosity is one condition that will cause decreased resistance. Blood viscosity is the thickness of the blood and has a direct relationship with resistance: the higher the viscosity, the greater the resistance, and the lower the flow, which applies conversely for low blood viscosity.
Vessel length and diameter also affect resistance to blood flow. Resistance is directly proportional to vessel length and dramatically inversely proportional to the vessel's diameter, especially as resistance is a function of the radius raised to the fourth power.
Conditions like anemia, which reduce red blood cell concentration, or liver diseases that cause lower plasma protein levels, can lead to reduced blood viscosity and, therefore, reduced resistance to blood flow.