Final answer:
Resistance to blood flow is determined by vessel diameter, vessel length, and blood viscosity. Factors like venous valves, muscle contractions, and breathing-related pressure changes affect venous blood flow.
Step-by-step explanation:
Resistance affects blood flow by impeding the movement of blood through the vessels, which can influence the overall blood pressure.
The three major sources of resistance to blood flow include vessel diameter, vessel length, and blood viscosity.
Vessel diameter plays a crucial role as the constriction or dilation of blood vessels alters resistance levels and changes blood flow accordingly.
Vessel length impacts resistance since longer vessels present more surface area, causing higher resistance.
Lastly, blood viscosity, which relates to the thickness and stickiness of blood, can increase resistance; thicker blood requires more force to move through vessels.
Several factors affecting blood flow in the venous system include venous valves that prevent backflow, muscle contractions that help pump blood back to the heart, and the pressure changes during breathing that facilitate venous return.
Blood flow through the body starts from the heart and moves through a network of vessels, and is regulated by blood pressure, which adjusts in response to changes in cardiac output and blood volume. The balance between these factors influences blood flow.