oThe pressure drops 55mmHg in the arterioles.oArterioles = Resistance VesselsoPressure of blood which leaves the arterioles to enter the capillaries is about40mmHg.-The pressure drops ~20mmHg in the capillary.oPressure of blood which leaves the capillaries to enter the venules is ~10-15mmHg.oCapillaries = Exchange vessels-A small but significant amount of resistance occurs in the venous side of circulationsuch that by the time blood reaches the right atrium the pressure is almost 0.
<3 establishes high pressure just before the vessel Want high pressure in distribution vessels to distribute blood throughout the body. ∴Blood flowis affected by the pressure gradientbetween two points and resistance in the circulatory system. Describe the relationship between blood flow, pressure and resistance. Write out the equation showing this relationship. The pressure gradient in the circulatory system drives blood through vessels. -Blood flows from high pressure (P1) to low pressure (P2) down a pressure gradient. o↑ Pressure gradient ↑Blood flow -Blood flow is decreased by resistance encountered by the blood o↑ Resistance ↓ Bloodflow Blood flow =Pressure gradientResistance=P1 − P2ResistanceBlood flow =Pressure gradientResistance=P1 − P21?4= (P1 − P2) × r4-To change blood flow, it is easier to change radius of blood vessel than to change the pressure gradient. If you want to change blood flow, change radius of a blood vessel. -A small change in radius will have a large effect on blood flow! What factors determine the resistance to flow in a tube (or blood vessel)? Which of these is the most important contributing factor to resistance in the circulatory system and why? Resistance =Lŋr4Where: -L = length of the vessel o↑Length vessel ↑ResistanceoThe length of your vessels doesn’t change from minute to minute-ŋ = viscosity of the fluido↑Thicker fluid ↑ResistanceoThe viscosity of your blood doesn’t change from minute to minute-r = radius of the vessel o↑Radius ↓Resistance
Simplified: 𝑅𝑒?𝑖??𝑎𝑛𝑐𝑒 =1?4Describe what would happen to blood pressure, resistance and blood flow at a constriction in a blood vessel. How would blood pressure be different before/above and after/below the site of the constriction? -Pressure before constriction (↓radius) increases. Pressure after constriction (arterioles) decreases. -↑ Pressure gradientP1 –P2 -Even though the pressure gradient has increased, the constriction ↓r causes a decrease in blood flow because the smaller radius has a larger effect on blood flow (r4). Blood Vessels -The special structural properties contribute to the characteristics seen throughout the circulation. -Components in each vessel include: oElastic tissue oSmooth muscle oFibrous connective tissue Mean Blood Velocity and Total Cross Sectional Area -Vena cava (3.0cm) has a larger lumen diameter than aorta (2.5cm) -Capillaries has largest total cross-sectional area and slowest mean velocity.