21.3 Hemodynamics: Factors Affecting Blood Flow

Question 1

hemodynamics

Answer 1

-the forces involved in circulating blood throughout the body

Question 2

blood flow

Answer 2

• the volume of blood which moves through any tissue in a given period (measured in mL/min)
• blood moves from areas of high pressure to areas of low pressure
• large pressure differentials and low resistance both increase this

Question 3

blood pressure

Answer 3

• the hydrostatic pressure exerted by blood on the walls of a blood vessel
• determined by cardiac output, blood volume, and vascular resistance
• highest (~110mmg) during systole in the aorta and lowest (~0mmg) just before entering the right ventricle

Question 4

systolic blood pressure

Answer 4

-the highest arterial pressure during systole

Question 5

diastolic blood pressure

Answer 5

-the lowest arterial pressure during diastole

Question 6

mean arterial pressure

Answer 6

• the average blood pressure in arteries
• typically 1/3 of the way between diastolic and systolic pressure ie. MAP=DBP + (1/3 * (SBP - DBP))
• typically around 83mmHg

Question 7

vascular resistance

Answer 7

• the opposition of blood flow due to friction between blood and the walls of blood vessels
• depends on the size of the lumen, blood viscosity, and total blood vessel length

Question 8

size of the lumen

Answer 8

• one of the three factors contributing to vascular resistance
• changed via vasoconstriction and vasodilation, resistance is proportional to 1/d^4 meaning cutting this in half leads to a 16x increase in resistance

Question 9

blood viscosity

Answer 9

• one of the three factors contributing to vascular resistance
• the thickness of blood, mostly dependant on the ratio of RBCs to plasma
• the higher this is, the higher the resistance

Question 10

total blood vessel length

Answer 10

• one of the three factors contributing to vascular resistance
• the main reason why obese people have hypertension: the increase in vascularization of the adipose tissue increases this factor, leading to higher resistance and higher BP

Question 11

systemic vascular resistance (SVR)

Answer 11

• also known as total peripheral resistance (TPR)
• the total resistance of all systemic blood vessels
• capillaries, arterioles, and venules are the largest contributors as they are tiny leading to high resistance
• major function of arterioles is to control TPR as a small change in there diameters leads to a large change in resistance

Question 12

venous return

Answer 12

• the volume of blood flowing back to the heart through the systemic veins
• caused by the pressure difference from venules (16mmHg) to the right ventricle (0mmHg)
• decreased if pressure increases in the right ventricle, such as due to a leaky tricuspid valve

Question 13

skeletal muscle pump

Answer 13

• one of two mechanisms which pump blood from the lower body back up to the heart
• caused by alternating contracting and relaxing of the lower limbs pushing blood up and past valves when contracted and allowing the valves to close when relaxed, preventing backflow

Question 14

respiratory pump

Answer 14

• one of two mechanism which pump blood against gravity from the lower body back to the heart
• caused by inhaling (which increases thoracic pressure, pushing blood past valves) and exhaling (reducing thoracic pressure, allowing valves to close, preventing backflow)

Question 15

velocity of blood flow

Answer 15

• the speed at which blood travels through a tissue at any given time (measured in cm/second)
• inversely related to the cross-sectional area, slowest in capillaries and venules, and highest in the aorta and venae cavae

Question 16

circulation time

Answer 16

• the amount of time required for a drop of blood to pass from the right atrium, through pulmonary circulation,through the left atrium, through systemic circulation down to the foot, and back to the right atrium
• typically 1 minute at rest