Lecture 29 - Cardiovascular System: Physiology of Blood Flow and Blood Pressure Flashcards
How will pressure gradient help with blood flow?
It will produce a force that moves fluid in the direction of lower pressure. Larger pressure gradient creates more force
What affects rate of blood flow?
Blood flow through a vessel is function of the opposing forces of pressure and resistance
How does resistance affect blood flow?
Resistance slows down the velocity/volume flow rate of blood caused by the friction between the walls of the tube and the fluid
T/F? Vessel resistance does not increase linearly with vessel length
False - it does increase linearly with vessel length. The longer the vessel, the more surface that’s in contact with blood, causing more friction
T/F? Vessel luminal diameter is inversely related to resistance
True - smaller diameter = larger resistance; more blood will be in contact with the smaller vessel wall
Does vessel diameter or vessel length have a larger impact on resistance?
Vessel diameter - change in diameter of a vessel will always produce a larger change in resistance than an equivalent change in length
What is viscosity?
A measure of resistance due to interactions among the molecules in the moving fluid
The more the molecules and materials suspended in the fluid interact with each other, the more viscous it is, causing internal friction -> slows down overall flow
How does turbulent (non-laminar) flow affect resistance?
It increases resistance
Laminar flow is when liquid is moving unidirectionally in smooth layers. In turbulent, these layers are disrupted and movement is not unidirectional, decreasing overall flow
How does turbulent flow occur?
Occurs due to shifts or changes in the geometry of the vessel wall:
- branch points
- tight curves
- irregular surfaces
Describe arterial pressure
It fluctuates with the changes in pressure due to the cardiac cycle - it is the highest during and just after ventricular systole, and lowest during diastole
How is blood pressure reported?
Systolic pressure/diastolic pressure
What is pulse pressure?
Difference between systolic pressure and diastolic pressure
What is mean arterial pressure (MAP)
Diastolic pressure plus 1/3 pulse pressure
How is blood pressure measured?
Measured through a cuff (sphygmomanometer) that tracks how much external pressure it takes to block blood flow
What do elastic arteries do?
They help buffer pulse pressure, reducing the variability in blood flow and pressures in capillaries
Arteries with larger amounts of elastic tissue stretch when blood is forced into them with high pressure, temporarily reducing blood flow rate
Why does average blood pressure decline as it passes through the systemic circuit?
Pressure reduces due to the resistance the blood flow encounters throughout the length of the vessel. The further the vessels are from the ventricle (source of the pressure gradient), the lower the average pressure within them
Where is the largest pressure drop-off?
Arterioles - this shows that these vessels provide the highest total resistance to volume flow
Where is the cross-sectional area of all blood vessels largest and smallest in?
Largest - capillaries; smallest - elastic arteries
Capillaries have tiny vessels and have relatively high resistance because of its small individual diameter - but its parallel arrangement makes the overall resistance more moderate
Where is the velocity of blood flow the highest? Lowest?
Highest - arteries; lowest - capillaries
4 factors that affect blood flow through circuits and cardiac output
- Cardiac output affects pressures
- Pressures affect blood flow
- Blood flow affects venous return
- Venous return affects cardiac output
How does gravity affect blood flow
It can oppose or enhance blood flow depending on the location of the heart
Ex. arteries supplying blood to the head must generate enough pressure to pusch blood directly against the force of gravity. Arteries supplying blood to regions below the heart get an assiset from the force of gravity
How do veins in limbs help prevent backflow of blood due to gravity?
Valves
T/F? Skeletal muscle contractions work with valves to provide a secondary pump that helps propel blood toward the trunk
True - muscles contracting around the vein compress the vein, providing extra pressure which helps squeeze blood upward towards the heart, countering the force of gravity
