Peripheral Circulation Flashcards
Explainthemeaningofeachofthefollowing a) hydrostatic pressure
b) Korotkoff sounds c) cardiacoutput
d) compliance
a) the force of the blood against the walls of the blood vessels
b) The sounds, heard with a stethoscope, of blood flowing through a partially compressed artery
c) the volume of blood pumped by one side of the heart in one minute
d) the ability of a vessel to enlarge to accomodate a larger volume of fluid
Describe how blood pressure varies in different parts of the circulatory system by sketching a graph with pressure on the Y axis and distance from the heart on the X axis. Label the vessels that the blood passes through and include some representative values for pressure (5 marks).
see notes
Complete the following relationship ______ = (P1 – P2/R)
and explain what P1, P2 and R refer to (2marks).
flow
P1 and P2 are the hydrostatic pressures at two places along a vessel; R is the resistance to flow
Explain what hematocrit is and list two ways it influences the cardiovascular system (2
marks).
hematocrit is the percentage of the blood that is made up of erythrocytes
increasing the hematocrit increases the amount of oxygen that can be carried by the blood and increases the resistance to flow
Describe the difference between laminar and turbulent flow, giving an example of
each, and their relevance to cardiovascular function (2 marks).
laminar flow - the molecules of the fluid move in parallel to each other and the walls of the vessel (an example is movement of the blood through a straight, unbranched vessel); turbulent flow - the molecules of the fluid move at angles to the walls of the chamber and collide with each other and the walls of the chamber (an example is the movement of blood through a partially blocked vessel).
Name and describe the three main factors that affect cardiovascular resistance and
list them in order of importance (3 marks).
resistance increases as the radius of the vessel decreases; resistance increases as viscosity and length of the vessel increases
Explain the principles underlying taking a blood pressure using a sphygmomanometer
(3 marks).
- a blood pressure cuff around the arm is inflated to the point where the flow of blood through the artery of the arm stops completely
- the pressure in the cuff is reduced gradually while a stethoscope is applied to the artery distal to the cuff
- the appearance of beating sounds signals the systolic pressure
the disappearance of sounds signals the diastolic pressure
Explain what pulse pressure is.
= the difference between systolic pressure and diastolic pressure
Describe how compliance changes with age and list three effects this has on cardiovascular function (4 marks).
compliance decreases with age
1) this lowers the diastolic pressure
2) the systolic pressure increases to compensate
3) the mean arterial pressure increases
4) the workload of the heart increases
Describe capillary exchange; the structures involved and the forces involved (4
marks).
- the blood that enters the capillary from the arteriole has a blood pressure of about 30 mm Hg; greater than the blood pressure of the blood that leaves the capillary at the venule end (about 15 mm Hg)
- the osmotic pressure remains constant along the capillary and acts in the opposite direction to blood pressure
- at the arteriole end, the blood pressure is greater than osmotic pressure and fluid moves out of the blood
- at the venule end, the blood pressure is less than the osmotic pressure and fluid moves into the capillary
- excess fluid in the interstitial space is drained by lymphatic vessels
- water and solutes move because of differences between blood pressure and osmotic pressure (bulk flow) but they can also move in and out of the blood by diffusion
Explain what edema is and describe four processes that can cause it (5 marks).
-look up
- edema is the accumulation of excess fluid in the interstitial space
1. increased permeability of capillaries (due to chemical mediator of inflammation like histamine & bradykinin) - protein leaks into interstitial fluid
- colloid osmotic pressure inc. in ISF resulting in reduced return of fluid to capillary
2. decreased plasma protein concentration (due to albumin synthesis in liver) - reduces BCOP
3. blockage of veins - increases resistance and CHP at venous end of capillary
4. blockage or removal of lymphatic vessel (blockage: elephantiasis; removal: cancer)
List three possible effects of vasoconstriction
increased peripheral resistance
- increased flow to downstream tissues
- increased blood pressure
Explain how decreased urinary output could influence cardiovascular function.
-it will lead to decreased blood volume which will result in decreased blood pressure
List three ways in which blood flow to tissues is regulated (3 marks).
1) compounds released from cells cause vasodilation or vasoconstriction of vessels supplying those cells
2) sympathetic nerves control smooth muscles of blood vessels
3) hormones cause vasoconstriction or vasodilation of blood vessels that have receptors.
Explain the mechanism for local control of blood flow (hyperemia).
CO2 and H+ are produced as a result of glycolysis and the citric acid cycle, causing vasodilation and increased blood flow to metabolically active tissues
- other substances released by metabolically active cells also contribute to vasodilation
