What does blood flow refer to?
the volume of blood moved
What is blood flow measured in?
What are the two factors that blood flow is dependent on?
blood pressure difference at each end of blood vesselresistance to blood flow
What is resistance?
the friction which impedes blood flow between two points
What are the factors that resistance is dependent on?
vessel lumen diameterblood viscositytotal vessel length
What are the two changes that blood flow change can be attributed to?
change in pressurechange in vessel diameter
If pressure stays the same but resistance increases, what happens to blood flow?
blood flow decreases
If pressure difference increases, what happens to blood flow?
blood flow increases
What are the neurovascular effects at blood vessels?
sympathetic nerves release norepinephrine - vasoconstrictionparasympathetic and sympathetic cholinergic nerves release acetylcholine - vasodilation
How does nitric oxide induce vasodilation?
nitric oxide is released from vascular endothelial cells which stimulates the formation of a 2nd messenger in the smooth muscle cell causing muscle relaxation
What are the physical factors that affect blood pressure?
arterial blood volume arterial compliance
What is compliance?
indicates elasticitythe ability to expand then contract passively
Why do blood vessels expand?
expands so that systolic pressure doesn't rapidly increase
What is the function of elastic arteries?
conductingblood from heart to small artery
How does an elastic artery act as a pressure reservoir?
during diastole elastic recoil generates pressure to propel blood distally
What is the function of muscular arteries?
distributingblood goes to organ and tissues
Why are arterioles called resistance vessels?
because they can vasoconstrict
Functions of arterioles
determine minute-to-minute blood flow into capillary bed lumen size has direct impact on blood pressure
What is systemic vascular resistance?
how we measure compliance
What is the major influence on systemic vascular resistance?
What is the function of precapillary sphincters?
guard entrance to each capillary open to allow blood through capillary for normal capillary functionclose with SNS stimulation which leads to blood being "shunted" to venous side using metarteriole
What happens to the flow of water in the capillary bed when hydrostatic pressure is high?
What happens to the flow of water in the capillary bed when osmotic pressure is high?
water comes back in
What happens to the total area of the vascular bed as blood vessels start branching?
What happens to blood flow as vessels branch and their lumens get narrower?
blood flow decreases
What is blood flow inversely proportional to?
cross-sectional area of blood vessels
What is hydrostatic pressure?
the force exerted by the fluid pressing against a wall
What is osmotic pressure?
force created by large nondiffusible molecules, such as albumin
Does hydrostatic pressure change as blood moves along the length of the capillary bed?
hydrostatic pressure decreases along its length
Does osmotic pressure change as blood moves along the length of the capillary bed?
it does not change along the length of the vessel
Where does diapedesis occur?
Skeletal muscle pump
skeletal muscle contraction propels blood proximally one-way valves prevent backflow
At rest, what proportion of the body's blood do the veins contain?
veins contain almost 2/3 of the body's blood
What are the causes of increased venous pressure?
increased activity of sympathetic nerves to veinsincrease in skeletal muscle pumpincrease in blood volumeincreased inspiration movements
What is stroke volume?
volume (mL) of blood ejected per heart beat from the ventricle
What is stroke volume the difference of?
the difference between ventricular end-diastolic volume and end-systolic volume
What is end-diastolic volume?
how much blood is in the ventricle before the ventricle contracts max amount that can possibly leave the ventricle
What is end-systolic volume?
how much blood is in the ventricle at the end of systole
What is preload?
end-diastolic volume or venous return
How can you increase preload?
increase in blood volumeslower heart rate
How does an increase in preload affect stroke volume?
increase in preloadincrease in end-diastolic volumeincrease in stroke volume
What does an increase in venous pressure lead to?
increase in venous returnincrease in atrial pressureincrease in end-diastolic volumeincrease in stroke volume
What is afterload?
resistance that the heart must overcome to circulate blood
What happens if you increase afterload?
heart has to work harder thereby increasing cardiac workload which increases the oxygen requirement
How does an increase in afterload affect stroke volume?
increase in afterload leads to a increase in end-systolic volume leads to a decrease in stroke volume
What is an inotropic effect?
force that the muscle can create at a given length
How does preload affect inotropy?
increasing preload (increasing end-diastolic volume) increases muscle fiber lengthincreases magnitude of muscle shorteningincrease in inotropic effect
What is the Frank-Starling law?
states that the amount of blood ejected by the ventricle depends upon volume present in the ventricle at the end of diastole
What does stroke volume and cardiac output directly correlate with?
What does the Frank-Starling law say about the relationship of stroke volume and cardiac output to venous return?
stroke volume and cardiac output are directly proportion to venous return
Does contractility increase or decrease stroke volume?
increase stroke volume
What can lead to an increase and decrease in contractility?
increase: exercisedecrease: heart failure
What is the ejection fraction?
measurement of the percentage of blood that exits the ventricle during one ventricular systole
What is the normal range for ejection fraction?
at rest, a normal heart only pumps out around 60% of the blood with each heartbeat
How can ejection fraction be increased?
increased contractility may increase the ejection fraction but will also increase cardiac muscle workload
What effect does an increase in end-diastolic volume have on stroke volume and ejection fraction?
increases stroke volume without changing ejection fraction- PSNS has negative chronotropic effect which allows higher preload - increased preload results in increased muscle stretch which then causes a positive inotropic effect
What effect does an increased force of contraction have on stroke volume and ejection fraction?
increase in stroke volume by increasing ejection fraction
Extrinsic control of stroke volume via positive inotropic effect include
sympathetic stimulation to ventricular muscle fibershormonal control (thyroid hormone, epinephrine/norepinephrine)
What is cardiac output?
total amount of blood (L) pumped out of ventricle in one minute
Generally how do you increase cardiac output?
increase heart rate and/or stroke volume
What neurotransmitters produce neuromuscular effects in the heart?
sympathetic nerves: norepinephrineparasympathetic nerves (vagus nerve): acetylcholine
What are the different neuromuscular effects of the heart?
chronotropy: timing, heart rateinotropy: (+) effect = more forceful contraction dromotropy: speed of conduction going through AV node lusitropy: rate of myocardial relaxation (speed of decrease of cytosolic calcium)
To speed up the heart rate (positive chronotropic effect):
deliver sympathetic hormone (epinephrine)release more sympathetic neurotransmitter (norepinephrine) reduce release of parasympathetic neurotransmitter (acetylcholine)
Negative chronotropic effect can be seen with:
increasing ageincreasing fitness level
How does heart rate affect preload?
a fast heart rate will leave no time for preloading
What is pulse pressure?
the difference between systolic blood pressure and diastolic blood pressure
What are the factors determining pulse pressure?
stroke volume- increase stroke volume will increase systolic blood pressurearterial compliance- a decrease of compliance occurs with atherosclerosis which can lead to increased systolic blood pressure
What is mean arterial blood pressure?
average driving pressure of blood throughout cardiac cyclebest indicator of tissue perfusion
How much time does the heart spend in diastole?
twice as long in diastole
How does short-term blood pressure regulation work?
every few secondsstretch-sensitive mechanoreceptors located in walls of specific arteriesmonitor pressure of blood flow to brain and body action potential fired continuously at normal blood pressure- rise in pressure stretches baroreceptor which leads to increased signals sent via ANS to CNS - low pressure decreases signals to CNS
in wall of arteryaortic archcarotid sinus (most proximal portion of carotid artery)all these baroreceptors send signals to medulla oblongata
What nerves are involved in baroreceptor messaging?
CN IX glossopharyngeal nerve- from carotid sinus receptorsCN X vagus nerve- from aortic arch receptors
What affects the stretch of baroreceptors?
mean arterial pressure