Overview of Circulation Flashcards
What is the main function of the CV system?
transport and distribute essential substances to the tissues and remove metabolic by-products
What are the secondary functions of the CV system?
hemostatic mechanisms: body temp regulation, humoral communication throughout the body, O2 adjustments, nutrient supply
What are the two pumps in the CV system?
Two pumps in series
1. pulmonary circulation - right ventricle -> lungs for O2 and CO2 exchange
2. systemic circulation - left ventricle -> all other tissues
What is cardiac output?
total blood flow out of the left ventricle (flow rate)
How are action potentials generated?
by the sino-atrial node spontaneously generating action potentials
What does the automaticity of the heart mean?
does not need to be innervated to contract
What are the five phases of an action potential?
phase 0 - upstroke
phase 1 - early partial repolarization
phase 2 - plateau
phase 3 - final repolarization
phase 4 - resting potential
Explain phase 0 of an action potential
a suprathreshold stimulus rapidly depolarizes the membrane by activating the fast Na+ channels
Explain phase 1 of an action potential
achieved by the effect of k+ through channels that conduct the transient outward current
Explain phase 2 of an action potential
achieved by a balance between the influx of Ca2+ through Ca2+ channels and the efflux of K+ through several types of K+ channels
Explain phase 3 of an action potential
initiated when the efflux of K+ exceeds the influx of Ca2+, the resulting partial repolarization rapidly increases the K+ conductance and rapidly restores full repolarization
Explain phase 4 of an action potential
the transmembrane of the fully repolarized cell is determined mainly by the conductance of the cell membrane to K+
What facilitates how an action potential functions?
K+
When generates the voltage of an action potential?
ion exchange (K+ and Ca2+)
Infusion of what will stop the heart?
infusion of enough K+ (permanent phase 4)
needs to be flushed out to start again
What are the main differences between a fast and slow response cardiac fibre action potential?
Slow (SI node)
- no phase 1
- phase 0 is less steep
- less negative resting potential
- smaller amplitude (Ca2+ driven)
- RRP extends into phase 4, after fiber has fully repolarized
What is the ARP and RRP?
absolute refractory period - cannot start new repolarization
relative refractory period - may be able to start new depolarization
How is unidirectional flow achieved?
the arrangement of the heart valves
How is continuous flow through the periphery achieved when CO is intermittent?
by the distension of the aorta and its branches during ventricular contraction (systole) and elastic recoil of the walls of large arteries that propel the blood forward during ventricular relaxation (diastole)
What is systole and diastole?
systole - ventricular contraction
diastole - ventricular relaxation
What are the histological changes of the arterial branches toward to periphery?
become more narrow and walls become thinner
the aorta is more elastic, while arteries become more muscular until the muscle layer predominates at the arteries (controls the direction of flow and major source of peripheral resistance)
How do vessels change with age?
elastic tissue decreases and fibrous tissue increases
How do the small arteries and arterioles regulate flow to individual tissues?
by regulating the resistance to flow
small arteries moderate resistance to blood flow and arterioles offer maximal resistance (stopcocks)
Where is the pressure drop the greatest?
small arteries and arterioles
- adjustment in contraction permits regulation of tissue blood flow and aids in the control of arterial blood flow
How does flow change from the arterial to the venous end of the capillaries?
change from pulsatile (caused by the phasic ejection from the heart) to steady flow (a combination of distensibility of large arteries and frictional resistance in arterioles) as pressure declines
Why do capillaries have a very large total cross-sectional area?
creates ideal conditions for the diffusion
- slow velocity of blood flow, short tubes, only one cell thick
How do the vessels change as blood returns to the heart?
venuels -> veins increase in size and decrease in pressure until the vena cava
number of veins decreases toward the heart, TCSA decreases and blood flow velocity increases
What is the relationship between blood velocity and total cross-sectional area?
Inverse relationship
As velocity decreases towards the capillary TCSA increases
What is the pressure gradient?
the constant decrease in pressure throughout the system
drives O2 and blood forwards
Why does blood pressure not drop to zero during relaxation?
so there is no interruption in perfusion
How much does TCSA increase from the aorta to the capillaries?
500 fold
Where is blood volume the greatest in the systemic system?
veins/small veins (64%)
about 6% in capillaries and 14% in aorta, arteries, and arterioles
about equal between arteries and capillaries
Why is TCSA larger in the vena cava than in the aorta?
creates a slower velocity in the vena cava and facilitates low pressure (pressure gradient)
What is the pathway of blood?
enters the RV via the RA through the pulmonary arterial system at a mean pressure 1/7 that of systemic -> passes through lung capillaries for CO2 release and O2 uptake -> O2-rich blood returns via four pulmonary veins to LA and LV to complete the cycle
What is cardiac output controlled by?
heart rate
cardiac contractility
venous return (pre-load)
arterial contractility (afterload)
What is the distribution of circulating blood to organs determined by?
the output of the LV and contractile state of arterioles
What is total peripheral resistance?
total resistance of blood flow of the systemic blood vessels
What is total pulmonary resistance?
total resistance of blood flow of the pulmonary blood vessels
What is the equation for MAP?
MAP = TPR x CO
What does no change in MAP during exercise indicate?
a cardiac issue
CO is not increasing as it should
How do CO and TPR change during normal exercise?
TPR will decrease
CO will increase
How does blood contribute to homeostasis?
maitenance of constant internal environent
- carrying O2 and CO2 removal
- transport: hormones, WBC, platelets
- distribution: fluids, solutes, heat
What does the difference between Pa and Pra equal?
the driving force for flow through resistance of blood vessels of individual tissues
What is blood flow like in a steady state?
total blood flow leaving the heart = total blood flow returning to the heart
Pa - Pra = R x CO
Why is it important Pa is maintained relatively constant
allows individual tissues to obtain blood flow for function
critical to not endanger life -> blood flow to brain and heart cannot be interrupted
