Overview of Circulation Flashcards
(45 cards)
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
