Intro to CVS (#1) Flashcards
What is function of SVC?
Takes blood from head, neck and arms into R atrium
What is P in vena cavae?
~ 3-8mmHg (near atmospheric)
What is blood velocity and its function?
~ 25cm/sec gives blood momentum helping its entry into R atrium + vent
What is blood made up of and not abundant cells ?
- 55% plasma
- 45% cells (RBCs most abundant)
What type of sol is blood and ions it contains?
Saline with Na+ + Cl- as most abundant cation + anion
What is osm + amount of albumin in blood?
~ 290mosmol/l
~ 70g/l
What is pO2, oxyHb sat and O2 content of blood?
~ 40mmHg
~ 75%
~ 150ml/l
What is pCO2 + CO2 content?
~ 46mmHg
~ 520ml/l
How is CO2 transported in blood?
- HCO3-
- bound to proteins
Why is there higher pCO2 than pO2?
when blood goes through cap, it picks up CO2 + drops off O2
Which gases have less O2 - venous/arteriole?
venous
Describe process of heart contraction (atrial contraction)
- wave of dep/AP/contraction arises in SAN in R atrium
- Dep spreads into atria (R then L)
- Atrial contraction of myocytes + blood injected into vent
- Dep cond through AVN slowly to allow delay between atrial + vent contraction (both systole) so atria contract before vent
- Atria rep
- Atrial relaxation - can accept blood
What is cardiac contraction triggered by?
coord dep of myocytes
What is special about SAN AP?
- never stable - mem begins to dep as soon as AP finished + get AP once reaches threshold
- spontaneously recurring as mem pot between each AP not stable + continually dep
Describe SAN AP
- Pacemaker currents e.g. funny current
- VG L-type channels activated when dep reaches certain threshold + Ca2+ entry
- K+ channels open + K+ loss (rep)
- Phase 4 dep - rate of AP dep - controlled by ANS
Decsribe AP of other areas e.g. vent
- Rapid dep due to high conductance Na+ channels (phase 4 dep) - fast Na+ entry
- Ca2+ entry triggers contraction
- K+ loss (rep)
What is vent contraction triggered by?
- triggered by Ca2+ (tension dev)
What is special about vent AP?
- stable RMP as v.few ions moving mem (no phase 4 dep)
- longer AP (300ms)
Describe cardiac cond pathways of SAN
- stim initiated in SAN located at junction of SVC + R
atrium - diffuse cond through myocytes in atria (faster near origin of SAN so blood milked from top of atrium to bottom (1m/sec)
How does wave of dep move through heart?
- excitation can only pass through AVN
- atria rep as vent begin to dep emphasising the gap
List 7 stages of cardiac cycle
- Atrial systole
- Isovol vent systole
- Rapid vent ejection
- Red vent contraction
- Isovol vent relaxation
- Rapid vent filling
- Red vent filling
Describe Phase 1 of cardiac cycle
- Atria contract - inc blood flow into vent by 10% - gives extra kick of blood via tricuspid + mitral valves.
- Vent relaxed and therefore accept blood easily, allowing them to ~120ml = EDV
What is EDV?
Vol at end of being filled (determine strength of heart contraction)
What is sig of there being no valve between VC + RA?
- nothing stopping blood going into R atrium from veins
- blood continually pouring into R atrium depending on P gradient
Describe Phase 2 of cardiac cycle
- Vent begin to contract.
- As P within them inc, T + M valves close preventing back-flux of blood into atria.
- P in vent builds up rapidly as blood has nowhere to go (so vol doesn’t change as a result).
- (Outflow valves - aortic (L) + pul (R) valves still closed due to P in aortic + pul veins keep them shut so blood can’t go forwards either
What is ejection fraction?
= diff between EDV + ESV
- 60% of blood in both vent ejected, 40% remains and topped up during next diastole
What happens in ejection fraction below 40%?
- sign of heart failure as its not pumping enough blood
Describe process of heart contraction (vent contraction)
- Dep enters vent + is rapidly dis throughout them through cond through Bundle of His to Purkinje fibres
- Vent contraction
- Vent rep
- Vent relaxation - so can be filled during diastole
Describe cardiac cond pathways Purkinjie fibres, AVN + endo + epicardium
- Dispersion via Bundle of His, L + R bundle branches + Purkinje fibres to vent mass (4m/sec)
- Cond via AVN (0.05m/sec) - slow - delay to allow atria to help fill vent with blood
- Finally from endocardium to epicardium (0.3m/sec)
Describe Phase 3 of cardiac cycle
- When P in vent exceeds that in pul artery + aorta, pul + aortic valves open.
- Vent begin to eject blood rapidly due to build up of P into lungs from R side + into aorta from L side
Describe Phase 4 of cardiac cycle
- As action pot ends, contraction becomes less forceful and ejection slows.
- P peaks in aorta ~ 120 (LV) + 20 (RV) mmHg in pul artery.
- Ejection stops when pul + aortic valves close as P in pul artery + aorta exceeds that in RV + LV.
What is ESV?
vol at end of ejection (50ml)
What is cardiac output?
- amount of blood heart pumping out in a min
- ~5 l/min at HR of ~70bpm
- ranges dep on age, size etc
Describe what happens in Phase 5 of cardiac cycle
- isovol vent relaxation
- vent relax rapidly as P dec within them
Describe what happens in Phase 6 of cardiac cycle
- rapid vent filling
- as P in vent falls below P in atria, T + M valves open
- vent begin to suck blood from venae cavae + pul veins via relaxed atria
Describe what happens in Phase 7 of cardiac cycle
- red vent filling
- as vent relax completely, refilling progressively slows
Where is most Ca2+ found?
T-tubules
Briefly describe Ca2+ induced-Ca2+ release?
- v. narrow space between SR + T-tubules gets large + rapid inc in Ca2+
- opens Ca2+ channels on SR
- Ca2+ released causes inc Ca2+ in cardiac cells
What happens after CICR and how is Ca2+ cleared?
- Ca2+ binds to troponin - form cross-bridge cycling
- Ca2+ channels close
- Ca2+ pumped through Na+/Ca2+ exchanger out of cell + ATP pumps on mem
- clears Ca2+ from cells + goes back to resting level
How much blood do vent eject?
~ 70ml
