exam 4- cardiovascular 2 Flashcards
in the heart, first AP generated on the ___, then has to be propagated to ___, then to ___ to get all those to contract
SA node
atria
ventricles
what are the 2 types of modified cardiac muscle cells in SA node and how do they function
round cells & elongated cells
- both cardiac muscle fibers that have lost their ability to contract, but retained ability to generate and conduct APs (no nerves running through heart, instead, these modified muscle cells that act like nerves and help spread AP from SA node to the two atria
in the SA node, ___ cells are the cells that actually generate the pacemaker potential
round cells
these cells come out of SA node and travel to right and left atrium
elongated cells
AP is propagated from SA node to the two atria by 2 mechanisms:
1- elongated cells: Bachmann’s bundle take the AP to the left atrium and right bundle cells take the AP to right atrium
2- once APs get to atria, the AP can jump directly from one cell to another cell (what allows this jumping is the intercalated disc- connection b/w 2 membranes of muscle cells by gap junctions- large transmembrane proteins that form a channel & connect cytoplasm of 2 adjacent cells –> ion current that occurs in one cell can go to next cell and depolarize it as well, without use of any neurotransmitter b/c none in heart)
- also, membranes at points of intercalated discs are very thin –> makes membrane very easy to depolarize to threshold
what are the 2 electrical adaptations that help move an AP from cell to cell in the heart?
presence of gap junctions & thinness of cell membranes
( also structural adaptation called desmosome- protein connection b/w 2 cells that hold them together –> when one cell contracts and other contracts, they don’t pull apart, stay together)
AP travels along atria at this speed
0.5 - 1 m/s
when AP reaches atria, causes them to contract and push blood into the ___…
ventricles
now AP has to move from atria to ventricles in order for ventricles to contract and push blood into circulation
when the AP first leaves the atria, what does it encounter?
the 2 AV valves (which are tough, fibrous, and do not conduct electricity) - so AP has to get from atria to ventricles by another way
describe the first mechanism of how AP gets from atria to ventricles
through another set of modified cardiac fibers called the AV node (lost ability to contract, but can generate and conduct APs) , AV node represents the major electrical connection b/w atria & ventricles
muscle fibers in AV node are long- they alternate thick and thin fibers (large & small diameters), AP has to travel along both muscle fibers (remember AP velocity directly proportional to diameter)
–> hits small diameter fibers and slows down (speed thru AV node is 0-0.5 m/s), this creates a little decay, 1/10 of a second (.09 sec) b/w AP passing across atria and ventricles, this delay allows atria enough time to fully contract & pump blood into ventricles before ventricles themselves are stimulated to contract
describe the second mechanism of how AP gets from atria to ventricles (after AV node)
from AV node, AP then distributed to ventricles by another set of modified cardiac fibers:
- large diameter group of fibers called Group of His –> branches into right and left bundles –> travels directly to the bottom/apex of the heart –> then AP doubles back and branches into the Perkinje fibers –> AP spreads out as they go back up the ventricles by way of the Purkinje fibers and b/c ventricular cells also have gap junctions b/w them (stimulated to contract from the apex back up to AV valves)
AP velocity is 4-5 m/s, allows to spread/contract very quickly
in what fashion do the ventricles contract?
in spiral fashion from bottom to top (contract in spiral, which squeezes ventricle from bottom to top, like ringing blood out of a sponge –> pushes blood out of ventricles through aorta or pulmonary artery)
a spiral contraction, then a spiral relaxation
the heart’s work is to pump blood, work of a pump = ___ x ___
work of pump = pressure x flow
(flow measured as volume/time, so,
work of pump = pressure x volume
describe changes in pressure and volume in left ventricle throughout diastole & systole
start in diastole (heart has contracted, now relaxed- left ventricle has its lowest volume of blood and low pressure), heart begins to expand, volume of ventricle increases and creates a little bit of negative pressure and suction, pulls blood in from superior and inferior vena cava, left ventricle fills mostly passively (when close to filling, slight increase in pressure due to atrial contraction, pushing in last bit of blood, topping off volume of ventricle) –> mitral valve then closes and ventricle begins to contract (pressure increases, but volume stays the same)- takes 80 mmHg before blood ejected out of ventricle (isovolumic contraction- increase pressure, same volume) –> when hit 80 mmHg, largest pressure, now start reducing volume –> starts to drop as ventricle is completely emptied –> heart relaxes and pressure and volume go back to their minimum
describe changes in pressure in volume in right ventricle as opposed to LV
right ventricle pumps roughly the same volume of blood, but it generates a lot less pressure (much thinner ventricular wall), can accomplish its work with less pressure- the loop for right ventricle is much smaller, RV does less work during a cycle of contraction & relaxation)
