Lecture 2 – Circ Sys II – ECG and blood vessels Flashcards
(61 cards)
the cardiac cycle:
systole and diastole –> which is contraction/relaxation?
systole –> contraction
diastole –> relaxation
LO: flow of blood in cardiac cycle:
what happens when ventricles relax?
- pressure (drops/rises?) inside the ventricles
- ___ close as blood attempts to back up into the ventricles from the vessels
- AV valves (open/close)…why?
- blood flows from ___ to ventricles
pressure drops inside the ventricles
semilunar valves close
AV valves open –> (when ventricles relax, pressure inside ventricles is less than inside atria. AV valves open so that atria can pump blood into ventricles to even out the pressure differences)
blood flows from atria to ventricles
LO: flow of blood in cardiac cycle:
what happens when ventricles contract?
- AV valves (open/close?) as blood attempts to back up into atria
- pressure (drops/rises) inside of the ventricles
- semilunar valves (open/close?) and blood flows into great vessels
AV valves close
pressure rises inside of the ventricles
semilunar valves open and blood flows into great vessels
LO: coronary circulation –> describe the arteries that nourish the myocardium and the veins that draw it
why is coronary circulation necessary? what are the vessels that make up coronary circulation?
heart is a muscle and needs oxygen to sustain its workload. 5% of blood pumped by heart goes to the heart itself thru coronary circulation
right coronary artery
left coronary artery
coronary sinus
LO: describe the arteries that nourish the myocardium
what is angina pectoris?
chest pain from partial obstruction of coronary blood flow
LO: describe the arteries that nourish the myocardium
what is myocardial infarction (MI)?
sudden death of a patch of myocardium resulting from long-term obstruction of coronary circulation
LO: describe the unique structural and metabolic characteristics of cardiac muscle
cardiomyocytes (describe):
- striations?
- length?
- thickness?
- branching in cells?
- cell structure?
striated
short
thick
branched cells
one nucleus surrounded by light-staining mass of glycogen
LO: structure of cardiac muscle –> explain the nature and functional significance of the intercellular junctions b/n cardiac muscle cells
intercalated discs (describe)
join cardiomyocytes end to end w/ 3 features
(1) interdigitating folds – interlock and increase area of contact
(2) mechanical junctions – fascia adherent and desmosomes
(3) electrical junctions (gap junctions) – ions flow b/n cells; allow entire myocardium of either 2 atria or 2 ventricles to act like single, unified cell
LO: metabolism of cardiac muscle
cardiac muscle depends almost exclusively on ___ to make ATP
as such, cardiac muscle is rich in ___ and ___
cardiac muscle have (tiny/huge?) mitochondria that fill ~___% of cell
aerobic respiration
rich in myoglobin and glycogen
huge mitochondria –> fill 25% of cell
LO: metabolism of cardiac muscle
cardiac muscle metabolism is adaptable to different ___ ___, such as….
organic fuels
fatty acids (60%), glucose (35%), ketones, lactate, and amino acids (5%)
LO: metabolism of cardiac muscle
cardiac muscle is more vulnerable to ___ ___ than a lack fo a specific fuel
vulnerable to oxygen deficiency
LO: metabolism of cardiac muscle
is cardiac muscle easily fatigued?
no; does not fatigue for a lifetime
it mostly uses aerobic respiration and not anaerobic fermentation or oxygen debt mechanisms
LO: describe the heart’s pacemaker and electrical conduction system
what does the pacemaker and electrical conduction system do?
how much of the myocardium is made of this electrical conduction system?
coordinates heartbeat
~1% of the myocardium
LO: describe the heart’s pacemaker and electrical conduction system
what is the system composed of?
internal pacemaker (SA node) and nerve-like conduction pathways (made of modified cardiomyocytes) thru the myocardium
structures:
- Sino-atrial (SA) node
- atrioventricular (AV) node
- atrioventricular bundle
- interventricular septum
- right and left bundle branches
- Purkinje fibers
LO: describe the heart’s pacemaker and electrical conduction system
describe the steps:
(1) SA node fires
(2) excitation spread thru atrial myocardium
(3) AV node fires
(4) excitation spreads down AV bundle
(5) subendocardial conducting network distributes excitation thru ventricular myocardium
LO: explain why the SA node fires spontaneously and rhythmically:
cardiac rhythm:
what is the sinus rhythm?
what is ectopic focus?
normal heartbeat triggered by the SA node
a region of spontaneous firing other than the SA node
LO: explain why the SA node fires spontaneously and rhythmically:
describe pacemaker physiology
describe pacemaker potential:
SA node does not have a stable resting membrane potential
starts at -60 mV and drifts upward due to slow Na+ inflow
gradual depolarization is called pacemaker potential
LO: explain why the SA node fires spontaneously and rhythmically:
describe pacemaker physiology
describe pacemaker threshold and depolarization:
when SA node reaches threshold of -40 mV, voltage-gated fast Ca2+ and Na+ channels open
faster depolarization occurs, peaking at 0 mV
this generates an action potential –> allows SA node to fire –> sets of heartbeat (muscle contraction)
LO: explain why the SA node fires spontaneously and rhythmically:
describe pacemaker physiology
describe pacemaker repolarization:
depolarization peaks at 0 mV
K+ channels then open and K+ leaves cell –> causes repolarization
once K+ channels close, pacemaker potential starts over
LO: explain how the SA node excites the myocardium
SA node stimulates 2 atria to contract almost simultaneously
signal slows down thru AV node
signals travel very quickly thru AV bundle and subendocardial conducting network (Purkinje fibers)
ventricular systole (contraction) progresses up from apex
basically, signal goes down interventricular septum and then to outer walls of ventricles
LO: describe the unusual action potentials of cardiac muscle and relate them to the contractile behavior of the heart
electrical behavior of the myocardium:
depolarization:
(1) voltage-gated Na+ channels open
(2) Na+ inflow depolarizes the membrane and triggers the opening of still more Na+ channels, creating a positive feedback cycle and a rapidly rising membrane voltage
(3) Na+ channels close when the cell depolarizes, and the voltage peaks at nearly +30 mV
plateau:
(4) Ca2+ entering thru slow Ca2+ channels prolongs depolarization of membrane, creating a plateau. Plateau falls slightly because of some K+ leakage, but most K+ channels remain closed until end of plateau
repolarization:
(5) Ca2+ channels close and Ca2+ is transported out of cell. K+ channels open, and rapid K+ outflow returns membrane to its resting potential
the heartbeat is coordinated by the cardiac ___ system
conduction
in a healthy person at rest, the SA node normally fires about how many times per minute?
70-80
a spontaneously developing local potential that generates action potentials in the SA node is called what?
pacemaker potential
