18 6-10 Flashcards
Trace the pathway of blood through the heart and vasculature. Start with the L ventricle.
LV -- Aortic semilunar valve -- Aorta -- (systemic circ) -- Sup/inf vena cavae + Coronary sinus -- RA -- Tricuspid valve -- RV -- Pulmonary semilunar valve -- Pulmonary trunk -- Lungs -- Pulmonary veins -- LA -- Bicuspid/mitral valve
Left coronary artery
Runs towards the L side of the heart then branches into the:
anterior interventricular artery
circumflex artery.
Anterior interventricular artery
AKA left anterior decending artery - follows the anterior interventricular sulcus and supplies blood to the interventricular septum and anterior wall of both ventricles.
Known as the “widowmaker”
Circumflex artery
Supplies the left atrium and the posterior walls of the left ventricle.
Right coronary artery
Courses to the right side of the heart and gives rise to two branches:
Right marginal artery,
Posterior interventricular artery.
Right marginal artery
Serves the myocardium of the lateral right side of the heart
Posterior ventricular artery
Runs to heart apex and supplies the posterior ventricular walls. At apex, merges with the anterior interventricular artery.
R and L coronary arteries travel..?
Within the coronary sulcus and originate off the ascending aorta.
Adenosine?
A vasodilator. Can be released by the heart to open up coronary vessels.
What veins feed the coronary sinus?
Great cardiac, middle cardiac, small cardiac.
MI
Myocardial infarction, aka heart attack. Results from prolonged coronary blockage that leads to cell death.
Myocardial ischemia
Decrease in blood flow to the heart.
Angina pectoris
Thoracic pain caused by a fleeting deficiency in blood delivery to the myocardium.
AV valves
prevent backflow from the ventricles to atria. Relaxed heart = open
Semilunar valves
Prevent backflow into the ventricles from the arteries. Relaxed heart = closed
Skeletal vs. Cardiac
MECH OF CONTRACT Neurogenic Cardiac
INNERVATION SNS/Voluntary ANS/Involuntary
CALCIUM SR SR+ECF
HORMONE INFLUENCE — Yes-E/NE
SHAPE Long/cylindrical Short/branch
MITOCHONDRIA Few/2% of cell/Anaerobic+aerobic Many/25% of cell/aerobic
ATTACHMENT — Intercalated disc
NUCLEUS Multi-nucleated/Periphery
Uni-nucleated/centrally located
How are cardiac and skeletal muscle similar?
Use ATP, Actin/myosin, Sliding filament theory, sarcomeres, striated
How are cardiac and smooth muscle similar?
Both have gap junctions
What are the inercellular spaces of cardiac muscle filled with?
Loose connective tissue, endomysium.
It is connected to the fibrous cardiac skeleton which acts as a tendon and as an insertion giving cardiac cells something to pull or exert force against.
Intercalated discs
Junctions that link cells together both mechanically and electrically by: desmosomes (physical bond, prevents adjacent cells from separating during contraction) and gap junctions (electrical - transmits current across heart).
These connections allow cardiac cells to act as a functional syncytium.
Briefly describe the events of cardiac muscle cell contraction that are the same as skeletal muscle cell contraction.
- Depolarization, fast voltage gated Na+ channels open.
- Transmission of the depolarization wave down the T tubules (ultimately) causes the SR to release Ca2+ into the sarcoplasm.
- Excitation-contraction coupling occurs as Ca2+ (binding to troponin) signals for cross bridge activation and couples the depolarization wave to the sliding of the myofilaments.
Briefly describe the events of cardiac muscle cell contraction that are unique to cardiac muscle.
Cardiac muscle is unique in the way the SR is stimulated to release Ca2+.
Ca2+ is barred from entering nonstimulated cells, but when Na+ dependent membrane depolarization occurs the voltage change also opens slow Ca2+ channels that allow Ca2+ to enter (10-20%). Once inside, it triggers the Ca2+ sensitive channels in the SR to release the other 80% of the Ca2+ that is needed.
3 steps in the action potential of contractile cardiac muscle cells.
- Depolarization, fast voltage gated channels open.
- Plateau phase - Calcium influx through slow Ca2+ channels - cell remains depolarized even though Na+ channels are inactivated (few K+ channels are open yet).
- Repolarization - Ca2+ channels iactivate and K+ channels open.
What is the significance of the plateau phase?
When the sodium channels have inactivated, and repolarization has started, Ca2+ surges in.
This prolongs depolarization and the cells continue to contract.
What is the significance of the extended absolute refractory period?
Cardiac = 250ms, skeletal = 1-2ms. This prevents sustained tetany contraction in the heart which would stop the heart’s pumping action.
Tetany
Sustained contraction
Continuous tonic spasm of a muscle; steady contraction of a muscle without distinct twitching.
Ischemia
Reduced flood flow
Hypoxia
Decreased oxygen
Skeletal muscle are stimulated by a nerve ending, how are cardiac muscles stimulated?
Some cardiac cells are self excitable - they can initiate not only their own depolarization, but the rest of the heart as well. (in a spontaneous and rythmic way - automaticity or autorythmicity)
Skeletal muscle operates in motor units, how does cardiac muscle operate?
As an organ rather than motor unit. Either all the muscles in the heart contract, or none of them do. Happens because of gap junctions - depolarization wave travels from cell to cell.
functional syncytium
Behaving like a single coordinated unit - acting as a multi-nucleated mass - single functional unit.
Intrinsic conduction system
Heart’s internal NS
Nodal cells establish and maintain RMP and conduct APs.
Cardiac APs last for? Absolute refractory period for? Tension development?
Hundreds of ms, 250 ms, 200+ms
Skeletal is 1-2 ms, 1-2 ms, 15-100
