Lecture 18- cardiovascular foundations I Flashcards
99% of the cardiac muscle cells are
force-producing
myocardial cells or myocytes
the force producing cells are which muscle fibers?
striated muscle fibers
what is the other 1% of cardiac muscle cells?
autorhythmic (pacemaker) cells
what do pacemaker cells do?
generate spontaneous, rhythmic APs
- the signal for myocyte contraction
do pacemaker cells contribute to the contractile force?
very few contractile fibers
no organized sarcomeres
Can both types of cells generate action potentials?
yes!!
myocytes and pacemaker cells can generate APs
Autorhythmic cells: 2 characteristics of AP and contraction
spontaneously generate APs
do not contribute significantly to the contractile force of the heart
Contractile cells (striated muscle cells): 2 characteristics of AP and contraction
generate APs when depolarized
source of contraction force of the heart muscle
Cardiac myocytes: shape and what do they contain?
irregularly shaped striated muscle fibers with sarcomeres
-contain actin and myosin
-cross-bridge cycling mirrors skeletal muslce cross-bridge cycling
Cardiac myocytes: how are they connected?
connected in series by intercalated disks which contain
- desmosomes: physical coupling, allows force to be transferred to neighbours
- gap junctions: electrical coupling
What are 5 differences between cardiac vs skeletal muscle fibers?
cardiac:
- smaller and have 1-2 nuclei per fiber
- irregular, branching cells connected by intercalated disks
- T tubules are larger
- SR is smaller
- mitochondria occupy 1/3 of cell volume
Excitation-contraction coupling in cardiac myocytes: describe the 7 steps
- action potential enters from adjacent cell
- voltage-gated Ca2+ channels open. Ca2+ enters cell
- Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR)
- local release causes Ca2+ spark
- summed Ca2+ sparks to create a Ca2+ signal
- Ca2+ ions bind to troponin to initiate contraction
- relaxation occurs when Ca2+ unbinds from troponin
How does Ca2+ induce Ca2+ release through RyR?
Ca2+ binds to SR ryanodine receptor-channels (RyR) which triggers channel opening
Calcium-induced calcium release (CICR)
Where is the the summed Ca2+ signal from?
90% from SR and 10% from ECF
Mechanism of myocyte relaxation
- Ca2+ is pumped back into the SR for storage
- Ca2+ is exchanged with Na+ by the NCX antiporter
- Na+ gradient is maintained by the Na+-K+-ATPase
NCX antiporter=
Na+ Ca2+ exchanger
SERCA
SR Ca2+ ATPase
cardiovascular system transport
the arteries take blood away from the heart
the veins bring blood back to the heart
where is the heart located?
on the ventral side of the thoracic cavity
sandwiched between the lungs
What is the heart composed of?
myocardium (cardiac muscle cells).
there are myocardial cells of the atria and ventricles.
4 major blood vessels
- vena cava (superior and inferior)
- pulmonary arteries
- pulmonary veins
- aorta
4 chambers of the heart
1,2. right atria and ventricle
3,4. left atria and ventricle
4 valves of the heart
- tricuspid valve (RA and RV)
- pulmonary valve (RV to pulmonary artery)
- bicuspid (or mitral) valve (LA to LV)
- aortic valve (LV to aorta)
what do valves do?
Valves isolate chambers and ensure unidirectional flow!
–> Atrioventricular valves (AV) between atria and ventricles
–> Semilunar valves between ventricles and arteries
Describe a ventricular contraction in terms of valves
AV valves close
semilunar valves open
how does blood flow in the heart?
veins –> atria –> ventricles –> arteries
happens simultaneously on both sides of the heart
Describe ventricular relaxation in terms of valves
AV valves open
semilunar valves close
What do AV valve flaps have to provide stability and prevent backflow?
chordae tendinae (attached to papillary muscles)
what do semilunar valves have to prevent backflow?
they are cup shaped!!
they don’t require tendons to prevent backflow
