Lecture 7 - Cardiac Muslce Tissue Flashcards
Describe the flow of blood through the heart.
- superior/inferior vena cava
- right atrium
- tricuspid valve
- right ventricle
- pulmonary valve
- pulmonary artery
- lungs
- pulmonary vein
- left atrium
- mitral (bicuspid) valve
- left ventricle
- aortic valve
- aorta
What are the histological characteristics of cardiac tissue?
- striated
- mononucleated, central nuclei
- syncytium
- intercalated discs
- branched
What are special requirements for a cardiac action potential?
- self generating
- prolonged (plateau)
- propagate from myocyte to myocyte (proper order and rate)
Distinguish between the types of cardiac APs and where they are found.
Fast:
- contractile in atria and ventricle
- non-contractile in Purkinje
- depolarization caused by fast sodium channels and calcium channels
- high amplitude (100mV)
Slow
- SA and AV
- depolarizers during resting phase (self generating AP)
- depolarization caused by slow sodium channels and calcium channels
- low amplitude (60mV)
What are the phases of cardiac action potential?
Phase 0:
-rapid depolarization
Phase 1: incomplete repolarization
Phase 2: plateau
Phase 3: repolarization
Phase 4: resting potential
What caused the plateau exhibited in cardiac muscle APs?
Fast sodium channels close, however, calcium channels stay open for a period of time while potassium flows out of the cell.
Describe calcium-induced calcium release in cardiac muscle cells. How is this different than what occurs in skeletal muscle?
DHP receptors lets in extracellular calcium from the T tubules. This increase in intracellular calcium causes ryanodine receptors to open in the SR.
In skeletal muscle, conformation changes in the DHP receptors induce opening of ryanodine receptors.
Differentiate between absolute and relative refractory periods.
Identify the factor responsible for the length of a refractory period.
Absolute refractory period:
-no strength of stimulus can cause an action potential
Relative refractory period:
-stronger than normal stimuli can generate and action potential
The rate at which ion channels return to their phase 4 configuration determines the length of a refractory period.
What is automaticity and where is it observed?
Gradual depolarization of tissues in the SA node, AV node, and Purkinje fibers during stage 4.
Occurs most rapidly in SA node causing it to act as the pacemaker.
Caused by opening of special sodium channels during phase 3.
Describe the path of a cardiac action potential.
- Originates in SA node in right atrium and spreads through atrial muscle
- AP travels to AV node where it slows
- AP travels down Purkinje fibers where it speeds up
- AP spreads through ventricular muslce
What is responsible for cardiac muscle relaxation?
Movement of calcium back in to the SR by SERCA.
Movement of calcium back into the extracellular matrix via sodium-calcium exchanger.
Describe the events in the cardiac cycle starting after ventricular contraction.
- Aortic valve closes
- Isovolumic relaxation
- Mitral value opens
- First third of diastole; rapid filling of ventricle, 80% of blood from atrium
- Second third of diastole; diastasis, filling of ventricle from passive flow of blood into the atrium
- Last third of diastole; filling of ventricle by atrial contraction, last 20% of blood from atrium
- Mitral valve closes
- Isovolumic contraction; contraction of ventricle while pulmonary/aortic valve is closed resulting in increased pressure
- Aortic valve opening (80 mmHg)
- Rapid ejection; 70% of blood ejected, first third of systole
- Slow ejection; remaining 30% of blood ejected, last two thirds of systole
What is the Frank-Starling Law?
The greater heart muscle is stretched by filling the greater the force of contraction and quantity of blood will be. This is due to actin and myosin filaments overlapping more ideally for force generation.
What is meant by end diastolic volume, end systolic volume, stroke volume, and ejection fraction?
EDV: ventricular volume prior to contraction (avg. 110-120mL, can be increased to 150-180mL)
ESV: ventricular volume following contraction (avg. 40-50mL, can be decreased to 10-20mL)
SV: amount of blood pumped out of the ventricle (~70mL)
EF: SV/EDV, percent of blood pumped from the ventricle
How can stroke volume be increased?
Increase the amount of blood in the heart prior to contraction (EDV) which stretches heart muscle so it make contract with more force which decreases the amount of blood in the heart after contraction (ESV).
