Myocardial Anatomy and Phys Flashcards by Abbey Mayer

6 characteristics of cardiac muscle cells

Rectangular to elongated
Branching
Contains actin and myosin (Striated)
1-2 nuclei per cell 
Many mitochondria
Very extensive capillary network

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Intercalated disks

Connect cardiac cells and allow for cell-to-cell communication

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Conduction system

Made of modified myocardial cells that are larger in diameter with few myofibrils with well-developed intercalated discs to conduct action potentials

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SA node

Pace-maker, generates the first action potential located in the superior aspect of the right atrium

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AV node location

Ventral aspect of the right atria at the junction of the atria and ventricle

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Purkinje fibers

Extensions of the right and left bundle branches found in lateral myocardial wall

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Pathway of action potential

SA node
AV node
AV bundle
Right and left bundle branches 
Purkinje fibers

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Auto-rhythmicity

All myocardial cells have the capacity to generate spontaneous action potentials

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Ectopic foci

Area of myocardium other than SA node that sets the heart rate that results in the action potential following a different pathway and reducing cardiac output

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Where does the action potential slow down at?

AV node to allow for atrial contraction and ventricle filling before ventricle contraction

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Cardiac muscle duration of action potential

200-500msec, longer than skeletal to prohibit tetany

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Why does myocardium have long refractory period?

To ensure that the muscle will be nearly totally relaxed before accepting another ap

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Pre-potential

Sodium ions leak into the cell through ion channels that bring the cell to threshold

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What is the primary ion responsible for depolarization of SA node cells?

Calcium

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Plateau phase

Sodium channels close, potassium channels begin to open, calcium channels stay open, causes prolongation of AP transmission

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Electrocardiogram

Detection and measurement of electrical currents generated by ap in the myocardium

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P wave

Atrial depolarization

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P-Q segment

Atrial contraction, not detected by the EKG

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QRS wave

Ventricular depolarization

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S-T segment

Ventricular contraction, not detected by EKG

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T wave

Ventricular repolarization

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Why check the EKG?

Tells the conditon of the heart muscle

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Elevated P wave

Enlarged atria

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Elevated R wave

Enlarged ventricles

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Elongated Q-T segment

Acute myocardial infarction of ventricles that causes ischemia and abnormal conduction of AP

Elongation of PR interval

Ischemia of AV nodal region, dilation of atria, ischemia of atria due to blocked blood supply

What is the cardiac cycle?

Repetitive pumping process of the heart that begins with the onset of contraction and ends with the beginning of the next contraction

What does the cardiac cycle cause?

Increase in pressure in one area over another and the movement of blood

What is the normal duration of the cardiac cycle?

0.7-0.8 seconds

Pulmonary pump

Moves blood to the luungs and back to the beart, causes oxygenation of the blood

Systemic pump

Moves blood to the systemic circulation and back to the heart

Systole

Contraction

Diastole

Dilation or relaxation

Why is diastole critcally important?

To allow for filling of the ventricles

Period of isovolumic contraction

At the completion of the QRS complex when the AV valves close, pressure rises in the ventricle, and no blood flows from ventricle

Period of ejection

Pressure within the ventricles exceeds that within the aorta and pulmonary trunk causing semilunar valves to open and blood ejection, pressure increases in left ventricle to 120mmHg

At what pressure does the aortic semilunar valve open?

80mmHg

At what pressure does the pulmonary semilunar valve open?

8mmHg

Period of isovolumic relaxation

At the completion of the T wave when ventricles begin to relax, pressure drops, semilunar valves close, and no blood flows back into the ventricles

Passive ventricular filling

Occurs during ventricular diastole when pressure drops below atrial, AV valves open to allow blood flow into the ventricles without atrial contraction

What percent filled are the ventricles after apssive ventricular filling?

70%

Active ventricular filling

Atrial systole when blood is pushed into ventricles to complete ventricular filling

When is active ventricular filling most important?

Diuring excerise to increase heart rate and cardiac output

Lubb

Closure of the AV valves

Dubb

Closure of the semilunar valves

Heart murmur

Abnormal heart sound that usually causes reduction in cardiac output and increase in work for the heart

What can cause a heart murmur?

Leaky valves or blockage of a vessel

Stenosis

Narrowing of blood vessels that causes turbulence of blood flow, more common in young people and congenital

Leakage of valves

Common in older people that is characterized by a roughness of valve edges or improper closure

Mitral valve disease

Most common and most serious type of leaky valve

Abnormal openings

Non-closure of vessels between the aorta and pulmonary trunk that forces blood from left side to the right side causing oxygenated blood to return to the lungs

Cardiac output

A measure of the ability of the heart to pump blood | Stroke volume in mL x heart rate

Average cardiac output

5,000mL/min

Sympathetic stimulation's affect on cardiac output

Faster depolarization of the SA node, faster heart rate, greater force of contraction

Parasympathetic stimulation's affect on cardiac output

Hyperpolarization of the neurons and a slower heart rate

Bradycardia

Slower heart rate

Tachycardia

Faster heart rate

Frank starling law

Stretching of the muscle cells causes increased efficiency of contraction and a stronger contraction

Will increasing or decreasing venous return increase the cardiac output?

Increasing like moving body parts or inhaling deeply

What will decrease venous return?

Exhalation, standing still, decrease sympathetic stimulation, decrease in CO2

Why is the resistance in skeletal muscle arterioles high?

Low CO2 levels at rest, precapillary sphincters are closed and blood flow is reduced

How much does blood flow to skeletal muscles increase when exercising?

20 fold

How can you increase blood flow to the viscera?

Eating a meal

Ischemia

Any condition resulting in insufficient blood flow to the myocardium and therefore O2 deficiency

3 causes of ischemia

Athersclerosis blood clot spasms of coronary arterioles

Angina pectoris

Pain produced by ischemia

Myocardial infarction

Complete blockage of blood vessel to myocardium