Ch. 9 Cardiac Muscle

Flashcards covering the key concepts of cardiac muscle, the cardiac cycle, and heart regulation.

What are the two separate pumps of the heart?

The right heart (pulmonary circulation) Chamber:

• responsible for venous return

• distributes blood to lungs to create oxygenated blood

Left heart (peripheral circulation)

• related to process of cardiac output

• distributes blood to entire body system

Each side has two chambers, the atrium is the primer pump and the ventricles are the Main pump

What are the three types of cardiac muscle?

Atrial muscle

Ventricular muscle

Excitatory and conductive muscle

How does atrial and ventricular cardiac muscle contract compared to skeletal muscle?

Like skeletal muscle except the duration of contraction is longer in cardiac muscle due to the slow closing of voltage-gated calcium channels prolonging depolarization.

Both uses Calcium for muscle contraction however, cardiac muscle uses calcium from the ECF because there is not enough calcium in the SR

What unique property do excitatory cardiac muscles exhibit?

Automatic rhythmical electrical discharge (action potential or conduction).

Describe the anatomy of the cardiac muscle

• Fibers form a latticework of fibers of dividing, recombining, and spreading again

• Have actin and myosin filaments like skeletal muscle

• Unique Features:

  • longer contraction duration

  • Intercalated discs

  • Functional syncytium: atrial and ventricular

What are intercalated discs?

• make the cardiac tissue one that connects cardiac muscle cells, allowing for synchronized contraction and communication between cells.

• joined with gap junctions for cell-to-cell communication and ion diffusion

Why do cardiac cells have the ability to spread action potential easily?

Because they have specialized intercalated discs and gap junctions that facilitate rapid electrical communication between cells.

• lack of intercalated discs would slow the contraction rate and due to slow signal conduction

What are the two syncytium in the heart?

Why are they separated?

Atrial syncytium and ventricular syncytium.

Separated by the fibrous tissue - Atrioventricular Valve (a non-conductive tissue) because the atria and ventricles do not contract together, but the ventricles are delayed to ensure proper blood pumping of the heart

How do action potentials travel within the heart?

By way of a specialized conductive system (A-V bundle).

1. What is the resting membrane potential (RMP) of cardiac muscle?

2. What about action potential?

1. -85 mV

2. +20 mV during an action potential

   • After the spike, the membrane remains depolarized for 0.2 seconds (plateau) followed by rapid repolarization

Why does ventricular contraction last 15 times as long in cardiac muscle than skeletal muscle?

Due to the depolarization plateau

• influx of Na+ (fast channel) and Ca+ (slow channel)

• The slow channels open longer causing more Ca+ to enter the cell for contraction

What happens to K+ permeability at the onset of action potential in cardiac muscle?

It decreases about 5-fold, preventing early return of RMP.

What is the difference between absolute and relative refractory?

• absolute - when a cell can’t respond to any stimulus regardless of how strong

• Relative - when a second action potential can be generated but only with a stronger than usual stimulus; occurs after absolute

T/F: Ventricles have a shorter refractory period?

False - atrias do

• Atria need to be ready to contract more frequently to accommodate the rapid filling and pushing cycles to the ventricles

• Atria have thinner walls and work with lower pressure than ventricles so they don’t have stronger contractions than ventricles = shorter action potential = shorter refractory period

What is E-C coupling?

The mechanism by which an action potential causes myofibrils of muscle to contract.

• Action potential will travel down the T-Tubles and large number of calcium ions enter from the T-tubles

  • the SR in cardiac muscle is less developed so they are unable to store the volume of calcium needed for contraction

  • Calcium will come from ECF

How many calcium pumps are present in the cardiac cycle?

Two

• first is at the SR as Calcium is pumped into the SR

• second is at the cell membrane, pumping Ca out into the ECF and Na in with counter-transport (secondary active transport) to establish a membrane potential

What is the cardiac cycle?

Cardiac events from the beginning of one heartbeat to the beginning of the next and stimulated by action potential of the sinus node

• Action potential travels through the atria, to the AV node, to the ventricles and causes the ventricles to contract

Where is the sinus node located?

In the superior lateral wall of the right atrium.

Describe the Atria as Primer Pumps

1. 80% of the blood flow from the great veins flow (passively) into the right atria and to the right ventricles

2. Atrial contraction is responsible for the additional 20% filling of ventricles with pumping - important for exercise

T/F: atrial pumping is not necessary and will become useful with exercise

true

• example of seeing function of full heart function and atria function is applying a stress-test to patient

What are the three atrial pressure waves?

A wave - for atrial contraction

• The right atrium increases by 4-8 mm Hg in pressure which will lead to an increase in the ventricles as well

• left atrium increases pressure to 7-8 mmHg

  • left atrium will always have a greater pressure than the right atrium.

C wave - begins at ventricular contraction and is caused by backflow of blood of blood into the atria by bulging of the AV valve as the pressure in the ventricle increases. Bulging will occur in atria.

V Wave - at the end of ventricular contraction and occurs at atrial filling while AV valve is closed.

• V wave will disappear when the A-V valve opens

• source of 80% of venous return

Describe the relationship between Atrial pressure and Ventricular volume

• Prior to atrial contraction, ventricular volume increases due to passive blood flow

• Atrial contraction will occur when atrial pressure is greater than ventricular pressure

• Between the cessation of atrial contraction and the c-wave is the occurance of isovolumic contraction = same volume of blood in the ventricles

• C-wave occurs due to bulging of AV valve BUT valve is not open

• At the C wave, there will be a decrease in ventricular volume due to decrease in ventricular volume and will cause atrial pressure to decrease too

• the V-wave is the end of ventriular contraction and blood flows into the atria, and AV valve is now open

• Repeat cycle

What occurs during isovolumic contraction during the emptying of the ventricles?

Contraction of ventricles increasing pressure to the point of opening the aortic and pulmonary valves without emptying.

What is the approximate pressure when the left ventricle valve opens?

Approximately 80 mm Hg.

Describe how the Ventricles work as pumps.

Undergo a Rapid filling phase

• Atria will collect blood during ventricular systole.

• Once ventricles relax, the atrial pressure will excede ventricular pressure and the AV valve will open

  • phase lasts for a 1/3 of distally = very fast

Emptying of Ventricles

• Ventricles will undergo isovolumic contraction - contraction of ventricles increasing pressure to point of opening the aortic and pulmonary valves without emptying

• Ejection of blood from ventricles with 70% with rapid ejection and 30% slowly

• Isovolumic Relaxation - ventricles relax but there is no change in volume because the AV valve is closed (intraventricular pressure decreases with no change in volume)

What are the four phases of the Pressure-Volume curve/Ventricular pumping?

Period of Filling, Period of Isovolumic Contraction, Period of Ejection, Period of Isovolumic Relaxation.

Describe each part of the Pressure Volume curve

*shows cardiac output in the left side of the heart

Mitral Valve Closed = End diastolic volume

• Mitral valve (between L atria and L ventricle) is closed because ventricular pressure > atrial pressure

• Max volume in LV

LVentricle contracts (systole) increasing Ventricular pressure

• both mitral and aortic valve are closed to the volume remains the constant = isovolumetric contraction

Aortic Valve will open when ventricular pressure > Aortic pressure

Ejection phase as blood flows from LVentricle to Aorta

Aortic Valve closes because Aortic pressure > ventricular pressure due to ventricular volume decrease = decrease in pressure

• end of Systole

Isovolumetric relaxation - constant volume

Mitral Valve open

• Atrial pressure > ventricular pressure

• blood flows from atria to ventricle

Ventricle fills with blood till ventricular pressure > atrial pressure

REPEAT

What is preload vs afterload

Preload is End diastolic pressure (increased blood volume, increased pressure, and vise versa)

Afterload is pressure in the artery leaving ventricles (resistance)

• pressure in the aorta

• Has a greater resistance to stroke volume

How is the volume pumped by the heart regulated?

Intrinsic regulation determined by volume, and heart rate and strength of contraction by the ANS.

What are the two equations to find cardiac output?

• CO = HR x SV

• CO = Arterial Pressure / TPR

What is baseline cardiac output in males and females about?

5 L/min

If person A has a baseline cardiac output of 5 L/min and their heart rate is 70 compared to person B has a heart rate of 40. What can you say about how their heart is working?

Person A will make more work for their heart

Person B will have a higher SV (CO=HR x SV) but less work for the heart and better contractility

What is the Frank-Starling mechanism?

Intrinsic ability of heart to adapt to increasing volumes of venous return. The greater the heart is stretched (preload), the greater the force of contraction. Which will create optimal amount of overlap of filaments. Stretch of the right atrium (increases firing of SA node) increases heart rate, increasing CO.

• venous return determines the amount of blood pumped by the heart

• peripheral tissues control and regulate own local blood flow

How does the sympathetic nervous system affect the heart?

Increases heart rate and increases force of heart contraction.

How does the parasympathetic (Vagal) nervous system affect the heart?

Decreases heart rate and decreases force of muscle contraction; distributed mainly to atria.

What is the effect of sympathetic stimulation on cardiac pumping?

• It can increase rate from rest (70 to 200 bpm)

• increase contractility which will increase volume of blood pumped (increase SV)

• sympathetic stimulation can’t reduce cardiac pumping below 30% normal

What is the effect of strong Vagal stimulation on the heart?

Strong stimulation can stop the heartbeat for a few seconds, but then the heart “escapes”.

It can decrease strength of heart muscle.

The rate is impacted greater than the strength

What is normal right atrial pressure value?

0 mmHg

What effect does excess K+ have on the heart?

Causes the heart to become dilated, flaccid, and slows heart rate.

It can also block conduction from atria to ventricles leading to stopping HR

Decreases RMP and intensity of AP = inability to move blood beyond aortic pressure

What could cause blood to not move beyond aortic pressure?

High K+ levels

What effect does excess Ca2+ have on the heart? How about deficiency?

Should we be concerned?

Causes the heart to go toward spastic contraction.

Deficiency causes flaccidity, similar to high K+

No, calcium is regulated tightly

How does increased temperature affect heart rate? How about decreased?

It causes increased heart rate due to increased permeability of ions.

Decreased temp decreases heart rate