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Heart ActionsHeart Actions

Chapter 13: Cardiovascular Chapter 13: Cardiovascular SystemSystem

Unit 4: TransportUnit 4: Transport

Cardiac CycleCardiac Cycle

A A coordinatedcoordinated series of events series of events occuring in the heart to ensure occuring in the heart to ensure proper flow of blood in the CV proper flow of blood in the CV systemsystem– If interrupted or compromised, results If interrupted or compromised, results

in poor in poor perfusionperfusion Blood moves between chambers Blood moves between chambers

based on differences in based on differences in pressurepressure– Blood always moves from high pressure Blood always moves from high pressure

area to low pressure areaarea to low pressure area


Some important terminology:Some important terminology:– SystoleSystole When a chamber is When a chamber is

contractingcontracting Contraction makes the chamber smallerContraction makes the chamber smaller As chamber shrinks, pressure goes upAs chamber shrinks, pressure goes up

– Diastole Diastole When a chamber is relaxing When a chamber is relaxing Relaxing chambers get biggerRelaxing chambers get bigger Pressure goes downPressure goes down


The atria contract while the The atria contract while the ventricles relax.ventricles relax.

The ventricles contract while the The ventricles contract while the atria relax.atria relax.

Pressure within the chambers Pressure within the chambers rises and falls in repeated cycles.rises and falls in repeated cycles.

Steps of the CycleSteps of the Cycle

1. 1. Atrial Systole/Ventricular DiastoleAtrial Systole/Ventricular Diastole– Let’s start with blood flowing into both the left Let’s start with blood flowing into both the left

and right atriaand right atria Atria swell with blood returning to the heart via large Atria swell with blood returning to the heart via large

veins (veins (vena cava vena cava & & pulmonary veinspulmonary veins)) Atria have a determined volume (they can only hold a Atria have a determined volume (they can only hold a

certain amount of blood)certain amount of blood) PressurePressure in atria increases due to increased volume in atria increases due to increased volume

pushing on the inside wallspushing on the inside walls

– As ventricles relax, pressure drops below the As ventricles relax, pressure drops below the pressure in atriapressure in atria

Lower pressure in ventricles opens the A-V valvesLower pressure in ventricles opens the A-V valves Blood pours into ventriclesBlood pours into ventricles


1. 1. Atrial Systole/Ventricular Atrial Systole/Ventricular DiastoleDiastole– As muscles of ventricles relax, pressure As muscles of ventricles relax, pressure

drops below the pressure in atriadrops below the pressure in atria Lower pressure in ventricles opens the A-V Lower pressure in ventricles opens the A-V

valvesvalves Blood pours into ventriclesBlood pours into ventricles


1. 1. Atrial Systole/Ventricular Atrial Systole/Ventricular DiastoleDiastole– Blood flows into ventricles, filling them Blood flows into ventricles, filling them

and increasing the pressure.and increasing the pressure.– 70% of blood in atria pour into vent’s 70% of blood in atria pour into vent’s

passivelypassively– Finally, atria contract (systole), forcing Finally, atria contract (systole), forcing

the other 30% of blood into ventriclesthe other 30% of blood into ventricles


2. 2. Ventricular Systole/Atrial DiastoleVentricular Systole/Atrial Diastole– Ventricles swell with blood, increasing Ventricles swell with blood, increasing

pressurepressure– Ventricles contract, increasing the pressure Ventricles contract, increasing the pressure

(high press) as atria relax (low press), closing (high press) as atria relax (low press), closing the A-V valvesthe A-V valves

Prevents backflow of blood into the atriaPrevents backflow of blood into the atria

– As ventricle contracts…As ventricle contracts… Pressure increases to a point greater than the aorta Pressure increases to a point greater than the aorta

and pulmonary trunkand pulmonary trunk Blood is forced into aorta/pulm trunk & through Blood is forced into aorta/pulm trunk & through

systemic circuitsystemic circuit


3. 3. Atrial Systole/Ventricular Atrial Systole/Ventricular DiastoleDiastole– After pumping blood out, ventricles After pumping blood out, ventricles

begin to relax (low pressure) as atria begin to relax (low pressure) as atria begin filling with more blood.begin filling with more blood.

– When pressure in ventricle drops below When pressure in ventricle drops below that in the aorta/pulm trunk, semilunar that in the aorta/pulm trunk, semilunar valves closevalves close

– Cycle repeatsCycle repeats

Heart SoundsHeart Sounds

Heart sounds are due to the Heart sounds are due to the vibrations that valve movements vibrations that valve movements produce.produce.

– The heart sound is a lubb-dubb.The heart sound is a lubb-dubb.

Lubb Lubb occurs during ventricular occurs during ventricular contractions, when the A-V valves are contractions, when the A-V valves are closingclosing

Dubb Dubb occurs during ventricular occurs during ventricular relaxation, when the pulmonary and aortic relaxation, when the pulmonary and aortic valves are closing.valves are closing.



Heart sounds are due to the Heart sounds are due to the vibrations that valve movements vibrations that valve movements produce.produce.

– A A heart murmurheart murmur is the result of one is the result of one or more valves that do not close or more valves that do not close properlyproperly

– Results in blood leaking backwards Results in blood leaking backwards in the heartin the heart

– Heart MurmursHeart Murmurs

Cardiac Muscle FibersCardiac Muscle Fibers

Cardiac muscle functions similarly Cardiac muscle functions similarly to skeletal muscleto skeletal muscle– StriatedStriated– Myosin and actin slide past each other Myosin and actin slide past each other

in a contraction cycle similar to in a contraction cycle similar to skeletal muscleskeletal muscle

– Require ATP produced by cellular Require ATP produced by cellular respirationrespiration

Cardiac Muscle FibersCardiac Muscle Fibers

Major difference: The fibers connect in a Major difference: The fibers connect in a branching fashion, allowing electrical branching fashion, allowing electrical signals to pass easily from one cardiac signals to pass easily from one cardiac mucle cell to another.mucle cell to another.

– Stimulation to any part of the network sends Stimulation to any part of the network sends impulses throughout the heart, which impulses throughout the heart, which contracts as a unit.contracts as a unit.

There are two networks in the heart, each called a There are two networks in the heart, each called a Functional SyncytiumFunctional Syncytium

One syncytium operates the atria, the second One syncytium operates the atria, the second operates the ventricles.operates the ventricles.

Cardiac Conduction Cardiac Conduction SystemSystem Made of two functional syncytiaMade of two functional syncytia Coordinates the heart beat Coordinates the heart beat

((Cardiac CycleCardiac Cycle).). Made of special cells that Made of special cells that

themselves do not contract.themselves do not contract. Performs two functions:Performs two functions:

– InitiatesInitiates electrical signal electrical signal– ConductsConducts the signal to heart the signal to heart

musclemuscle

Sinoatrial NodeSinoatrial Node

The The Sinoatrial NodeSinoatrial Node (S-A node) is a small (S-A node) is a small mass of specialized cardiac muscle tissue mass of specialized cardiac muscle tissue found in the wall of the right atrium.found in the wall of the right atrium.

– These cells reach threshold These cells reach threshold on their ownon their own, , producing a muscle impulse (No CNS input producing a muscle impulse (No CNS input needed)needed)

– Surrounding Surrounding myocardialmyocardial cells contract in cells contract in response to the impulse from the S-A node.response to the impulse from the S-A node.

– Only the Only the AtriaAtria contract due to the S-A node’s contract due to the S-A node’s actionaction

*S-A node activity is rhythmic, and initiates one impulse *S-A node activity is rhythmic, and initiates one impulse after another (70 to 80 times a minute in an adult)after another (70 to 80 times a minute in an adult)

– *Pacemaker**Pacemaker*

Atrioventricular Node Atrioventricular Node

Cardiac impulse travels from the S-A node Cardiac impulse travels from the S-A node into the atrial into the atrial syncytiumsyncytium, causing the right , causing the right and left atria to contract almost and left atria to contract almost simultaneously.simultaneously.

– Impulse from S-A node passes through Impulse from S-A node passes through myocardium to the myocardium to the Atrioventricular nodeAtrioventricular node, , found near the top of the found near the top of the septumseptum. .

The A-V node slows down the impulseThe A-V node slows down the impulse Impulse is sent down Impulse is sent down Purkinje Fibers Purkinje Fibers into the inferior into the inferior

walls of the ventricleswalls of the ventricles Ventricular walls contract, squeezing from inferior Ventricular walls contract, squeezing from inferior

toward superior due to Purkinje fibers taking electrical toward superior due to Purkinje fibers taking electrical signal to the bottom of heart firstsignal to the bottom of heart first

Electrocardiogram Electrocardiogram (ECG)(ECG) An ECG (An ECG (EKGEKG) records electrical changes ) records electrical changes

in the myocardium during a cardiac cycle.in the myocardium during a cardiac cycle.– Super-sensitive electrodes are placed on the Super-sensitive electrodes are placed on the

skin near the heart.skin near the heart.– Changes in electrical activity caused by Changes in electrical activity caused by

cardiac muscle contractions are detectedcardiac muscle contractions are detected– A graph is producedA graph is produced

– The pattern contains several waves.The pattern contains several waves.

1.1. The P wave represents atrial depolarization.The P wave represents atrial depolarization.

2.2. The QRS complex represents ventricular The QRS complex represents ventricular depolarization (contraction).depolarization (contraction).

3.3. The T wave represents ventricular repolarization The T wave represents ventricular repolarization (relaxation).(relaxation).

Electrocardiogram Electrocardiogram (ECG)(ECG)

The graph pattern contains several The graph pattern contains several waves.waves.

1.1. The P wave represents atrial depolarization The P wave represents atrial depolarization (contraction).(contraction).

2.2. The QRS complex represents ventricular The QRS complex represents ventricular depolarization.depolarization.

3.3. The T wave represents ventricular The T wave represents ventricular repolarization (relaxation).repolarization (relaxation).

Regulation of the Regulation of the Cardiac CycleCardiac Cycle Physical exercise, body temperature, Physical exercise, body temperature,

and the concentration of various ions and the concentration of various ions affect heartbeat.affect heartbeat.– Branches of sympathetic and Branches of sympathetic and

parasympathetic nerve fibers innervate parasympathetic nerve fibers innervate the S-A node and controls its pacethe S-A node and controls its pace

What effect does the parasympathetic NS have What effect does the parasympathetic NS have on heart rate and blood pressure?on heart rate and blood pressure?

What effect does the sympathetic NS have on What effect does the sympathetic NS have on heart rate and blood pressure?heart rate and blood pressure?

– Most people at rest have a HR lower than Most people at rest have a HR lower than the S-A’s pace. Nervous system has a the S-A’s pace. Nervous system has a “brake” on the heart“brake” on the heart

Regulation of the Regulation of the Cardiac CycleCardiac Cycle Physical exercise, body temperature, Physical exercise, body temperature,

and the concentration of various ions and the concentration of various ions affect heartbeat.affect heartbeat.– Most people at rest have a HR lower than Most people at rest have a HR lower than

the S-A’s pace. Parasympathetic nervous the S-A’s pace. Parasympathetic nervous system has a “brake” on the heartsystem has a “brake” on the heart

S-A node has a “typical” cycle of 100 beats per S-A node has a “typical” cycle of 100 beats per minuteminute

Parasymthpathetic nervous system slows down Parasymthpathetic nervous system slows down heart rate.heart rate.

When a faster rate is required, the nervous When a faster rate is required, the nervous system “brake” is removed, and sympathetic system “brake” is removed, and sympathetic innervation may also increase HR more.innervation may also increase HR more.

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