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The scientific study of the heart and treatment of its disorders

cardiovascular system

WHAT consists of the heart and the blood vessels. The heart functions as a muscular pump that keeps blood flowing through the vessels. The vessels deliver the blood to all the body's organs and then return it to the heart.

pulmonary and systemic circuit

The cardiovascular system has two major divisions: WHAT and WHAT?

pulmonary circuit

WHAT carries blood to the lungs for gas exchange and returns it to the heart? (supplies lungs only. Serves to exchange CO2 for O2)

systemic circuit

WHAT supplies blood to every organ of the body, including other parts of the lungs and the wall of the heart itself. (Supplies entire body, serves exchange O2 for CO2, supplies organs with nutrients, removes wastes and heat)

pulmonary circuit

The right side of the heart furnishes blood to the WHAT. It receives blood that has circulated through the body, unloaded its oxygen and nutrients, and picked up a load of carbon dioxide and other wastes.

systemic circuit

The left side of the heart supplies the WHAT?

coronary arteries

In most organs, blood flow peaks when the ventricles contract and eject blood into the arteries, and diminishes when the ventricles relax and refill The opposite is true in the WHAT? 3 reasons why: 1. Contraction of the myocardium compresses the arteries and obstructs blood flow 2. During ventricular systole (contraction of the ventricles), the aortic valve is forced open and the valve cusps cover the openings to the coronary arteries, blocking blood from flowing into them. 3. During ventricular diastole (relaxation), blood in the aorta briefly surges back toward the heart. It fills the aortic valve cusps and some of it flows into the coronary arteries. In the coronary blood vessels, therefore, blood flow increases during ventricular relaxation


The most obvious physiological fact about the heart is its rhythmicity. It contracts at regular intervals, typically about 75 beats per minute (WHAT?)


Cardiocytes are said to be WHAT? Thus the heart is not dependent on the nervous system for its rhythm. It has its own pacemaker and electrical system.


WHAT are relatively short, thick, branched cells. The ends of the cell are slightly branched. Through these branches, each cardiocyte contacts several others, so collectively they form a network throughout each pair of heart chambers- one network in the atria and one in the ventricles.

intercalated discs

Cardiocytes are joined end to end by thick connections called WHAT? These appear as dark lines thicker than the striations. As intercalated disc is a complex steplike structure with three distinctive features not found in skeletal muscles: interdigitating folds, mechanical junctions, and electrical junctions

interdigitating folds

(feature found in intercalated disc) the plasma membrane at the end of the cell. The folds of adjoining cells interlock with each other and increase the surface area of intercellular contact.

mechanical junctions

(feature found in intercalated disc) The cells are tightly joined by two types of mechanical junctions: the fascia adherens and the desmosomes.

fascia adherens

(part of mechanical junction). It is the most extensive. It is a broad band in which the actin of the thin myofilaments is anchored to the plasma membrane and each cell is linked to the next via transmembrane proteins.


(part of mechanical junction). The fascia adherens is interrupted here and there by WHAT? They are weldlike mechanical junctions between cells. They prevent the cardiocytes from pulling apart when they contract.

electrical junctions

(feature found in intercalated disc) The intercalated discs also contain gap junctions, which form channels that allow ions to flow from the cytoplasm of one cardiocyte directly to the next. They enable each cardiocyte to electrically stimulate its neighbors.

Basic Cardiac Cycle

Basic Cardiac Cycle: 1. All 4 chambers are relaxed (diastole) 2. Ventricles are filling 3. Atria contract in unison (atrial systole) 4. Atria finish filling the ventricles 5. Ventricles contract in unison (ventricular systole) 6. Blood is expelled into pulmonary trunk and aorta 7. Heart relaxes

cardiac conduction system

The heartbeat is coordinated by a WHAT composed of an internal pacemaker and nervelike conduction pathways through the myocardium.t generates and conducts rhythmic electrical signals in the following order: 1. The SA node, a a patch of modified cardiocytes in the right atrium. This is the pacemaker that initiates each heartbeat and determines the heart rate. 2. Signals from the SA node spread throughout the atria 3. The AV node, located near the right AV valve at the lower end of the interatrial septum. This node acts as an electrical gateway to the ventricles. 4. The AV bundle (bundle of His) a pathway by which signals leave the AV node. The AV bundle soon forks into right and left bundle branches, which enter the interventricular septum and descends toward the apex 5. Purkinje fibers, nervelike processes that arise from the lower end of the bundle branches and turn upward to spread throughout the ventriclar myocardium. Purkinje fibers distribute the electrical excitation tot he cardiocytes of the ventricles.

sinoatrial node

(cardiac conduction system) 1. WHAT, a patch of modified cardiocytes in the right atrium. This is the pacemaker that initiates each heartbeat and determines the heart rate.

atrioventricular node

(cardiac conduction system) 3. The WHAT, located near the right AV valve at the lower end of the interatrial septum. This node acts as an electrical gateway to the ventricles.

atrioventricular bundle

(cardiac conduction system) 4. (bundle of His), a pathway by which signals leave the AV node. The AV bundle soon forks into right and left bundle branches, which enter the interventricular septum and descend toward the apex.

purkinje fibers

(cardiac conduction system) 5. WHAT, nervelike processes that arise from the lower end of the bundle branches and turn upward to spread throughout the ventricular myocardium. WHAT distribute the electrical excitation and to the cardiocytes of the ventricles. They form a more elaborate network in the left ventricle than in the right.

cardiac conduction system

cardiac conduction system: 1. SA node fires 2. Excitation spreads through atrial myocardium 3. AV node fires 4. Excitation spreads down AV bundle 5. Purkinje fibers distribute excitation through ventricular myocardium.


Contraction is called WHAT?


Relaxation is called WHAT?

sinus rhythm

The normal heartbeat triggered by the SA node is called the WHAT? At rest, the adult heart typically beats about 70 to 80 times per minute.

premature ventricular contraction

Stimuli such as hypoxia, electrolyte imbalances, caffeine, nicotine, and other drugs can cause other parts of the conduction system to fire before the SA node does, setting off an extra heartbeat called WHAT? (PVC)

ectopic focus

Any region of spontaneous firing other than the SA node is called a WHAT?

nodal rhythm

The most common ectopic focus is the AV node, which produces a slower heartbeat of 40 to 50 bpm called a WHAT?

ectopic foci

If neither the SA nor AV node is functioning, other WHAT fire at rates of 20 to 40 bpm. The nodal rhythm is sufficient to sustain life, but a rate of 20 to 40 bpm provides little flow to the brain to be survivable.


Any abnormal cardiac rhythm is called WHAT?

heart block

One cause of arrhythmia is a WHAT- the failure of any part of the cardiac conduction system to transmit signals, usually as a result of disease and degeneration of conduction system fibers. Ex.) A bundle branch block is due to damage to one or both bundle branches. Ex. 2) Damage to the AV node causes total heart block, in which signals from the atria fail to reach the ventricles and the ventricles beat at their own intrinsic rhythm of 20 to 40 bpm.

pacemaker potential

Why does the SA node spontaneously fire at regular intervals? SA nodes do not have a stable resting membrane potential, unlike skeletal muscle or neurons. This membrane potential starts at about -60 mV and drifts upward, showing a gradual depolarization called WHAT? This results from a slow inflow of Na+ without a compensating outflow of K+.

fast calcium-sodium channels

When the pacemaker potential reaches a threshold of -40 mV, voltage-regulated WHAT open and both Ca2+ and Na+ flow in from the extracellular fluid. The produces the rising (depolarizing) phase of the action potential, which peaks slightly above 0 mV. At that point, K+ channels open and K+ leaves the cell.


The produces the rising (depolarizing) phase of the action potential, which peaks slightly above 0 mV. At that point, K+ channels open and K+ leaves the cell. This makes the cytosol increasingly negative and creates the falling WHAT phase of the action potential. When the repolarization is complete, the K+ channels close and the pacemaker potential starts over, on its way to producing the next heartbeat.


Each WHAT of the SA node sets off one heartbeat. When the SA node fires, it excites the other components in the conduction system; thus, the SA node serves as the system's pacemaker.


Firing of the SA node excites atrial cardiocytes and stimulates the two atria to contract almost simultaneously. The signal travels at a speed of about HOW MANY m/sec through the atrial myocardium and reaches the AV node in about 50 msec.


In the AV node, the signal slows down to about HOW MANY m/sec, because they have fewer gap junctions over which the signal can be transmitted. This delays the signal at the AV node for about 100 msec. This delay is essential because it gives the ventricles time to fill with bleed before they begin to contract.


Signals travel through the AV bundle and Purkinje fibers at a speed of HOW MANY m/sec, the fastest in the conduction system. Consequently, the entire ventricular myocardium depolarizes within 200 msec after the SA node fires, causing the ventricles to contract in near unison.


Ventricular systole begins at the WHAT of the heart, which is first to be stimulated, and progresses upward-pushing the blood upward toward the semilunar valves. Because of the spiral arrangement of ventricular cardiocytes, the ventricles twist slightly as they contract.

Electrical behavior of the myocardium

Electrical behavior of the myocardium: 1. voltage-gated Na+ channels open. 2. Na+ inflow depolarizes the membrane and triggers the opening of still more Na+ channels, creating a positive feedback cycle and a rapidly rising membrane voltage. 3. Na+ channels close when the cell depolarizes, and the voltage peaks at nearly +30 mV. 4. Ca2+ entering through slow Ca2+ channels prolongs depolarization of membrane, creating a plateau. Plateau falls slightly because of some K+ leakage, but most K+ channels remain closed until end of plateau. 5. Ca2+ channels close and Ca2+ is transported out of the cell. K+ channels open, and rapid K+ outflow returns membrane to its resting potential.


(Electrical behavior of the myocardium) 2. WHAT inflow depolarizes the membrane and triggers the opening of still more Na+ channels, creating a positive feedback cycle and a rapidly rising membrane voltage.


(Electrical behavior of the myocardium) 3. Na+ channels close when the cell depolarizes, and the voltage peaks at nearly WHAT mV.


(Electrical behavior of the myocardium) 4. Ca2+ entering through slow Ca2+ channels prolongs depolarization of membrane, creating a WHAT? Plateau falls slightly because of some K+ leakage, but most K+ channels remain closed until end of plateau.


(Electrical behavior of the myocardium) 5. Ca2+ channels close and Ca2+ is transported out of the cell. K+ channels open, and rapid K+ outflow returns membrane to its resting potential.


We can detect electrical currents in the heart by means of electrodes (leads) applied to the skin. An instrument amplifies these signals and produces a record called a WHAT (ECG)

P wave

WHAT is produced when a signal from the SA node spreads through the atria and depolarizes them. (SA node fires, Atrial Depolarize, Atrial systole)

QRS complex

WHAT consists of a small downward deflection (Q), a tall sharp peak (R), and a final downward deflection (S). It is produced when the signal from the AV node spreads through the ventricular myocardium and depolarizes the muscle. Its complex shape is due to the different sizes of the two ventricles and the different times required for them to depolarize. (AV node fires, Ventricles depolarize, Ventricular systole, Atrial repolarization, diastole) (first heart sound occurs)

T wave

WHAT is generated by ventricular depolarization. The ventricles take longer to repolarize than to depolarize; the T wave is therefore smaller and more spread out than the QRS complex and has a rounder peak. (Ventricles repolarize, ventricular diastole)

cardiac cycle

WHAT consists of one complete contraction and relaxation of all four heart chambers


Impels a fluid to move


opposes flow


Blood pressure is usually measured with a WHAT- a calibrated mercury manometer with its open lower end attached to an inflatable pressure cuff wrapped around the arm.

pressure gradient

A fluid flows only if it is subjected to more pressure at one point in space than at another. The difference creates a WHAT and fluids always flow down their pressure gradients, from the high-pressure point to the low-pressure point.


Pressure is WHAT proportional to the volume of the container- the greater the volume, the lower the pressure, and vice versa. Ex.) You pull back the plunger of the syringe. This increase the volume and thus lowers the air pressure within the barrel. Ex. 2) If you push the plunger in, pressure inside the barrel will rise above the pressure outside, and air will flow out-again going down its pressure gradient but in the reverse direction.

atrioventricular valves

The WHAT- when atrial pressure is greater than ventricular pressure, the valve opens and blood flows through. When ventricular pressure rises above atrial pressure, the blood in the ventricle pushes the valve cusps closed.

semilunar valves

The WHAT- when the pressure in the ventricles is greater than the pressure in the great arteries, the WHAT are forced open and blood is ejected. When ventricular pressure is lower than arterial pressure, arterial blood holds these valves closed.


Listening to sounds made by the body is called WHAT?


Closing of AV valves


Closing of aortic and pulmonary valves


Ventricular refilling

ventricular filling

AV valves open and blood flows into the ventricles, causing ventricular pressure to rise and atrial pressure to fall. It occurs in three phase: rapid ventricular filling, diastasis, atrial systole.

rapid ventricular filling

One of the phases of ventricular filling: The first one-third is WHAT when blood enters especially rapidly.


One of the phases of ventricular filling: The second one-third called WHAT is marked by slower filling. The P wave of the electrocardiogram occurs at the end of diastasis, marking the depolarization of the atria.

atrial systole

One of the phases of ventricular filling: In the last one-third, WHAT completes the filling process. The right atrium contracts slightly before the left because it is the first to receive the signal from the SA node.

end-diastolic volume

At the end of ventricular filling, each ventricle contains an WHAT (EDV) of about 130 mL of blood. Only 40 mL (31%) of this is contributed by atrial systole.

isovolumetric contraction

The atria repolarize, relax, and remain in diastole for the rest of the cardiac cycle. The ventricles depolarize, generate the QRS complex, and begin to contract. The AV valves close. Heart S1 occurs at the beginning of this phase and is produced mainly by the left ventricle. This phase is called WHAT because even though the ventricles contract, they do not eject blood yet and there is no change in their volume.

ventricular ejection

The ejection of blood begins when ventricular pressure exceeds arterial pressure and forces the semilunar valves open. Blood spurts out of each ventricle rapidly at first (rapid ejection), then flows out more slowly under less pressure (reduced ejection). WHAT lasts about 200-250 msec, which corresponds to the plateau of the myocardial action potential but lags somewhat behind it. The T wave occurs late in this phase, beginning at the moment of peak ventricular pressure.

stroke volume

The amount of blood in the ventricles ejected, about 70 mL, is called the WHAT (SV).

ejection fraction

The percentage of the EDV ejected, about 54%, is the WHAT?

end-systolic volume

The blood remaining behind, about 60 mL, is called the WHAT?



ejection fraction

In vigorous exercise, the ejection fraction may be as high as 90%. If you exercise, WHAT gets higher?

isovolumetric relaxation

This is early ventricular diastole, when the T wave ends and the ventricles begin to expand. At the beginning of ventricular diastole, blood from the aorta and pulmonary trunk briefly flows backward through the semilunar valves. The backflow, however, quickly fills the cusps and closes them, creating a slight pressure rebound that appears as the DICROTIC NOTCH of the aortic pressure curve.


(isovolumetric relaxation) Heart sound WHAT occurs as blood rebounds from the closed semilunar valves and the ventricles expand.


This phase is called WHAT because the semilunar valves are closed, the AV valves have not yet opened, and the ventricles are therefore taking in no blood. When the AV valves open, ventricular filling (phase 1) begins again.


Heart sound WHAT, if it occurs, is thought to result from the transition from expansion of the empty ventricles to their sudden filling with blood.

atrial systole

WHAT lasts abou 0.1 seconds

ventricular systole

WHAT lasts about 0.3 seconds

quiescent period

(when all four chambers are in diastole) lasts 0.4 seconds.


Total duration of the cardiac cycle is HOW MANY second (800 msec) in a heart beating at 75 bpm.


Both ventricles eject the WHAT amount of blood even though pressure int he right ventricle is only about one-fifth the pressure in the left.

pulmonary edema

If the right ventricle pumped more blood into the lungs than the left side of the heart, blood would accumulate in the lungs and cause WHAT? This would put a person at risk of suffocation as fluid filled the lungs and interfered with gas exchange.

systemic edema

If the left ventricle pumped out more blood than the right heart could handle, blood would accumulate in the systemic circuit and cause WHAT? Over the long term, this could lead to aneurysms (weakened, bulging arteries) stroke, kidney failure, or heart failure.

cardiac output

The amount ejected by each ventricle in 1 minute is called the WHAT?


If HR is heart rate (beats/min) and SC is stroke volume (mL/beat), CO= WHAT? At typical resting values, CO= 75 beats/min x 70 mL/beat= 5,250


A RBC leaving the left ventricle will arrive back to the left ventricle in about HOW MANY minutes?

cardiac reserve

The difference between the maximum and resting cardiac output is called WHAT? People with severe heart disease may have little or no cardiac reserve and little tolerance of physical exertion.


Given that cardiac output equals HR x SV, you can see that there are only HOW MANY ways to change it: 1. change the heart rate 2. change the stroke volume. They usually change together and in opposite directions. As heart rate goes up, stroke volume goes down, and vice versa.


Heart rate is most easily measured by taking a person's WHAT at some point where an artery runs close to the body surface, such as the radial artery in the wrist of common carotid artery in the neck


WHAT is persistent, resting adult heart rate above 100 bpm. It can be caused by stress, anxiety, drugs, heart disease, or fever. Heart rate also rises to compensate to some extent for a drop in stroke volume. Thus, the heart races when the body has lost a significant quantity of blood.


WHAT is a persistent, resting adult heart rate below 60 bpm. It is common during sleep and in endurance-trained athletes. Endurance training enlarges the heart and increases its stroke volume. Thus, the heart can maintain the same output with fewer beats.

cardiac reserve

CO max- CO resting= WHAT? A measure of the extra cardiac output one can draw on when needed, above the resting level. Determines one's tolerance of physical exertion. Relatively high in people with good aerobic fitness; can be very low (near zero) in people with severe heart disease.

cardiac centers

The nervous system modulates the heart's rhythm and force. The reticular formation of the medulla oblongata contains WHAT?

cardioacceleratory center

Cardiac center in medulla oblongata divided into two parts: WHAT connected via sympathetic nerves to SA and AV nodes. Positive chronotropic effect.

cardioinhibitory center

Cardiac center in medulla oblongata divided into two parts: WHAT connected to SA and AV nodes via vagus nerves. Vagal tone holds resting HR down. Parasympathetic. Slows down heart rate.


Chemicals with WHAT chronotropic effects: Epinephrine and norepinephrine (catecholamines), thyroid hormone, hypercalcemia, nicotine


Chemicals with WHAT chronotropic effects: hypernatremia- a potassium excess, K+ diffuses into the cardiocytes and keeps the membrane voltage elevated, inhibiting cardiocyte repolarization. The myocardium becomes less excitable, the heart rate because slow and irregular, and the heart may arrest in diastole. In hyperkalemia- a potassium deficiency, K+ diffuses out of the cardiocytes and they become hyperpolarized- the membrane potential is more negative than normal. This makes them harder to stimulate.


WHAT variables that affect heart rate: age, sex, temperature of SA node.

stroke volume

The other factor in cardiac output is WHAT. This is governed by three variables called preload, contractility, and afterload.


WHAT is the amount of tension in the ventricular myocardium immediately before it begins to contract. Because of the length-tension relationship of striated muscle, moderate stretch enables the cardiocytes to generate more tension when they contract- that is, stretch increases preload.

frank-starling law of the heart

Stroke volume is directly proportional to the end-diastolic volume. In other words, the ventricles tend to eject as much blood as they receive. Within limits, the more they are stretched, the harder they contract on the next beat.


WHAT refers to how hard the myocardium contracts for a given preload. It does not describe the increase in tension produced by stretching the muscle, but rather an increase caused by factors that make the cardiocytes more responsive to stimulation. Factors that increase contractility are called positive inotropic: calcium, digitails.


WHAT is the blood pressure in the aorta and pulmonary trunk immediately distal to the semilunar valves. Anything that impedes arterial circulation can also increase the afterload. Ex.) lung disease, scar tissue forms in the lungs and restricts pulmonary circulation (pulmonary fibrosis). This increases the afterload in the pulmonary trunk. As the right ventricle works harder to overcome this resistance, it gets larger.


Rapid heartbeat allows less time for filling on each cycle. Therefore stroke volume on next contraction is reduced. These may counterbalance each other so CO remains WHAT?


Severe blood loss reduces venous return and stroke volume. Sympathetic nervous system compensates by increasing heart rate (hemorrhage->tachycardia). Cardiac output may remain WHAT (depending on amount of blood lost).


Sympathetic activity rises in fear, anger, exercise, etc. Increases heart rate by acting on SA node. Increases stroke volume by acting on myocardial contractility. Thus, HR and SV both increase; CO and ejection fraction WHAT?

valvular incompetence

WHAT refers to any failure of a valve to prevent reflex- the backward flow of blood.

valvular stenosis

WHAT is a form of insufficiency in which the cusps are stiffened and the opening is constricted by scar tissue. It frequently results from rheumatic fever, a disease in which antibodies produced to fight a bacterial infection also attack the mitral and aortic valves. As the valves become scarred, the heart is overworked by the effort to force blood through the openings and may become enlarged.

heart murmur

Regurgitation of blood through the incompetent valves creates turbulence that can be heard with a stethoscope as a WHAT?

mitral valve prolapse

(MVP) WHAT is an insufficiency in which one or both mitral valve cusps bulge into the atrium during ventricular contraction. It is often hereditary and affects about 1 out of 40 people. It causes no serious dysfunction, but in some people it causes chest pain, fatigue, and shortness of breath.


Atrial flutter, premature ventricular contractions, and ventricular fibrillation are common cardiac wHAT?

premature ventricular contractions

(PVCs) WHAT occur singly or in bursts as a result of early firing of an ectopic focus. PVCs are often due to irritation of the heart by stimulants, emotional stress, or lack of sleep.

ventricular fibrillation

WHAT is a serious arrhythmia caused by electrical signals arriving at different regions of the myocardium at widely different times. A fibrillating ventricle exhibits squirming, uncoordinated contractions.

heart block

WHAT in which some P waves are not transmitted through the AV node and thus fail to generate QRS complexes

congestive heart failure

(CHF) WHAT results from the failure of either ventricle to eject blood effectively. It is usually due to a heart weakened by myocardial infarction, chronic hypertension, valvular insufficiency, or congenital defects in cardiac structure. If the left ventricle fails, blood backs up into the lungs and causes pulmonary edema (fluid in lungs). If the right ventricle fails, blood backs up into the venae cavae and causes systemic edema.

myocardial infarction

(MI) WHAT is the sudden death of a patch of myocardium resulting from long-term obstruction of the coronary circulation. As cardiac muscle downstream from obstruction dies, the individual commonly feels a sense of heavy pressure or squeezing pain in the chest, often "radiating" to the shoulder and left arm. Infarctions weaken the heart wall and disrupt electrical conduction pathways, potentially leading to fibrillation and cardiac arrest.

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