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What is the cardiovascular system?

The cardiovascular system includes the heart blood vessels and blood.

What is the heart?

The heart is a muscular organ that acts as a pump to deliver blood to the body.

Why is the heart considered two pumps?

The heart consists of two pumps that propel blood through two different circuits.

Where is the heart located?

The heart is situated in the chest slightly to the left in the mediastinum.

What is the mediastinum?

The mediastinum is a subdivision of the thoracic cavity that contains the heart great blood vessels trachea and esophagus.

What is the pericardial cavity?

The pericardial cavity is a subcavity of the mediastinum that contains the heart.

What shape is the heart?

The heart is cone-shaped.

What is the apex of the heart?

The apex is the pointed end of the heart that points toward the left hip.

What is the base of the heart?

The base is the flattened portion of the heart that faces the posterior rib cage.

How much does the heart weigh?

The heart weighs about 250 to 350 grams which is slightly less than one pound.

How many chambers does the heart have?

The heart has four hollow chambers consisting of the right atrium left atrium right ventricle and left ventricle.

What is the atrioventricular sulcus?

The atrioventricular sulcus is an external indentation at the boundary between the atria and ventricles.

What is the interventricular sulcus?

The interventricular sulcus is an external groove located between the right and left ventricles.

What do the atria do?

The atria receive blood from veins and deliver it to the ventricles.

What do the ventricles do?

The ventricles pump blood into arteries that carry blood away from the heart.

What vessels deliver blood to the right atrium?

The superior vena cava and inferior vena cava deliver blood to the right atrium.

What vessels deliver blood to the left atrium?

The pulmonary veins deliver blood to the left atrium.

What vessel receives blood from the right ventricle?

The pulmonary trunk receives blood from the right ventricle.

What vessel receives blood from the left ventricle?

The aorta receives blood from the left ventricle.

What are the great vessels?

The great vessels are the major veins and arteries connected to the heart.

What is the pulmonary pump?

The pulmonary pump is the right side of the heart which pumps blood to the lungs.

What is the pulmonary circuit?

The pulmonary circuit is the series of blood vessels leading to and within the lungs.

Is the pulmonary circuit a high-pressure or low-pressure circuit?

The pulmonary circuit is a low-pressure circuit.

What type of blood does the right side of the heart pump to the lungs?

The right side of the heart pumps deoxygenated blood to the lungs through the pulmonary arteries.

Where does gas exchange occur in the pulmonary circuit?

Gas exchange occurs between air in the alveoli and blood in the pulmonary capillaries.

How does oxygenated blood return from the lungs to the heart?

Oxygenated blood returns to the left side of the heart through the pulmonary veins.

What is the systemic pump?

The systemic pump is the left side of the heart which pumps blood to the rest of the body.

What is the systemic circuit?

The systemic circuit is the series of blood vessels that serve the body.

Is the systemic circuit a high-pressure or low-pressure circuit?

The systemic circuit is a high-pressure circuit.

What type of blood does the left side of the heart pump to the body?

The left side of the heart pumps oxygenated blood to the body through the aorta.

Where does gas exchange occur in the systemic circuit?

Gas exchange occurs between tissues and blood in the systemic capillaries.

How does deoxygenated blood return from the body to the heart?

Deoxygenated blood returns to the right side of the heart through the vena cava.

What does the heart help maintain besides blood flow?

The heart helps maintain homeostasis of blood pressure.

What is blood pressure?

Blood pressure is the pressure that blood exerts on blood vessels.

How does the heart influence blood pressure?

The rate and force of heart contractions influence blood pressure and blood flow to organs.

Why is the heart considered an endocrine organ?

The atria produce a hormone called atrial natriuretic peptide.

What is atrial natriuretic peptide?

Atrial natriuretic peptide is a hormone produced by the atria that lowers blood pressure by decreasing sodium retention in the kidneys.

How does atrial natriuretic peptide lower blood pressure?

It decreases sodium retention which reduces osmotic water retention and reduces blood volume and pressure.

What is the pericardial cavity filled with?

The pericardial cavity contains a thin layer of pericardial fluid.

What is the function of pericardial fluid?

Pericardial fluid lubricates the heart as it moves and decreases friction.

What is the myocardium?

The myocardium is the thickest layer of the heart wall and is composed of cardiac muscle cells and their extracellular matrix.

How are the cardiac muscle cells of the myocardium arranged?

The cardiac muscle cells and their extracellular matrix are arranged in a spiral manner around the chambers.

What is the fibrous skeleton of the heart?

The fibrous skeleton is structural connective tissue associated with the heart and its chambers and valves.

What are trabeculae carneae?

Trabeculae carneae are irregular protrusions of cardiac muscle tissue found inside both ventricles.

What are papillary muscles?

Papillary muscles are finger-like projections of cardiac muscle in the ventricular walls.

What are chordae tendineae?

Chordae tendineae are tendon-like cords that attach papillary muscles to the valves between the atria and ventricles.

What is the function of the chordae tendineae?

Chordae tendineae connect the papillary muscles to the atrioventricular valves.

What is the interventricular septum?

The interventricular septum separates the right and left ventricles and contracts with the ventricular muscle.

Why are valves needed in the heart?

Valves ensure that blood flows through the heart in only one direction and prevent backflow.

Why is backflow prevented in the ventricles?

High pressure produced when the ventricles contract could push blood backward into the atria.

Why could blood flow backward from the arteries into the ventricles?

Blood leaves the ventricles into high-pressure arteries and moves against gravity which could cause backward flow.

What are semilunar valves?

Semilunar valves are outflow valves located between the ventricles and arteries.

How many cusps do semilunar valves have?

Semilunar valves have three cusps with half-moon shapes.

Where is the pulmonary valve located?

The pulmonary valve is located between the right ventricle and the pulmonary trunk.

Where is the aortic valve located?

The aortic valve is located between the left ventricle and the aorta.

Do semilunar valves have chordae tendineae or papillary muscles?

No semilunar valves do not have chordae tendineae or papillary muscles.

Where is the SA node located?

The sinoatrial node is located in the right atrium inferior and lateral to the opening of the superior vena cava.

What is the intrinsic rate of the SA node?

The SA node has an intrinsic rate of about 60 to 70 or more depolarizations per minute.

What can influence the SA node?

The sympathetic and parasympathetic nervous systems can influence the SA node.

Where is the AV node located?

The atrioventricular node is located posterior and medial to the tricuspid valve.

What is the intrinsic rate of the AV node?

The AV node has an intrinsic rate of about 40 to 50 depolarizations per minute.

What is the Purkinje fiber system?

The Purkinje fiber system is the slowest group of pacemaker cells with an intrinsic rate of about 20 depolarizations per minute.

What are atypical pacemakers?

Atypical pacemakers are pacemaker cells whose action potentials rely on different ion channels.

What structures are included in the Purkinje fiber system?

The Purkinje fiber system includes the AV bundle right and left bundle branches and terminal branches.

What is the AV bundle?

The AV bundle penetrates the fibrous skeleton in the inferior interatrial septum and superior interventricular septum.

Where do the right and left bundle branches travel?

The right and left bundle branches course along the right and left sides of the interventricular septum.

What do the terminal branches do?

Terminal branches penetrate the ventricles and contact contractile cardiac muscle cells.

What percentage of cardiac muscle cells are contractile cells?

Contractile cells make up about 99 percent of cardiac muscle cells.

How are pacemaker cell action potentials transmitted to contractile cells?

Pacemaker cell action potentials are transmitted to contractile cells through intercalated discs.

What happens during the rapid depolarization phase of a contractile cell action potential?

Voltage-gated sodium channels in the sarcolemma open and sodium ions flow into the cell causing rapid depolarization.

Why is contractile cell depolarization faster than pacemaker cell depolarization?

Contractile cell depolarization is faster because sodium channels activate more quickly than calcium channels.

What causes the initial repolarization phase?

Initial repolarization occurs when sodium channels abruptly inactivate and a small amount of potassium leaves through potassium channels.

What is the plateau phase?

The plateau phase is a period when depolarization is sustained at about 0 mV.

What causes the plateau phase?

Slow calcium channels open and calcium enters while potassium leaves resulting in little net change in membrane potential.

How are cardiac contractile cell action potentials different from skeletal muscle action potentials?

Cardiac contractile cell action potentials have a plateau phase that skeletal muscle action potentials do not have.

What is an electrocardiogram?

An electrocardiogram is a graphic depiction of the electrical activity occurring in cardiac muscle cells over time.

What does an ECG record?

An ECG records changes in electrical activity from the heart using electrodes placed on the skin.

Where are ECG electrodes placed?

ECG electrodes are placed on the chest and extremities.

What type of cardiac cells are primarily measured by a standard ECG?

A standard ECG measures electrical changes from contractile cells because there are not enough pacemaker cells to measure their activity directly.

What does the P wave represent?

The P wave represents depolarization of the cells in the atria except the SA node.

What does the flat segment before the P wave represent?

The flat segment before the P wave represents depolarization of the SA node.

What does the QRS complex represent?

The QRS complex represents ventricular depolarization.

Why is the QRS complex larger than the P wave?

The QRS complex is larger because the ventricles contain more muscle than the atria.

What happens to atrial repolarization during the QRS complex?

Atrial repolarization occurs during the QRS complex but is obscured by the large QRS complex.

What does the T wave represent?

The T wave represents ventricular repolarization.

What can an inverted T wave indicate?

An inverted T wave can occur with some pathologies because of changes in electrical activity.

What is an ECG interval?

An ECG interval is a period between waves that includes a component of at least one wave.

What is an ECG segment?

An ECG segment is a period that does not include any wave components.

What does the R-R interval represent?

The R-R interval represents the entire duration of generation and spread of an action potential through the heart.

What does the R-R interval determine?

The R-R interval determines heart rate.

What does the P-R interval represent?

The P-R interval represents the time required for depolarization to spread from the SA node through the atria to the ventricles.

What is included in the P-R interval?

The P-R interval includes the delay at the AV node.

What does the Q-T interval represent?

The Q-T interval represents the period during which ventricular cells are undergoing action potentials.

What is the S-T segment?

The S-T segment is recorded during the plateau phase of the ventricles when there are no net changes in electrical activity.

What can elevations or depressions of the S-T segment indicate?

S-T segment elevations or depressions can occur with clinical conditions such as myocardial infarction.

What information can an ECG provide?

An ECG can provide information about the structure conduction pathways and overall health of the heart.

What is a dysrhythmia?

A dysrhythmia is a disturbance in the electrical rhythm of the heart.