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1. Anatomy and physiology
1.1 Nervous system
1.2 Cardiovascular system
1.2.1 Heart
1.2.2 Blood vessels
1.2.3 Blood
1.3 Lymphatic system
1.4 Digestive system
1.5 Respiratory system
1.6 Urinary system
2. Kinesiology
3. Pathology & special populations
4. Benefits and effects
5. Assessment and planning
6. Sandbox Folder
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1.2.1 Heart
Achievable MBLEx
1. Anatomy and physiology
1.2. Cardiovascular system
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Heart

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Revised 2025-08-28 12:33:33 PM EDT

This and the following sections focus on the cardiovascular system which includes the heart, blood, and blood vessels, which are the tubes that carry blood. The cardiovascular system moves oxygen, carbon dioxide, nutrients, hormones, and waste products throughout the body, ensuring that tissues receive what they need and that byproducts are removed. For massage therapists, understanding this system provides insight into how blood circulation interacts with 1) the beneficial effects of massage, 2) the benign side effects of massage, and 3) massage contraindications.

Sidenote
Circulatory system vs. cardiovascular system

The term “circulatory system” refers to the cardiovascular system (which carries blood) plus the lymphatic system (which carries lymph). The lymphatic system is covered separately.

Structure and function of the heart

The heart pumps blood through the cardiovascular system. It is a muscular organ roughly the size of a fist, located in a space between the lungs and superior to the diaphragm: the mediastinum. Its internal structure is divided into four chambers that pump blood: two upper chamber called atria (singular: “atrium”) and two lower chambers called ventricles. Blood moves through these chambers in order:

  1. The right atrium receives deoxygenated blood returning from the cells of the body and pumps it to the right ventricle.
  2. After the right ventricle receives deoxygenated blood from the right atrium, it pumps it to the lungs for gas exchange.
  3. The left atrium receives the recently oxygenated blood from the lungs and pumps it to the left ventricle.
  4. After the left ventricle receives this oxygen-rich blood from the left atrium it then pumps the blood out to the tissues and cells of the rest of the body.

To keep blood flowing in one direction, the heart relies on a number of one-way valves. The atrioventricular (AV) valves prevent blood from being pushed back up into the atria from the ventricles.

Definitions
Tricuspid valve
The right AV valve is called the tricuspid valve because it has three “cusps” (flaps).
Mitral valve (or bicuspid valve)
The left AV valve is called the bicuspid valve (“two flaps”), or mitral valve (because it it shaped like a religious figure’s hat called a “mitre”).
Sidenote
Where the name "mitral valve" comes from

These names were assigned during a time when the Catholic church was powerful even in scientific life.

These AV valves are supported by connective tissue cords anchored to tiny mound-shaped muscles in the ventricles. This support prevents the valve cusps from being pushed back up into the atria, which would allow the backflow of blood. These connective tissue cords are called chordae tendineae and the muscles they are anchored to are called the papillary muscles.

At the exits of the ventricles are the semilunar valves, which prevent backflow into the heart from the lungs (the pulmonary valve), and from the rest of the body via the aorta (the aortic valve).

Tissue layers of the heart

Though the heart is made of multiple layers of tissue, the thickest layer by far and the majority of the heart’s mass is the layer that contains its muscle cells.

Definitions
Myocardium
Though the heart is made of multiple layers of tissue, the thickest layer by far and the majority of the heart’s mass is the layer that contains its muscle cells: the myocardium.
Pericardium
Superficial to the myocardium is a multi-layered protective sac that contains fluid to reduce friction as the heart beats and the body moves: the pericardium.
Endocardium
Deep to the myocardium is the lining of the heart chambers, which provides a smooth surface to minimize resistance and helps form heart valves: the endocardium.

How the heart beats

Students often incorrectly assume that each heartbeat is triggered by the brain. Though the brain can influence heart rate, the heart’s rhythmic contractions are generated by an intrinsic conduction system that includes specialized pace-making cells and the connections that carry their signals to the rest of the muscle cells in the heart. The sinoatrial (SA) node, located in the right atrium, serves as the heart’s natural pacemaker, generating impulses that initiate each heart beat (and effectively set the heart rate). These impulses first spread through the atria, causing them to contract. The SA node’s impulses also reach the atrioventricular (AV) node, which introduces a brief delay so the ventricles can fully fill before they contract. Once the ventricles have filled the AV node sends a “ventricles contract!” signal that moves through progressively finer pathways: starting in the thick bundle of His, which splits into the smaller right and left bundle branches, which each branch into even thinner Purkinje fibers that penetrate the ventricular muscle and deliver the AV node’s signal and trigger a coordinated ventricular contraction.

Each heartbeat – or cardiac cycle – includes two phases:

  1. Contraction of the ventricles (“systole”), which propels blood away from the heart, to the lungs and other tissues of the body;
  2. The relaxing and refilling of the all chambers of the heart (“diastole”). Late in diastole is when the atria contract to complete the filling of the ventricles.

There are two ways that you might already be familiar with your own cardiac cycle. First, you might recognize these words from when your blood pressure is assessed. Blood pressure is expressed as the higher systolic pressure over the lower diastolic pressure. Second, the familiar heart sounds, “lubb” and “dubb”, correspond to the closing of valves during the cardiac cycle: the first sound marks the closure of the AV valves at the start of ventricular contraction, and the second reflects the closing of semilunar valves as the ventricles relax.

Cardiovascular system overview

  • Includes heart, blood, blood vessels
  • Transports oxygen, carbon dioxide, nutrients, hormones, waste
  • Circulatory system = cardiovascular + lymphatic systems

Structure and function of the heart

  • Four chambers: right atrium, right ventricle, left atrium, left ventricle
  • Right side: receives deoxygenated blood, sends to lungs
  • Left side: receives oxygenated blood, pumps to body
  • One-way valves:
    • AV valves: tricuspid (right), bicuspid/mitral (left)
    • Semilunar valves: pulmonary (to lungs), aortic (to body)
    • Chordae tendineae and papillary muscles prevent backflow

Tissue layers of the heart

  • Myocardium: thick, muscular middle layer
  • Pericardium: protective, fluid-filled sac around heart
  • Endocardium: smooth inner lining, forms heart valves

How the heart beats

  • Intrinsic conduction system controls rhythm (not brain)
    • SA node: pacemaker, initiates heartbeat
    • AV node: delays signal, allows ventricular filling
    • Bundle of His → bundle branches → Purkinje fibers: coordinate contraction
  • Cardiac cycle phases:
    • Systole: ventricular contraction, blood ejected
    • Diastole: chambers relax and refill
  • Heart sounds:
    • “Lubb”: AV valves close (start of systole)
    • “Dubb”: semilunar valves close (start of diastole)
  • Blood pressure: systolic (higher, during contraction) / diastolic (lower, during relaxation)
Previous
Next  | 1.2.2 Blood vessels
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Heart

Revised 2025-08-28 12:33:33 PM EDT

This and the following sections focus on the cardiovascular system which includes the heart, blood, and blood vessels, which are the tubes that carry blood. The cardiovascular system moves oxygen, carbon dioxide, nutrients, hormones, and waste products throughout the body, ensuring that tissues receive what they need and that byproducts are removed. For massage therapists, understanding this system provides insight into how blood circulation interacts with 1) the beneficial effects of massage, 2) the benign side effects of massage, and 3) massage contraindications.

Sidenote
Circulatory system vs. cardiovascular system

The term “circulatory system” refers to the cardiovascular system (which carries blood) plus the lymphatic system (which carries lymph). The lymphatic system is covered separately.

Structure and function of the heart

The heart pumps blood through the cardiovascular system. It is a muscular organ roughly the size of a fist, located in a space between the lungs and superior to the diaphragm: the mediastinum. Its internal structure is divided into four chambers that pump blood: two upper chamber called atria (singular: “atrium”) and two lower chambers called ventricles. Blood moves through these chambers in order:

  1. The right atrium receives deoxygenated blood returning from the cells of the body and pumps it to the right ventricle.
  2. After the right ventricle receives deoxygenated blood from the right atrium, it pumps it to the lungs for gas exchange.
  3. The left atrium receives the recently oxygenated blood from the lungs and pumps it to the left ventricle.
  4. After the left ventricle receives this oxygen-rich blood from the left atrium it then pumps the blood out to the tissues and cells of the rest of the body.

To keep blood flowing in one direction, the heart relies on a number of one-way valves. The atrioventricular (AV) valves prevent blood from being pushed back up into the atria from the ventricles.

Definitions
Tricuspid valve
The right AV valve is called the tricuspid valve because it has three “cusps” (flaps).
Mitral valve (or bicuspid valve)
The left AV valve is called the bicuspid valve (“two flaps”), or mitral valve (because it it shaped like a religious figure’s hat called a “mitre”).
Sidenote
Where the name "mitral valve" comes from

These names were assigned during a time when the Catholic church was powerful even in scientific life.

These AV valves are supported by connective tissue cords anchored to tiny mound-shaped muscles in the ventricles. This support prevents the valve cusps from being pushed back up into the atria, which would allow the backflow of blood. These connective tissue cords are called chordae tendineae and the muscles they are anchored to are called the papillary muscles.

At the exits of the ventricles are the semilunar valves, which prevent backflow into the heart from the lungs (the pulmonary valve), and from the rest of the body via the aorta (the aortic valve).

Tissue layers of the heart

Though the heart is made of multiple layers of tissue, the thickest layer by far and the majority of the heart’s mass is the layer that contains its muscle cells.

Definitions
Myocardium
Though the heart is made of multiple layers of tissue, the thickest layer by far and the majority of the heart’s mass is the layer that contains its muscle cells: the myocardium.
Pericardium
Superficial to the myocardium is a multi-layered protective sac that contains fluid to reduce friction as the heart beats and the body moves: the pericardium.
Endocardium
Deep to the myocardium is the lining of the heart chambers, which provides a smooth surface to minimize resistance and helps form heart valves: the endocardium.

How the heart beats

Students often incorrectly assume that each heartbeat is triggered by the brain. Though the brain can influence heart rate, the heart’s rhythmic contractions are generated by an intrinsic conduction system that includes specialized pace-making cells and the connections that carry their signals to the rest of the muscle cells in the heart. The sinoatrial (SA) node, located in the right atrium, serves as the heart’s natural pacemaker, generating impulses that initiate each heart beat (and effectively set the heart rate). These impulses first spread through the atria, causing them to contract. The SA node’s impulses also reach the atrioventricular (AV) node, which introduces a brief delay so the ventricles can fully fill before they contract. Once the ventricles have filled the AV node sends a “ventricles contract!” signal that moves through progressively finer pathways: starting in the thick bundle of His, which splits into the smaller right and left bundle branches, which each branch into even thinner Purkinje fibers that penetrate the ventricular muscle and deliver the AV node’s signal and trigger a coordinated ventricular contraction.

Each heartbeat – or cardiac cycle – includes two phases:

  1. Contraction of the ventricles (“systole”), which propels blood away from the heart, to the lungs and other tissues of the body;
  2. The relaxing and refilling of the all chambers of the heart (“diastole”). Late in diastole is when the atria contract to complete the filling of the ventricles.

There are two ways that you might already be familiar with your own cardiac cycle. First, you might recognize these words from when your blood pressure is assessed. Blood pressure is expressed as the higher systolic pressure over the lower diastolic pressure. Second, the familiar heart sounds, “lubb” and “dubb”, correspond to the closing of valves during the cardiac cycle: the first sound marks the closure of the AV valves at the start of ventricular contraction, and the second reflects the closing of semilunar valves as the ventricles relax.

Key points

Cardiovascular system overview

  • Includes heart, blood, blood vessels
  • Transports oxygen, carbon dioxide, nutrients, hormones, waste
  • Circulatory system = cardiovascular + lymphatic systems

Structure and function of the heart

  • Four chambers: right atrium, right ventricle, left atrium, left ventricle
  • Right side: receives deoxygenated blood, sends to lungs
  • Left side: receives oxygenated blood, pumps to body
  • One-way valves:
    • AV valves: tricuspid (right), bicuspid/mitral (left)
    • Semilunar valves: pulmonary (to lungs), aortic (to body)
    • Chordae tendineae and papillary muscles prevent backflow

Tissue layers of the heart

  • Myocardium: thick, muscular middle layer
  • Pericardium: protective, fluid-filled sac around heart
  • Endocardium: smooth inner lining, forms heart valves

How the heart beats

  • Intrinsic conduction system controls rhythm (not brain)
    • SA node: pacemaker, initiates heartbeat
    • AV node: delays signal, allows ventricular filling
    • Bundle of His → bundle branches → Purkinje fibers: coordinate contraction
  • Cardiac cycle phases:
    • Systole: ventricular contraction, blood ejected
    • Diastole: chambers relax and refill
  • Heart sounds:
    • “Lubb”: AV valves close (start of systole)
    • “Dubb”: semilunar valves close (start of diastole)
  • Blood pressure: systolic (higher, during contraction) / diastolic (lower, during relaxation)

More from Cardiovascular system

  • Blood vessels
  • Blood