CHAMBERS

The Chambers of the Heart

    The heart has 4 chambers; 1) the right atrium, 2) the right ventricle, 3) the left atrium, and 4) the left ventricle. The word "atrium" comes from the Latin word for "entrance". The atria (plural for atrium)  of the heart function to RECEIVE blood. The word "ventricle" comes from the Latin word for "belly". This origin probably comes from the fact that the ventricles of the heart are the larger of the 4 chambers. They are muscular and perform the rhythmic contraction and relaxation of the cardiac muscle that creates the "pumping" action of the heart. The ventricles both SEND blood out of the heart. 

The Flow of Blood Through the Chambers of the Heart

    The left atrium is the chamber of the heart that receives the oxygenated blood returning from the lungs through the PULMONARY VEINS. From the LEFT ATRIUM, this oxygenated blood travels to the LEFT VENTRICLE and then gets pumped to the body, to deliver oxygen and nutrients and to pick up carbon dioxide and waste products. The blood vessels that transport blood to and from all the body make up the SYSTEMIC CIRCUIT. So the 2 chambers of the heart that receive blood are the ATRIA (atria= plural;  atrium= singular) and the two chambers of the heart that send blood are the VENTRICLES. The ventricles contract and relax rhythmically to create the pumping action of the heart. 

     The right atrium receives the deoxygenated blood that has traveled through the body. This blood has a low level of oxygen and a high level of carbon dioxide. This blood also has low pressure since it has traveled a good distance since it got its last "push" from the heart.
    This deoxygenated blood from the lower and upper body travels to the right atrium, and then travels to the right ventricle. When the right ventricle contracts, it pushes the deoxygenated blood out of the heart and sends it to the lungs. (This is the pulmonary circuit).  As this blood passes by the lungs, it picks up oxygen and gets rid of carbon dioxide.
     The oxygenated blood from the lungs then travels back to the heart to get another "push" before it goes to the body (this is the systemic circuit).  The left atrium receives the oxygenated blood coming from the lungs. This blood enters the left atrium and then travels to the left ventricle. The left ventricle contracts to push the oxygenated blood out of the heart and to the body in order to deliver oxygen and nutrients to the cells and to pick up unwanted substances like waste and carbon dioxide. 

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The Valves of the Heart

Animated Heart Valve GIF Courtesy Of: By DrJanaOfficial - ​ Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=50477765

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​     The function of the heart valves is to assure that blood flows in only one direction through the heart. When there is an increase in pressure of the blood, that pressure acts to push the valve open. The valves only open in one direction, which prevents back flow and guides the blood to flow in the proper direction.

The four main valves of the heart are as follows:
    Two of your heart valves are considered atrioventricular (AV) valves. The atrioventricular (AV) valves include the  tricuspid valve and the mitral valve (also known as the bicuspid valve). The atrioventricular valves, as you might expect, lie between the atria and the ventricles of the heart. 
    The other two heart valves are known as the the semilunar (SL) valves. The two semilunar (SL) valves include the pulmonary semilunar valve and the aortic semilunar valve. 

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  Heart Valve

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1. The Tricuspid Valve is an atrioventricular (AV) valve that allows for the one-way movement of blood from the right atrium to the right ventricle.
2. The Pulmonary Semilunar Valve is a semilunar (SV) valve that allows for the one-way movement of blood from the right ventricle to the pulmonary arteries (which travel to the lungs).
   
3. The Mitral (Bicuspid) Valve is an atrioventricular (AV) valve that allows for the one-way movement of blood from the left atrium to the left ventricle.
   
4. The Aortic Semilunar Valve is a semilunar (SV) valve that allows for the one-way movement of blood from the left ventricle to the aorta (which travel to the body).
   

The Flow of Blood Through the Heart INCLUDING THE VALVES

​    Deoxygenated blood comes from the body and goes to the right atrium. The blood then travels through the TRICUSPID VALVE to get to the right ventricle. Once the right ventricle contracts, this blood is then pumped through the PULMONARY SEMILUNAR VALVE to the pulmonary arteries which will carry the blood to the lungs.

    Oxygenated blood comes from the lungs and enters the left atrium. The blood then travels through the MITRAL (BICUSPID) VALVE to the left ventricle. When the left ventricle contracts, the blood is pumped through the AORTIC SEMILUNAR VALVE to the aorta where it will travel to the body.

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The Vessels of the Circulatory System

The circulatory system has specialized vessels that transport blood around the body.
​These vessels fall into one of two broad categories; arteries and veins. 

ARTERIES = Arteries are the blood vessels that are carrying blood AWAY FROM the heart. The arteries have high pressure, and thick elastic walls. 

VEINS = Veins are the blood vessels that are carrying blood TOWARDS the heart. ​The veins have low pressure and thin walls.  Since they are further away from the heart. Veins have one-way valves that prevent the blood from flowing backward. 

The Arteries

     We begin our discussion on blood vessels with the AORTA. The aorta is the largest and strongest artery in the body and it marks the beginning of the systemic circuit (HEART --> BODY --> HEART). Oxygenated blood gets pumped out of the left ventricle through the aortic semilunar valve, into the aorta.​

     The aorta is separated into 3 segments; The ascending aorta, 2) the aortic arch, and 3) the descending aorta.

   The aortic arch functions to send blood to the upper body. The aortic arch contains 3 branches, 1) the brachiocephalic trunk 2) the left common carotid artery and 3) the left subclavian artery. 

      The first branch is the brachiocephalic trunk (brachiocephalic artery). The brachiocephalic trunk sends blood to the right arm, and the head and neck. The brachiocephalic trunk branches off to form the right subclavian artery and the right common carotid artery. The right subclavian artery supplies blood to the right arm and the right common carotid artery supplies blood to the right side of the head and neck. 

     The second branch is the left common carotid artery and it supplies blood to the left side of the head and neck.  

     The third branch is the left subclavian artery and it supplies blood to the left arm.

    The descending aorta  supplies blood to the lower body and has  branches out to the abdomen, pelvis, perineum and the lower limbs.

The next largest artery you see in the heart is colored BLUE because it is carrying deoxygenated blood from the right ventricle to the lungs. This artery is called the pulmonary trunk. The pulmonary trunk branches off to form the right and left pulmonary arteries. The right pulmonary artery carries the blood to the right lung and the left pulmonary artery carries blood to the left lung.

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   The heart itself needs a supply of blood. There are two arteries that begin at the base of the aorta called the right and left coronary arteries. The right coronary artery supplies oxygenated blood to the cardiac muscles on the right side of the heart and the left coronary artery supplies oxygenated blood to the cardiac muscles on the left side of the heart. 

     The right and left coronary arteries begin at the base of the aorta and travel to the surface of the heart. The right coronary artery runs along the surface of the right atrium. The left coronary artery reaches the surface of the heart and quickly branches off to form two different arteries (see next image). 

     The left coronary artery branches off to form the circumflex artery and the anterior interventricular artery. The circumflex artery circles around the inferior border of the left atrium. The anterior interventricular artery continues downward lying in between the right and left ventricles.  

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THE VEINS

    The largest veins of the body are the superior and inferior vena cava. The superior vena cava brings deoxygenated blood from the upper body to the right atrium. The inferior vena cava brings deoxygenated blood from the lower body to the right atrium. 

     The right and left brachiocephalic veins come together to form the superior vena cava. The right brachiocephalic vein brings deoxygenated blood from the right side of the head and neck and the right arm, to the superior vena cava. The left brachiocephalic vein brings deoxygenated blood from the left side of the head and neck and the left arm, to the superior vena cava.

        Oxygenated blood coming from the lungs returns to the heart through the right and left pulmonary veins. The right pulmonary veins bring oxygenated blood from the right lung to the left atrium of the heart. The left pulmonary veins bring oxygenated blood from the left lung to the left atrium of the heart.

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THE CIRCUITS OF THE CIRCULATORY SYSTEM

     The circulatory system circulates blood around two loops.

1. 1) THE PULMONARY CIRCUIT 

•                - Functions to bring blood from the heart to the lungs and back to the                           heart   
• 2) THE SYSTEMIC CIRCUIT
  • ​               - Functions to bring blood from the heart to all the parts of the                                           body except the lungs and then back to the heart 

In pulmonary circulation, deoxygenated blood travels from the heart to the lungs to gain oxygen and get rid of carbon dioxide before returning to the heart. In contrast, in systemic circulation, oxygenated blood is pumped from the heart to the body and deoxygenated blood is returned back to the heart. ​

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    The right side of the heart receives oxygen-poor blood from the body. (The blood from the body is low in oxygen and high in carbon dioxide.) The chamber of the heart that receives the deoxygenated blood is the RIGHT ATRIUM. From the right atrium, the blood travels to the heart's RIGHT VENTRICLE. From the right ventricle, this deoxygenated blood gets pumped out of the heart and travels to the lungs through PULMONARY ARTERIES. An artery is defined as any blood vessel that carries blood AWAY from the heart. POINTER: This is sometimes a point of confusion for students, because we usually think of arteries as carrying oxygenated blood, and the arteries are often colored in RED to illustrate this idea. HOWEVER, in the pulmonary circuit of the circulatory system, this IS NOT the case. In the pulmonary circuit of the circulatory system, the pulmonary arteries contain deoxygenated blood that travels from the heart to the lungs. When this blood passes by the lungs (the alveoli of the lungs), it gains oxygen molecules and releases carbon dioxide molecules. At this point, the blood becomes oxygenated and appears more reddish in color. This oxygenated blood then travels from the lungs back to the heart through the PULMONARY VEINS. A vein is any blood vessel that carries blood TO the heart. The blood vessels that carry blood to and from the lungs make up the pulmonary circuit (pulmonos = lung).

THE SYSTEMIC CIRCUIT

     Systemic Circulation is the movement of blood from the heart through ALL OF THE PARTS OF THE BODY except THE LUNGS. As the blood travels around the body, the blood delivers oxygen and nutrients to the cells of the body and picks up the unwanted waste products and carbon dioxide from the cells.  while bringing deoxygenated blood back to the heart.
      The systemic circuit begins when the oxygenated blood is pumped out of the left ventricle to the aorta (the largest artery in the body). The aorta branches into major arteries that travel to the upper and lower body. Once the blood has delivered the nutrients and oxygen to the and picked up the carbon dioxide and waste products from the cells, this deoxygenated blood returns to the heart  through the superior and inferior vena cavae. 

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The blood from the upper part of the body enters the right atrium through the SUPERIOR VENA CAVA and the blood from the lower part of the body enters the right atrium though the INFERIOR VENA CAVA. The term"vena cava" comes from the Latin words meaning "hollow" and " vein". 
   

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Summary of White Blood Cells

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OTHER PARTS OF THE HEART YOU NEED TO KNOW

The Walls of the Heart

  Your heart lies within the thoracic (chest) cavity. You may recall that the thoracic cavity is subdivided into the two pleural cavities (one for each of the lungs) and the mediastinum (which is the cavity lying between the pleural cavities). The heart lies in a triple-layered sac called the pericardium which lies within the mediastinum and actively anchors the heart to the mediastinum.  

The word, "pericardium" comes from the the combination of the Greek words for "around" and "heart". 


The outer layer of the pericardium is the fibrous layer. Under (deep to) the fibrous layer, lies the double-layered serous pericardium. The outer layer of the serous pericardium is the parietal pericardium and the inner layer is the visceral pericardium, which is known as the EPICARDIUM. 

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​The walls of the heart have 3 layers.

1. The Epicardium
   
   1. The Visceral Layer of the Serous Pericardium Makes Up the Epicardium
      
2. The Myocardium
   
   1. Thick Layer of Cardiac Muscle Tissue
      
3. The Endocardium
   
   1. Inner lining 

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The left ventricular walls are much thicker than those in the right ventricle.
This is a GREAT way to know which side of the heart you are looking at on the practical exam! 

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The aortic arch is the portion of the main artery that bends between the ascending and descending aorta. It leaves the heart and ascends, then descends back to create the arch. The aorta distributes blood from the left ventricle of the heart to the rest of the body.

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THE LIGAMENTUM ARTERIOSUM

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     The ligamentum arteriosum comes from the Latin term for arterial ligament. This ligament attaches to the aotra and the left pulmonary artery.

     This ligament exists as a remnant (leftover) from a structure called the ductus arteriosus which is a structure that exists only in the fetus and functions to redirects blood from the pulmonary arteries to the aorta. In other words, the ductus arteriosus allows the blood to bypass the lungs. The lungs of the fetus don't function until after they are born, when they take their first breath. 

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The chordae tendinae are better known as your “heart strings”. The chordae tendinae, are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart. They function to add tension to the valves to hold them closed when they are not supposed to open. 

Test Your Skills with this Slide Show

Structure	Function
ASCENDING AORTA	LARGEST ARTERY - BRINGS OXYGENATED BLOOD FROM THE LEFT VENTRICLE TO THE BODY
SUPERIOR VENA CAVA	BRINGS DEOXYGENATED BLOOD FROM THE UPPER BODY TO THE RIGHT ATRIUM
INFERIOR VENA CAVA (NOT SHOWN)	BRINGS DEOXYGENATED BLOOD FROM THE LOWER BODY TO THE RIGHT ATRIUM
RIGHT BRACHIOCEPHALIC VEIN	BRINGS BLOOD FROM RIGHT SIDE OF UPPER BODY (Right Side of Head and Neck and the Right Arm) TO THE SUPERIOR VENA CAVA
LEFT BRACHIOCEPHALIC VEIN	​BRINGS BLOOD FROM LEFT SIDE OF UPPER BODY (Left Side of Head and Neck and the Left Arm) TO THE SUPERIOR VENA CAVA
BRACHIOCEPHALIC TRUNK	THE BRACHIOCEPHALIC TRUNK  IS THE FIRST OF THE 3 ARTERIES THAT SPLIT OFF OF THE AORTIC ARCH. THE BRACHIOCEPHALIC TRUNK SPLITS OFF TO FORM THE RIGHT COMMON CAROTID ARTERY AND THE RIGHT SUBCLAVIAN ARTERY. The common carotid artery sends oxygenated blood to the right side of the head and neck. The right subclavian artery send oxygenated blood to the right arm.
LEFT COMMON CAROTID ARTERY	THE LEFT COMMON CAROTID ARTERY IS THE 2nd OF THE 3 BRANCHES COMING OFF OF THE AORTIC ARCH. THE LEFT COMMON CAROTID ARTERY BLOOD FROM THE AORTIC ARCH TO THE LEFT SIDE OF THE HEAD AND NECK.
LEFT SUBCAVIAN ARTERY	THE LEFT SUBCLAVIAN ARTERY IS THE 3rd (LAST) OF THE BRANCHES COMING OFF OF THE AORTIC ARCH. THE LEFT SUBCLAVIAN ARTERY BRINGS BLOOD FROM THE AORTIC ARCH TO THE LEFT ARM.
AORTIC ARCH	HOLDS THE 3 ARTERIES THAT BRANCH UPWARD TO SEND BLOOD TO UPPER BODY (the brachiocephalic trunk, the left common carotid artery and the left subclavian artery)
DESCENDING AORTA (NOT SHOWN)	THIS IS THE PORTION OFTHE AORTA THAT COMES AFTER THE AORTIC ARCH AND TURNS INFERIORLY TO SUPPLY OXYGENATED BLOOD TO THE LOWER BODY.
PULMONARY TRUNK	BRINGS DEOXYGENATED BLOOD FROM THE RIGHT VENTRICLE TO THE RIGHT AND LEFT PULMONARY ARTERIES.
LEFT PULMONARY ARTERIES	BRINGS DEOXYGENATED BLOOD TO THE LEFT LUNG
RIGHT PULMONARY ARTERIES (NOT SHOWN)	BRINGS DEOXYGENATED BLOOD TO RIGHT LUNG
LEFT PULMONARY VEINS	BRINGS OXYGENATED BLOOD FROM THE LEFT LUNG TO THE LEFT ATRIUM
RIGHT PULMONARY VEINS (NOT SHOWN)	BRINGS OXYGENATED BLOOD FROM THE RIGHT LUNG TO THE LEFT ATRIUM