Note: There are several sub pages for the the Cardiac Unit, including Cardiac Development & Aging, Cardiac Functions & Structures, Cardiac Clinical View, Cardiac News Articles, and Cardiac Review

Learning Objectives

• Detail the blood pathway through the chambers of the heart
• Identify the mechanisms that regulate blood pressure
• Understand the three main functions of the Cardiovascular System (heart, blood and blood vessels)
• Understand and describe the cardiac cycle and cardiac output

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• Did you know that the heart beats approximately 4500 times per hour or 108,000 times per day or about 2.5 billion times during a 72 year lifetime?
• Did you know that the heart can increase its output up to 5 or 6 fold when the body requires more oxygen or nutrients?

• Did you know that the blood in your body travels approximately 12 miles as it is circulated throughout the body each day?
• Did you know that your heart is approximately the size of two of your fists as an adult and only one if your a child?
• Did you know the Aorta is approximately the same diameter as a garden hose?
• Did you know that the heart in one lifetime will pump approximately 1 million barrels (200,000,000 liters) of blood?

Introduction to the HUMAN HEART

The Heart also known as the Ol' ticker or the window into your soul has been associated with not only an organ beating inside the chest cavity in all vertebrates, it has also been associated with Valentines, Love, Honor, Courage and Spirit. So when you read further into this page let us clarify that it is the organ beating inside the chest cavity that will be discussed, but have heart you might learn something very interesting.

What comes to mind when you place your hand on over your heart during the national anthem? Most response would be that you place your hand over the left side of chest to cover your heart, but why? The actual location of the heart is in the Mediastenium, which is the cavity between the lungs. The heart is a hollow muscular chambered organ with the Apex of the heart (pointed end) pointing downward and towards the left hip and the Base of the heart (the top) facing upwards toward the right shoulder.

Basic Anatomy of the Heart

About the heart The heart is the hardest working muscle in the human body. Located almost in the center of the chest, the adult human heart is about the size of two fists held side-by-side. At an average rate of 80 times a minute, the heart beats about 115,000 times in one day or 42 million times in a year. During an average lifetime, the human heart will beat more than 3 billion times - pumping an amount of blood that equals about 1 million barrels. Even at rest, the heart continuously works hard. How the heart works The cardiovascular system, composed of the heart and blood vessels, is responsible for circulating blood throughout your body to supply the body with oxygen and nutrients. The heart is the muscle that pumps blood filled with oxygen and nutrients through the blood vessels to the body tissues. It is made up of: Four chambers (two atria and two ventricles) that receive blood from the body and pump out blood to it. The atria receive blood coming back to the heart. The ventricles pump the blood out of the heart. Blood vessels, which compose a network of arteries and veins that carry blood throughout the body. Arteries transport blood from the heart to the body tissues. Veins carry blood back to the heart. Four valves to prevent backward flow of blood. Each valve has flaps, called leaflets, that allow the forward flow of blood and prevent the backward flow. An electrical system of the heart that controls how fast it beats. * This video identifies the basic functions of the heart, including the separation of chambers, the different valves involved, the flow of blood through the heart, and general composition of heart tissue. After viewing this video, you should have a basic understanding of how the heart works, and what happens for each beat of the heart. This video should make review much easier, and it should help in studying and reviewing this page. What are Heart Valves The heart consists of four chambers, two atria (upper chambers) and two ventricles (lower chambers). There is a valve through which blood passes before leaving each chamber of the heart. The valves prevent the backward flow of blood. These valves are actual flaps that are located on each end of the two ventricles (lower chambers of the heart). They act as one-way inlets of blood on one side of a ventricle and one-way outlets of blood on the other side of a ventricle. Each valve actually has three flaps, except the mitral valve, which has two flaps. The four heart valves include the following: tricuspid valve: located between the right atrium and the right ventricle pulmonary valve: located between the right ventricle and the pulmonary artery mitral valve: located between the left atrium and the left ventricle aortic valve: located between the left ventricle and the aorta How do the Heart Valves Function As the heart muscle contracts and relaxes, the valves open and shut, letting blood flow into the ventricles and atria at alternate times. The following is a step-by-step illustration of how the valves function normally in the left ventricle: After the left ventricle contracts, the aortic valve closes and the mitral valve opens, to allow blood to flow from the left atrium into the left ventricle. As the left atrium contracts, more blood flows into the left ventricle. When the left ventricle contracts again, the mitral valve closes and the aortic valve opens, so blood flows into the aorta. What is Heart Valve Disease Heart valves can have one of two malfunctions: The regurgitation valve(s) does not close completely, causing the blood to flow backward instead of forward through the valve. valve(s) opening becomes narrowed or does not form properly, inhibiting the flow of blood out of the ventricle or atria. The heart is forced to pump blood with increased force in order to move blood through the stiff (stenotic) valve(s). Heart valves can have both malfunctions at the same time (regurgitation and stenosis). When heart valves fail to open and close properly, the implications for the heart can be serious, possibly hampering the heart's ability to pump blood adequately through the body. Heart valve problems are one cause of heart failure.

Anatomy and Function of the Coronary Arteries

Coronary arteries supply blood to the heart muscle. Like all other tissues in the body, the heart muscle needs oxygen-rich blood to function, and oxygen-depleted blood must be carried away. The coronary arteries consist of two main arteries: the right and left coronary arteries, and their two branches, the circumflex artery and the left anterior descending artery. What are the different coronary arteries? The two main coronary arteries are the left and right coronary arteries. The left coronary artery (LCA), which divides into the left anterior descending artery and the circumflex branch, supplies blood to the heart ventricles and left atrium. The right coronary artery (RCA), which divides into the right posterior descending artery and a large marginal branch, supplies blood to the heart ventricles, right atrium, and sinoatrial node (cluster of cells in the right atrial wall that regulates the heart's rhythmic rate). Additional arteries branch off the two main coronary arteries to supply the heart muscle with blood. These include the following: circumflex artery (Cx) The circumflex artery branches off the left coronary artery and encircles the heart muscle. This artery supplies blood to the back of the heart. left anterior descending artery (LAD) The left anterior descending artery branches off the left coronary artery and supplies blood to the front of the heart. Smaller branches of the coronary arteries include: acute marginal, posterior descending (PDA), obtuse marginal (OM), and diagonals. Why are the coronary arteries important? Since coronary arteries deliver blood to the heart muscle, any coronary artery disorder or disease can have serious implications by reducing the flow of oxygen and nutrients to the heart, which may lead to a heart attack and possibly death. Atherosclerosis (a build-up of plaque in the inner lining of an artery causing it to narrow or become blocked) is the most common form of coronary artery disease.

The Pathway of Blood

Superior Vena Cava: receives blood from the head and upper body and drains it into the right atrium.

Inferior Vena Cava: receives blood from the legs and trunk and drains it into the right atrium.

Coronary Veins: return deoxygenated blood from myocardium to coronary sinus.

Coronary Sinus: receives venous blood from the veins within myocardium and drains into the right atrium.

Right Atrium: superior chamber of the heart that receives blood from the vena cavae and coronary sinus.

Right Atrioventricular (tricuspid) Valve: located between the right atrium and right ventricle, prevents back flow into the right atrium during ventricular contraction.

Right Ventricle: right inferior portion of the heart, sends blood to the pulmonary trunk.

Pulmonary (semi-lunar) Valve: prevents back flow of blood from the pulmonary trunk to the right ventricle during ventricular relaxation

Pulmonary Trunk: a large vessel on the anterior superior portion of the heart that receives blood from right ventricle and directs
to the lungs via the pulmonary arteries.

Pulmonary Arteries: paired branches of the pulmonary trunk that direct deoxygenated blood to the lungs to be oxygenated. One of the few places that deoxygenated blood gets carried by arteries.

Pulmonary Veins: two vessels from each lung that return oxygenated blood to the heart's left atrium. One of the few places that oxygenated blood gets carried by veins. Left Atrium: receives blood from the lungs via the pulmonary veins.

Left Atrioventricular (bicuspid or mitral) Valve: located between atrium and ventricle on the left side, prevents back flow of blood into the left atrium during ventricular contraction.

Left Ventricle: Composed of an unusually thick myocardial wall for contraction against high pressure.

Aortic (semi-lunar) Valve: three half-moon shaped cusps that prevent back flow of blood from the aorta to the relaxed left ventricle.

Ascending Aorta: receives blood immediately from the ascending aorta. supply blood to the myocardium.

Aortic Arch: curved portion of the aorta that extends superiorly and posteriorly to the pulmonary trunk.

Descending Aorta: portion of the aorta that descends from the aortic arch and continues inferiorly until it divides into the common iliac arteries.

Branches of the Descending Aorta

The Intercostal, Renal artery, Gonadal artery, Common Iliac artery are all paired.
The three that are not paired are the Celiac Trunk, Superior Mesenteric artery, Inferior Mesenteric artery

Systemic Vs Pulmonary Circulation

Table 8­1. Systemic and pulmonary circulations.
	Systemic circulation	Pulmonary circulation
Path of blood	Left atrium Left ventricle Systemic arteries Systemic capillaries Systemic veins Right atrium Right ventricle	Right atrium Right ventricle Pulmonary arteries Pulmonary capillaries Pulmonary veins Left atrium Left ventricle
Function	Carries oxygenated blood from the left side of the heart through the systemic arteries to all the organs and tissues After delivering oxygen and receiving carbon dioxide in the systemic capillaries, returns deoxygenated blood through the systemic veins to the right atrium where the pulmonary circulation begins	Carries deoxygenated blood from the right side of the heart through the pulmonary arteries to the lungs After receiving oxygen and delivering carbon dioxide in the pulmonary capillaries, returns oxygenated blood through the pulmonary veins to the left atrium where the systemic circulation begins
Pressure	Relatively high­pressure system; range of normal mean systemic arterial pressure is 70 to 105 mm Hg; easily measured with blood pressure cuff	Relatively low­pressure system; range of normal mean pulmonary artery pressure is 10 to 22 mm Hg; can only be measured with pulmonary artery catheter
Cause of elevated pressure	Unknown in majority of cases; renal disease in some patients; hypoxemia not a cause	Usually can be determined from full clinical picture; hypoxemia, left­sided heart failure, and destruction of pulmonary vascular bed among known causes
Treatment of elevated pressure	Low­salt diet; weight reduction if overweight; if necessary, many different types of anti-hypertensive drugs are available, including diuretics	Depends on cause; for heart failure, digoxin and diuretics often effective; for hypoxemia­induced pulmonary hypertension, continuous oxygen therapy is treatment of choice; in some cases, e.g., primary pulmonary hypertension, there is no effective treatment

Right heart failure is a decompensated state of the right ventricle and can result from sustained or severe pulmonary hypertension of any origin. When the right ventricle is unable to pump its full cardiac output against the elevated pulmonary pressure, systemic venous pressure increases and fluid "backs up" in the systemic veins. Untreated, the patient will manifest leg edema, ascites, liver engorgement, and weight gain. In the absence of left ventricular failure, there is no excess fluid in the alveoli, and the lungs will remain clear on chest x­ray. A chest x­ray from a patient with right­side heart failure is shown in Fig. 8­1; note the cardiomegaly and the absence of pulmonary infiltrates. Treatment of right heart failure attempts to relieve the pulmonary hypertension and uses low sodium intake and diuretic therapy to help mobilize excess body fluid.

Table 8­2. Causes of pulmonary hypertension
Disease or condition	Underlying mechanisms
Lung diseases, including all forms of restrictive and obstructive lung conditions	Hypoxemia; loss of pulmonary blood vessels; acidosis
Heart disease including left ventricular heart failure, mitral valve disease congenital heart disease	Increased pulmonary capillary hydrostatic pressure
Pulmonary thromboembolic disease	Pulmonary artery narrowing; loss of pulmonary blood vessels
Pulmonary arteritis	Pulmonary artery narrowing; loss of pulmonary blood vessels
High altitude	Hypoxemia
Hypoventilation	Hypoxemia; acidosis
Chest wall deformity	Hypoxemia acidosis; pulmonary artery narrowing
Idiopathic	Loss of pulmonary blood vessels; pulmonary artery narrowing

Glossary

Epicardium

• Outermost heart layer also known as visceral layer

Myocardium

• Middle layer of the heart wall thickest of the three heart walls

Endocardium

• Composed of simple squamous epithelium and a layer of aurole connective tissue

Arteries

• Carry blood away from the heart.

Veins

• Carry blood back to the the heart.

The Pulmonary circulation

• Consists of the chambers on the right side of the heart right atrium and right ventricle ) as well as the pulmonary arteries and veins.

The systemic circulation

• Consists of the chambers on the left side of the heart ( left atrium and left ventricle ) along with the other named blood vessels.

Auricle

• Wrinkled flap like extension on top of the atria, it resembles an ear

Tachycardia

• rapid, quick heart beat. Reduced blood flow to the myocardium of the ventricles.

Bradycardia

• atypically slow heartbeat (less than 50 bpm). Can be beneficial when it's a result of exercise - a sign of a muscular heart, healthy circulatory system, and excellent lung capacity

Parietal Pericardium

• The protective sac that encloses the heart.

Papillary Muscle

• small muscles that fasten the chordae tendineae to the ventricular wall.

Chordae Tendineae

• strands of connective tissue that hold the valves in position while the heart is contracting.

Apex

• inferior pointed portion of the heart.

Cardiac Tamponade

• caused by inflammation or bleeding into the pericardial cavity (pericarditis).
• characterized by:
  • pulsus paradoxus (weak heartbeat on inhalation, stronger heartbeat on exhalation)
  • jugular vein distension (usually the external - if internal....yikes)
  • falling blood pressure

Fibrous Skeleton

• located between the atria and ventricles of the heart - it separates them, anchors heart valves and provides electrical insulation between the atria and ventricles (so all four chambers do not contract at once).
• also functions as a framework for the attachment of cardiac muscle tissue (similar to how our bones serve as attachments for skeletal muscles)

Sinoatrial node

• cardiac fibers that initiate the heartbeat. Located in the posterior wall of the right atrium, adjacent to the the entrance to the superior vena cava.
  (this is also referred to as 'the pacemaker' for the heart)

Arteries from the Aortic Arch

1. Brachiocephalic Artery

• unpaired vessel originating from the aortic arch that supplies the blood to the right arm and head through the right subclavian and right common carotid arteries, respectively.

• 2. Left Common Carotid Artery

• middle branch originating from the aortic arch, supplies the left side of the neck and head through the external and internal carotid arteries.

3. Left Subclavian Artery

• the last branch of the aortic arch, supplies the left upper limb through the axillary artery.

Connections to other body systems

Circulatory System

• The heart pumps blood to various parts of the body through arteries and veins.

The Nervous System

• The Vagus nerve has many branches that wander around the heart and can also influence the heart rate

The Integumentary system
The Skeletal system

• The bones supply the red blood cells through hemopoeisis. The heart then pumps blood back to all the bones of the body to keep them healthy.

The Muscular System

• The muscular system helps the blood to circulate. Use of the muscles squeezes the veins and arteries helping to push the blood through the body. The heart itself is mostly muscle tissue. The heart also pumps blood to all the muscles to keep them healthy.

The Endocrine System

• The heart pumps the blood which carries the hormones produced by the endocrine glands to the rest of the body

The Lymphatic System

• The heart is instrumental in the bodies immune system

The Respiratory System

• The Heart pumps the blood to the lungs where oxygen is obtained and carbon dioxide is given up. It then pumps the oxygenated blood to every part of the body.

The Digestive System

• The blood gets the nutrients from the digested food, and carries to all the cells of the body.

The Urinary System

• Filters waste products from the blood

The Reproductive System

• The blood is instrumental in carrying hormones, making sex organs work, development of fetus, etc.

So, as you can see, the heart is vital for our existence. Every Body system depends on the heart and the blood it pumps in order to do its job in keeping us alive. EVERY cell of the body depends on our heart to keep on beating.

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