Cardiovascular System




System of vessels that convey blood to and from tissues throughout the body, bringing nutrients and oxygen and removing wastes and carbon dioxide. It is essentially a long, closed tube through which blood moves in a double circuit — one through the lungs (pulmonary circulation) and one through the rest of the body (systemic circulation). The heart pumps blood through the arteries, which branch into smaller arterioles, which feed into microscopic capillaries (see artery; capillary). These converge to form small venules, which join to become larger veins, generally following the same path as the arteries back to the heart

The cardiovascular/circulatory system transports food, hormones, metabolic wastes, and gases (oxygen, carbon dioxide) to and from cells. Components of the circulatory system include:

• blood: consisting of liquid plasma and cells
• blood vessels (vascular system): the "channels" (arteries, veins, capillaries) which carry blood to/from all tissues. (Arteries carry blood away from the heart. Veins return blood to the heart. Capillaries are thin-walled blood vessels in which gas/ nutrient/ waste exchange occurs.)
• heart: a muscular pump to move the blood

There are two circulatory "circuits": Pulmonary circulation, involving the "right heart," delivers blood to and from the lungs. The pulmonary artery carries oxygen-poor blood from the "right heart" to the lungs, where oxygenation and carbon-dioxide removal occur. Pulmonary veins carry oxygen-rich blood from tbe lungs back to the "left heart." Systemic circulation, driven by the "left heart," carries blood to the rest of the body. Food products enter the sytem from the digestive organs into the portal vein. Waste products are removed by the liver and kidneys. All systems ultimately return to the "right heart" via the inferior and superior vena cavae.
A specialized component of the circulatory system is the lymphatic system, consisting of a moving fluid (lymph/interstitial fluid); vessels (lymphatics); lymph nodes, and organs (bone marrow, liver, spleen, thymus). Through the flow of blood in and out of arteries, and into the veins, and through the lymph nodes and into the lymph, the body is able to eliminate the products of cellular breakdown and bacterial invasion.











Blood Components

• Forty-five percent (45%) consists of cells - platelets, red blood cells, and white blood cells (neutrophils, basophils, eosinophils, lymphocytes, monocytes). Of the white blood cells, neutrophils and lymphocytes are the most important.
• Fifty-five percent (55%) consists of plasma, the liquid component of blood.

Heart Anatomy




Coronary Arteries

Because the heart is composed primarily of cardiac muscle tissue that continuously contracts and relaxes, it must have a constant supply of oxygen and nutrients. The coronary arteries are the network of blood vessels that carry oxygen- and nutrient-rich blood to the cardiac muscle tissue.
The blood leaving the left ventricle exits through the aorta, the body’s main artery. Two coronary arteries, referred to as the "left" and "right" coronary arteries, emerge from the beginning of the aorta, near the top of the heart.
The initial segment of the left coronary artery is called the left main coronary. This blood vessel is approximately the width of a soda straw and is less than an inch long. It branches into two slightly smaller arteries: the left anterior descending coronary artery and the left circumflex coronary artery. The left anterior descending coronary artery is embedded in the surface of the front side of the heart. The left circumflex coronary artery circles around the left side of the heart and is embedded in the surface of the back of the heart.
Just like branches on a tree, the coronary arteries branch into progressively smaller vessels. The larger vessels travel along the surface of the heart; however, the smaller branches penetrate the heart muscle. The smallest branches, called capillaries, are so narrow that the red blood cells must travel in single file. In the capillaries, the red blood cells provide oxygen and nutrients to the cardiac muscle tissue and bond with carbon dioxide and other metabolic waste products, taking them away from the heart for disposal through the lungs, kidneys and liver.
When cholesterol plaque accumulates to the point of blocking the flow of blood through a coronary artery, the cardiac muscle tissue fed by the coronary artery beyond the point of the blockage is deprived of oxygen and nutrients. This area of cardiac muscle tissue ceases to function properly. The condition when a coronary artery becomes blocked causing damage to the cardiac muscle tissue it serves is called a myocardial infarction or heart attack.
Superior Vena Cava





The superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.
Inferior Vena Cava

The inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.
Aorta

The aorta is the largest single blood vessel in the body. It is approximately the diameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.


Pulmonary Artery

The pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs. A common misconception is that all arteries carry oxygen-rich blood. It is more appropriate to classify arteries as vessels carrying blood away from the heart.

Pulmonary Vein

The pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium. A common misconception is that all veins carry de-oxygenated blood. It is more appropriate to classify veins as vessels carrying blood to the heart.

Right Atrium

The right atrium receives de-oxygenated blood from the body through the superior vena cava (head and upper body) and inferior vena cava (legs and lower torso). The sinoatrial node sends an impulse that causes the cardiac muscle tissue of the atrium to contract in a coordinated, wave-like manner. The tricuspid valve, which separates the right atrium from the right ventricle, opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle.
Right Ventricle

The right ventricle receives de-oxygenated blood as the right atrium contracts. The pulmonary valve leading into the pulmonary artery is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the right ventricle contracts, the tricuspid valve closes and the pulmonary valve opens. The closure of the tricuspid valve prevents blood from backing into the right atrium and the opening of the pulmonary valve allows the blood to flow into the pulmonary artery toward the lungs.

Left Atrium

The left atrium receives oxygenated blood from the lungs through the pulmonary vein. As the contraction triggered by the sinoatrial node progresses through the atria, the blood passes through the mitral valve into the left ventricle.
Left Ventricle

The left ventricle receives oxygenated blood as the left atrium contracts. The blood passes through the mitral valve into the left ventricle. The aortic valve leading into the aorta is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the left ventricle contracts, the mitral valve closes and the aortic valve opens. The closure of the mitral valve prevents blood from backing into the left atrium and the opening of the aortic valve allows the blood to flow into the aorta and flow throughout the body.

Papillary Muscles

The papillary muscles attach to the lower portion of the interior wall of the ventricles. They connect to the chordae tendineae, which attach to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. The contraction of the papillary muscles closes these valves. When the papillary muscles relax, the valves open.

Chordae Tendineae

The chordae tendineae are tendons linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. As the papillary muscles contract and relax, the chordae tendineae transmit the resulting increase and decrease in tension to the respective valves, causing them to open and close. The chordae tendineae are string-like in appearance and are sometimes referred to as "heart strings."

Tricuspid Valve

The tricuspid valve separates the right atrium from the right ventricle. It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle. It closes as the right ventricle contracts, preventing blood from returning to the right atrium; thereby, forcing it to exit through the pulmonary valve into the pulmonary artery.

Mitral Value

The mitral valve separates the left atrium from the left ventricle. It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. It closes as the left ventricle contracts, preventing blood from returning to the left atrium; thereby, forcing it to exit through the aortic valve into the aorta.
Pulmonary Valve

The pulmonary valve separates the right ventricle from the pulmonary artery. As the ventricles contract, it opens to allow the de-oxygenated blood collected in the right ventricle to flow to the lungs. It closes as the ventricles relax, preventing blood from returning to the heart.
Aortic Valve

The aortic valve separates the left ventricle from the aorta. As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body. It closes as the ventricles relax, preventing blood from returning to the heart.



This cross section of the heart shows the right ventricle, tricuspid valve, left ventricle, bicuspid (mitral) valve, left atrium, right atrium, superior vena cava, inferior vena cava, aorta, aortic valve, papillary muscle, chordae tendineae, and trabeculae carneae.

The heart ventricular walls consist of three layers: the 1.epicardium, the 2.myocardium (cardiac muscle), and the 3.endocardium.

The muscular wall separating the two ventricles is the interventricular septum



Capillaries
The arterioles branch into the microscopic capillaries, or capillary beds, which lie bathed in interstitial fluid, or lymph, produced by the lymphatic system. Capillaries are the points of exchange between the blood and surrounding tissues. Materials cross in and out of the capillaries by passing through or between the cells that line the capillary. The extensive network of capillaries is estimated at between 50,000 and 60,000 miles long.1
Veins
Blood leaving the capillary beds flows into a series of progressively larger vessels, called venules, which in turn unite to form veins. Veins are responsible for returning blood to the heart after the blood and the body cells exchange gases, nutrients, and wastes. Pressure in veins is low, so veins depend on nearby muscular contractions to move blood along. Veins have valves that prevent back-flow of blood.
Blood in veins is oxygen-poor, with the exception of the pulmonary veins, which carry oxygenated blood from the lungs back to the heart. The major veins, like their companion arteries, often take the name of the organ served. The exceptions are the superior vena cava and the inferior vena cava, which collect body from all parts of the body (except from the lungs) and channel it back to the heart.


Red blood cells .and heart function

Blood Pressure and Heart Rate
The heart beats or contracts around 70 times per minute.1 The human heart will undergo over 3 billion contraction/cardiac cycles during a normal lifetime.
One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause. Atria contract while ventricles relax, and vice versa. Heart valves open and close to limit flow to a single direction. The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound.
The cardiac cycle consists of two parts: systole (contraction of the heart muscle in the ventricles) and diastole (relaxation of the ventricular heart muscles). When the ventricles contract, they force the blood from their chambers into the arteries leaving the heart. The left ventricle empties into the aorta (systemic circuit) and the right ventricle into the pulmonary artery (pulmonary circuit). The increased pressure on the arteries due to the contraction of the ventricles (heart pumping) is called systolic pressure.
When the ventricles relax, blood flows in from the atria. The decreased pressure due to the relaxation of the ventricles (heart resting) is called diastolic pressure.
Blood pressure is measured in mm of mercury, with the systole in ratio to the diastole. Healthy young adults should have a ventricular systole of 120mm, and 80mm at ventricular diastole, or 120/80.
Receptors in the arteries and atria sense systemic pressure. Nerve messages from these sensors communicate conditions to the medulla in the brain. Signals from the medulla regulate blood pressure.
Electrocardiography (ECG, EKG)
An electrocardiogram measures changes in electrical potential across the heart and detects contraction pulses that pass over the surface of the heart. There are three slow, negative changes, known as P, R, and T. Positive deflections are the Q and S waves. The P wave represents atrial contraction ("the lub"), the T wave the ventricular contraction ("the dub").
The Lymphatic System
The lymphatic system functions 1) to absorb excess fluid, thus preventing tissues from swelling; 2) to defend the body against microorganisms and harmful foreign particles; and 3) to facilitate the absorption of fat (in the villi of the small intestine).

Capillaries release excess water and plasma into intracellular spaces, where they mix with lymph, or interstitial fluid. "Lymph" is a milky body fluid that also contains proteins, fats, and a type of white blood cells, called "lymphocytes," which are the body's first-line defense in the immune system.

Lymph flows from small lymph capillaries into lymph vessels that are similar to veins in having valves that prevent backflow. Contraction of skeletal muscle causes movement of the lymph fluid through valves. Lymph vessels connect to lymph nodes, lymph organs (bone marrow, liver, spleen, thymus), or to the cardiovascular system.

• Lymph nodes are small irregularly shaped masses through which lymph vessels flow. Clusters of nodes occur in the armpits, groin, and neck. All lymph nodes have the primary function (along with bone marrow) of producing lymphocytes.
• The spleen filters, or purifies, the blood and lymph flowing through it.
• The thymus secretes a hormone, thymosin, that produces T-cells, a form of lymphocyte.

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