Tuesday, April 30, 2019

The Human Heart

            The Human Heart 

The Human Heart

The cardiovascular system (CV), also called the circulatory system, circulates blood to organs of the body through the pump action of the heart. This process supplies the body's cells with oxygen and nutrients and removes waste materials and carbon dioxide. The heart, a muscle pump, is the central organ of the system. It affects around 100,000 times a day, pumping around 8,000 liters of blood, enough to fill around 8,500 quartons of milk. Arteries, veins and capillaries comprise the network of vessels that transport blood (fluid made up of blood cells and plasma) throughout the body. Blood flows through the heart, lungs, heart and various parts of the body

• Heart: the muscle pump, circulates blood through the heart, lungs (pulmonary circulation) and the rest of the body (systemic circulation)

• Arteries: a branched system of vessels that transports blood from the left and right ventricles of the heart to all parts of the body; carries blood away from the heart

• Veins: vessels that transport blood from peripheral tissues back to the heart muscle

• Capillaries: microscopic blood vessels that connect the arterioles to the venules; Facilitate the passage of fluids containing oxygen and nutrients in cell bodies and the elimination of accumulated waste and carbon dioxide

• Blood: fluid composed of formed elements (erythrocytes, thrombocytes, leukocytes) and plasma. It is a specialized body fluid that supplies the necessary substances to the body's cells (oxygen, food, salts, hormones) and transports the waste products (carbon dioxide, urea, lactic acid) away from those same cells. Blood circulates through the body through the blood vessels by the pumping action of the heart. Blood and Lymphatic System, for more information on blood

There are two divisions in the circulatory system: the pulmonary division - the pulmonary capillaries that serve the structures where oxygen is obtained and carbon dioxide is removed through breathing rather than through the blood supply. The systemic division: all the other organs and tissues in which oxygen is provided by blood rich with oxygen  in the incoming arteries and carbon dioxide is transported by the outgoing veins. HEART is actually two pumps:
  • The right heart pumps the oxygenated (low oxygen) blood received by the systemic division in the lungs for oxygenation
  • The left heart pumps this oxygenated (oxygen-rich) blood into the systemic division to supply oxygen to the tissues and collect carbon dioxide


The heart pumps blood to circulate throughout the body. The heart is a very strong muscle that can contract rhythmically and relax during a person's life. Every day, the heart beats an average of 100,000 times, pumping over 7,500 liters of blood

The heart is the center of the cardiovascular system from which the blood vessels come and then return. It is slightly larger than a person's fist and weighs about 300 g in the average adult. It is located slightly to the left of the midline of the body, behind the sternum. The heart has three layers or coatings:

• Endocardium: the inner lining of the heart

• Myocardium: the center, or middle  layer of the heart muscle

• Pericardium: the external membranous sac that surrounds the heart

Anatomy of the Heart :

The Human Heart

Right atrium

The higher right part is known as the right atrium (RA). It is a thin-walled space that receives blood from the upper and lower parts of the body except the lungs. Two large veins, the superior vena cava and the inferior vena cava, carry the oxygenated blood into the right atrium. Deoxygenated blood fills the right atrium before passing through the tricuspid (atrioventricular) valve and right ventricle

Right ventricle

The lower right part of the heart is called the right ventricle (RV). It gets blood from the right atrium through the tricuspid valve. If filled, the motorhome contracts. This creates pressure, closes the right atrium and forces the pulmonary (semilunar) valve to open, sending blood to the left and right pulmonary arteries, which carry it to the lungs. The pulmonary artery is the only artery in the body that carries oxygen-deficient blood. In the lungs, the blood releases waste and absorbs oxygen as it passes through the capillary beds in the veins. Oxygenated blood leaves the lungs through the left and right pulmonary veins, which take it to the left atrium of the heart. Lung veins are the only veins in the body that carry oxygen-rich (oxygenated) blood. The circulation of blood through the vessels from the heart to the lungs and then back to the heart is pulmonary circulation

Left atrium

The upper left part of the heart is called the left atrium (LA). You will receive oxygen-rich blood when it returns from the lungs through the left and right pulmonary veins. As oxygenated blood fills the LA, it creates pressure that forces the opening of the mitral valve (bicuspid) and allows blood to fill the left ventricle

Left ventricle

The lower left part of the heart is called the left ventricle (LV). It gets blood from the left atrium through the mitral valve. When full, the LV contract. This creates pressure by closing the mitral valve and forcing the opening of the aortic valve. LV oxygenated blood flows through the aortic valve to a large artery known as the aorta and from there to all parts of the body (except the lungs) through an arterial and capillary branching system

Heart valves

The heart valves are located at the entrance and exit of each ventricle and, as you learned in the previous section, they control the flow of blood into the heart

The valves are shown from above. Observe the origin of the coronary arteries behind the aortic semilunar valves. Also note the anastomosis between them that produces collateral circulation. Slight gaps can allow small amounts of blood to escape, creating a sound known as heart murmur. Most puffs are insignificant, but if the leak is significant, blood flow will be affected and heart valve replacement will be required

Tricuspid valve

The right atrioventricular or tricuspid valve protects the opening between the right atrium and the right ventricle. In a normal state, the tricuspid valve opens to allow blood flow to the ventricle, then closes to prevent any blood flow

Pulmonary (semilunar) valve The exit for blood from the right ventricle is called the pulmonary (semilunar) valve. Situated between the right ventricle and the pulmonary artery that it allows blood to flow from the right ventricle through the pulmonary artery to the lungs

Mitral valve (bicuspid) The left atrioventricular valve between the left atrium and the left ventricle is called the mitral valve (MV) or bicuspid valve. Allows blood to flow into the left ventricle and closes to prevent it from returning to the left atrium

Aortic valve (semilunar) Blood leaves the left ventricle through the aortic valve (semilunar). Situated between the left ventricle and the aorta thatit allows blood to flow into the aorta and prevents it from flowing back into the ventricle

Vascular System of the heart

The heart has its own vascular system, due to the membranous lining of the heart (endocardium) and the thickness of the myocardium to meet its high oxygen demand.The coronary arteries supply the heart with oxygen-rich blood and the cardiac veins, which flow into the coronary sinus, collect the blood (low in oxygen) and return it to the right atrium

Conduction System of the heart 

The autonomic nervous system controls the frequency and rhythm of the heart beat. It is normally generated by the specialized neuromuscular tissue of the heart capable of rhythmically contracting the heart muscle. This tissue of the heart includes the sinoatrial node, the atrioventricular node and the atrioventricular bundle

Sinoatrial node (sa node)

Called a cardiac pacemaker, the SA node is located on the upper wall of the right atrium, just below the opening of the superior vena cava.It contains of a dense network of Purkinje fibers, atypical muscle fibers. Considered the source of the impulses that start the heart beat. The electrical impulses discharged from the SA node are distributed to the right and left atria and lead to known as contraction

Atrioventricular node (av node)

Located under the endocardium of the right atrium, the AV node transmits electrical impulses to the bundle of His (atrioventricular bundle)

Atrioventricular bundle (its bundle) The atrioventricular bundle or bundle is part of the conduction system of the heart. It is a group of specialized cardiac muscle cells by electrical conduction that transmits electrical impulses from the AV node to the apical point of the fascicular branches. The bundle of its branches in the two branches of the bundle that runs along the interventricular septum. The bundles distribute the impulse to the ventricular muscle, that ive rise to thin filaments known as Purkinje fibers. Together, the bundle branches and the Purkinje network consist of the ventricular conduction system

The average adult heart rate (pulse) is between 60 and 90 beats per minute. Heart rate can be affected by emotions, smoking, illness, body size, age, stress, environment and many other factors

The electrical activity of the heart can be recorded by an electrocardiogram (ECG, ECG), which provides valuable information for the diagnosis of cardiac abnormalities, such as myocardial damage and arrhythmias

 How The Heart Works

The Human Heart

1. The heart can be thought of as two pumps placed side by side, each of which has an upper atrium and a lower ventricle, for a total of 4 chambers. It works like two pumps inside one

2. The right side of the heart pumps "deoxygenated blood" (actually low oxygen blood) from the body to the lungs, where gas exchange occurs. In this process, carbon dioxide is lost in the air and oxygen is absorbed. Almost all this oxygen is carried by the red blood cells (red blood cells)

3. The left side of the heart pumps blood with oxygen from the lungs to the rest of the body's organs

4. The heart is enclosed in a membrane-like protective bag called the pericardium, which surrounds the heart and secretes a fluid that reduces friction as the heart beats

5. The atria (upper chambers) of the heart receive blood which enters the heart. So they have thin walls, so that they can be easily filled. They pump blood into the ventricles (lower chambers), thereby filling them

6. The ventricles pump blood from the heart and the left ventricle has the thicker walls of the heart because it has to do most of the work to pump blood to all parts of the body. This is where blood has the highest pressure

7. The vertical division of the two sides of the heart is a wall, known as the septum. The septum prevents the mixing of oxygenated blood for left side and right side

8. It also carries electrical signals that indicate to the ventricles when to contract. These impulses transmit specially modified muscle cells (Purkinje fibers), collectively known as His Pack

Flow of Blood

The heart is made up of large muscles that cause the heart to contract and relax, and when these muscles alternate to contract, blood passes through the valves that separate the chambers, from one chamber to another. The two right chambers (the right atrium and the right ventricle) are responsible for pumping blood to the lungs. When this blood passes through the lungs, it collects oxygen (enters the body during inhalation) and releases carbon dioxide (leaves the body during exhalation). The newly oxygenated blood returns to the left side of the heart (left atrium and left ventricle), from where it is pumped into the aorta. The aorta divides into the other blood vessels in the body and distributes oxygenated blood

When cells use oxygen, they replace it with carbon dioxide. Blood accumulates through the blood vessels and returns to the right side of the heart. From here, the cycle repeats itself, with the right side of the heart pumping oxygenated blood into the lungs where it is oxygenated
  • Blood flow = Δ BP / resistance to blood flow
Blood flow is directly proportional to the pressure gradient on a section of a blood vessel and inversely proportional to flow resistance. Resistance is produced by friction along the vascular wall and increases with vasoconstriction, atherosclerosis and hypertension

Beating of the Heart

We know it is the contraction of the heart that pumps blood throughout the body, but what causes these contractions? The heartbeat is created by small electrical impulses that cause perpetual contraction of the heart muscles. A network of nerve fibers is present between the muscles of the heart and these fibers act as electrical cables, coordinating the contraction and relaxation of the different chambers. By keeping all these muscles contracting and relaxing in a coordinated way, the heart creates a wave-like pumping action that effectively moves blood throughout the body. The constant pumping action of the heart is often described as its "rhythm"

It is normal the heartbeat is of varying rates throughout the day. Sometimes people can experience harmless changes in heart rhythm, called palpitations. In contrast, an abnormally constant heart rate is known as arrhythmia. The heart can beat too fast, too slowly or with an irregular pattern. Changes in heart rhythm are caused by irregularities in the transmission of electrical impulses that cause the heart muscles to contract. An arrhythmia does not necessarily mean that the heart is not healthy, but some types of arrhythmias are worrying. Syncope (fainting) is associated with some arrhythmias. Arrhythmias must be diagnosed by a doctor, often using an electrocardiogram (ECG) or other cardiac monitoring device

The most common arrhythmia is atrial fibrillation, characterized by an accelerated and irregular heart beat. Due the abnormal electrical impulses in the upper chambers of the heart, it cause atrial fibrillation (left atrium and right atrium). These abnormal electrical impulses cause the upper chambers to contract very quickly and irregularly, compared to the lower chambers of the heart (left and right ventricles). Therefore, the pumping action of the heart is not coordinated, so the heart does not pump blood efficiently. Atrial fibrillation reduces the pumping efficiency of the heart and increases the risk of blood clots forming in the heart and arteries. These effects can lead to a person's risk of congestive heart failure, heart attack and stroke

The Cardiac Cycle

The sequence of events that occur in the heart during a beat is called the heart cycle. The events occur almost simultaneously on both sides of the heart. The typical resting heart rate in adults is between 60 and 90 beats / min (bpm). A physically fit person has a lower heart rate than an inactive person. Each heart beat is commonly divided into two main stages: systole and diastole. Systole is contraction of the heart muscle, however diastole is relaxation. Both the atria and ventricles go through these two stages in each heartbeat, but the terms only diastole and systole often refer to the ventricular stages

I. Systole

Systole is the condition in which both ventricles contract. When these two chambers contract, the muscles forcefully push the blood into the blood vessels away from the heart. As noted above, the right ventricle pushes blood into the lungs, while the left ventricle pushes blood into the aorta before it is distributed to the rest of the body. During this phase, the contractions cause an increase in pressure within the blood vessels

II Diastole

Diastole is the phase in which both ventricles relax. When these two chambers relax, they are filled with blood from each atrium, getting new blood to pump from the heart into the blood vessels when the cycle begins again. During this phase, new blood is not pumped into the blood vessels and therefore the pressure in the blood vessels is lower than in the systole

The cycle of systole and diastole phases continues to repeat itself and is called the cardiac cycle. A normal human heart beats about 60-70 times per minute when it is at rest

It is the contraction and relaxation of the heart that pushes the blood through the blood vessels
  • Systole is when the heart muscle contracts (upper pressure)
  • Diastole is when the heart muscle is relaxed (lower pressure)

Important events in the cardiac cycle

1) period of inactivity - period in which all the rooms are inactive and fill up. 70% of ventricular filling occurs during this period. AV valves are open, semilunar valves are closed

2) atrial systole : it pushes the last 30% of blood into the ventricle

3) atrial diastole: the atria begin to fill. This occurs almost simultaneously with the next event ...

4) ventricular systole: the ventricles contract, close the AV valves first and cause the first heart sound ...
The semilunar valves are then opened allowing the ventricular expulsion of blood to the arteries

5) Ventricular diastole: while the ventricles relax, the semilunar valves close first producing the second heart sound, then ...
AV valves open allowing ventricular filling

Physiology of the Aorta

The aorta, which extends from the left ventricle upwards and then penetrates the abdomen, is the largest and strongest artery in the human body. Oxygenated blood is transported through this artery to the body's organs through systemic circulation. In the anatomy,  the entire aorta is contained of three main segments: ascending aorta; Aortic arch; and the descending aorta, that it comprising the thoracic aorta and the abdominal aorta

The aorta is a heterogeneous combination of smooth muscles, nerves, intimate cells, endothelial cells, fibroblast-like cells and a complex extracellular matrix. Its wall is composed of several layers: the adventitious garment, the central garment and the intimate garment, which are mainly made up of collagen which gives it stability helping to anchor it to nearby organs. Once the blood is expelled from the left ventricle, it transports high pressure and pulsating blood to the rest of the body. Being extensible and elastic, blood pressure decreases in strength and becomes less pulsating from the aorta to the arteries and capillaries

Blood flows from the aorta to the rest of the arteries which are scattered throughout the body in a branched pattern. As known, the term arterial tree to describe the branching pattern of all the arteries in the body. Blood travels through the arteries in a pulsating way. The reflected waves bounce from the bifurcations to the semilunar valves and aorta, creating a dichrotic notch on the aortic pressure waveform when they push onto the aortic semilunar valve. This can be viewed in the cardiac cycle profile showing a small drop that coincides with the closure of the aortic valve. This decrease is immediately followed by a short increase, called a dichrotic wave, and then gradually decreases

As the body ages, the artery stiffens, causing the pulse wave to circulate faster and the reflected waves to return to the heart at a faster rate before the lunate valve closes, resulting in increased blood pressure. high. Determining the speed of the pulse wave using invasive or non-invasive techniques can assess arterial stiffness, which is related to the degree of disease

Physiology of The carotid Bifuction

The carotid bifurcation, which includes the common carotid artery (CCA), the external carotid artery (ACE) and the internal carotid artery (ICA), transports oxygenated blood to the regions of the head and neck. CCA is the main channel for the supply of this oxygenated blood. It commonly exists as a bifurcation from which the ECA and the ICA originate

Both of the left and right CCA are branching from the aortic arch in the thoracic region and from the brachiocephalic artery. This artery, also known as trunk or innominate artery, extends from the first branch of the aortic arch and is divided into the right common carotid artery and the right subclavian artery. It connects to the mediastinum which provides blood to the head and neck, as well as to the right arm

The ICA and ECA branches supply blood to different organs through the downstream arteries. In specific, the brain and eyes located under the ICA branch have consum a large amount of oxygen and  requiring a high volume of blood supply per unit of time, are the most active and important part of the human body

Therefore, the volume of blood flow through the ICA branch is greater than that of the RCT. Common carotid artery (CCA) The common carotid artery rises through the upper mediastinum2 anterolaterally in the neck and is medial to the jugular vein3. The two CCAs are not symmetrical, since the left artery is longer than the right. This explains the longest path from the aortic arch

The carotid artery, jugular vein and vagus nerve are enclosed in the carotid sheath. CCA branches on the internal carotid artery and the external carotid artery on the upper edge of the thyroid cartilage with interindividual variations in terms of bifurcation angle and asymmetry. The diameter of the CCA in adults varies from 0.2 to 0.8 cm with an average value of 0.7 cm

Higher brain center: The hypothalamus

Stimulates the heart center in response to exercise, emotions, struggle or flight, etc.

An important input to the heart center is the hypothalamus, which increases the cardiac output when you get excited, go to "Fight or run" and practice

The main control center for cardiac output is the cardiac center in the brain cord. The marrow sends impulses to the heart through the parasympathetic (vagus nerve) and sympathetic (cardiac nerves) divisions. The vagus nerve innervates the SA and AV nodes and, by increasing the threshold for depolarization, decreases the heart rate. The butt has no effect on contractility. Sympathetic stimuli lead to the myocardium itself, not only to the SA and AV nodes. Its effect on the myocardium is to increase contractility, thereby increasing the strength and volume of contraction

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