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HEART

* William Harvey was an English physician, was the first known to describe completely and in detail the systemic circulation and properties of blood being pumped to the brain and body by the heart.
* The study of heart is called Cardiology.
* Professor Christian Barnard performed the first human heart transplant on the third of December 1967.
* Venu Gopal performed the first human heart transplantation in 1984.
* The first artificial heart to be successfully implanted in a human was the Jarvik-7 in 1982, designed by a team including Willem Johan Kolff and Robert Jarvik.
* An adult heart has a mass of 250 – 350 grams. The heart is typically the size of a fist - 12 cm (5 in) in length, 8 cm (3.5 in) wide, and 6 cm (2.5 in) in thickness. Well-trained athletes can have much larger hearts due to the effects of exercise on the heart muscle, similar to the response of skeletal muscle.
* The heart is situated in the middle of the Mediastinum behind the breastbone in the chest, at the level of thoracic vertebrae T5-T8. The largest part of the heart is usually slightly offset to the left (though occasionally it may be offset to the right) and is felt to be on the left because the left heart is stronger, since it pumps to all body parts. The left lung in turn is smaller than the right lung  because it has to accommodate the heart.
                                                  
      

* Pericardium: The membrane enclosing the heart, consisting of an outer fibrous layer and an inner double layer of serous membrane.
i. Structure of human heart: The heart is a muscular organ in humans and other animals, which pumps blood through the blood vessels of the circulatory system. Blood provides the body with oxygen and nutrients, and also assists in the removal of metabolic wastes. The heart is located in the middle compartment of the mediastinum in the chest.
     The heart wall is made up of the inner endocardium, middle myocardium and outer epicardium. These are surrounded by a double-membraned sac called the pericardium.


 

Heart wall:
     The innermost layer of the heart is called the endocardium. It is made up of a lining of simple squamous epithelium, and covers heart chambers and valves. It is continuous with the endothelium of the veins and arteries of the heart, and is joined to the myocardium with a thin layer of connective tissue. The endocardium, by secreting endothelins, may also play a role in regulating the contraction of the myocardium.
   The swirling pattern of myocardium helps the heart pump effectively. The middle layer of the heart wall is the myocardium, which is the cardiac muscle a layer of involuntary striated muscle tissue surrounded by a framework of collagen. The myocardium is also supplied with blood vessels, and nerve fibers by way of the epicardium that help to regulate the heartrate. Cardiac muscle tissue has autorhythmicity, the unique ability to initiate a cardiac action potential at a fixed rate, spreading the impulse rapidly from cell to cell to trigger the contraction of the entire heart. This autorhythmicity is still modulated by the endocrine and nervous systems.

     There are two types of cardiac muscle cell - cardiomyocytes which have the ability to  contract easily, and modified cardiomyocytes the pacemaker cells of the conducting system. The cardiomyocytes make up the bulk (99%) of cells in the atria and ventricles. These contractile cells are connected by intercalated discs which allow a rapid respond to impulses of action potential from the pacemaker cells. The intercalated discs allow the cells to act as a syncytium and enable the contractions that pump blood through the heart and into the major arteries.
     The pacemaker cells make up just (1% of cells) and form the conduction system of the heart. They are generally much smaller than the contractile cells and have few myofibrils which gives them limited contractibility. Their function is similar in many respects to neurons.
    The cardiac muscle pattern is elegant and complex, as the muscle cells swirl and spiral around the chambers of the heart. More superficial layers of ventricular muscle wrap around both ventricles. This complex swirling pattern allows the heart to pump blood more effectively than a simple linear pattern would.
      As with skeletal muscles the heart can increase in size and efficiency with exercise. Thus endurance athletes such as marathon runners may have a heart that has hypertrophied by up to 40%.
     The pericardium surrounds the heart. It consists of two membranes: an inner serous membrane called the epicardium, and an outer fibrous membrane.These enclose the pericardial cavity. The pericardial cavity contains fluid which lubricates the surface of the heart.

 

Chambers:
      The heart has four chambers, two upper atria, the receiving chambers, and two lower ventricles, the discharging chambers. The atria are connected to the ventricles by the atrioventricular valves and separated from the ventricles by the coronary sulcus. There is an ear - shaped structure in the upper right atrium called the right atrial appendage, or auricle, and another in the upper left atrium, the left atrial appendage. The right atrium and the right ventricle together are sometimes referred to as the right heart and this sometimes includes the pulmonary artery. Similarly, the left atrium and the left ventricle together are sometimes referred to as the left heart. The ventricles are separated by the anterior longitudinal sulcus and the posterior interventricular sulcus.


       The cardiac skeleton is made of dense connective tissue and this gives structure to the heart. It forms the atrioventricular septum which separates the atria from the ventricles, and the fibrous rings which serve as bases for the four heart valves. The cardiac skeleton also provides an important boundary in the heart’s electrical conduction system since collagen cannot conduct electricity. The interatrial septum separates the atria and the interventricular septum separates the ventricles. The interventricular septum is much thicker than the interatrial septum, since the ventricles need to generate greater pressure when they contract.
 

Valves:
     All four heart valves lie along the same plane. The valves ensure unidirectional blood flow through the heart and prevent backflow. Between the right atrium and the right ventricle is the tricuspid valve. This consists of three cusps (flaps or leaflets), made of endocardium reinforced with additional connective tissue. Each of the three valve cusps is attached to several strands of connective tissue, the chordae tendineae, sometimes referred to as the heart strings. They are composed of approximately 80 percent collagenous fibers with the remainder consisting of elastic fibers and endothelium. They connect each of the cusps to a papillary muscle that extends from the lower ventricular surface. These muscles control the opening and closing of the valves. The three papillary muscles in the right ventricle are called the anterior, posterior, and septal muscles, which correspond to the three positions of the valve cusps.

   Between the left atrium and left ventricle is the mitral valve, also known as the bicuspid valve due to its having two cusps, an anterior and a posterior medial cusp. These cusps are also attached via chordae tendinae to two papillary muscles projecting from the ventricular wall.
      The tricuspid and the mitral valves are the atrioventricular valves. During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight. However, as the ventricle contracts, so do the papillary muscles. This creates tension on the chordae tendineae, helping to hold the cusps of the atrioventricular valves in place and preventing them from being blown back into the atria.
      The semilunar pulmonary valve is located at the base of the pulmonary artery. This has three cusps which are not attached to any papillary muscles. When the ventricle relaxes blood flows back into the ventricle from the artery and this flow of blood fills the pocket-like valve, pressing against the cusps which close to seal the valve. The semilunar aortic valve is at the base of the aorta and also is not attached to papillary muscles. This too has three cusps which close with the pressure of the blood flowing back from the aorta.

 

Right heart:
     The two major systemic veins, the superior and inferior venae cavae, and the collection of veins that make up the coronary sinus which drains the myocardium, empty into the right atrium. The superior vena cava drains blood from above the diaphragm and empties into the upper back part of the right atrium.
The inferior vena cava drains the blood from below the diaphragm and empties into the back part of the atrium below the opening for the superior vena cava. Immediately above and to the middle of the opening of the inferior vena cava is the opening of the thin-walled coronary sinus.
       In the wall of the right atrium is an oval-shaped depression known as the fossa ovalis, which is a remnant of an opening in the fetal heart known as the foramen ovale. The foramen ovale allowed blood in the fetal heart to pass directly from the right atrium to the left atrium, allowing some blood to bypass the pulmonary circuit. Within seconds after birth, a flap of tissue known as the septum primum that previously acted as a valve closes the foramen ovale and establishes the typical cardiac circulation pattern. Most of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface has prominent ridges of pectinate muscles, which are also present in the right atrial appendage.
    The atria receive venous blood on a nearly continuous basis, preventing venous flow from stopping while the ventricles are contracting. While most ventricular filling occurs while the atria are relaxed, they do demonstrate a contractile phase when they actively pump blood into the ventricles just prior to ventricular contraction. The right atrium is connected to the right ventricle by the tricuspid valve.
    When the myocardium of the ventricle contracts, pressure within the ventricular chamber rises. Blood, like any fluid, flows from higher pressure to lower pressure areas, in this case, toward the pulmonary artery and the atrium.
To prevent any potential backflow, the papillary muscles also contract, generating tension on the chordae tendineae. This prevents the flaps of the valves from being forced into the atria and regurgitation of the blood back into the atria during ventricular contraction.
     The walls of the right ventricle are lined with trabeculae carneae, ridges of cardiac muscle covered by endocardium. In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction. It arises from the lower part of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.
     When the right ventricle contracts, it ejects blood into the pulmonary artery, which branches into the left and right pulmonary arteries that carry it to each lung. The upper surface of the right ventricle begins to taper as it approaches the pulmonary artery. At the base of the pulmonary artery is the pulmonary semilunar valve that prevents backflow from the pulmonary artery.

 

Left heart:


     After gas exchange in the pulmonary capillaries, blood returns to the left atrium high in oxygen via one of the four pulmonary veins. Only the left atrial appendage contains pectinate muscles.
Blood flows nearly continuously from the pulmonary veins back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period, the left atrium will contract, pumping blood into the ventricle. This atrial contraction accounts for approximately 20 percent of ventricular filling. The left atrium is connected to the left ventricle by the mitral valve.
     Although both sides of the heart will pump the same amount of blood, the muscular layer is much thicker in the left ventricle compared to the right, due to the greater force needed here. Like the right ventricle, the left also has trabeculae carneae, but there is no moderator band. The left ventricle is the major pumping chamber for the systemic circuit; it ejects blood into the aorta through the aortic semilunar valve.

 

Coronary circulation:

     Cardiomyocytes like all other cells need to be supplied with oxygen, nutrients and a way of removing metabolic wastes. This is achieved by the coronary circulation. The coronary circulation cycles in peaks and troughs relating to the heart muscle relaxing or contracting.
     Coronary arteries supply blood to the heart and the coronary veins remove the deoxygenated blood. There is a left and a right coronary artery supplying the left and right hearts respectively, and the septa. Smaller branches of these arteries anastomose, which in other parts of the body serve to divert blood due to a blockage. In the heart these are very small and cannot form other interconnections with the result that a coronary artery blockage can cause a myocardial infarction and with it, tissue damage.
      The great cardiac vein receives the major branches of the posterior, middle, and small cardiac veins and drains into the coronary sinus a large vein that empties into the right atrium. The anterior cardiac veins drain the front of the right ventricle and drain directly into the right atrium.

 

ii. The Heartbeat:

     A heartbeat is a two-part pumping action that takes about a second. As blood collects in the upper chambers (the right and left atria), the heart's natural pacemaker (the SA node) sends out an electrical signal that causes the atria to contract. This contraction pushes blood through the tricuspid and mitral valves into the resting lower chambers (the right and left ventricles). This part of the two-part pumping phase (the longer of the two) is called diastole.
    The second part of the pumping phase begins when the ventricles are full of blood. The electrical signals from the SA node travel along a pathway of cells to the ventricles, causing them to contract. This is called systole. As the tricuspid and mitral valves shut tight to prevent a back flow of blood, the pulmonary and aortic valves are pushed open. While blood is pushed from the right ventricle into the lungs to pick up oxygen, oxygen-rich blood flows from the left ventricle to the heart and other parts of the body.
    After blood moves into the pulmonary artery and the aorta, the ventricles relax, and the pulmonary and aortic valves close. The lower pressure in the ventricles causes the tricuspid and mitral valves to open, and the cycle begins again. This series of contractions is repeated over and over again, increasing during times of exertion and decreasing while at rest. The heart normally beats about 60 to 80 times a minute when rest, but this can vary. As you get older, your resting heart rate rises. Also, it is usually lower in people who are physically fit.
     Your heart does not work alone, though. Your brain tracks the conditions around you, climate, stress, and level of physical activity and adjusts your cardiovascular system to meet those needs.
    The human heart is a muscle designed to remain strong and reliable for a hundred years or longer. By reducing your risk factors for cardiovascular disease, you may help your heart stay healthy longer.

 

iii. Blood pressure (BP):
    Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels. When used without further specification, "blood pressure" usually refers to the arterial pressure in the systemic circulation. It is usually measured at a person's upper arm. Blood pressure is usually expressed in terms of the systolic (maximum) pressure over diastolic (minimum) pressure and is measured in millimeters of mercury (mm Hg). It is one of the vital signs along with respiratory rate, heart rate, oxygen saturation, and body temperature. Normal resting blood pressure in an adult is approximately 120/80 mm Hg.
    A sphygmomanometer, blood pressure meter, blood pressure monitor or blood pressure gauge (also referred to as a sphygmometer) is a device used to measure blood pressure, composed of an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.
High Blood Pressure: Probably have high blood pressure (hypertension) if your blood pressure readings are consistently 140 over 90, or higher, over a number of weeks.
Low Blood Pressure: A low blood pressure reading is having a level that is 90/60mm Hg, or lower.
Open heart surgery: Open heart surgery is any surgery in which the chest is opened and surgery is done on the heart muscle, valves, arteries, or other parts of the heart (such as the aorta). The term "open" means that the chest is "cut" open.
Bypass heart Surgery: This surgery is used when your coronary arteries are blocked or damaged. The coronary arteries supply the heart’s muscles with oxygenated blood. They are very important to your health. If they are blocked or the flow of blood is restricted, your heart cannot function properly. This can lead to heart failure.

 

iv. Heart Attack:
     Heart muscle needs oxygen to survive. A heart attack occurs when the blood flow that brings oxygen to the heart muscle is severely reduced or cut off completely. This happens because coronary arteries that supply the heart muscle with blood flow can slowly become narrow from a buildup of fat, cholesterol and other substances that together are called plaque. This slow process is known as atherosclerosis. When a plaque in a heart artery breaks, a blood clot forms around the plaque. This blood clot can block the blood flow through the heart muscle. When the heart muscle is starved for oxygen and nutrients, it is called ischemia. When damage or death of part of the heart muscle occurs as a result of ischemia, it is called a heart attack or myocardial infarction (MI). About every 34 seconds, someone in the United States has a myocardial infarction (heart attack).

 

Types of heart attack:
* Cardiomegaly is a medical condition wherein the heart is enlarged. Cardiomegaly can be caused by a number of different conditions, including diseases of the heart muscle or heart valves, high blood pressure, arrhythmias, and pulmonary hypertension. Cardiomegaly can also sometimes accompany longstanding anemia and thyroid diseases, among other conditions.
* Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to part of the heart causing damage to the heart muscle.
* Arteriosclerosis occurs when the blood vessels that carry oxygen and nutrients from your heart to the rest of your body (arteries) become thick and stiff. sometimes restricting blood flow to your organs and tissues. Healthy arteries are flexible and elastic, but over time, the walls in your arteries can harden, a condition commonly called hardening of the arteries.
* Atherosclerosis (or arteriosclerotic vascular disease) is a condition where the arteries become narrowed and hardened due to an excessive build up of plaque around the artery wall. The disease disrupts the flow of blood around the body, posing serious cardiovascular complications.


The causes of a heart attack:
* Age - the largest risk factor.
* Angina - angina is an illness where not enough oxygen is reaching the patient's heart.
* Blood cholesterol levels - if a person's blood cholesterol levels are high, he/she runs a higher risk of developing blood clots in the arteries.


Most Common Symptoms:
    The most common warning symptoms of a heart attack for both men and women are:
Chest pain or discomfort: Most heart attacks involve discomfort in the center or left side of the chest. The discomfort usually lasts for more than a few minutes or goes away and comes back. It can feel like pressure, squeezing, fullness, or pain. It also can feel like heartburn or indigestion. The feeling can be mild or severe.
* Upper body discomfort: You may feel pain or discomfort in one or both arms, the back, shoulders, neck, jaw, or upper part of the stomach (above the belly button).
* Shortness of breath: This may be your only symptom, or it may occur before or along with chest pain or discomfort. It can occur when you are resting or doing a little bit of physical activity.

 

Posted Date : 03-02-2021

 

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