Dr. Mervat Abdelrahman M Lecture ( 1 ) 1

 The heart is a hollow, muscular organ, about the size of a fist. It is responsible for pumping blood through the blood vessels by repeated, rhythmic contractions.  It has four-chambers, double pump and is located in the thoracic cavity between the lungs. The cardiac muscle has its own conduction system. 2

The surface markings of the heart can be traced by joining four points over the anterior chest wall. On the right, the heart extends from the third to the sixth costal caltilages at a distance of about 10 to 15 mm from the sternum. On the left, the heart extends from the second costal cartilage to the fifth intercostal space 12 to 15 mm, and 9 cm from the left sternal border, respectively 3

The heart wall consists of three layers Pericardium:  The pericardium is the thick, membranous sac that surrounds the heart.  Protects and lubricates the heart, keeps the heart suspended inside mediastinum, protects the heart from surroundings, prevent friction against each other, prevent over filling of the heart. 4

 There are two layers to the pericardium, the fibrous pericardium and the serous pericardium.  The serous pericardium is divided into two layers, in between these two layers there is a space called the pericardial cavity. 5

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 The myocardium is the muscular tissue of the heart (middle layer).  Cardiac muscle, like other muscles, can contract, but it can also conduct electricity, like nerves. The blood to the myocardium is supplied by the coronary arteries.  If these arteries are occluded by atherosclerosis and/or thrombosis, this can lead to angina pectoris or myocardial infarction due to ischemia (lack of oxygen). 7

 The innermost layer of the heart.  It is a serous membrane that lines the inner surface of the heart, its valves, and the chordae tendinae Interventricular septum  The interventricular septum is the thick wall separating the lower chambers (the ventricles) of the heart from one another. The ventricular septum is directed backward and to the right, and is curved toward the right ventricle. The greater portion of its thickness constitutes the muscular ventricular septum. 8

Contractility: ●It is ability of the heart muscle to contract and pump blood into the circulation ●The whole heart acts as single unit because it is a functional syncytium. Factors affecting cardiac properties:  1- Nervous factors: Autonomic nervous system  2- Physical factors: Temperature, warming increase heart rate, conductivity, excitability and contractility, while cooling decreases all cardiac properties.  3- Chemical factors. 9

Heart Chambers  The heart has four chambers, two atria and two ventricles.  Atria  There are two atria, one on either side of the heart. On the right side is the atrium that contains blood which is poor in oxygen. The left atrium contains blood which has been oxygenated. The right atrium receives deoxygenated blood from the superior vena cava and inferior vena cava. The left atrium receives oxygenated blood from the left and right pulmonary veins. 10

Ventricles  ●The ventricle is a heart chamber which collects blood from an atrium and pumps it out of the heart. There are two ventricles, the right ventricle pumps blood into the pulmonary circulation for the lungs, and the left ventricle pumps blood into the systemic circulation for the rest of the body.  ●Ventricles have thicker walls than the atria, and thus can create the higher blood pressure. Comparing the left and right ventricle, the left ventricle has thicker walls because it needs to pump blood to the whole body. 11

●The two atrioventricular (AV) valves are one-way valves that ensure that blood flows from the atria to the ventricles. The two Semilunar valves are present in the arteries leaving the heart; they prevent blood from flowing back into the ventricles. The sound heard in a heart beat is the heart valves shutting. 12

 Right AV (Tricuspid) ◦ separates the right atrium from the right ventricle. Prevents backflow into atrium.  Left AV (Bicuspid) ◦ separates the left atrium from the left ventricle. Prevents backflow into atrium.  Pulmonary valve ◦ separates the right ventricle from the pulmonary arteries. Prevents backflow after ventricular contraction.  Aortic valve ◦ separates the left ventricle from the aorta. Prevents backflow after ventricular contraction. Atrioventricular valves Semilunar valves 13

Pulmonary semilunar valve Aortic semilunar valve Left AV (bicuspid) valve Right AV (tricuspid) valve Chordai tendineae Papillary muscle 14

 Control of Heart beat: ●The heart contains two cardiac pacemakers that spontaneously cause the heart to beat. These can be controlled by the autonomic nervous system and circulating adrenaline. ●If the cardiac muscles just contracted and relaxed randomly at a natural rhythm the cycle would become disordered and the heart would become unable to carry on its function of being a pump. 15

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. 16

● The blood leaving the left ventricle exits through the aorta. Two coronary arteries, referred to as the left and right coronary arteries. Both of these arteries originate from the left side of the heart at the beginning (root) of the aorta, immediately above the aortic valve. Left coronary artery originates from the left aortic sinus, while the right coronary artery originates from the right aortic sinus.aortaaortic valveaortic sinus 17

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 Heart Systole  -The pressure exerted on the blood stream by the heart when it contracts, forcing blood from the ventricles of the heart into the pulmonary artery and the aorta.  -Heart systole is initiated by the electrical cells of the SA node, which is the heart's natural pacemaker. These cells are activated spontaneously by depolarization of their membranes beyond a certain threshold for excitation. 19

Heart Diastole:  Cardiac diastole is the period of time when the heart relaxes after contraction in preparation for refilling with circulating blood.  -During ventricular diastole, the pressure in the (left and right) ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the mitral valve opens, and the left ventricle fills with blood that was accumulating in the left atrium. Likewise, when the pressure in the right ventricle drops below that in the right atrium, the tricuspid valve opens and the right ventricle fills with blood that was in the right atrium. 20

 Cardiac output (CO) is the volume of blood pumped by each ventricle per minute.Under resting condition the CO is about five litres per minute.  The stroke volume (SV) is the volume of blood pumped by each ventricle per beat, it is about 70 ml. Therefore, cardiac output is the SV times the heart rate per minute. 21

Cardiac output varies widely with the level of activity of the body. The following factors, among others, directly affect cardiac output: (1) the basic level of body metabolism, (2) whether the person is exercising, (3) the person’s age, and (4) size of the body.  For young, healthy men, resting cardiac output averages about 5.6 L/min.  For women, this value is about 4.9 L/min.When one considers the factor of age as well-because with increasing age, body activity diminishes—the average cardiac output for the resting adult, in round numbers, is often stated to be almost exactly 5 L/min. 22

 Intrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulation ◦ Starling’s law of the heart  Extrinsic regulation: Involves neural and hormonal control ◦ Parasympathetic stimulation  Supplied by vagus nerve, decreases heart rate, acetylcholine secreted ◦ Sympathetic stimulation  Supplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released. 23