Cardiovascular System Prof Abdulameer AlNuaimi Email a alnuaimisheffield

Cardiovascular System Prof. Abdulameer Al-Nuaimi E-mail: a. al-nuaimi@sheffield. ac. uk E. mail: abdulameerh@yahoo. com

LOCATION AND SURFACE PROJECTION OF THE HEART • The cone-shaped heart is relatively small, roughly the same size as a closed fist. • The heart rests on the diaphragm, near the midline of the thoracic cavity in the mediastinum (an anatomical region that extends from the sternum to the vertebral column, the first rib to the diaphragm, and between the coverings (pleurae) of the lungs). • About two-thirds of the mass of the heart lies to the left of the body’s midline. • Visualize the heart as a cone lying on its side. • The pointed end of the heart, the apex, is formed by the tip of the left ventricle (lower chamber of the heart and rests on the diaphragm). • The apex is directed anteriorly, inferiorly, and to the left • The base faces posteriorly, it is square in outline.

• The heart has many surfaces • The posterior surface of the heart is the base, it is formed mainly by the left atrium which receives four pulmonary veins. • The anterior surface of the heart is deep to the sternum and ribs. It is formed mainly by the right ventricle which is separated from right atrium by coronary sulcus and anterior interventricular sulcus from the left ventricle. • The inferior surface rests on the diaphragm. It is formed by the left and right ventricles anteriorly and part of the right atrium posteriorly • The right surface is formed by the right atrium which receives the superior vena cava above and inferior vena cava below. It is in contact with the right lung. • the left surface is formed by the left ventricle and small part of the left atrium. It is in contact with the left lung and extends from the base to the apex.

The Heart

The Pericardium • Pericardium: Is a membranous flask shaped sac that surrounds and protects the heart. • It is formed by two principal portions: • An outer fibrous pericardium: Is tough, inelastic, dense irregular connective tissue. It blends inferiorly with the central tendon of the diaphragm and superiorly with the adventitia of the great vessels • An inner serous pericardium: is a thin, more delicate membrane that forms a double layer around the heart. • The outer parietal layer of the serous pericardium is fused with the fibrous pericardium. • The inner visceral layer of the serous pericardium, called the epicardium. It is combined with the underlying delicate areolar tissue and adipose tissue and adheres tightly to the surface of the heart.

• Between the parietal and visceral layers of the serous pericardium is a thin film of lubricating fluid known as pericardial fluid. • The space that contains the few milliliters of pericardial fluid is called the pericardial cavity. • The heart is suspended freely inside the pericardial cavity. It is only fixed by the junction between fibrous pericardium and the adventitia of the aorta, pulmonary trunk and superior vena cava superiorly and adventitia of pulmonary veins posteriorly

Mediastinum

Layers of the Heart Wall • The wall of the heart consists of three layers: epicardium, the myocardium, and the endocardium. • Epicardium (external layer): is composed of two tissue layers. The outermost is the visceral layer of the serous pericardium (mesothelium). Beneath the mesosthelium is a variable amount of delicate areolar tissue and adipose tissue. It contains blood vessels, lymphatics, and nerves that supply the myocardium. • The middle myocardium (muscle 95% of the heart) is responsible for the pumping action of the heart and is composed of cardiac muscle tissue. • Endocardium (innermost layer): is a thin layer of endothelium overlying a thin layer of connective tissue. Provides a smooth lining for the chambers of the heart and covers the valves of the heart. The smooth endothelial lining minimizes the surface friction.

Chambers of the Heart • The heart is a dual pump that contains four chambers, two upper or receiving chambers called the atria and the two lower or pumping chambers called the ventricles. The paired atria receive blood from blood vessels returning blood to the heart, called veins, while the ventricles Eject the blood from the heart into blood vessels called arteries. • Thickness of myocardium varies according to the function of the chamber Atria are thin walled, deliver blood to adjacent ventricles. • Ventricle walls are much thicker and stronger. Right ventricle supplies blood to the lungs. Left ventricle wall is the thickest to supply systemic circulation.

Atria of the Heart • Atria are the receiving chambers of the heart. • Each atrium has a protruding auricle • Pectinate muscles mark the anterior wall of the right atrium. Left atrium has smooth walls • Blood enters right atria from superior and inferior venae cavae and coronary sinus. • Blood enters left atria from pulmonary veins Left atrium right atrium

Ventricles of the Heart • Ventricles are the discharging chambers of the heart. • Papillary muscles and trabeculae carneae muscles mark ventricular walls. • Right ventricle pumps blood into the pulmonary trunk. • Left ventricle pumps blood into the aorta.

Fibrous Skeleton of the Heart • the heart wall contains dense connective tissue that forms the fibrous skeleton of the heart. • fibrous skeleton consists of: four dense connective tissue rings that surround the valves of the heart, fuse with one another, and merge with the interventricular septum. • Fibrous skeleton prevents overstretching of the valves as blood passes through them. • Serves as a point of insertion for bundles of cardiac muscle fibers. • Acts as an electrical insulator between the atria and ventricles.

Heart Valves • The heart has four valves that open and close in response to pressure changes as the heart contracts and relaxes. • Each of the four valves helps to ensure one-way flow of blood by opening to let blood through and then closing to prevent its backflow. • Atrioventricular Valves: they are located between the atria and ventricles. Chordae tendineae anchor AV valves to papillary muscles. • The tricuspid valve (on the right side of the heart between right atrium and right ventricle) has three cusps. • The bicuspid valve (on the left side of the heart between left atrium and left ventricle )has two cusps • Semilunar Valves: Each valve has three semilunar cusps • The aortic valve: lies between the left ventricle and the aorta. • The pulmonary valves: lies between the right ventricle and pulmonary trunk.

Systemic and Pulmonary Circulations • With each beat, the heart pumps blood into two circuits: • The systemic circulation. • The pulmonary circulation. • The amount of blood pumped out from a ventricle per each beat is 7 o ml (stroke volume) • The two circuits are arranged in series so that the output of one becomes the input of the other.

The systemic circulation • The left side of the heart, which receives bright-red freshly oxygenated (oxygen-rich) blood from the lungs, is the pump for systemic circulation. • The left ventricle ejects blood into the aorta, which branches into smaller systemic arteries that carry the blood to all organs throughout the body (except for the air sacs (alveoli) of the lungs, which are supplied by the pulmonary circulation). • In systemic tissues, arteries give rise to smaller-diameter arterioles, which lead into extensive beds of systemic capillaries. • Exchange of nutrients and gases occurs across the thin capillary walls: In the tissues, blood unloads O 2 (oxygen) and picks up CO 2. • In most cases, blood flows through only one capillary and then enters a systemic venule. • Venules carry deoxygenated blood away from tissues and merge to form larger systemic veins, and ultimately the blood flows back to the right atrium

The pulmonary circulation • The right side of the heart is the pump for pulmonary circulation • It receives all the dark-red deoxygenated blood returning from the systemic circulation. • Blood ejected from the right ventricle flows into the pulmonary trunk, which branches into pulmonary arteries that carry blood to the right and left lungs. • In pulmonary capillaries, blood unloads CO 2, which is exhaled, and picks up O 2 from inhaled air. • The freshly oxygenated blood then flows into pulmonary veins and returns to the left atrium.

Coronary Circulation • The flow of blood through the vessels that pierce the myocardium is called the coronary circulation. • It is called coronary because the arteries encircle the heart like a crown. • Arterial blood runs through the right and left coronary arteries (branches of ascending aorta) and returns back to the right atrium through the coronary sinus • While it is contracting, the heart receives little oxygenated blood by way of the coronary arteries. • When the heart relaxes, the high pressure of blood in the aorta propels blood through the coronary arteries, into capillaries, and then into coronary veins.

Conductive system of the heart The system is formed of specialised cardiac muscle cells which are difficult to distinguish from cardiac muscle. It comprises the Sinuatrial (SA) node, the Atrioventricular (AV) node, the Atrioventricular bundle (AV bundle, or bundle of His), its right and left branches and a terminal subendocardial plexus (Purkinje fibres). This system initiates the complex cardiac muscle contractions comprising the cardiac cycle, and controls its regularity. Conductive system of the heart Purkinje fibres

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