STRUCTURES AND FUNCTIONS OF THE HEART COVERINGS Pericardium

STRUCTURES AND FUNCTIONS OF THE HEART COVERINGS • Pericardium • Sac around the heart. • Fibrous pericardium: tough, loose-fitting, inextensible sac • Serous pericardium: parietal layer lies inside the fibrous pericardium; visceral layer (epicardium) covers the outside of the heart • Pericardial space: lies between visceral and parietal layers and contains 10 to 15 ml of pericardial fluid • Function of the heart coverings: to provide protection against friction 1

PERICARDIUM 2

STRUCTURE OF THE HEART • The wall of the heart is made up of three distinct layers: • Epicardium: outer layer • Myocardium: thick, contractile middle layer; compresses the heart cavities and the blood within them with great force • Endocardium: delicate inner layer of endothelial tissue 3

WALL OF THE HEART 4

CHAMBERS OF THE HEART • Atria • Two superior chambers known as “receiving chambers” because they receive blood from veins • Atria alternately relax to receive blood and then contract to push blood into ventricles • Myocardial wall of each atrium is not very thick because little pressure is needed to move blood such a short distance • Auricle: earlike flap protruding from each atrium 5

INTERIOR OF THE HEART 6

CHAMBERS AND VALVES OF THE HEART 7

CHAMBERS AND VALVES OF THE HEART (CONT. ) 8

CHAMBERS OF THE HEART • Ventricles • Two lower chambers; known as “pumping chambers” because they push blood into the large network of vessels • Ventricular myocardium is thicker (the left ventricle more than the right) than the myocardium of the atria because great force must be generated to pump the blood a large distance 9

VALVES OF THE HEART • Atrioventricular (AV) valves prevent blood from flowing back into the atria from the ventricles when the ventricles contract • Tricuspid valve (right AV valve): guards the right atrioventricular orifice; free edges of three flaps of endocardium are attached to papillary muscles by chordae tendineae • Bicuspid (mitral) valve (left AV valve): similar in structure to tricuspid valve except has only two flaps 10

VALVES OF THE HEART (CONT. ) • Semilunar (SL) valves prevent blood from flowing back into the ventricles from the aorta and pulmonary trunk • Pulmonary valve is at the entrance of the pulmonary trunk • Aortic valve is at the entrance of the aorta 11

BLOOD SUPPLY OF THE HEART TISSUE • Coronary arteries: myocardial cells receive blood from the right and left coronary arteries • First branches to come off of the aorta • Ventricles receive blood from branches of both the right and left coronary arteries • Each ventricle receives blood only from a small branch of the corresponding coronary artery • Most abundant blood supply goes to the myocardium of the left ventricle 12

CORONARY ARTERIES 13

BLOOD SUPPLY OF THE HEART TISSUE • Cardiac veins • As a rule, veins follow a course that closely parallels that of coronary arteries • After passing through the cardiac veins, blood enters the coronary sinus to drain into the right atrium 14

CORONARY VEINS 15

CONDUCTION SYSTEM OF THE HEART • Composed of four major structures: • Sinoatrial (SA) node • Atrioventricular (AV) node • AV bundle (bundle of his) • Subendocardial branches (purkinje fibers) • System generates rhythmic impulses and distributes them to regions of the myocardium 16

CONDUCTION SYSTEM OF THE HEART (CONT. ) • SA node (pacemaker) • Initiates each heartbeat and sets its pace • Specialized pacemaker cells in the node have an intrinsic rhythm • Sequence of cardiac stimulation • After generation by the SA node, each impulse travels throughout the muscle fibers of both atria and the atria begin to contract 17

CONDUCTION SYSTEM OF THE HEART 18