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CADIOVASCULAR SYSTEM

Learn about the cardiovascular system and the human heart through a well-labelled diagram and comprehensive overview of its anatomy, functions, and coverings.

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CADIOVASCULAR SYSTEM

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  1. CADIOVASCULAR SYSTEM MR OGUNDELE

  2. Human Heart

  3. Well Labelled diagram of the Heargt

  4. Preamble • About three weeks after conception, the heart of the developing embryo starts to function. It is the first organ to become functional. • In human with an average life span, the heart contracts about 3 billion times, never stopping except for a fraction of a second to fill between beats.

  5. Cardiovascular System The Cardiovascular system has three basic components: 1. The heart serves as the pump that imparts pressure to the blood to establish the pressure gradient needed for blood to flow to the tissues. (Cardiac System) 2. The blood vessels serve as the passageways through which blood is directed and distributed from the heart to all parts of the body and subsequently returned to the heart. (Vascular System) 3. Bloodis the transport medium within which materials such as O2, CO2, nutrients, wastes, electrolytes, and hormones being are been transported.

  6. THE HEART • The heart is a hollow, muscular organ about the size of a clenched fist. • It lies in the thoracic (chest) cavity about midline between the sternum (breastbone) anteriorly and the vertebrae(backbone) posteriorly. • Its mass is between 250 and 350 grams.

  7. THE HEART • The heart extends obliquely for 12 to 14 cm from the second rib to the fifth intercostal space and rest on the superior surface of the diaphragm. • The heart lies anterior to the vertebral column and posterior to the sternum. • The lungs flank the heart laterally and partially obscure it. About two-thirds of its mass lies to the left of the midsternal line.

  8. THE HEART • Its broad, flat base, or posterior surface, is about 9 cm (3.5 in) wide and directed toward the right shoulder. Its apex points inferiorly toward the left hip.

  9. Coverings of the Heart • The heart is enclosed in a double-walled sac called the PERICARDIUM. • The loosely fitting superficial part of this sac is the fibrous pericardium. This tough, dense connective tissue layer (1) protects the heart, (2) anchors it to surrounding structures, and (3) prevents overfilling of the heart with blood.

  10. Coverings of the Heart • Deep to the fibrous pericardium is the serous pericardium, a thin, slippery, double-layer serous membrane. Its parietal layer lines the internal surface of the fibrous pericardium • On the surface of the heart muscle is the visceral pericardium, often called the epicardium(“upon the heart”), which is an integral part of the heart wall

  11. Coverings of the Heart •  Between the parietal and visceral layers is the slit-like pericardial cavity, which contains a film of serous fluid. • The serous membranes, lubricated by the fluid, glide smoothly past one another during heart activity, allowing the mobile heart to work in a relatively friction-free environment.

  12. Layers of the Heart Wall The heart wall has three distinct layers: • A thin inner layer, the endothelium, a unique type of epithelial tissue that lines the entire circulatory system • A middle layer, the myocardium, which is composed of cardiac muscle and constitutes the bulk of the heart wall • A thin external layer, the epicardium, that covers the heart

  13. Coverings of the heart

  14. Chambers and Associated Great Vessels The heart has four chambers : two superior ATRIA and two inferior VENTRICLES. • The upper chambers of the heart are the right and left atria (singular: atrium), which have relatively thin walls and are separated by a common wall of myocardium called the interatrial septum. • The lower chambers are the right and left ventricles, which have thicker walls and are separated by the interventricularseptum

  15. RIGHT ATRIUM • The two large caval veins return blood from the body to the right atrium . • From the right atrium, blood will flow through the right atrioventricular (AV) valve, or tricuspid valve, into the right ventricle. • The tricuspid valve is made of three flaps (or cusps) of endocardium reinforced with connective tissue. The general purpose of all valves in the circulatory system is to prevent backflow of blood.

  16. LEFT ATRIUM • The left atrium receives blood from the lungs, by way of four pulmonary veins. • This blood will then flow into the left ventricle through the left atrioventricular (AV) valve, also called the mitral valve or bicuspid (two flaps) valve. • The mitral valve prevents backflow of blood from the left ventricle to the left atrium when the left ventricle contracts.

  17. Atria • Another function of the atria is the production of a hormone involved in blood pressure maintenance. • Atrialnatriuretic peptide (ANP), also called atrialnatriuretic hormone (ANH) is produced when atria walls are stretched and (ANP) decreases thereabsorption of sodium ions by the kidneys, so that more sodium ions are excreted in urine, which in turn increases the elimination of water.

  18. RIGHT VENTRICLE • When the right ventricle contracts, the tricuspid valve closes and the blood is pumped to the lungs through the pulmonary artery (or trunk). • Between the pulmonary artery and the right ventricle is the pulmonarysemilunar valve (or more simply, pulmonary valve).

  19. LEFT VENTRICLE • The walls of the left ventricle are thicker than those of the right ventricle, which enables the left ventricle to contract more forcefully. • The left ventricle pumps blood to the body through the aorta, the largest artery of the body. At the junction of the aorta and the left ventricle is the aortic semilunar valve (or aortic valve).

  20. PATHWAY OF BLOOD THROUGH THE HEART • The blood vessels that carry blood to and from the lungs form the PULMONARY CIRCUIT (pulmonos = lung), which serves gas exchange. • The blood vessels that carry the functional blood supply to and from all body tissues constitute the SYSTEMIC CIRCUIT.

  21. CORONARY CIRCULATION • The coronary circulation, the functional blood supply of the heart, is the shortest circulation in the body. • The arterial supply of the coronary circulation is provided by the right and left coronary arteries, both arising from the base of the aorta and encircling the heart in the coronary sulcus. • The purpose of the coronary vessels is to supply blood to the myocardium itself, because oxygen is essential for normal myocardial contraction.

  22. Electrical Activity of the Heart • Contraction of cardiac muscle cells to eject blood is triggered by action potentials sweeping across the muscle cell membranes. • The heart contracts, or beats, rhythmically as a result of action potentials that it generates by itself, a property called autorhythmicity.

  23. Electrical Activity of the Heart • The physiologic characteristics of the cardiac conduction cells account for this coordination: • Automaticity:ability to initiate an electrical impulse • Excitability: ability to respond to an electrical impulse • Conductivity: ability to transmit an electrical impulse from one cell to another

  24. Electrical Activity of the Heart There are two specialized types of cardiac muscle cells: • 1. Contractile cells, which are 99% of the cardiac muscle cells, they do the mechanical work of pumping and do not initiate their own action potentials. • 2. In contrast, the small but extremely important remainder of the cardiac cells, the autorhythmic cells, do not contract but instead are specialized for initiating and conducting the action potentials responsible for contraction of the working cells.

  25. Cardiac Conduction System

  26. Sequence of Excitation/ Conduction pathways • Sinoatrial Node: The sinoatrial (SA) node is located in the right atrial wall, just inferior to the entrance of the superior vena cava. • The SA node typically generates impulses about 75 times every minute. (However, its inherent rate in the absence of extrinsic neural and hormonal factors is closer to 100 times per minute.)

  27. Conduction pathways • Because no other region of the conduction system or the myocardium has a faster depolarization rate, the SA sets the pace for the heart as a whole. Hence, it is the heart’s pacemaker, and its characteristic rhythm, called sinus rhythm, determines heart rate.

  28. Conduction pathways • Atrioventricular Node: From the SA node, the depolarization wave spreads via gap junctions throughout the atria and via the internodal pathway to the atrioventricular (AV) node. • At the AV node, the impulse is delayed for about 0.1 s, allowing the atria to respond and complete their contraction before the ventricles contract.

  29. Conduction pathways • Atrioventricular Bundle: From the AV node, the impulse sweeps to the atrioventricular (AV) bundle (also called the bundle of His) in the superior part of the interventricular septum. • Right and left bundle branches. The AV bundle persists only briefly before splitting into two pathways—the right and left bundle branches, which course along the interventricular septum toward the heart apex

  30. Conduction pathways • Purkinje fibers: The Purkinje fibers complete the pathway through the interventricular septum, penetrate into the heart apex, and then turn superiorly into the ventricular walls. • Because the left ventricle is much larger than the right, the Purkinje network is more elaborate in that side of the heart.

  31. Mechanical Activity of the Heart • Ventricular filling: mid-diastole.  Pressure in the heart is low, blood returning from the circulation is flowing passively through the atria and the open AV valves into the ventricles, and the aortic and pulmonary valves are closed. • Approximately 80% of ventricular filling occurs during this period, and the AV valve flaps begin to drift toward the closed position. The remaining 20% is delivered to the ventricles when the atria contract toward the end of this phase. This stage corresponds to the TP interval on the ECG

  32. Blood Flow Through the Heart Oxygenated blood out to body Deoxygenated blood in from body Oxygenated blood in lungs Deoxygenated blood out to lungs Atria Contract Ventricles Contract

  33. Blood Flow Through the Heart (cont.) Right Atrium TricuspidValve Right Ventricle PulmonaryValve Lungs Body AorticSemilunarValve Left Ventricle BicuspidValve Left Atrium PulmonarySemilunarValve

  34. Mechanical Activity of the Heart • LATE VENTRICULAR DIASTOLE Late in ventricular diastole, the SA node reaches threshold and fires. The impulse spreads throughout the atria, which appears on the ECG as the P wave. • END OF VENTRICULAR DIASTOLE Ventricular diastole ends at the onset of ventricular contraction. By this time, atrial contraction and ventricular filling are completed. The volume of blood in the ventricle at the end of diastole is known as the end-diastolic volume (EDV), which averages about 135 ml.

  35. Mechanical Activity of the Heart • Ventricular systole.  As the atria relax, the ventricles begin contracting. Their walls close in on the blood in their chambers, and ventricular pressure rises rapidly and sharply, closing the AV valves. • Ventricular pressure continues to rise and when it finally exceeds the pressure in the large arteries issuing from the ventricles, the isovolumetric stage ends as the SL valves are forced open and blood is expelled from the ventricles into the aorta and pulmonary trunk. During this ventricular ejection phase, the pressure in the aorta normally reaches about 120 mm Hg.

  36. Mechanical Activity of the Heart • The amount of blood pumped out of each ventricle with each contraction is called the stroke volume (SV). • The T wave signifies ventricular repolarization at the end of ventricular systole. As the ventricle starts to relax, on repolarization, ventricular pressure falls below aortic pressure and the aortic valve closes

  37. Mechanical Activity of the Heart • Isovolumetric relaxation: early diastole.  During this brief phase following the T wave, the ventricles relax. Because the blood remaining in their chambers, referred to as the end systolic volume (ESV), is no longer compressed, ventricular pressure drops rapidly

  38. Mechanical Activity of the Heart • NB: When the body is at rest, one complete cardiac cycle lasts 0.8 sec, with 0.3 sec devoted to ventricular systole and 0.5 sec taken up by ventricular diastole. • Significantly, much of ventricular filling occurs early in diastole during the rapid filling phase. • During times of rapid heart rate, diastole length is shortened much more than systole length is. 

  39. Heart Sounds • Heart sounds (lub-dup) are associated with closing of heart valves • First sound occurs as AV valves close and signifies beginning of systole (contraction) • Second sound occurs when SL valves close at the beginning of ventricular diastole (relaxation)

  40. Cardiac Conduction System

  41. Blood Flow Through the Heart Oxygenated blood out to body Deoxygenated blood in from body Oxygenated blood in lungs Deoxygenated blood out to lungs Atria Contract Ventricles Contract

  42. Blood Flow Through the Heart (cont.) Right Atrium TricuspidValve Right Ventricle PulmonaryValve Lungs Body AorticSemilunarValve Left Ventricle BicuspidValve Left Atrium PulmonarySemilunarValve

  43. Cardiac Output and Its Control • Cardiac output (CO) is the volume of blood pumped by each ventricle per minute (not the total amount of blood pumpedby the heart). • The average resting heart rate is 75 beats per minute, established by SA node rhythmicity; the average resting stroke volume is 70 ml per beat, producing an average resting cardiac output is 5min to 6 L/min

  44. Cardiac Output • The two determinants of cardiac output are heart rate (beats per minute) and stroke volume(volume of blood pumped per beat or stroke). • With an average resting heart rate of 75 beats per minute, an average resting cardiac output is 5 to 6 L

  45. Cardiac Output • Cardiac output (CO) = heart rate * stroke volume =75 beats/min * 70 ml/beat =5250 ml/min

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