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The Heart

The Heart. Chapter 18. Introduction. The heart is the pump of our circulatory system The cardiovascular system provides the transport system of the body

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The Heart

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  1. The Heart Chapter 18

  2. Introduction • The heart is the pump of our circulatory system • The cardiovascular system provides the transport system of the body • Using blood as the transport medium, the heart continually propels oxygen, nutrients, wastes, and many other substances into the interconnecting blood vessels that move past the body cells

  3. Introduction • The heart is a muscular double pump with two functions • Its right side receives oxygen poor blood from the body tissues and then pumps it to the lungs • Its left side receives oxygenated blood from the lungs and then pumps it to the body

  4. Introduction • The blood vessels that carry blood from the lungs form the pulmonary circuit • The vessels that carry blood to all the body tissues form the systemic circuit

  5. Heart Size, Location and Position • The heart is about the size of a fist • It weighs between 250 - 350 grams (less than a pound) • Located in the medial cavity of the thorax, the mediastinum • It extends from the 2nd rib to 5th intercostal space • Rests on the superior surface of diaphram

  6. Heart Size, Location and Position • The lungs flank the heart laterally and partially obscure it

  7. Heart Size, Location and Position • The heart lies anterior to the vertebral column and posterior to the sternum • Two thirds of the heart lies to the left of the mid- sternal line; the balance projects to the right • Its broad flat base, or posterior surface, points to right shoulder • The apex points toward the left hip

  8. Location - 4 Corners • The heart is has four corners projected onto the anterior thoracic wall • Superior right - where the costal cartilage joins the 3rd rib • Superior left - costal cartilage of 2nd rib a fingers breadth lateral to the sternum

  9. Location - 4 Corners • The inferior right - lies at the costal cartilage of the sixth rib, a finger’s breath lateral to the sternum • The inferior left (apex) lies in the fifth intercostal space at the mid-clavicular line • These points depict the normal heart size and placement

  10. Coverings of the Heart • The heart is enclosed in a triple-walled sac called the pericardium • The loose fitting outer layer of the sac is the fibrous pericardium • This tough, dense connective tissue layer 1) protects the heart; 2) anchors the heart; and 3) prevents overfilling

  11. Coverings of the Heart • Deep to the fibrous pericardium is the double-layered serous pericardium, a closed sac sandwiched between the fibrous pericardium and the heart • The two layers are… • Parietal layer • Visceral layer

  12. Coverings of the Heart • The outer parietal layer adheres to the internal surface of the fibrous pericardium • At the superior reflection of the heart, the parietal layer is continuous with the visceral layer of the serous pericardium or epicardium

  13. Coverings of the Heart • The visceral layer, also called the epicardium, is an integral part of the heart wall • The two-layer membrane conforms around the heart much like pushing your fist into a double layer membrane with an air pocket in between

  14. Coverings of the Heart • Between the two layers of serous pericardium is the slitlike pericardial cavity • The cavity contain pericardial fluid • The serous membranes, lubricated by fluid, glide smoothly against one another during heart activity, creating a relatively friction-free environment

  15. Inflammation • Inflammation of the heart can lead to serious problems • Pericarditis / hinders production of serous fluid production causing the heart to rub • Cardiac tamponade / inflammatory fluid seep into the pericardial cavity, compressing the heart and limiting its ability to pump blood

  16. Layers of the Heart Wall • The heart wall is composed of three layers • Superficial layer of epicardium • Middle layer of myocardium • Deep layer of endocardium • All three layers are richly supplied with blood vessels

  17. Layers of the Heart Wall • The epicardium is the visceral layer of the serous pericardium • The epicardium is often infiltrated with fat, especially in older people

  18. Layers of the Heart Wall • The myocardium is the layer of cardiac muscle that forms the bulk of the heart • It is the layer that actually contracts • The myocardium’s elongated circularly spirally arranged muscle cells squeeze the blood though the heart

  19. Layers of the Heart Wall • Within the myocardium, the branching cardiac muscle cells are tethered to each other by crisscrossing connective tissue fibers also arranged in spiral or circular bundles • These interlacing bundles effectively link all parts of the heart together

  20. Layers of the Heart Wall • The connective tissue forms a dense network called the internal skeleton of the heart • It reinforces the myocardium internally and anchors the cardiac muscle • This network of fibers is thicker in some areas than in others to rein- force valves and where the major vessels exit

  21. Layers of the Heart Wall • The internal skeleton prevents overdilation of vessels due to the continual stress of blood pressure • Additionally, since connective tissue is not electrically excitable, it limits action potentials across the heart to specific pathways

  22. Layers of the Heart Wall • The endocardium is a glistening white sheet of endothelium (squamous epithelium) resting on a thin layer of connective tissue

  23. Layers of the Heart Wall • Located on the inner myocardial surface, it lines the heart chambers and covers the connective tissue skeleton of the valves • The endocardium is continuous with the endothelial linings of the blood vessels leaving and entering the heart

  24. Heart Chambers • The heart has four chambers • Two superior atria • Two inferior ventricles • The longitudinal wall separating the chambers is called the • Interartial septum • Between atria • Interventricular septum • Between ventricles Atria Septum Ventricles

  25. Heart Chambers • The right ventricle forms most of the anterior surface of the heart • The left ventricle dominates the inferio- posterior aspect of the heart and forms the heart apex Left Ventricle Right Ventricle

  26. Heart Chambers • Two grooves visible on the surface of the heart indicate the boundaries of its four chambers and carry the blood vessels that supply myocardium • The Atrioventricular groove or coronary sulcus encircles the junction of the atria and ventricles Coronary Sulcus

  27. Heart Chambers • The anterior inter- ventricular sulcus, separates the right and left ventricles • It continues as the posterior inter-ventricular sulcus which provides a similar landmark on the heart’s posterio- inferior surface Anterior Interventricular Sulcus Posterior Interventricular Sulcus

  28. Heart Chambers • Except for the small, wrinkled, protruding appendages called auricles, the atria are free of distinguishing surface features • The auricles increase the atrial volume slightly Atria Auricles

  29. Heart Chambers • Internally, the posterior walls are smooth, but the anterior walls are ridged by bundles of muscle tissue • These muscle bundles are called pectinate muscles Pectinate Muscle

  30. Heart Chambers • The interatrial septum bears a shallow depression, the fovea ovalis • This landmark marks the spot where an opening, the foramen ovale, existed in the fetal heart Fovea Ovalis

  31. Heart Chambers • Functionally, the atria are receiving chambers for blood returning to the heart from the circulation • Because they need to contract only minimally to push blood into the ventricles, the atria are relatively small, thin walled chambers • As a rule they contribute little to the propulsive pumping of the heart

  32. Atria: The Receiving Chambers • Blood enters the right atrium via three veins • Superior vena cava • Returns blood from body regions superior to diaphragm • Inferiorn vena cava • Returns blood from body areas below the diaphragm • Coronary sinus • Collects blood draining from the myocardium itself Superior vena cava Coronary sinus Inferior vena cava

  33. Atria: The Receiving Chambers • Blood enters the left atrium via four veins • Right and left pulmonary veins • The pulmonary veins transport blood from the lungs back to the heart Right Pulmonary veins Left pulmonary veins Posterior view

  34. Ventricles: Discharging Chambers • Marking the internal walls of the ventricle chambers are irregular ridges of muscle called trabeculae carneae • The papillary muscles project into the cavity and play a role in valve function Papillary muscles Trabeculae carneae

  35. Ventricles: Discharging Chambers • The ventricles are the discharging chambers of the heart • Note the difference in thickness of the wall • When the ventricles contract blood is propelled out of the heart and into circulation Atrial Wall Ventricular Wall

  36. Ventricles: Discharging Chambers • The right ventricle pumps blood into the pulmonary trunk, which routes blood to the lungs for gas exchange • The left ventricle pumps blood into the aorta, the largest artery in the systemic circulation Aorta Left ventricle Pulmonary trunk Right ventricle

  37. Pathway of Blood: Heart • The heart is actually two pumps, each serving a separate blood circuit • Blood vessels that carry blood to the lung form the pulmonary circuit (gas exchange) • Vessels carrying blood to the body form the systemic circuit

  38. Pathway of Blood: Heart • The right side of the heart forms the pulmonary circuit • Blood returning from the body enters the right atrium and passes into the right ventricle • The ventricle pumps the blood to the lungs via the pulmonary trunk

  39. Pathway of Blood: Heart • Blood in the pulmonary circuit is oxygen poor and carbon dioxide rich • Once in the lungs the blood unloads carbon dioxide and picks up oxygen • Freshly oxygenated is carried back to the heart by the pulmonary veins

  40. Pathway of Blood: Heart • Note that the circulation of the pulmonary circuit is unique • Typically veins carry oxygen poor blood to the heart and arteries carry oxygen rich blood • The pattern is reversed in the pulmonary circuit with the pulmonary arteries carrying oxygen poor blood to the lungs and the pulmonary veins carrying oxygen rich blood back to the heart

  41. Pathway of Blood: Heart • The left side of the heart is the systemic system pump • Freshly oxygenated blood leaving the lungs enters the left atrium and passes into the left ventricle • The left ventricle pumps blood into the aorta and from there into many distributing arteries

  42. Pathway of Blood: Heart • Smaller distributing arteries carry the blood to all parts of the body • Gases, wastes and nutrients are exchanged across capillary walls • Blood then returns to the right atrium of the heart via systemic veins and the cycle continues

  43. Pathway of Blood: Heart • Although equal volumes of blood are flowing in the pulmonary and systemic circuits at any one moment the two ventricles have very unequal work loads • The pulmonary circuit, served by the right ventricle, is a low pressure circulation • The systemic circuit, served by the left ventricle, circulates through the entire body and encounters about five times as much resistance to blood flow

  44. Pathway of Blood: Heart • The fact that blood passes through heart chambers sequentially does not mean that the four chambers contract in that order • Rather the two atria contract together, followed by the simultaneous contraction of the two venticles

  45. Pathway of Blood: Heart • A single sequence of atrial contraction followed by the ventricular contraction is a called a heartbeat • The heart of the average adult person at rest beats 70-80 times a minute

  46. Pathway of Blood: Heart • The contraction of a heart chamber is called a systole • The time during which a heart chamber is relaxing and filling with blood is termed diastole • Although both atrial and ventricular chambers experience systole and diastole the terms usually reference the ventricles which are the dominant heart chambers

  47. Ventricles: Discharging Chambers • The difference in system work load is revealed in the comparative anatomy of the two ventricles • The walls of the left ventricle are three times as thick as those of the right ventricle Left ventricle

  48. Ventricles: Discharging Chambers • The cavity of the left ventricle is circular • The right ventricle wraps around the left and is crescent shaped • The left can generate much more pressure than the right and is a far more powerful pump Left ventricle

  49. Pathway of Blood: System • Blood flows through the heart and other parts of the circulatory system in one direction • Right atrium  right ventricle  pulmonary arteries  lungs • Lungs  pulmonary veins  left atrium  left ventricle  body • This one way flow of blood is controlled by four heart valves

  50. Heart Valves • Heart valves are positioned between the atria and the ventricles and between the ventricles and the large arteries that leave the heart • Valves open and close in response to differences in blood pressure Bicuspid (mitral) valve Aortic valve Pulmonary valve Tricuspid valve

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