The Cardiovascular System: The Heart

1. The Cardiovascular System:The Heart Chapter 19

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. 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

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

5. 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

6. Coverings of the Heart • The heart is enclosed in a double-walled sac called the pericardium • The loose fitting superficial part 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

7. Coverings of the Heart • The loose fitting superficial part of the sac is the fibrous pericardium • This tough, dense connective tissue layer • Protects the heart • Anchors it to surrounding structures (diaphragm/large vessels) • Prevents overfilling of the heart with blood

8. Coverings of the Heart • Deep to the fibrous pericardium is the serous pericardium, a thin slippery serous membrane composed of two layers • Parietal layer • Visceral layer

9. Coverings of the Heart • The parietal layer lines the internal surface of the fibrous pericardium • At the superior margin of the heart, the parietal layer attaches to the large arteries exiting from the heart • It then turns inferiorly and continues over the external heart surface as the visceral layer

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

11. 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

12. 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

13. 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

14. 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

15. 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

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

17. 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

18. 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

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

20. 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

21. Chambers and Great Vessels • 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

22. Chambers and Great Vessels • 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

23. Chambers and Great Vessels • 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

24. Chambers and Great Vessels • 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

25. Atria: The Receiving 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

26. Atria: The Receiving 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

27. Atria: The Receiving 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

28. Atria: The Receiving 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. Heart Valves • The valves of the heart allow for the blood to flow in only one direction • Note: View of the heart with the superior atria removed

46. Atrioventricular (AV) Valves • The AV valves are located at each atrial-ventricular junction • The valves are positioned to prevent a backflow of blood into the atria when the ventricles are contracting • The valves are the • Tricuspid valve • Bicuspid valve Bicuspid (mitral) valve Tricuspid valve

47. Atrioventricular (AV) Valves • The right AV valve, the tricuspid, has three flexible cusps • The left AV valve, the bicuspid, has two flexible cusps • The cusps are flaps of endocardium reinforced by connective tissue Bicuspid (mitral) valve Tricuspid valve

48. Atrioventricular (AV) Valves • Attached to each of the AV valve flaps are tiny collagen cords called chordae tendoneae • The cords anchor the cusps to the papillary muscles protruding from the ventricular walls Chordae tendoneae Papillary muscles

49. Atrioventricular (AV) Valves • When the heart is completed relaxed, the AV valve flaps hang limply into the ventricular chambers • Blood flows into the atria and then through the open AV valves into the ventricles • Atria contract, forcing additional blood into ventricles

50. Atrioventricular (AV) Valves • When the ventricles begin to contract, compressing the blood in the chambers, intra- ventricular pressure rises forcing blood superiorly against the valve flaps • The chordae tendoneae and the papillary muscles anchor the flaps in their closed position