The Cardiovascular System

1. The Cardiovascular System

2. The Cardiovascular System • A closed system of the heart and blood vessels • The heart pumps blood • Blood vessels allow blood to circulate to all parts of the body • The function of the cardiovascular system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products

3. The Heart • Location • Thorax between the lungs • Pointed apex directed toward left hip & rests on diaphragm • Base from which great vessels emerge points toward right shoulder & lies beneath 2nd rib • About the size of your fist • Less than 1 pound

4. The Heart Figure 11.1

5. The Heart: Coverings • Pericardium – a double serous membrane • Visceral pericardium (epicardium) • Next to heart; part of heart wall • Parietal pericardium • Outside layer • Reinforced by dense connective tissue (fibrous pericardium) • Protects heart • Anchors it to the diaphragm & sternum • Serous fluid fills the space between the layers of pericardium

6. The Heart: Heart Wall • Three layers • Epicardium (visceral pericardium) • Outside layer • Continuous with the parietal pericardium • Connective tissue layer • Myocardium • Middle layer • Mostly cardiac muscle • Reinforced internally by dense fibrous connective tissue (“Skeleton of the heart”) • Endocardium • Inner layer • Endothelium lines chambers; continuous w/ vessels entering & leaving heart – helps blood flow smoothly through heart

7. External Heart Anatomy Figure 11.2a

8. The Heart: Chambers • Right and left side act as separate pumps • Four chambers • 2 Atria = Receiving chambers • Right atrium • Left atrium • 2 Ventricles = Discharging chambers (Pumps) • Right ventricle • Forms most of heart’s anterior surface; pulmonary circuit pump • Left ventricle • Forms apex; systemic circuit pump • Walls are substantially thicker; more powerful to pump blood throughout body Figure 11.2c

9. The Heart: Chambers

10. Pulmonary Circulation • Right side = pulmonary circuit pump • Right atria receives deoxygenated blood from the body via the superior and inferior vena cava • Blood flows through the right atrioventricular (AV) valve (tricuspid valve) into the right ventricle • Right ventricle pumps deoxygenated blood out through the pulmonary semilunar valves into the pulmonary trunk that splits into right & left pulmonary arteries, which carry blood to the lungs • Oxygen is picked up & carbon dioxide is unloaded • Oxygen-rich blood is returned to the left atria via 4 pulmonary veins

11. Systemic Circulation • Left side = systemic circuit pump • Blood flows from the left atria through the left atrioventricular (AV) valve (bicuspid,or mitral valve) into the left ventricle • Left ventricle pumps oxygenated blood out through the aortic semilunar valves into the aorta from which the systemic arteries branch to supply body tissues • From left ventricle to the aorta to arteries to arterioles to capillaries to venules to veins to the vena cava to the right atrium

12. Blood Circulation Figure 11.3

13. The Heart: Valves • Allow blood to flow in only one direction • Four valves • Atrioventricular valves between atria and ventricles prevent backflow into atria when ventricles contract – hang limply when heart is relaxed • Bicuspid or mitral valve (left) • 2 flaps, or cusps, of endocardium • Tricuspid valve (right) • 3 flaps • Semilunar valves between ventricle and artery with 3 leaflets that fit tightly together when closed • Pulmonary semilunar valve • Aortic semilunar valve

14. The Heart: Valves • Valves open as blood is pumped through • Held in place by chordae tendineae (“heart strings”) • Close to prevent backflow

15. Operation of Heart Valves Figure 11.4

16. The Heart: Associated Great Vessels • Aorta • Leaves left ventricle • Pulmonary arteries • Leave right ventricle • Vena cava • Enters right atrium • Pulmonary veins (four) • Enter left atrium

17. Coronary Circulation • Blood in the heart chambers does not nourish the myocardium • The heart has its own nourishing circulatory system • Coronary arteries branch from base of aorta encircling heart in coronary sulcus (AV groove) • Cardiac veins empty into the coronary sinus on the back side of the heart which empties into the right atrium

18. The Heart: Conduction System • Intrinsic conduction system (nodal system) • Heart muscle cells contract, without nerve impulses, in a regular, continuous way

19. The Heart: Conduction System • Special tissue sets the pace • Sinoatrial node • In right atrium • Pacemaker • Atrioventricular node • At junction of the atria & ventricles • Atrioventricular bundle • a.k.a. bundle of His • Bundle branches • Right & left located in the interventricular septum • Purkinje fibers • Spread within muscles of ventricle walls

20. Heart Contractions • Contraction is initiated by the sinoatrial node • Sequential stimulation occurs at other autorhythmic cells

21. Heart Contractions Figure 11.5

22. Filling of Heart Chambers – the Cardiac Cycle = one complete heartbeat Figure 11.6

23. The Heart: Cardiac Cycle • Average heart beats 75 times/minute, so cardiac cycle = 0.8 seconds • Atria contract simultaneously • Atria relax, then ventricles contract starting at the apex and moving toward the atria • Systole = contraction • Diastole = relaxation

24. The Heart: Cardiac Cycle • Cardiac cycle – events of one complete heart beat • Mid-to-late diastole – blood flows into ventricles • Ventricular systole – blood pressure builds before ventricle contracts, pushing out blood; atria are relaxed & filling again • Early diastole – atria finish re-filling, ventricular pressure is low

25. Heart Sounds • When using a stethoscope, 2 distinct sounds • “Lub” • Caused by the closing of the AV valves • Longer and louder • “Dup” or “dub” • Occurs when the semilunar valves close at the end of systole • Short and sharp • Lub-dup, pause, lub-dup, pause, and so on

26. The Heart: Cardiac Output • Cardiac output (CO) • Amount of blood pumped out by each side of the heart in one minute (ventricles) • CO = (heart rate [HR]) x (stroke volume [SV]) • Stroke volume • Volume of blood pumped by each ventricle in one contraction • Average adult CO = 75 beats/min. X 70 ml/min. = 5250ml/min.

27. Cardiac Output Regulation Figure 11.7

28. The Heart: Regulation of Heart Rate • Stroke volume usually remains relatively constant • Starling’s law of the heart – the more that the cardiac muscle is stretched, the stronger the contraction • Changing heart rate is the most common way to change cardiac output

29. The Heart: Regulation of Heart Rate • Increased heart rate • Sympathetic nervous system • Crisis • Low blood pressure • Hormones • Epinephrine • Thyroxine • Exercise • Decreased blood volume

30. The Heart: Regulation of Heart Rate • Decreased heart rate • Parasympathetic nervous system • High blood pressure or blood volume • Decreased venous return

31. Blood Vessels: The Vascular System • Taking blood to the tissues and back • Arteries • Arterioles • Capillaries • Venules • Veins Figure 11.8a

32. The Vascular System • Vessels have 3 layers or tunics Figure 11.8b

33. Differences Between Blood Vessel Types • Walls of arteries are the thickest • Lumens of veins are larger • Larger veins have valves that prevent backflow of blood • Skeletal muscle “milks” blood in veins toward the heart • Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue

34. Movement of Blood Through Vessels • Most arterial blood is pumped by the heart • Veins use the milking action of muscles to help move blood Figure 11.9

35. Capillary Exchange • Substances exchanged due to concentration gradients • Oxygen and nutrients leave the blood • Carbon dioxide and other wastes leave the cells

36. Capillary Exchange: Mechanisms • Direct diffusion across plasma membranes • Endocytosis or exocytosis • Some capillaries have gaps (intercellular clefts) • Plasma membrane not joined by tight junctions • Fenestrations of some capillaries • Fenestrations = pores

37. Diffusion at Capillary Beds Figure 11.20

38. Special Circulations: Hepatic Portal Circulation • Veins of the hepatic portal circulation drain the digestive organs, spleen and pancreas and deliver this blood to the liver via hepatic portal vein • Liver processes glucose, fat and protein before they enter the systemic circulation • Some nutrients are removed to be stored for later release to the blood • Veins feed the liver circulation

39. Hepatic Portal Circulation Figure 11.14

40. Special Circulations: Circulation to the Fetus • Lungs and digestive system are not functional • All nutrient, excretory and gas exchanges occur through the placenta • Umbilical cord contains 3 blood vessels • 1 large umbilical vein • Carries nutrients and oxygen to the fetus • 2 smaller umbilical arteries • Carries carbon dioxide and waste from fetus to placenta

41. Circulation to the Fetus • As blood flows to the fetal heart, most of it bypasses the immature liver via the ductus venosus and enters the inferior vena cava and is carried to the right atrium • Since lungs are nonfunctional, 2 shunts bypass them • Blood entering right atrium is shunted into the left atrium via foramen ovale, an opening in the interatrial septum • Blood that enters the right ventricle is pumped out the pulmonary trunk and shunted into the ductus arteriosus, which connects it to the aorta • Aorta carries blood to fetal tissues and ultimately back to the placenta via the umbilical arteries • Shortly after birth, the foramen ovale closes and the ductus arteriosus collapses and is converted to the ligamentum arteriosum

42. Circulation to the Fetus Figure 11.15

43. Developmental Aspects of the Cardiovascular System • A simple “tube heart” develops in the embryo and pumps by the fourth week • The heart becomes a four-chambered organ by the end of seven weeks • Few structural changes occur after the seventh week

44. Pulse • Pulse – pressure wave of blood • Monitored at “pressure points” where pulse is easily palpated • Resting pulse averages 70-76 beats/min Figure 11.16

45. Blood Pressure • Measurements by health professionals are made on the pressure in large arteries • Systolic – pressure at the peak of ventricular contraction • Diastolic – pressure when ventricles relax • Pressure in blood vessels decreases as the distance away from the heart increases

46. Measuring Arterial Blood Pressure Figure 11.18

47. Comparison of Blood Pressures in Different Vessels Figure 11.17

48. Blood Pressure: Effects of Factors • Neural factors • Autonomic nervous system adjustments (sympathetic division) cause vasoconstriction, which increases BP • Renal factors • Regulation by altering blood volume • Allowing more water to leave as urine, lowers BP • Retaining water raises BP • Renin – hormonal control – raises BP (vasoconstriction)

49. Blood Pressure: Effects of Factors • Temperature • Heat has a vasodilation effect • Cold has a vasoconstricting effect • Chemicals • Various substances can cause increases or decreases • Increase BP – epinephrine and nicotine • Decrease BP – alcohol and histamine • Diet

50. Factors Determining Blood Pressure Figure 11.19