Chapter 11- Part 2 The Cardiovascular System

1. Chapter 11- Part 2The Cardiovascular System

2. Coronary Circulation • Blood in the heart chambers does not nourish the myocardium • The heart has its own nourishing circulatory system • Coronary Arteries • Branch from the base of the aorta and encircle the heart in the atrioventricular groove • Cardiac Veins • Blood empties into the right atrium via the Coronary Sinus

5. Heart Attacks • Angina Pectoris – Crushing chest pain • The result of a situation in which the myocardium is deprived of oxygen • This pain is a warning that should never be ignored, because if angina is prolonged, the ischemic heart cells may die.

6. Heart Attacks • Myocardial Infarction – “Heart attack”; Heart cells die because of a lack of oxygen

7. Amount of Work Done by the Heart • The amount of work the heart does is incredible! • In one day it pushes the body’s supply of ~6 quarts of blood through the blood vessels over 1000 times. • It actually pumps about 6000 quarts of blood in a single day!

8. The Heart: Conduction System • Two types of controlling systems act to regulate heart activity: • Autonomic Nervous System • Act like “brakes” and “accelerators” to decrease or increase the heart rate depending on which division is activated • Intrinsic Conduction System (Nodal System) • Built into the heart tissue • Heart muscle cells contract (without nerve impulses) in a regular, continuous, coordinated way • Causes heart muscle depolarization in only one direction – from the atria to the ventricles.

9. The Heart: Conduction System • Special tissue sets the pace: • Sinoatrial Node (SA Node) – Pacemaker • Tiny cell mass located in the right atrium • It starts each heartbeat and sets the pace for the whole heart • Atrioventricular Node (AV Node) • Located at the junction of the atria and ventricles • From the SA node, the impulse spreads through the atria to the AV node, and then the atria contract • At the AV node, the impulse is delayed briefly to give the atria time to finish contracting

10. Heart Contractions

11. The Heart: Conduction System • After the impulse travels through the AV node, it then passes rapidly through the: • Atrioventricular Bundle (AV bundle) • Also called bundle of His • Bundle Branches • Right and left branches • Located in the interventricular septum • Purkinje Fibers • Spreads within the muscles of the ventricle

13. The Heart: Conduction System • First the impulse travels from the SA Node → AV Node • Causes the atria to contract • Then the impulse travels from the AV Node → AV Bundle → Bundle Branches → Purkinje Fibers • Results in the “wringing” contraction of the ventricles that begins at the heart apex and moves toward the atria.

15. Some Heart Problems • Damage to the SA node • Can install artificial pace-makers • Ischemia - Lack of blood flow to the heart muscle • May lead to fibrillation • Fibrillation - A rapid uncoordinated shuddering of the heart muscle • It looks like a bag of worms • Makes the heart totally useless as a pump and is a major cause of death from heart attacks

16. The Heart: Cardiac Cycle • Atria contract simultaneously • Atria relax, then ventricles contract • Systole = Contraction of the ventricles • Diastole = Relaxation of the ventricles

17. The Heart: Cardiac Cycle • Cardiac Cycle – Events of one complete heart beat • Average heart beats ~75 times per minute • The length of the cardiac cycle is normally about 0.8 seconds

18. Heart Sounds • You can hear two distinct sounds during each cardiac cycle: “lub-dup” • The first heart sound (“lub”) is caused by the closing of the AV valves • Sound is longer and louder than the second sound • The second heart sound (“dup”) is caused by the closing of the semilunar valves • Sound tends to be short and sharp

19. Heart Sounds • Blood flows silently as long as the flow is smooth and uninterrupted. • If it strikes obstructions, its flow becomes turbulent and generates sounds, which can be heard with a stethoscope. • Unusual heart sounds, or murmurs, usually indicate valve problems.

20. The Heart: Cardiac Output • Cardiac Output (CO) - Amount of blood pumped by each side of the heart in one minute • CO = (heart rate [HR]) x (stroke volume [SV]) • Stroke Volume - Volume of blood pumped by each ventricle in one contraction

21. Regulation of Stroke Volume • The more the cardiac muscle cells are stretched, the stronger the contraction will be. • The important factor stretching the heart muscle is venous return, the amount of blood entering the heart and distending its ventricles. • Exercise speeds venous return because it results in increased heart rate and force. • Blood loss decreases venous return.

22. Cardiac Output Regulation Figure 11.7

23. Regulation of Heart Rate • Stroke volume tends to be relatively constant. • However, when blood volume drops suddenly or when the heart has been seriously weakened, SV declines, and CO is maintained by a faster heartbeat. • Regulation of Heart Rate • Although heart rate does not depend on the nervous system, its rate can be changed temporarily by the autonomic nervous system. • Also modified by various chemicals, hormones, and ions.

24. Congestive Heart Failure • Congestive Heart Failure – Occurs when the pumping efficiency of the heart is depressed so that circulation is inadequate to meet tissue needs. • Usually a progressive condition that reflects weakening of the heart by coronary atherosclerosis (clogging of the coronary vessels), persistent high blood pressure, or multiple myocardial infarcts.

25. Congestive Heart Failure • Each side can fail independently of the other. • Failure of one side puts a greater strain on the opposite side, and eventually the whole heart fails. • Pulmonary Congestion – Failure of the left heart • Left side is unable to eject the returning blood • Blood vessels within the lungs become swollen and fluid leaks into the lung tissue causing pulmonary edema. If untreated, the person suffocates. • Peripheral Congestion – Failure of the right heart • Blood backs up in the systemic circulation • Edema is noticeable in the distal parts of the body (feet, fingers)