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Chapter 11- Part 2 The Cardiovascular System

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1 Chapter 11- Part 2 The 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)

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