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)