Chapter 11- Part 2The Cardiovascular System

Coronary CirculationCoronary 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

Heart AttacksHeart 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.

Heart AttacksHeart Attacks

Myocardial Infarction – “Heart attack”; Heart cells die because of a lack of oxygen

Amount of Work Done by the HeartAmount 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!

The Heart: Conduction SystemThe Heart: Conduction System

Two types of controlling systems act to regulate heart activity:1. Autonomic Nervous System

Act like “brakes” and “accelerators” to decrease or increase the heart rate depending on which division is activated

2. 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.

The Heart: Conduction SystemThe 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

Heart ContractionsHeart Contractions

The Heart: Conduction SystemThe Heart: Conduction System After the impulse travels through the AV node, it

then passes rapidly through the:

1. Atrioventricular Bundle (AV bundle)

• Also called bundle of His

2. Bundle Branches

• Right and left branches

• Located in the interventricular septum

3. Purkinje Fibers

• Spreads within the muscles of the ventricle

The Heart: Conduction SystemThe Heart: Conduction System

1. First the impulse travels from the SA Node → AV Node• Causes the atria to contract

2. 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.

Some Heart ProblemsSome Heart Problems

1. Damage to the SA node • Can install artificial

pace-makers

2. 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

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

The Heart: Cardiac CycleThe 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

Heart SoundsHeart Sounds

You can hear two distinct sounds during each cardiac cycle: “lub-dup”

1. The first heart sound (“lub”) is caused by the closing of the AV valves

Sound is longer and louder than the second sound

2. The second heart sound (“dup”) is caused by the closing of the semilunar valves

Sound tends to be short and sharp

Heart SoundsHeart 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.

The Heart: Cardiac OutputThe 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

Regulation of Stroke VolumeRegulation 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.

Cardiac Output RegulationCardiac Output Regulation

Figure 11.7

Regulation of Heart RateRegulation 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

1. Although heart rate does not depend on the nervous system, its rate can be changed temporarily by the autonomic nervous system.

2. Also modified by various chemicals, hormones, and ions.

Congestive Heart FailureCongestive 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.

Congestive Heart FailureCongestive 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.

1.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.

2.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)