BACNursingStudents



Chapter 13: Heart Theory Lecture Outline

Objectives

1. Describe the functions of the circulatory system

2. List the components of the circulatory system

3. Describe the structure of the heart

4. Describe the function of the various structures of the heart

5. Describe the control of heart contractions

6. Discuss the diseases of the heart

7. Define the key words that relate to this chapter

Introduction

The circulatory system is the longest system of the body. It is made up of the heart, blood, and blood vessels (arteries, veins and capillaries). The lymphatic system is also a part of the circulatory system. A central pump, the heart, provides the force to move the blood through a system of blood vessels that extend throughout the body. Blood is the primary transport medium that is responsible for meeting the demands of the cells.

Functions of the Circulatory System

• Heart is the pump that circulates blood

• Arteries, veins, and capillaries transport the blood from the heart to the cells and return blood from the cells back to the heart

• Blood carries oxygen and nutrients to the cells and carries the waste products away

• Lymph system functions to return excess fluid from the tissues to the general circulation

Major Blood Circuits

• Blood leaves the heart through arteries and returns by veins

• Blood circulation routes

a. General or system circulation

o Carries blood throughout the body

b. Cardiopulmonary circulation

o Carries blood from the heart to the lungs and back

• Changes in the composition of circulating blood

a. Major substances are added to and removed from the blood as it circulates through organs along the various sites of the circulatory system

b. Table 13-1 pg. 262

The Heart

The heart is a muscular pump that provides the force necessary to circulate the blood to all the tissues in the body. Its function is extremely efficient and vital because, to survive, the tissues need a continuous supply of oxygen and nutrients, and metabolic waste products must be removed from them.

• About the size of a closed fist

• Weighs about 1 pound, 5 inches long and 3.5 inches wide

• Located in thoracic cavity; behind the sternum where apex of heart lies on the diaphragm and points to the left of the body

• After 4 to 5 minutes without blood flow, the brain cells are irreversibly damaged

• Can hear the heartbeat through the stethoscope

o Place the disc between the fifth and sixth ribs, along an imaginary line extending from the middle of the left clavicle

• Cardiac arrest – syndrome resulting from failure of heart as a pump

• Cardiopulmonary resuscitation (CPR) – life-saving technique of giving 30:2 compressions to breaths to be performed until a heart beat is restored or advanced medical treatment can be administered

Structure of the Heart

• Hollow, muscular, double pump that circulates the blood through the blood vessels to all parts of the body

• Pericardium and pericardial fluid

a. Pericardium surrounds the heart and is a double layer of fibrous tissue

b. Pericardial fluid is the lubricating fluid located between the two pericardial layers

o Fluid prevents rubbing and friction between the two layers

• Myocardium

o Cardiac muscle tissue make up the major portion of the heart

• Endocardium

o Smooth tissue that lines the inner chambers covering the valves and lines the blood vessels providing smooth transit for the flowing blood

• Septum – thick, muscular wall separating the heart into a right half and a left half

• Structures leading to and from the heart:

a. Superior and inferior vena cava

o Large veinous blood vessels which bring deoxygenated blood to the right atrium form all parts of the body

b. Coronary sinus

o A trough in the posterior wall of the right atrium that collects blood from the myocardium vessels

c. Pulmonary artery

o Takes deoxygenated blood away from the right ventricle to the lungs for oxygen

d. Pulmonary veins

o Brings oxygenated blood from the lungs to the left atrium

e. Aorta

o Takes blood away from the left ventricle to the rest of the body

Chambers and Valves

• Separated into right and left halves by septum; then each half separated into an upper and lower chamber

• Upper chambers

o Left and right atria (singular atrium)

• Low chambers

o Left and right ventricles

Valves

• Valves keep blood flow going in one direction

• Atrioventricular valves

Located between the atria and the ventricles

a. Tricuspid valve

1. Positioned between the right atrium and the right ventricle

2. Three points, or cusps, of attachment

3. Blood flow into the atria pushes the valve cusps open and the blood flows into the ventricles; when the ventricles contract, the force of the blood against the cusps causes them to close and prevents the backward flow of blood into the atria

4. The valve cusps are attached to the papillary muscles in the ventricles by small fibrous strands (connective tissue) that prevents the valve from opening back into the atria

b. Bicuspid or mitral valve

1. Positioned between the left atrium and the left ventricle

2. Two points, or cusps, of attachment

3. Functions in the same manner as the tricuspid valve

• Semilunar valves

Located at the bases of the large vessels that carry blood from the ventricles

a. Pulmonary semilunar valve

1. Positioned at the orifice (opening) of the pulmonary artery

2. 3 cuplike cusps

3. Contraction of the ventricles increases the pressure of the blood so that it pushes the valves open and the blood leaves the heart

4. As the ventricles relax and pressure decreases, the blood starts to flow back down the large vessels toward the ventricles and enters the “cups” of the valve cusps which closes the opening of the valves and prevents the flow of blood back into the ventricles

b. Aortic semilunar valve

1. Positioned at the orifice of the aorta

2. Functions in the same manner as the pulmonary semilunar valve

Physiology of the Heart

• The structure of the heart allows it to function as a Double pump

It is important to realize that both atria contract at the same time and that both ventricles contract at the same time

• Right heart

o Deoxygenated blood flows into the heart from the superior and inferior vena cava to the right atrium to the tricuspid valve to the right ventricle through the pulmonary semilunar valves to the pulmonary artery, which takes blood to the lungs for oxygen

• Left heart

o Oxygenated blood flows into the heart form the lungs by the pulmonary veins to the left atrium through the bicuspid valve (mitral) to the left ventricle to the aorta to general circulation

Heart Rate and Cardiac Output

• Normal adult rate is between 72 and 80 beats per minute

• Stroke volume

o Amount of blood ejected from the ventricles

with each heart beat

• Calculating the cardiac output

a. Total volume of blood ejected for the heart per

minute

b. Stroke volume X heart rate = cardiac output

• Exercise increases cardiac output

Heart Sounds

• Valves make a sound when they close

• Called lubb dupp sounds

• Lubb

a. Tricuspid and bicuspid valves (S1)

b. Heard loudest at the apex of the heart

• Dupp

a. Aortic and pulmonary valves (S2)

b. Heard second and is shorter and higher pitched

Conduction System

Contraction of the chambers is coordinated by specialized cardiac muscle cells that make up the conduction system of the heart

• Electrical impulses cause rhythmic beating of heart

• Sinoatrial (SA) node or pacemaker

a. The first part of the conduction system is the sinoatrial (SA) node, which is located in the right atrium, near the entrance of the superior vena cava

b. Because it establishes the basic rhythm of the heartbeat, it is called the pacemaker of the heart (the SA node will rhythmically initiate impulses 70 to 80 times per minute)

c. Impulses from the SA node rapidly travel throughout the atrial myocardium and cause the two atria to contract simultaneously (blood flows from the atria to the ventricles)

d. At the same time, the impulses reach the second part of the conduction system

• Atrioventricular (AV) node

a. The second part of the conduction system, is located in the floor of the right atrium, near the interatrial septum

b. Cells in the AV node conduct impulses more slowly than do other parts of the conduction system, so there is a brief time delay as the impulses travel through the node; this allows time for the atria to finish their contraction phase before the ventricles begin contracting

• Bundle of His

a. From the AV node, the impulses rapidly travel through the AV bundle or bundle of His to the right and left bundle branches

b. The bundle branches extend along the right and left sides of the interventricular septum to the apex

• Purkinje fibers

a. Bundles branch profusely to form Purkinje fibers that transmit the impulses to the myocardium surrounding the ventricles, causing them to contract (blood in the ventricles is pumped into the pulmonary artery and the aorta)

b. After the ventricles complete their contraction phase, they relax and the SA node initiates another impulse to start another cardiac cycle

ECG or EKG

• The electrocardiogram is a device to record the electrical activity of the heart (Figure 13-6 pg. 268)

a. Systole

o Contraction or depolarization

b. Diastole

o Relaxation or repolarization

The ECG exhibits the amount of electrical activity produced by the heart and the time required for the impulse to travel through the heart

• Positive and negative deflection

a. The flat, horizontal line that separates the various waves is the known as the baseline

b. The waves deflect either upward or downward from the baseline

• P, QRS, and T waves

a. P wave represents atrial depolarization

b. QRS complex represents ventricular depolarization

c. T wave represents ventricular repolarization

By observing the size, shape and location of each wave, the physician can analyze and interpret the conduction of electricity through the cardiac cells, the heart’s rate, the heart’s rhythm and the general health of the heart

Prevention of Heart Disease

• Heart disease is the leading cause of death

o Coronary heart disease

• Risk factors

a. Family history

b. High blood pressure

c. High cholesterol

d. Diabetes

e. Current smoking

f. Physical inactivity

g. Obesity

• Steps to lower risk or prevent heart disease

a. Prevention and control of high blood cholesterol levels and triglycerides

b. Prevention and control of high blood pressure

c. Prevention and control of diabetes

d. No tobacco usage

e. Moderate alcohol use

f. Maintain a healthy weight

g. Regular physical exercise

h. Diet and nutrition

• Blood cholesterol levels and triglycerides

a. Total cholesterol – less than 200 mg/dl

b. LDL (bad cholesterol) – less than 100 mg/dl

c. HDL (good cholesterol) – 40 mg/dl or higher

d. Triglycerides – less than 150 mg/dl

Effects of Aging

• Heart muscle fibers replaced by fibrous tissue

• Heart valves increase in thickness

• Cardiac output decreases

• Changes become more significant when elderly person becomes physically or mentally stressed

Diseases of the Heart – Common Symptoms

• Arrhythmia (dysrhythmia)

o Any change or deviation from the normal rate or rhythm of the heart

• Bradycardia

o Slow heart rate usually less than 60 bpm

• Tachycardia

o Rapid heart rate usually more than 100 bpm

• Murmurs

o Defects in the valves of the heart causing a gurgling or hissing sound to occur

• Mitral valve prolapsed

a. Condition in which the valve between the left atria and the left ventricle closes imperfectly

b. Symptoms include fatigue, palpitations (heart feels like it’s racing), headache, chest pain and anxiety

Diseases of the Coronary Artery

• Coronary artery disease (CAD)

o Narrowing of the arteries that supply oxygen and nutrient-filled blood to the heart muscle

• Angina pectoris

o Severe chest pain that arises when the heart does not receive enough oxygen

• Myocardial infarction

a. MI or heart attack

b. Caused by a lack of blood supply to the heart muscle

Infectious Diseases of the Heart

A bacteria or virus is usually the cause of infectious diseases of the heart; may be treated with antibiotic therapy

• Pericarditis

o Inflammation of the outer membrane covering the heart

• Myocarditis

o Inflammation of the heart muscle

• Endocarditis

o Inflammation of the membrane that lines the heart and covers the valves

• Rheumatic heart disease

o A condition in which permanent damage to heart valves is caused as a result of frequent strep throat infections

Heart Failure

• When the ventricles of the heart are unable to contract effectively and blood pools in the heart

• Symptoms depend on which ventricle fails

• Left ventricle failure

o Dyspnea

• Right ventricle failure

o Engorgement of organs, edema (excessive fluid in tissues) and ascites (abnormal accumulation of serous fluid in the abdominal cavity)

Congestive Heart Failure

• Similar to heart failure plus edema of the lower extremities and blood backs up into the lungs

• Treatment consists of cardiotonics and diuretics

o Drugs that reduce the amount of fluid in the body

Rhythm/Conduction Defects

A conduction, or rhythm, defect is said to occur when the conduction system of the heart is affected

• Heart block

Interruption of the AV node message from the SA node and can be seen on an ECG

a. First-degree block

o Characterized by a momentary delay at the AV node before the impulse is transmitted to the ventricles

b. Second-degree block

o Two forms

1. Cycles of delayed impulses until the SA node fails to conduct to the AV node, then returns to near normal

2. Patterns of only every second, third or fourth impulse being conducted to the ventricles

c. Third-degree block or complete heart block

o There is no impulse carried over from the pacemaker

• Premature contractions

Disorder which occurs when an area of the heart not the SA node sparks and stimulates a contraction of the myocardium

a. PACs

o Cause the atria to contract ahead of the anticipated time

b. PVCs

o Originate in the ventricles and cause contractions ahead of the next anticipated beat

• Fibrillation

a. The rhythm breaks down and muscle fibers contract at random without coordination

b. Defibrillator used to discharge a strong electrical current through the patient’s heart to interfere with the uncoordinated action and attempt to shock the SA node to resume its control

Types of Heart Surgery

• Angioplasty (balloon surgery)

o A small deflated balloon is able to be threaded into the coronary artery to help open clogged vessels

• Coronary bypass

o Surgery to provide a detour or bypass to allow the blood supply to go around the blocked area of the coronary artery

• Cardiac stents

o Tiny webbed, stainless steel devices, which hold arteries open after an angioplasty

• Transmyocardial laser revascularization (TMR)

a. Use of lasers to puncture holes in the heart muscle to improve blood flow

b. The outside of the hole heals in a matter of minutes, but the channel created remains allowing blood from the heart chamber to reach the heart muscle and stimulates the growth of new blood vessels

Heart Transplants

• Used as last resort

o The individual’s own heart can no longer function properly

• Problems with heart transplants

a. Histocompatibility

o Matching of tissue type

b. Organ rejection

o May counteract rejection with immunosuppressants that inhibit the production of antibodies in the recipient

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