The Cardiovascular System: The Heart

Chapter 15

The Heart

• Beats 100,000 times everday=35 million beats/year

• Cardiology: The study of the normal heart and the diseases associated with it

The Heart• Situated b/w the two lungs in

the thoracic cavity, more of lying to the left of your midline

• Size of your closed fist• Apex: tip of the left ventricle• Base: atria (upper chambers

of the heart)• Pericardium: membrane that

surrounds and protects the heart holds it in place– 2 parts:

• 1. Fibrous pericardium– Tough, inelastic

• 2. serious pericardium– Thinner, more delicate

membrane

Serous Pericardium

• Outer parietal layer Is fused to fibrous pericardium• Inner visceral layer (epicardium) adheres to the heart• Pericardial fluid: b/w the parietal and visceral layers

– Reduces friction b/w membranes as heart moves• Pericardial cavity: space that contains the pericardial

fluid

Heart Wall

• 3 layers– Epicardium (external)

• Thin, transparent, outer layer

– Myocardium (middle)• Consists of cardiac muscle tissue, bulk of heart• Pumping action• Cardiac muscle fibers: involuntary, striated, and branched

– One atrial and one ventricular network– Intercalated discs hold cardiac muscles together and

propagate electrical currents– Electrical signal goes across gap junctions– Atria contract separately from ventricles

Heart Wall

• Epicardium• Myocardium• Endocardium (within)

– Lines inside of the myocardium and covers valves of the heart and tendons attached to valves

Chambers of the Heart• 4 chambers• 2 upper chambers: atria• 2 lower chambers:

ventricles• Interatrial Septum: b/w

the right and left atrium– Fossa ovalis: oval

depression on septum which is remnant of foramen ovale (opening in fetal heart that directs blood from right left atrium to bypass nonfunctional lungs. Closes soon after birth)

• Interventricular septum: separates the right from the left ventricle

• Auricle: on anterior side of each atrium• Atrial walls thinner than ventricle

– Left ventricle pumps blood to other parts of body, so works harder

Vessels of the Heart• Right atrium receives

deoxygenated blood through three veins (blood vessels that return blood to the heart)– 1. Superior vena cava

brings blood mainly from parts of the body above the heart

– 2. Inferior vena cava: brings blood mostly from parts below the heart

– 3. Coronary sinus: drains blood from most of the vessels supplying the wall of the heart

• Anastomoses: – Most parts of body receive blood from

branches of more than one artery– Where two or more arteries supply the same

region, they usually connect=anastomoses– Provide alternate routes for blood to reach an

organ or tissue

• Certain cardiac muscle fibers act as pacemakers forming the conduction system of the heart

• Stimulate cardiac chambers to contract

Conduction System

• 1. Sinoatrial Node (SA): – Pacemaker of the

heart– AcH slows SA node– Right atrial wall– AP arises here on SA

node AP goes to both atria via gap junctions and intercalated discs atria contract

• 2. AV (atrioventricular) node:– AP reaches AV node– Interatrial septum– AP here slows down provides time for the atria to empty blood into ventricles

• 3. AV (atrioventricular) bundle (bundle of His)– AP leaves AV node AV

bundle– AP goes from atria

ventricles• 4. AP right and left

bundle branches apex of the heart

• 5. Purkinje fibers rapidly conduct the AP apex of ventricle– After atria contract,

ventricles contract

Electrocardiogram (ECG or EKG)

• A recording of the electrical changes that accompany the heartbeat

• 3 waves– P wave– QRS complex– T wave

P wave

– P wave• Small upward deflection • Atrial depolarization of the AP as spreads from SA node

both atria• Depolarization causes contraction, so atria contracts after P

wave

QRS complex

• Downward deflection (Q)• Continues as large, upright, triangular wave (R)• And ends as downward wave (S)• Ventricular depolarization• Ventricles start to contact

T wave

• Indicates ventricular repolarization

• Not evident in EKG b/c masked by QRS complex

The Cardiac Cycle

• Includes all the events associated with one heartbeat

• Two atria contract while two ventricles relax

• When two ventricles contract, atria relax

• Systole-refers to the phase of contraction

• Diastole-phase of relaxation

Cardiac Cycle

• 1. Relaxation Period– Begins at end of cardiac cycle when ventricles

start to relax and all 4 chambers in diastole– Repolarization of ventricular muscle fibers (T

wave) relaxation– Ventricular pressure drops below atrial

pressure AV valves open ventricles filled

Cardiac Cycle

• 2. Atrial Systole (contraction)– AP from SA node atrial depolarization (P

wave)– Atrial systol follows P wave (end of relaxation)– Atria contract blood ventricles– AV valves still open and semilunar valves

closed

Cardiac Cycle

• Ventricular systole (contraction)– QRS complex = ventricular depolarization

ventricular contraction– Blood pushes against AV valves AV valves shut– Pressure rises– Left ventricular pressure surpasses aortic pressure

and right ventricular pressure rises above the pulmonary trunk pressure semilunar valves open ejection of blood from heart]when ventricles relax ventricular pressure drops semilunar valves close relaxation period begins

Heart Sounds

• Lubb– First sound from AV

valves closing• Dupp

– Second sound from semilunar valves closing

• Heart murmur: abnormal sound consisting of a rushing or gurgling noise that is heard before, b/w, or after the normal heart sounds– Indicates valve disorder

Cardiac Output (CO)

• Volume of blood ejected per minute from the left ventricle into the aorta

• Determined by– 1. stroke volume (SV): amount of blood

ejected by the left ventricle during each beat (contraction)

– 2. heart rate (HR): number of heart beats per minute

Regulation of Stroke Volume

• 3 factors regulate it to ensure equal pumping of blood from left and right ventricles– 1. The degree of stretch in the heart

before it contracts• Frank-Starling law of the heart: the more the

heart is stretched as it fills during diastole, the greater the force of contraction during systole

Regulation of Stroke Volume

• 2. The forcefulness of contraction of individual ventricular muscle fibers– Sympathetic NS

• Epinephrine and norepinephrine

Regulation of Stroke Volume

• 3. The pressure required to eject blood from the ventricles– Semilunar valves open ejection of blood

when pressure in right ventricle is more than pulmonary trunk and when pressure in left ventricle is more than aorta

– When pressure is higher than normal valves open later than normal stroke volume decreases more blood remain in ventricles at end of systole

Congestive Heart Failure (CHF)• Heart failing to pump• Caused by long-term high

blood pressure, valve disorders

• Less and less effective• Leaving more blood in

ventricles at end of cycle• One side of heart starts to

fail before other• Can cause

– Pulmonary edema– Peripheral edema

• Swelling in feet and ankles

Regulation of HR

• Autonomic Regulation– Cardiovascular center (CV) in medulla oblongata – Receives input from variety of sensory receptors and

higher brain centers– Cardiac accelerator nerves: sympathetic neurons

that reach the heart• Norepinephrine increases HR

– Vagus (X) nerves: parasympathetic neurons that reach the heart• Extends to atria• Ach decreases the heart rate by slowing SA node

Regulation of HR

• Autonomic Regulation– Sensory Receptors

• Baroreceptors : neurons sensitive to blood pressure changes

• Chemoreceptors– neurons sensitive to

chemical changes in the blood

Chemical Regulation of HR

• 1. Hormones– Epinephrine and norepinephrine enhance the

heart’s pumping by increasing HR and contraction force

– Exercise, stress, excitement release of more hormones

• 2. Ions– Elevated blood levels of K+ or Na+ decrease

HR and contraction force

Other Factors in HR Regulation

• Age– Resting HR declines

through childhood– And then increases as

adults age• Gender

– Females have higher resting rate than males

• Physical fitness– Decreases resting HR in

both males and females• Body temperature

– Fever increase HR

Exercise

• Aerobic exercise– Any activity that works large body muscles for at least

20 min. elevates cardiac output and accelerates metabolic rate

– 3-5 sessions per week recommended