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Chapter 20 The Cardiovascular System: The Heart

• Heart pumps over 1 million gallons per year

• Over 60,000 miles of blood vessels

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Heart Location

• Heart is located in the mediastinum– area from the sternum to the vertebral column and

between the lungs

Anterior surfaceof heart

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Heart Orientation

• Apex - directed anteriorly, inferiorly and to the left

• Base - directed posteriorly, superiorly and to the right

• Anterior surface - deep to the sternum and ribs

• Inferior surface - rests on the diaphragm

• Right border - faces right lung

• Left border (pulmonary border) - faces left lung

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Heart Orientation

• Heart has 2 surfaces: anterior and inferior, and 2 borders: right and left

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Surface Projection of the Heart

• Superior right point at the superior border of the 3rd right costal cartilage

• Superior left point at the inferior border of the 2nd left costal cartilage 3cm to the left of midline

• Inferior left point at the 5th intercostal space, 9 cm from the midline

• Inferior right point at superior border of the 6th right costal cartilage, 3 cm from the midline

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Pericardium• Fibrous pericardium

– dense irregular CT– protects and anchors

the heart, prevents overstretching

• Serous pericardium– thin delicate membrane– contains

• parietal layer-outer layer• pericardial cavity with

pericardial fluid• visceral layer

(epicardium)

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Layers of Heart Wall

• Epicardium– visceral layer of

serous pericardium

• Myocardium – cardiac muscle layer

is the bulk of the heart

• Endocardium– chamber lining &

valves

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Muscle Bundles of the Myocardium

• Cardiac muscle fibers swirl diagonally around the heart in interlacing bundles

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Chambers and Sulci of the Heart• Four chambers

– 2 upper atria– 2 lower ventricles

• Sulci - grooves on surface of heart containing coronary blood vessels and fat– coronary sulcus

• encircles heart and marks the boundary between the atria and the ventricles

– anterior interventricular sulcus • marks the boundary between the ventricles

anteriorly– posterior interventricular sulcus

• marks the boundary between the ventricles posteriorly

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Chambers and Sulci

Anterior View

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Posterior View

Chambers and Sulci

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Right Atrium

• Receives blood from 3 sources– superior vena cava, inferior vena cava and coronary sinus

• Interatrial septum partitions the atria• Fossa ovalis is a remnant of the fetal foramen ovale• Tricuspid valve

– Blood flows through into right ventricle– has three cusps composed of dense CT covered by

endocardium

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Right Ventricle

• Forms most of anterior surface of heart• Papillary muscles are cone shaped trabeculae carneae (raised bundles

of cardiac muscle)• Chordae tendineae: cords between valve cusps and papillary muscles• Interventricular septum: partitions ventricles• Pulmonary semilunar valve: blood flows into pulmonary trunk

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Left Atrium

• Forms most of the base of the heart• Receives blood from lungs - 4 pulmonary veins (2 right +

2 left)• Bicuspid valve: blood passes through into left ventricle

– has two cusps– to remember names of this valve, try the pneumonic LAMB

• Left Atrioventricular, Mitral, or Bicuspid valve

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Left Ventricle

• Forms the apex of heart • Chordae tendineae anchor bicuspid valve to papillary

muscles (also has trabeculae carneae like right ventricle)

• Aortic semilunar valve: – blood passes through valve into the ascending aorta– just above valve are the openings to the coronary arteries

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Myocardial Thickness and Function

• Thickness of myocardium varies according to the function of the chamber

• Atria are thin walled, deliver blood to adjacent ventricles

• Ventricle walls are much thicker and stronger– right ventricle supplies blood to the lungs (little flow resistance)– left ventricle wall is the thickest to supply systemic circulation

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Thickness of Cardiac Walls

Myocardium of left ventricle is much thicker than the right.

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Fibrous Skeleton of Heart

• Dense CT rings surround the valves of the heart, fuse and merge with the interventricular septum

• Support structure for heart valves• Insertion point for cardiac muscle bundles• Electrical insulator between atria and ventricles

– prevents direct propagation of AP’s to ventricles

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• A-V valves open and allow blood to flow from atria into ventricles when ventricular pressure is lower than atrial pressure– occurs when ventricles are relaxed, chordae tendineae

are slack and papillary muscles are relaxed

Atrioventricular Valves Open

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• A-V valves close preventing backflow of blood into atria – occurs when ventricles contract, pushing valve cusps

closed, chordae tendinae are pulled taut and papillary muscles contract to pull cords and prevent cusps from everting

Atrioventricular Valves Close

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Semilunar Valves

• SL valves open with ventricular contraction– allow blood to flow into pulmonary trunk and aorta

• SL valves close with ventricular relaxation– prevents blood from returning to ventricles, blood fills

valve cusps, tightly closing the SL valves

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Atria contract, blood fills ventricles through A-V valves

Ventricles contract, blood pumped into aorta and pulmonary trunk through SL valves

Valve Function Review

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• Two closed circuits, the systemic and pulmonic • Systemic circulation

– left side of heart pumps blood through body– left ventricle pumps oxygenated blood into aorta– aorta branches into many arteries that travel to organs– arteries branch into many arterioles in tissue– arterioles branch into thin-walled capillaries for

exchange of gases and nutrients– deoxygenated blood begins its return in venules– venules merge into veins and return to right atrium

Blood Circulation

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• Pulmonary circulation– right side of heart pumps deoxygenated blood to lungs– right ventricle pumps blood to pulmonary trunk

– pulmonary trunk branches into pulmonary arteries– pulmonary arteries carry blood to lungs for exchange

of gases– oxygenated blood returns to heart in pulmonary veins

Blood Circulation (cont.)

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Blood Circulation

• Blood flow– blue = deoxygenated– red = oxygenated

– www.sitcomsonline.com/themesonglyrics.html

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Coronary Circulation

• Coronary circulation is blood supply to the heart

• Heart as a very active muscle needs lots of O2

• When the heart relaxes high pressure of blood in aorta pushes blood into coronary vessels

• Many anastomoses– connections between arteries supplying blood to the

same region, provide alternate routes if one artery becomes occluded

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Coronary Arteries• Branches off aorta above

aortic semilunar valve• Left coronary artery

– circumflex branch • in coronary sulcus, supplies

left atrium and left ventricle– LAD.

• supplies both ventricles• Right coronary artery

– marginal branch• in coronary sulcus, supplies

right ventricle– posterior interventricular art.

• supplies both ventricles

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Coronary Veins

• Collects wastes from cardiac muscle• Drains into a large sinus on posterior surface of heart

called the coronary sinus• Coronary sinus empties into right atrium

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Conduction System of Heart

Coordinates contraction of heart muscle.

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• Autorhythmic Cells– Cells fire spontaneously, act as pacemaker and form

conduction system for the heart• SA node

– cluster of cells in wall of Rt. Atria– begins heart activity that spreads to both atria– excitation spreads to AV node

• AV node– in atrial septum, transmits signal to bundle of His

• AV bundle of His – the connection between atria and ventricles– divides into bundle branches & purkinje fibers, large

diameter fibers that conduct signals quickly

Conduction System of Heart

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Rhythm of Conduction System

• SA node fires spontaneously 80-100 times per minute

• AV node fires at 40-60 times per minute

• If both nodes are suppressed fibers in ventricles by themselves fire only 20-40 times per minute

• Artificial pacemaker needed if pace is too slow

• Extra beats forming at other sites are called ectopic pacemakers– caffeine & nicotine increase activity

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Timing of Atrial & Ventricular Excitation

• SA node setting pace since is the fastest

• In 50 msec excitation spreads through both atria and down to AV node

• 100 msec delay at AV node due to smaller diameter fibers- allows atria to fully contract filling ventricles before ventricles contract

• In 50 msec excitation spreads through both ventricles simultaneously

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Physiology of Contraction

• Depolarization, plateau, repolarization

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Depolarization & Repolarization• Depolarization

– Cardiac cell resting membrane potential is -90mv– excitation spreads through gap junctions– fast Na+ channels open for rapid depolarization

• Plateau phase – 250 msec (only 1msec in neuron) – slow Ca+2 channels open, let Ca +2 enter from outside cell and

from storage in sarcoplasmic reticulum, while K+ channels close– Ca +2 binds to troponin to allow for actin-myosin cross-bridge

formation & tension development• Repolarization

– Ca+2 channels close and K+ channels open & -90mv is restored as potassium leaves the cell

• Refractory period – very long so heart can fill

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Changes in cell membrane permeability.

Action Potential in Cardiac Muscle

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Electrocardiogram---ECG or EKG

• EKG– Action potentials of all active

cells can be detected and recorded

• P wave– atrial depolarization

• P to Q interval– conduction time from atrial to

ventricular excitation

• QRS complex – ventricular depolarization

• T wave– ventricular repolarization

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One Cardiac Cycle• At 75 beats/min, one cycle requires 0.8 sec.

– systole (contraction) and diastole (relaxation) of both atria, plus the systole and diastole of both ventricles

• End diastolic volume (EDV)– volume in ventricle at end of diastole, about

130ml• End systolic volume (ESV)

– volume in ventricle at end of systole, about 60ml• Stroke volume (SV)

– the volume ejected per beat from each ventricle, about 70ml

– SV = EDV - ESV

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CO Cardio Output

• CO = HR x SV

• BP = CO X SVR

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Phases of Cardiac Cycle• Isovolumetric relaxation

– brief period when volume in ventricles does not change--as ventricles relax, pressure drops and AV valves open

• Ventricular filling– rapid ventricular filling:as blood flows from full

atria– diastasis: as blood flows from atria in smaller

volume– atrial systole pushes final 20-25 ml blood into

ventricle• Ventricular systole

– ventricular systole– isovolumetric contraction

• brief period, AV valves close before SL valves open – ventricular ejection: as SL valves open and

blood is ejected

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Cardiac Cycle

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Ventricular Pressures

• Blood pressure in aorta is 120mm Hg

• Blood pressure in pulmonary trunk is 30mm Hg

• Differences in ventricle wall thickness allows heart to push the same amount of blood with more force from the left ventricle

• The volume of blood ejected from each ventricle is 70ml (stroke volume)

• Why do both stroke volumes need to be same?

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Auscultation

• Stethoscope• Sounds of heartbeat are from

turbulence in blood flow caused by valve closure– first heart sound (lubb) is created with the

closing of the atrioventricular valves– second heart sound (dupp) is created with

the closing of semilunar valves

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Heart Sounds

Where to listen on chest wall for heart sounds.

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Cardiac Output• Amount of blood pushed into aorta or

pulmonary trunk by ventricle• Determined by stroke volume and heart rate• CO = SV x HR

– at 70ml stroke volume & 75 beat/min----5 and 1/4 liters/min

– entire blood supply passes through circulatory system every minute

• Cardiac reserve is maximum output/output at rest– average is 4-5 while athlete is 7-8

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Influences on Stroke Volume• Preload (affect of stretching)

– Frank-Starling Law of Heart– more muscle is stretched, greater force of

contraction– more blood more force of contraction results

• Contractility– autonomic nerves, hormones, Ca+2 or K+

levels

• Afterload– amount of pressure created by the blood in

the way– high blood pressure creates high afterload

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Congestive Heart Failure

• Causes of CHF– coronary artery disease, hypertension, MI,

valve disorders, congenital defects

• Left side heart failure– less effective pump so more blood remains in

ventricle– heart is overstretched & even more blood

remains– blood backs up into lungs as pulmonary edema– suffocation & lack of oxygen to the tissues

• Right side failure – fluid builds up in tissues as peripheral edema

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Regulation of Heart Rate• Nervous control from the cardiovascular

center in the medulla– Sympathetic impulses increase heart rate and

force of contraction– parasympathetic impulses decrease heart rate. – Baroreceptors (pressure receptors) detect

change in BP and send info to the cardiovascular center• located in the arch of the aorta and carotid arteries

• Heart rate is also affected by hormones– epinephrine, norepinephrine, thyroid hormones– ions (Na+, K+, Ca2+)– age, gender, physical fitness, and temperature

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Regulation of Heart Rate

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Risk Factors for Heart Disease

• Risk factors in heart disease: – high blood cholesterol level– high blood pressure– cigarette smoking– obesity & lack of regular exercise.

• Other factors include:– diabetes mellitus– genetic predisposition– male gender– high blood levels of fibrinogen– left ventricular hypertrophy

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Plasma Lipids and Heart Disease• Risk factor for developing heart disease is

high blood cholesterol level.– promotes growth of fatty plaques – Most lipids are transported as lipoproteins

• low-density lipoproteins (LDLs)• high-density lipoproteins (HDLs)• very low-density lipoproteins (VLDLs)

– HDLs remove excess cholesterol from circulation

– LDLs are associated with the formation of fatty plaques

– VLDLs contribute to increased fatty plaque formation

• There are two sources of cholesterol in the body:– in foods we ingest & formed by liver

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Desirable Levels of Blood Cholesterol for Adults

• TC (total cholesterol) under 200 mg/dl• LDL under 130 mg/dl• HDL over 40 mg/dl• Normally, triglycerides are in the range of

10-190 mg/dl.• Among the therapies used to reduce

blood cholesterol level are exercise, diet, and drugs.

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Exercise and the Heart

• Sustained exercise increases oxygen demand in muscles.

• Benefits of aerobic exercise (any activity that works large body muscles for at least 20 minutes, preferably 3-5 times per week) are;– increased cardiac output– increased HDL and decreased triglycerides– improved lung function– decreased blood pressure– weight control.

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Clinical Problems

• MI = myocardial infarction– death of area of heart muscle from lack of O2

– replaced with scar tissue

– results depend on size & location of damage

• Blood clot– use clot dissolving drugs TNKor t-PA & heparin

– balloon angioplasty

• Angina pectoris----heart pain from ischemia of cardiac muscle

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By-pass Graft

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Homework: Chapter 20

• A2, A4, A5, A7, B1, B2, B6, B7, C3

• PLEASE LOOK AT Wiley Plus THAT ACCOMPANY YOUR TEXT

• WORK THROUGH THE ENTIRE INTERACTIONS