the cardiovascular system: the heart chapter 15. the heart beats 100,000 times everday=35 million...
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The Cardiovascular System: The Heart
Chapter 15
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The Heart
• Beats 100,000 times everday=35 million beats/year
• Cardiology: The study of the normal heart and the diseases associated with it
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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
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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
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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
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Heart Wall
• Epicardium• Myocardium• Endocardium (within)
– Lines inside of the myocardium and covers valves of the heart and tendons attached to valves
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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)
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• 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
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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
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• 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
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• Certain cardiac muscle fibers act as pacemakers forming the conduction system of the heart
• Stimulate cardiac chambers to contract
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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
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• 2. AV (atrioventricular) node:– AP reaches AV node– Interatrial septum– AP here slows down provides time for the atria to empty blood into ventricles
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• 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
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Electrocardiogram (ECG or EKG)
• A recording of the electrical changes that accompany the heartbeat
• 3 waves– P wave– QRS complex– T wave
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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
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QRS complex
• Downward deflection (Q)• Continues as large, upright, triangular wave (R)• And ends as downward wave (S)• Ventricular depolarization• Ventricles start to contact
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T wave
• Indicates ventricular repolarization
• Not evident in EKG b/c masked by QRS complex
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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
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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
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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
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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
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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
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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
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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
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Regulation of Stroke Volume
• 2. The forcefulness of contraction of individual ventricular muscle fibers– Sympathetic NS
• Epinephrine and norepinephrine
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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
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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
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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
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Regulation of HR
• Autonomic Regulation– Sensory Receptors
• Baroreceptors : neurons sensitive to blood pressure changes
• Chemoreceptors– neurons sensitive to
chemical changes in the blood
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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
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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
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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