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The Cardiovascular System: The Heart

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1 The Cardiovascular System: The Heart
Chapter 15

2 The Heart Beats 100,000 times everday=35 million beats/year
Cardiology: The study of the normal heart and the diseases associated with it

3 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

4 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

5 Heart Wall 3 layers Epicardium (external) Myocardium (middle)
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

6 Heart Wall Epicardium Myocardium Endocardium (within)
Lines inside of the myocardium and covers valves of the heart and tendons attached to valves

7 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)

8 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

9 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

10 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

11 Certain cardiac muscle fibers act as pacemakers forming the conduction system of the heart
Stimulate cardiac chambers to contract

12 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

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

14 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

15 Electrocardiogram (ECG or EKG)
A recording of the electrical changes that accompany the heartbeat 3 waves P wave QRS complex T wave

16 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

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

18 T wave Indicates ventricular repolarization
Not evident in EKG b/c masked by QRS complex

19 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

20 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

21 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

22 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

23 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

24 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


26 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

27 Regulation of Stroke Volume
2. The forcefulness of contraction of individual ventricular muscle fibers Sympathetic NS Epinephrine and norepinephrine

28 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

29 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

30 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

31 Regulation of HR Autonomic Regulation Sensory Receptors
Baroreceptors : neurons sensitive to blood pressure changes Chemoreceptors neurons sensitive to chemical changes in the blood

32 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

33 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

34 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

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