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Chapter 15: The Cardiovascular SystemHeart

Hold up your clenched fist

Your heart is about the size of your fistVaries by gender, and age of the ownerAge changes are due to increases in the size of cells, not number of cellsAverage mass of a heart 230-350 grams (0.5 0.8 pounds)Introduction to the Heart

Hand-out WSThe Circulatory System2STRUCTURE AND ORGANIZATION OF THE HEARTLocation and Coverings of the HeartHeart located between two lungs in thoracic cavity2/3 of mass is left of bodys midlineApex pointed end formed at tip of left ventricleBase formed by atria, mostly left atriumMajor blood vessels enter and exit at the base

Let them label the picture, page 370 textbookGive them 5 minutes, then reveal next slide3Check yourself.

Next lets talk about the pericardium4Pericardium: membrane that surrounds and protects the heart and holds it in place

Two parts of pericardium: (1) Fibrous pericardium (2) Serous pericardium

The heart, surrounded by thepericardial cavity, sits in the anterior portion of themediastinum. Themediastinum, theregionbetween the two pleural cavities, also contains the thymus, esophagus, and trachea.The PericardiumThe lining of the pericardial cavity is called thepericardium.The pericardium is lined by a delicate serous membrane that can be subdivided into the visceral pericardium and the parietal pericardium. Thevisceral pericardium, orepicardium, covers theouter surface of the heartand adheres closely to it; theparietal pericardiumlines theinner surfaceof the pericardial sac, which surrounds the heart. The pericardial sac, orfibrous pericardium, which consists of a dense network of collagen fibers,stabilizes the position of the heart and associated vessels within the mediastinum.The small space between the parietal and visceral surfaces is the pericardial cavity. It normally contains 1020 ml ofpericardial fluid, secreted by the pericardial membranes. This fluid acts as a lubricant, reducing friction between the opposing surfaces as the heart beats.(1) Fibrous pericardium -Outer; a tough, inelastic, dense irregular connective tissue. - Prevents overstretching of heart; provides protection; and anchors heart in place (2) Serous pericardium - Inner; delicate membrane that forms a double layer around the heart -Its outer layer, the parietal layer, fuses with fibrous pericardium -Its inner layer, the visceral layer, also called epicardium, adheres tightly to surface of heart -Between parietal layer and visceral layer lays a thin layer of fluid that reduces friction between the membranes as the heart moves pericardial fluid - Space that contains pericardial fluid pericardial cavity5Pericarditis build up of pericardial fluid; compresses the heart = cardiac tamponadeInflammation of the Pericardium

Pathogens can infect the pericardium, producing the conditionpericarditis. The inflamed pericardial surfaces rub against one another, producing a distinctive scratching sound. The pericardial irritation and inflammation also commonly result in an increased production of pericardial fluid. Fluid then collects in the pericardial cavity, restricting the movement of the heart. This condition, calledcardiac tamponade (tam-pon-AD),can also be caused by traumatic injuries, such as gunshot wounds, that produce bleeding into the pericardial cavity.

6Heart WallThree layers:EXTERNAL (1) epicardium or visceral layer of serous pericardium Thin, transparent outer layer of the wallComposed of mesothelium and connective tissue

MIDDLE (2) myocardiumBulk of heart wallConsists of cardiac muscleResponsible for pumping action of heart

8Cardiac muscle two separate networks connected by intercalated discsAtrialVentrical

Gap junctions in the discs allow action potential conduction from one muscle fiber to the next

INTERNAL (3) endocardiumThin layer of squamous epithelium lining inside of myocardiumCovers valves of heart and tendons attached to the valvesContinuous with epithelial lining of large blood vessels

HO: External Anatomy WS; let them work on in-class; complete and hand-in10Chambers of the HeartFour chambers:Two upper are the atriaRight atriumLeft atrium

Four chambers:Two upper are the atriaBetween right atrium and left atrium thin partition called interatrial septumOval depression in the interatrial septum called the fossa ovalis CLICKFossa ovalis is remnant of the foramen ovale (CLICK); opening in fetal heart that moved blood from right to left atrium to bypass non-functioning fetal lungs.Foramen ovale closes soon after birth.On anterior surface of each atrium; wrinkled pouch-like structure auricle CLICKIncreases atrium capacity to hold greater volume of blood

Interatrial septum.From the fifth week of embryonic development until birth, the foramen ovale, an oval opening, penetrates theinteratrial septumand connects the two atria. The foramen ovale permits blood flow from the right atrium to the left atrium while the lungs are developing before birth. At birth, the foramen ovale closes, and the opening will be permanently sealed off within three months of delivery.Thefossa ovalis, a small, shallow depression, persists at this site in the adult heart. If the foramen ovale does not close, blood will flow from the left atrium into the right atrium rather than the opposite way, because, after birth, blood pressure in the pulmonary circuit is lower than that in the systemic circuit.

11Two lower are the ventriclesRight ventricleLeft ventricle

Between the right ventricle and the left ventricle is the interventricular septum

12Great Vessels of the HeartRight atrium receives deoxygenated blood through three veinsSuperior vena cavaInferior vena cavaCoronary sinus

The Right AtriumThe right atrium >>CLICKCLICKCLICKCLICKCLICK>CLICKCLICK>CLICKCLICK>CLICKCLICK>CLICK>CLICKCLICK>CLICK ligamentum teresumbilical arteries --> median umbilical ligamentforamen ovale --> fossa ovalisductus arteriosus --> ligamentum arteriosum

16Valves of the Heart (4)Prevent blood from flowing backwardComposition: dense connective tissue covered by endothelium

TWO Atrioventricular (AV) valves lie between the atria and ventricles Between the right atrium and right ventricle is the AV called the (1) tricuspid valve, which has the three cusps

CLICK for tricuspid valve17Chordae tendineaetendon-like chords that connect the pointed ends of the cusps to cardiac muscle projections on inner surface of the ventriclesprevent the cusps from pushing up into the atria when the ventricles contract

KOR-de-ten-DIN-e-e

18AV between the left atrium and left ventricle is called the (2) bicuspid (mitral) valveIt has two cusps

What causes the valves to open and close? Chordae tendineae KOR-de-ten-DIN-e-eIs the valve open or closed when blood moves from an atrium to a ventricle? Open b/c papillary muscles relax and chordae tendineae slackenWhen ventricle contracts, pressure of blood drives cusps upward until edges meet and close opening19TWO Semilunar valves are located near origin of pulmonary trunk and aortaPrevent blood from flowing back into the heartPulmonary valveAortic valve Both consists of three semi-lunar cusps attached to the artery wall

These allow blood to flow in one direction from the ventricles into the arteriesWhere is the pulmonary valve found? Opening where pulmonary trunk leaves the right ventricleWhere is the aortic valve found? Opening between the left ventricle and the aorta

20Blood Flow Through the HeartFlow follows pressure high to lowBLOOD FLOW AND BLOOD SUPPLY OF THE HEART

Atria walls contract; pressure increases within them thus forcing AV (tricuspid, bicuspid) valves openblood flows from atria to ventriclesTHEN ventricle walls contract; pressure increases within them thus forcing blood through SL (pulmonary, aortic) valves into pulmonary trunk and aortaAt same time AV valves shut preventing blood backflow21Blood Supply of the Heart

Walls of the heart have their own blood vesselsIn the myocardium coronary (cardiac) circulationLeft and right coronary arteries-branches of ascending aortaDeoxygenated blood collects in coronary sinus (posterior) and empties into right atriumAnastomoses area where two or more arteries connectProvide alternative route for blood to reach a particular organ or tissue

22Natural pacemaker of the heartCONDUCTION SYSTEM OF THE HEART

What acts as the natural pacemaker of the heart? About 1% of cardiac muscle fiber can generate action potentials over and over in a rhythmical pattern, set the rhythm for the entire heartWhat is the conduction system? Route for propagating action potentials throughout the heart muscleConduction System:(1) Begins at sinoatrial (SA) node in right atrial wall, inferior to superior vena cava; sends action potential through gap junctions in intercalated discs atria contract(2) Action potential also triggered in atrioventricular (AV) node found in interatrial septum, anterior of coronary sinus here the action potential slows allowing atria to empty blood into ventricles(3) Now action potential travels to atrioventricular (AV) bundle or bundle of His in interventricular septum transferring action potential from atria to ventricles(4) Action potential then travels to right and left bundle branches that run along interventricular septum to apex of the heart(5) Lastly goes to Punkinje fibers, then rapidly conducts action potential from apex to ventricles and upward through ventricular myocardiumSA nodes generates action potentials about 100 times per minute

23Recordings of the electrical changes that accompany the heartbeat are called electrocardiograms or EKG or ECG

ELECTROCARDIOGRAM

Recordings of the electrical changes that accompany the heartbeat are called electrocardiograms or EKG or ECGEKGs record three different types of waves: P waves, QRS complex, and T waveP waves is a small upward deflection on EKG; represents atrial depolarizationSpreading of action potential from SA node throughout both atria; causes contractionQRS complex begins as downward deflection (Q), then large upright triangular wave (R), ends as downward wave (S); represents ventricular depolarizationCardiac action potential spreads through ventricle; causes contractionT wave is dome-shaped upward deflection; represents ventricular repolarizationOccurs right before ventricles start to relax***NOTE: Atrial repolarization masked by QRS complex; it is largerLABEL THE WAVES.What are EKGs used for? Diagnosing abnormal cardiac rhythms and conduction patterns in the course of recovery from a heart attack or presence of a living fetus

24ANSWER

25THE CARDIAC CYCLE

Single cardiac cycle = all events associated with one heartbeatWhen atria contract; ventricles relaxWhen ventricles contract; atria relaxSystole refers to phase of contractionDiastole refers to phase of relaxationThree phases of cardiac cycle:Relaxation period: end of cardiac cycle; all chambers in diastole; when ventricles relax; all four chambers in diastole; repolarization of ventricle muscle fibers initiated( T wave)pressure within drops below atrial pressureAV valves open ventricular filling begins to about 75% fullAtrial systole (contraction): action potential from SA node causes atrial depolarization (P wave); end of relaxation period; last 25% of blood flows into ventriclenow hold about 130mL of blood; AV valves still open and SL closedVentricular systole (contraction): QRS complexventricular depolarization, ventricles contract pushing blood against AV valves shutting them; pressure rises in the chambersSL valves open and blood begins to eject from the heart about 70mL from each ventricle; as pressure drops SL valves close; back to relaxation period

26Heart Sounds

Come mainly from turbulence created by blood flow when valves closeFirst sound lubb Loud booming sound from AV valves closing after ventricular systole beginsSecond sound dubbShort, sharp sound from SL valves closing at end of ventricular systole

Next a pauseso lubb, dubb, pause, lubb, dubb, pause

27Cardiac output volume of blood ejected per minute from left ventricle into aortaDetermined by stoke volume (SV) and heart rate (HR)Stroke volume amount of blood ejected by left ventricle during each beat Heart rate number of heart beats per minuteSample calculation of cardiac output:Average resting adult male stroke volume = 70 mLAverage heart rate = 75 beats per minuteSOaverage cardiac output SV X HR 70 mL/beat X 75 beats/min5250 mL/ min or 5.25 L / min

CARDIAC OUTPUT28Regulation of Stroke Volume

Three factors:The degree of stretch in the heart before it contractsMore stretch means more forceful contractionThe forcefulness of contraction of individual ventricular muscle fibersThe pressure required to eject blood from the ventricle

29Autonomic Regulation of Heart RateOriginates in cardiovascular center (CV) in medulla oblongata

Input comes in from a variety of sensory receptors (barorecptors and chemoreceptors) from higher brain centersThen output is directed through increasing or decreasing frequency of nerve impulses sent to sympathetic and parasympathetic branchesSympathetic neurons reach heart through cardiac accelerator nerves that innervate conduction system, atria, and ventricles releasing norepinephrine to increase heart rateParasympathetic neurons reach heart through vagus (X) nerves that extend conduction system and atria releasing acetylcholine (ACh) to decrease heart rate

30Chemical Regulation of Heart RateHormones EpinedrineNorepindrineIncrease heart pumping effectiveness by increasing heart rate and contraction forceIons K+ and Na+ Decrease heart rate and contraction forceCa+Increase heart rate and contraction force

31Other Factors in Heart Rate RegulationAgeGenderPhysical fitnessBody temperature32