The Heart LECTURE A&P II

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julianne.elizabeth
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172328
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The Heart LECTURE A&P II
Updated:
2012-09-21 01:57:26
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II heart LCCC cardiac muscles blood pressure EKG systemic pulmonary veins arteries electrical events sounds cycle developmental aspects
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The heart for LCCCs A&P II Exam 1
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  1. Give the location, size, and covering of the heart
    Located in the mediastinum

    about the size of a fist

    • covered in a 2 layer pericardium
    • -fibrous layer
    • -visceral layer (epicardium)
  2. Describe the Pericardium
    2 Layers

    Superficial fibrous pericardium: protects, anchors, and prevents over filling

    • Deep two layered serous pericardium: 
    • Parietal layer lines the interal surface of the fibrous pericardium
    • Visceral layer (epicardium) on the external area of the heart
    • *they are separated by a serous fluid filled pericardial cavity that decreases friction
  3. Describe the layers of the heart wall
    • Epicardium
    • -visceral layer of the serous pericardium

    • Myocardium
    • -forms the bulk of the heart  muscle
    • -spiral bundles of cardiac muscle
    • -anchors cardiac muscle fibers
    • -supports great vessels and valves
    • -limits spread of APs to specific paths

    • Endocardium
    • -continuous with endotheial lining of the blood vessels
  4. Describe the pressure that each side of the heart puts out as well as blood volume
    ***equal volumes of bloof are pumped thru both the systemic and the pulmonary circuits***

    Left side has much more pressure to pump to the entire body (systemic)

    Right side has much less pressure as it is only pumping to the lungs (pulmonary)
  5. What is Angina Pectoris?
    Thoracic pain cased by a fleeting deficiency in blood delivey to the myocardium (coronary circulation)

    Cells are weakened
  6. What is a Myocardial Infarction?
    HEART ATTACK!

    Prolonged coronary blockage

    Areas of cell death are repaued with noncontractile scar tissue (damage to LV is most serious)
  7. Describe the Microscopic Anatomy of Cardiac Muscle
    Cardiac muscle cells are short, fat, branched, and interconnected

    They have a central Nuclei

    Connective tissue matrix (endomysium) connects to the fobrous skeleton for both the origin and the insertion

    T Tubukes are wide but less numerous than in skeletal muscle and SR is much simpler

    Numerous large mitochondria create resistance to fatigue (25-30% of cell volume)
  8. Describe intercalated discs
    Intercalated discs: Junctions between cells that anchor cardiac cells

    desmosomes prevent cells from separating during contraction

    Gap junctions allow ions to pass; electrially couple adjacent cells

    **Heart muscle behaves as a functional syncytium**
  9. Describe Cardiac Muscle contraction
    Depolarization of the heart is rhythmic and spontaneous

    about 1% of cardiac cells have automaticity (are self excitable)

    Gap junctions ensure the heart contracts as a unit

    long absolute refractory period (250ms) prevents tetanic contractions
  10. Go thru the step by step process of Cardiac Muscle Contraction
    Depolarization opens the voltage-gates fast Na+ channels in the sarcolemma

    Reversal of membrane potential from -90 mV to +30 mV

    Depolarization wave in T tubules causes the SR to release Ca2+

    Depolarization wave also opens slow Ca2+ channels to the sarcolemma (allows Ca2+ to come in from extracellular space)

    Ca2+ surge prolongs depolarization phase (plateu)

    Ca2+ influz triggers the opening of Ca2+ sensitive channels in SR, which liberates bursts of Ca2+ (calcium triggered calcium release)

    E-C coupling occurs as Ca2+ binds to troponin and sliding filaments begins

    Duration of the AP and the contractile phase is much greater in cardiac muscle than in skeletal muscle

    Repolarization results from inactivation of Ca2+ channels and opening of voltage gated K+ channels
  11. What is the intrinsic cardiac conduction system?
    A network of noncontractile (autorythmic) cells that initiate and distribute impulses to coordinate the depolarization and contraction of the heart
  12. Describe Autorythmic cells
    They have automaticity or are self-excitable

    Have unstable resting potentials (pacemaker potentials or prepotentials) due to open sloe Na+ channels

    At threshold, Ca2+ channels open

    Explosive Ca2+ influx produces the rising phase of an AP

    Repolarization results from inactivation od Ca2+ channels and opening of voltage-gated K+ channels
  13. Describe the Electrical Pathway (Sequence of Excitation) in the Heart
    • 1. Sinoatrial Node (SA Node): The pacemaker
    • -generates impulses about 75x/min (sinus rhythm)
    • -depolarizes faster than any other part of the myocardium

    • 2. Atrioventricular Node (AV Node):
    • -smaller diameter fibers; fewer gap junctions
    • -slows down or delays impulses by .1 seconds
    • -depolarizes 50x/min in absence of SA node input

    • 3. Atrioventricular Bundles (AV Bundle) (Bundle of His)
    • -only electrical connection between atria and ventricles

    • 4. Right and left bundle branches
    • -two pathways in the interventricular septum carry impulses towards the apex

    • 5. Perkinje Fibers (from wall to wall)
    • -complete the pathway to the apex and ventricular walls
    • -AV bundle and Purkinje Fibers depolarize only 30x/min in absence of AV node input
  14. Defects in the intrinsic conduction system may result in...
    • 1. Arrythmias: irregular heart rhythms
    • 2. Uncoordinated atrial and ventricular contractions
    • 3. Fibrillation: rapid, irregular contractions; useless for pumping blood (like a squirming worm)
  15. Defective SA node may result in...
    • Ectopic Focus: abnnormal pacemaker takes over
    • -if the AV node takes over, there will be a junctional rhythm (40-60bpm)
  16. Defective AV node may result in...
    Partial or total heart block

    few oe no impulses from SA node reach the ventricles
  17. Describe the Extrinsic Innervation of the heart
    Heart is modified by the Automic Nervous System

    Cardiac centers located in the medulla oblongata

    -Cardioacceleratory center innervates the SA and NA nodes, heart muscle, and coronary arteries through sympathetic neurons

    -Cardioinhibitory center inhibits SA and AV nodes through the parasympathetic fibers in the vagus nerves
  18. What is an Electrocardiogram and describe the 3 waves
    EKG: a composite of all the action potentials generated by nodal and contractile cells at a given time (not tracing a single AP!)

    • 3 Waves:
    • 1. P wave: Atrial Depolarization
    • 2. QRS complex: Ventricular Depolarization
    • 3. T wave: Ventricular Repolarization
  19. Describe the Heart Sounds
    Two sounds LUB-DUP associated with closing of the heart valves

    First sound occurs as AV valves close and signifies the beginning of systole

    Second Sound occurs when SL valves close at the beginning of ventricular diastole

    Heart murmurs: abnormal heart sounds most often indicative of valve problems. Either an incompetant valve which leaks or a stenotic valve which doesn't open. The sound is caused by a turbulent flow
  20. What is the cardiac cycle?
    All events associated with blood flow through the heart during one complete heartbeat

    • Systole: contraction
    • Diastole: Relaxation
  21. Name the Phases of the Cardiac Cycle
    • 1. Ventricular Filling
    • 2. Ventricular Systole
    • 3. Isovolumetric Relacation
  22. Describe the first phase of the cardiac cycle
    • Ventricular Filling: takes place in mid-to-late diastole
    • -AV Valves are open
    • -80% of blood passively flows into ventricles
    • -Atrial Systole occurs delivering the remaining 20%

    End Diastolic Volume (EDV): volume of blood in each ventricle at the end of ventricular diastole
  23. Describe the second phase of the cardiac cycle
    • Ventricular Systole
    • -Atrial diastole and ventricles begin to contract
    • -Rising Ventricular pressure closes the AV valves
    • -Isovolumetric contraction phase (all valves closed)
    • -In ejection phase, ventricular pressure exceeds pressure in largr arteries and the SL valves open

    End systolic volume (ESV): volume of blood remaining in each ventricle at the end of systole
  24. Describe the third phase of the cardiac cycle
    • Isovolumetric Relaxation: occurs during early ventricular diastole
    • -ventricles relax
    • -backflow of blood in aorta and PAT close the SL valves and causes dicrotic notch (brief rise in aortic pressure)
  25. What is Cardiac Output?
    CO: volume of blood pumped by each ventricle in ONE MINUTE. measure as ml/min



    Heartrate (HR)- number of beats per minute

    Stroke Volume (SV)- volume of blood pumped out by one ventricle each beat
  26. What is cardiac reserve?
    The difference between resting and maximum CO



    • At rest: (average)
    • CO ml/min = HR (75bpm) x SV (70ml/beat)= 5.25L/min
    • *thats about all your blood in one minute!

    Maximum CO is 4-5 resting CO in nonathletic people

    COMax may reach 35/min in trained atheletes
  27. How is Stroke Volume Regulated


    • The three main factors affecting SV:
    • 1. Preload
    • 2. Contractility
    • 3. Afterload
  28. Describe Preload and the regulation of stroke volume
    Preload: degree of stretch of cardiac muscle cells before the contract (Frank-Starling law of the heart)

    • -Cardiac muscles exhibits a length tension relationship
    • -At rest, cardiac muscle cells are shortal than optimal length (more contractile force)
    • -Slow heartbeat and exercise increase venous return
    • -increased venous return distends or stretches the ventricles nad increases contraction force 
    • *increases EDV*
  29. Describe Contractility and the regulation of stroke volume
    Contractility: contractile strength at a given muscle length, independent of muscle stretch and EDV

    • Positive inotropic agents increase contractility (lowers ESV heightens SV)
    • -increased Ca2+ influx due to sympathetic stimulation
    • -hormones (thyroxine, glucagon, and epinephrine)

    • Negative inotropic agents decrease contractility
    • -Acidosis
    • -increased extracellular K+
    • -calcium channel blockers
  30. Describe Afterload and the regulation of stroke volume
    Afterload: pressure that must be overcome for ventricles to eject blood

    Hypertension increases afterload, resulting in increased ESV and lower SV
  31. How is Heart Rate (HR) regulated?
    Positive chronotropic factors increase heart rate

    Negative chronotropic factors decrease heart rate
  32. What role does the Sympathetic branch of the automic nervous system play in regulation?
    • Sympathetic nervous system is activated by emotional or physical stressors
    • -norepinephrine causes the pacemaker to fire more rapidly (and at the same time increases contractility)
  33. What role does the Parasympathetic branch of the automic nervous system play in regulation?
    • Parasympathetic nervous system opposes sympathetic effects
    • -Acetylcholine hyperpolarizes pacemaker cells by opening K+ channels

    The heart at rest exhibits vagal tone (dominant influence due to vagal nerve is inhibitory)
  34. What is the Bainbridge reflex?
    • The Atrial (Bainbridge reflex): a sympathetic reflec initiated by increased venous return
    • -stretch of atrial walls stimulates SA node
    • -also stimulates atrial stretch receptors activating aympathetic reflexes

  35. What is the chemical regulation of HR?
    • 1. Hormones
    • -Epinephrine from adrenal medulla enhances heart rate and contractility
    • -thyroxine increases heart rate and enhances the effects of norephinephrine and epinephrine

    • 2. Intracellular and Extracellular Ion concetrations (such as Ca2+ and K+)
    • -these must be maintained for normal heart function
  36. What are some other factors that could influence HR?
    • -Age (declines throughout life)
    • Gender (faster in females)
    • -Exercise
    • -Body Temperature
  37. What is Tachycardia?
    • Abnormally fast heart rate (above 100bpm)
    • -could be from fever, stress, drugs, or heart disease
    • -if persistent, could lead to fibrillation
  38. What is Bradycardia?
    • Heart rate slower than 60bpm
    • -could be from low body temp, drugs, or parasympathetic activation
    • -could be a sign of brain edema after head injury
    • -may result in grossly inadequate blood circulation
    • -may be a desireable result of endurance training
  39. What is congestive heart failure (CHF)?
    Progressive condition where the CO is so low that blood circulation is inadequate to meet tissue needs (resulting in a weakening of the myocardium)

    • Caused by:
    • -coronary atherosclerosis
    • -persistent high bp
    • -multiple myocardial infarcts (myocardium replaced with scar tissue)
    • -dilated cardiomyopathy (DCM): ventricles stretch and become flabby
  40. Name the Embryonic Heart chambers
    • 1. Sinous Venous
    • 2. Atrium
    • 3. Ventricle
    • 4. Bulbus cordis
  41. Name the two fetal heart structures that bypass pulmonary circulation
    Foramen Ovale connects the two atria

    Ductus Arteriosus connects the pulmonary trunk and the aorta
  42. Name two congenital heart defects
    1. septal defects-mixing of systemic and pulmoary blood

    2. Involving narrowed valves or vessels that increase heart workload
  43. Name the age related changes of the heart
    Schlerosis and thickening of valve flaps (more common in the mitral valve, murmurs common in elderly)

    Decline in Cardiac Reserve

    Fibrosis of cardiac muscle (Scarring of heart and nodes)

    Atherosclerosis (fat/hardening of arteries)

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