Cardiovascular System: The Heart

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Cardiovascular System The Heart

• Dr. Michael P. Gillespie

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Cardiovascular System

• Blood
• Heart
• Blood vessels

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Heart

• Propels the blood through the blood vessels to
  reach all of cells of the body.
• It circulates the blood through an estimated
  100,000 km (60,000 miles) of blood vessels.

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Heart

• It beats 100,000 times every day (35 million
  beats / year).
• It pumps about 5 liters (5.3 qt) each minute and
  14,000 liters (3,600 gal) each day.
• Cardiology the study of the normal heart and
  diseases associated with it.

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Size And Shape

• About the size of a closed fist.
• Cone-shaped.
• 12cm (5 in.) Long, 9cm (3.5 in.) Wide, and 6cm
  (2.5 in.) Thick.
• 250g (8 oz) in adult females and 300g (10 oz) in
  adult males.

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Location

• Lies in the mediastinum (a mass of tissue between
  the sternum and the vertebral column).
• 2/3 of the mass is left of midline.
• A cone lying on its side.

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Anatomical Landmarks

• The apex (pointed end) is directed anteriorly,
  inferiorly, and to the left.
• The base (broad portion) is directed posteriorly,
  superiorly, and to the right.
• Anterior surface deep to sternum ribs.

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Anatomical Landmarks

• Inferior surface rests upon diaphragm.
• Right border faces the right lung.
• Left border (pulmonary border) faces the left
  lung.

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Cardiopulmonary Resuscitation (CPR)

• External pressure (compression) can be used to
  force blood out of the heart and into the
  circulation.
• CPR is utilized when the heart suddenly stops
  beating.
• Cardiac compressions with artificial ventilation
  of the lungs keeps oxygenated blood circulating
  until the heart can be restarted.
• Self CPR (coughing).

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Pericardium

• Pericardium membrane that surrounds and
  protects the heart.
• Fibrous pericardium tough, inelastic, dense
  irregular CT. Prevents overstretching of the
  heart.
• Serous pericardium thinner, more delicate
  layer.
• Parietal layer.
• Visceral layer (epicardium) adheres to the
  heart.
• Pericardial fluid lies in between these two
  layers in the pericardial cavity.

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Layers Of The Heart Wall

• Epicardium (visceral layer of the serous
  pericardium).
• Myocardium cardiac muscle tissue.
• Endocardium smooth lining of the chambers of
  the heart and valves (continuous with blood
  vessels).

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Chambers Of The Heart

• Atria superior chambers.
• Auricle pouchlike structure.
• Ventricles inferior chambers.
• Sulci grooves on the surface of the heart that
  contain blood vessels.

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Chambers Of The Heart

• Right atrium receives blood from three veins
  superior vena cava, inferior vena cava, and
  coronary sinus.
• Tricuspid valve.
• Pectinate muscles.
• Interatrial septum.
• Fossa ovalis depression (remnant of foramen
  ovale).

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Chambers Of The Heart

• Right ventricle receives blood from right
  atrium.
• Trabeculae carneae bundles of cardiac muscle
  tissue.
• Chordae tendineae connects to the cusps of the
  tricuspid valve which are connected to papillary
  muscles.
• Interventricular septum.
• Pulmonary valve into pulmonary arteries.

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Chambers Of The Heart

• Left atrium receives blood from the lungs
  through the pulmonary veins.
• Bicuspid (mitral) valve.
• Left ventricle receives blood from left atrium.
• Trabeculae carneae bundles of cardiac muscle
  tissue.
• Chordae tendineae connects to the cusps of the
  bicuspid valve which are connected to papillary
  muscles.
• Aortic valve into the ascending aorta (largest
  artery).

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Myocardial Thickness

• The function of the individual chambers
  determines their thickness.
• The atria pump blood a short distance and
  consequently have thinner walls than the
  ventricles.
• The left ventricle pumps blood a greater distance
  than the right at higher pressures and has a
  thicker wall.

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Fibrous Skeleton Of The Heart

• Dense CT rings that surround the valves and
  prevent overstretching.
• Provides insertion points for bundles of cardiac
  muscle fibers.

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Atrioventricular (AV) Valves

• Tricuspid and bicuspid valves.
• When the valve is open, the pointed cusps point
  into the ventricle.

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Atrioventricular (AV) Valves

• When atrial pressure is higher than ventricular
  pressure the valves open (the papillary muscles
  are relaxed and the chordae tendinae is slack.
• When the ventricles contract the pressure forces
  the AV valves closed. The papillary muscles
  close concurrently.
• Damaged valves allow regurgitation (flow back).

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Semilunar (SL) Valves

• The aortic and pulmonary valves.
• The SL valves open when the pressure in the
  ventricles exceeds the pressure in the arteries.

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Heart Valve Disorders

• Stenosis (narrowing) failure of the heart valve
  to open fully.
• Insufficiency (incompetence) failure of a valve
  to close fully.
• Mitral stenosis due to scar formation of a
  congenital defect.

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Heart Valve Disorders

• Mitral insufficiency backflow of blood from the
  left ventricle to the left atrium.
• Mitral valve prolapse (MVP) one or both cusps
  protrude into the left atrium during ventricular
  contraction.
• Aortic stenosis the aortic valve is narrowed.

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Heart Valve Disorders

• Aortic insufficiency backflow of blood from the
  aorta into the left ventricle.
• Rheumatic fever an acute systemic inflammatory
  disease. Antibodies produced to destroy the
  bacteria attack and inflame the CT of joints,
  heart valves and other organs.

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Systemic And Pulmonary Circulations

• Two closed systems.
• The output of one becomes the input of another
  with each beat of the heart.

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Coronary Circulation

• The myocardium has its own blood vessels, the
  coronary circulation.
• The coronary arteries branch from the ascending
  aorta and encircle the heart.
• When the heart is contracting the coronary
  arteries are squeezed shut.
• When the heart is relaxed, the high pressure from
  the aorta pushes blood into the coronary arteries
  and from the arteries to the coronary veins.

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Coronary Arteries

• Two coronary arteries, right and left coronary
  arteries, branch from the ascending aorta and
  supply oxygenated blood to the myocardium.

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Coronary Arteries

• Left coronary artery branches into
• Anterior interventricular or left anterior
  descending LAD (supplies ventricle walls).
• Circumflex branches (supplies left ventricle and
  left atrium).

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Coronary Arteries

• Right coronary artery branches into
• Atrial branches (supplies right atrium).
• Posterior interventricular branch (supplies the
  two ventricles).
• Right marginal branch (supplies the right
  ventricle).

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Coronary Veins

• The great cardiac vein (anterior) and the middle
  cardiac vein (posterior) drain into the coronary
  sinus.
• Coronary Sinus a large bascular sinus on the
  posterior surface of the heart.

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Reperfusion Damage

• Reperfusion is reestablishing the blood flow to
  the heart muscle after a blockage of a coronary
  artery.
• Reperfusion damages the tissue further due to the
  formation of oxygen free radicals from the
  reintroduced oxygen.

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Histology Of Cardiac Muscle Tissue

• Cardiac muscle fibers are shorter in length and
  less circular than skeletal muscle fibers.
• Cardiac muscle fibers exhibit branching.

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Histology Of Cardiac Muscle Tissue

• Usually one centrally located nucleus is present,
  although it may occasionally have two nuclei.
• Intercalated disc connect neighboring fibers.
• The discs contain desmosomes, which hold the
  fibers together.
• Mitochondria are larger and more numerous in
  cardiac muscle fiber.
• Gap junctions allow for propagation of action
  potentials.

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Regeneration Of Heart Cells

• Infarcted (dead) cardiac muscle tissue is
  replaced with non-contractile fibrous scar
  tissue.
• A lack of stem cells limits the ability of the
  heart to repair damage.
• Some stem cells from the blood migrate into the
  heart tissues and differentiate into functional
  muscle cells and endothelial cells.

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Autorhythmic Fibers The Conduction System

• Autorhythmic fibers are self-excitable and
  maintain the hearts continuous beating.
• Act as a pacemaker, setting the rhythm of
  electrical excitation that causes contraction of
  a heart.
• Form a conduction system, that provides a path
  for the cycle of cardiac excitation through the
  heart.

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Sequence Of Cardiac Conduction

• Sinoatrial (SA) node undergo spontaneous
  depolarization (pacemaker potential) propagates
  through the atria through gap junctions.
• Atrioventricular (AV) node (bundle of his) site
  where action potentials are conducted from the
  atria to the ventricles.

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Sequence Of Cardiac Conduction

• Right and left bundle branches propagate action
  potentials through the ventricles and the
  interventricular septum to the apex of the heart.
• Purkinje fibers conduct the action potentials
  from the apex, through the remainder of the
  ventricles stimulating contraction.

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Pacemaker

• The SA node regulates the pace of the heart.
• At rest, it contracts approximately 100 time per
  minute.
• Nerve impulses from the ANS and blood born
  hormones (epinephrine) modify the timing and
  strength of each heartbeat.

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Pacemaker

• Acetylcholine from the ANS slows the heart rate
  to about 75 bpm.
• If the SA node becomes damaged, the AV node can
  pick up the job However, at a slower rate (40
  60 bpm).
• If both nodes are damaged, an artificial
  pacemaker sends out electrical currents to
  stimulate the heart to contract.

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Ectopic Pacemaker

• If a site other than the SA node becomes
  self-excitable, it becomes an ectopic pacemaker.
• It make operate occasionally, producing extra
  beats, or for a period of time.
• Triggers
• Caffeine, nicotine, electrolyte imbalances,
  hypoxia, and toxic reactions to drugs.

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Refractory Period

• In cardiac muscle tissue, the refractory period
  lasts longer than the contraction period.
• This prevents tetanus (maintained contraction).

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Electrocardiogram (ECG or EKG)

• As action potentials propagate through the heart,
  they generate electrical currents that can be
  detected on the surface of the body.
• An electrocardiogram is a recording of these
  signals.
• An electrocardiograph is the instrument used to
  record the signals.

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Electrocardiogram (ECG or EKG)

• Electrodes are positioned on the arms and legs
  (limb leads) and at six positions on the chest
  (chest leads).
• 12 different tracings are produced from different
  combinations of leads.

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Electrocardiogram (ECG or EKG)

• If these tracings are compared to one another and
  to a normal tracing, it is possible to determine
  the following
• If the conducting pathway is abnormal.
• If the heart is enlarged.
• If certain regions of the heart are damaged.

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Typical Lead II Record

• Three clearly recognizable waves appear with each
  heartbeat.
• P wave atrial depolarization.
• QRS complex rapid ventricular depolarization.
• T wave ventricular repolarization.

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Changes In Wave Size

• Large P waves enlargement of the atrium.
• Large Q waves myocardial infarction.
• Large R waves enlarged ventricles.
• Flat T wave insufficient oxygen.
• Large T wave hyperkalemia (high blood K
  levels).

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Stress Electrocardiogram (Stress Test)

• Elevate the hearts response to stress.
• Narrowed coronary arteries may carry adequate
  blood supply at rest, but not during exercise.

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Changes In Time Span Between Waves

• Time spans between waves are called intervals or
  segments.
• P-Q interval time between the beginning of the
  P wave and the beginning of the QRS complex.
• The P-Q interval represents the time required for
  an action potential to travel through the atria,
  AV node and remaining fibers of the conduction
  system.

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Changes In Time Span Between Waves

• The P-Q interval lengthens when the action
  potentials must travel around scar tissue from
  rheumatic fever.
• The S-T segement is elevated in acute myocardial
  infarction and depressed when the heart receives
  insufficient oxygen.
• The Q-T interval may be lengthened by myocardial
  damage, myocardial ischemia, or conduction
  abnormalities.

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Terminology

• Systole the phase of contraction.
• Diastole the phase of relaxation.
• Cardiac cycle all of the events associated with
  one heartbeat (systole and diastole of the atria
  and systole and diastole of the ventricles).

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Heart Sounds

• Auscultation listening to sounds within the
  body (performed with a stethoscope).
• During each cardiac cycle there are 4 heart
  sounds, but in a normal heart, only the first and
  second heart sounds (S1 and S2) are loud enough
  to be heard with a stethoscope.

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Heart Sounds

• The first sound (S1), described as a lubb sound,
  is louder and longer than the second.
• Caused by closure of the AV valves after
  ventricular systole begins.
• The second sound (S2), described as dupp sound,
  is shorter and not as loud as S1.
• Caused by closure of the semilunar valves as
  ventricular diastole begins.

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Heart Sounds

• S3 is due to blood turbulence from rapid
  ventricular filling.
• S4 is due to blood turbulence during atrial
  systole.
• S3 and S4 are not normally heard.

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Heart Murmurs

• A heart murmur is an abnormal sound consisting of
  a clicking, rushing, or gurgling noise that is
  heard before, between, or after the normal heart
  sounds. It can also mask the normal heart
  sounds.
• Some heart murmurs are innocent However, they
  usually represent a valve disorder.

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Congestive Heart Failure

• In CHF, the heart is a failing pump.
• Causes include coronary artery disease,
  congenital defects, long-term high blood pressure
  (increases afterload), myocardial infarctions,
  valve disorders.
• Pulmonary edema left ventricle fails first.
• Peripheral edema right ventricle fails first.

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Regulation Of Heart Rate

• Autonomic regulation of heart rate.
• Proprioceptors, chemoreceptors, baroreceptors.
• Cardiac accelerator nerves.
• Chemical regulation of heart rate.
• Hormones (epinephrine, norepinephrine, and
  thyroid hormones) accelerate the heart rate.
• Cations.

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Terminology

• Tachycardia elevated resting heart rate.
• Bradycardia a resting heart rate under 60 bpm.
• Hypothermia lowering of the body temperature,
  which slows the heart rate.

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Disorders Of The Heart

• Coronary artery disease (CAD).
• Arteriosclerosis and atherosclerosis.

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Disorders Of The Heart

• Myocardial ischemia and infarction.
• Hypoxia.
• Angina pectoris.

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Disorders Of The Heart

• Congenital defects.
• Coarctation of the aorta.
• Patent ductus arteriosus.
• Septal defect.
• Atrial and ventricular.
• Tetralogy of Fallot.

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Disorders Of The Heart

• Arrhythmias irregularity of the heart rhythm.
• Heart block.
• Flutter and fibrillation.
• Ventricular premature contraction.

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Medical Terminology

• Angiocardiography x-ray examination of the
  heart and great vessels with radiopaque dye.
• Cardiac arrest.
• Cardiomegaly.
• Cor pulmonale (CP) ventricular hypertrophy from
  disorders that bring about hypertension in the
  pulmonary circulation.
• Palpitation.