Cardiovascular System: The Heart
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Transcript Cardiovascular System: The Heart
Cardiovascular System:
The Heart
Dr. Michael P. Gillespie
Cardiovascular System
Blood
Heart
Blood vessels
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.
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.
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.
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.
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.
Anatomical Landmarks
Inferior surface – rests upon diaphragm.
Right border – faces the right lung.
Left border (pulmonary border) – faces the left lung.
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).
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.
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).
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.
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).
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.
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).
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.
Fibrous Skeleton Of The Heart
Dense CT rings that surround the valves and prevent overstretching.
Provides insertion points for bundles of cardiac muscle fibers.
Atrioventricular (AV) Valves
Tricuspid and bicuspid valves.
When the valve is open, the pointed cusps point into the ventricle.
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).
Semilunar (SL) Valves
The aortic and pulmonary valves.
The SL valves open when the pressure in the ventricles exceeds the
pressure in the arteries.
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.
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.
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.
Systemic And Pulmonary
Circulations
Two closed systems.
The output of one becomes the input of another with each beat of
the heart.
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.
Coronary Arteries
Two coronary arteries, right and left coronary arteries, branch from
the ascending aorta and supply oxygenated blood to the
myocardium.
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).
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).
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.
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.
Histology Of Cardiac Muscle
Tissue
Cardiac muscle fibers are shorter in length and less circular than
skeletal muscle fibers.
Cardiac muscle fibers exhibit branching.
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.
Regeneration Of Heart Cells
Infarcted (dead) cardiac muscle tissue is replaced with noncontractile 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.
Autorhythmic Fibers: The
Conduction System
Autorhythmic fibers are self-excitable and maintain the heart’s
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.
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.
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.
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.
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.
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.
Refractory Period
In cardiac muscle tissue, the refractory period lasts longer than the
contraction period.
This prevents tetanus (maintained contraction).
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.
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.
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.
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.
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).
Stress Electrocardiogram
(Stress Test)
Elevate the heart’s response to stress.
Narrowed coronary arteries may carry adequate blood supply at
rest, but not during exercise.
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.
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.
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).
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.
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.
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.
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.
Congestive Heart Failure
In CHF, the heart is a failing pump.
Causes include coronary artery disease, congenital defects, longterm high blood pressure (increases afterload), myocardial
infarctions, valve disorders.
Pulmonary edema – left ventricle fails first.
Peripheral edema – right ventricle fails first.
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.
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.
Disorders Of The Heart
Coronary artery disease (CAD).
Arteriosclerosis and atherosclerosis.
Disorders Of The Heart
Myocardial ischemia and infarction.
Hypoxia.
Angina pectoris.
Disorders Of The Heart
Congenital defects.
Coarctation of the aorta.
Patent ductus arteriosus.
Septal defect.
Atrial and ventricular.
Tetralogy of Fallot.
Disorders Of The Heart
Arrhythmias – irregularity of the heart rhythm.
Heart block.
Flutter and fibrillation.
Ventricular premature contraction.
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.