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The Heart


The Heart Chapter 18 Figure 18.24 Fetal Heart Structures Foramen ovale a hole in the interatrial septum allowing blood to pass from the right atrium to the left ... – PowerPoint PPT presentation

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Title: The Heart

The Heart Chapter 18
The Heart
  • Size 250-350 grams
  • Location in mediastinum of thoracic cavity
  • Function generates pressure to pump blood
    through circulatory system
  • Orientation flat base is directed toward right
    shoulder, and pointed apex points to left hip

Figure 18.1
Heart Coverings
Pericardium the two layered, membranous sac in
which the heart sits Fibrous pericardium the
outer, thick layer composed of dense connective
tissue, for protecting, anchoring the heart in
position, and preventing overfilling Serous
pericardium the inner thin layer composed of a
serous membrane Visceral layer membrane
clinging to the outer heart surface Parietal
layer membrane clinging to the inside of the
fibrous pericardium Pericardial cavity serous
fluid-filled space between the visceral and
parietal layers
Figure 18.2
Heart Layers
Epicardium the epithelium clinging to the outer
heart wall (is the visceral pericardium) Myocardiu
m the middle layer composed of cardiac muscle
tissue Endocardium the epithelium clinging to
the inner surfaces of the heart chambers
Figure 18.2
The Heart
  • 4 chambers 2 atria, 2 ventricles
  • Atria
  • the superior chambers
  • auricles ear-like extensions of the atria
  • receiving chambers, limited pumping means thin
  • Ventricles
  • the inferior chambers, the majority of the heart
  • pumping chambers, thick walls
  • Sulci
  • The indentations on the outer heart surface,
    corresponding to borderlines between chambers
  • contain fat and vessels
  • Ex interventricular sulcus

Figure 18.4 a, b
The Heart
  • Septa
  • The internal walls that divide the chambers
  • Correspond to the external sulci
  • Exs- Interventricular septum and Interatrial

Figure 18.4e, f
The Atria
  • Right Atrium Entrances
  • Superior Vena Cava blood returning from above
    the diaphragm
  • Inferior Vena Cava blood returning from below
    the diaphragm
  • Coronary sinus blood returning from the heart
  • Left Atrium Entrances
  • 4 pulmonary veins - blood returning from lungs

Figure 18.4e
The Ventricles
  • Right Ventricle
  • Receives blood from the right atrium
  • Blood exits into the pulmonary trunk to lungs
  • Left Ventricle
  • Receives blood from the left atrium
  • Blood exits into the aorta to the body

Figure 18.4e
  • Blood only passes through ½ of the heart at a
    time, and therefore must pass through the heart
    twice to complete circulation
  • Pulmonary circuit
  • the pathway from the heart to the lungs and back
  • is pumped by the right half of the heart
  • blood leaves O2 and returns O2
  • Systemic circuit
  • the pathway from the heart to the bodys tissues
    and back
  • is pumped by the left half of the heart
  • blood leaves O2 and returns O2
  • NOTE arteries do NOT always carry oxygenated
    blood, and veins do NOT always carry deoxygenated

Figure 18.5
  • The Systemic circuit is a longer circuit than
    the Pulmonary circuit
  • Greater pressure is needed to pump blood through
    the systemic circuit
  • The left ventricle therefore has more cardiac
    muscle tissue than the right ventricle

Figure 18.6
Coronary Circulation
Coronary circulation the series of vessels that
supply blood flow to the wall of the heart,
beginning at the aorta and ending at the right
atrium Anastomoses the merging of blood
vessels, providing more than one way to deliver
blood to one locationWhy? Myocardial Infarction
heart attack due to a blockage of a
coronary artery, causing the death of cardiac
muscle cells
Figure 18.7
Coronary Circulation
Coronary arteries deliver oxygen and nutrient
rich blood to the cardiac muscle
Figure 18.4b
Coronary Circulation
Cardiac veins drain the oxygen and nutrient
poor blood from the cardiac muscle Coronary sinus
large vein on posterior side that empties into
the right atrium
Figure 18.4d
Heart Valves
Function ensure a unidirectional flow of blood
through the heart Types there are 2
atrioventricular valves and 2 semilunar valves
Figure 18.8 a, b
Heart Valves
  • Atrioventricular valves
  • separate an atrium from a ventricle
  • prevent backflow into the atrium
  • Tricuspid (Right AV) valve separates right
    atrium from right ventricle
  • Bicuspid (Left AV) valve separates left atrium
    from left ventricle. Also known as mitral valve
  • Flaps (cusps) of these valves are supported by
    papillary muscles and chordae tendineae

Figure 18.8c
Heart Valves
  • Atrioventricular valves
  • Papillary muscles attach to valve flaps via
    chordae tendineae
  • These muscles contract to prevent the valve
    flaps from inverting into the atria

Figure 18.9
Heart Valves
  • Semilunar valves
  • separate a ventricle from a great vessel
  • prevent backflow into the ventricle
  • composed of three cup-like flaps
  • Pulmonary semilunar valve regulates movement
    of blood into pulmonary trunk
  • Aortic semilunar valve regulates movement of
    blood into the aorta
  • Flaps (cusps) of these valves are NOT supported
    by papillary muscles and chordae tendineae

Figure 18.8c
Heart Valves
  • Semilunar valves
  • during contraction, pressure forces these valves
    open, allowing blood into the large vessels
  • when the ventricles relax, the blood falls
    toward the ventricles, fills the cup-shaped
    flaps, closing the valves

Figure 18.10
Microscopic Anatomy
  • Cardiac muscle tissue
  • Striated a striped appearance
  • Involuntary no conscious control
  • Cardiac Muscle Fibers (cells)
  • shorter than skeletal muscle fibers, with
    central nuclei
  • large amount of mitochondria for endurance
  • branched fibers divide and unite
  • interconnected fibers are linked and work in

Figure 18.11
Cardiac Muscle
  • Cardiac Muscle Fibers (cells)
  • Intercalated discs- junctions where adjacent
    fibers connect
  • desmosomes hold fibers tightly together
  • gap junctions allow fibers to share cytoplasm
    and contract in unison

Figure 18.11a
Cardiac Muscle Contraction
Autorhythmicity The ability of cardiac muscle to
trigger its own contraction, not needing a
nervous system impulse Whole organ
contraction There is no partial contraction of
cardiac muscle, it is an all or none event
Figure 18.11
Cardiac Muscle Contraction
  • Action potentials in cardiac muscle involve 3
    ions (Na, K and Ca2), which produces a plateau
    phase of the impulse
  • This prolongs the contraction to ensure
    efficient blood ejection
  • Also increases the time of the absolute
    refractory period, ensuring separate heart
    contractions (not prolonged muscle tetanus)

Figure 18.12
Intrinsic Conduction System
  • Intrinsic Conduction System
  • Stimuli that trigger cardiac muscle contraction
    come from within the heart itself
  • Autorhythmic cells - specialized heart cells that
    generate action potentials which spread through
    the heart to trigger contraction
  • These cells have unstable resting potentials,
    and therefore depolarize regularly
  • These pacemaker potentials cause action
    potentials in the cardiac muscle fibers,
    triggering contraction

Figure 18.13
Intrinsic Conduction System
Sinoatrial node in the right atrium, the
pacemaker whose cells generate the sinus rhythm
of 75 beats/min Atrioventricular node - causes a
delay of .1sec to allow atrial contraction before
ventricular contraction. Rhythm is 40-60
beats/min Bundle of His pathway into the
interventricular septum
Figure 18.14
Intrinsic Conduction System
  • Bundle Branches the right and left pathways
    through the interventricular septum
  • Purkinje fibers pathways to the walls of the
  • The bundle of his, bundle branches and purkinje
    fibers would set a rhythm of only 30 beats/min

Figure 18.14
Extrinsic Innervation
Cardiac centers gray matter areas in the
medulla that can change heart rhythm Parasympathet
ic innervation via the vagus nerve, slows heart
rate Sympathetic innervation via the
sympathetic trunk, increases heart rate Heart
rate disorders Tachycardia an abnormally fast
heart rate 100 beats/min Bradycardia an
abnormally low heart rate 60- beats
/min Arrhythmias irregular heart
rhythms Fibrillation rapid, irregular
contractions that do not function to pump blood
Figure 18.15
Electrocardiogram ECG
ECG a graphic representation of all of the
action potentials in the heart in a given time P
wave shows the depolarization of the atria QRS
complex shows the depolarization of the
ventricles T wave shows the repolarization of
the ventricles
Figure 18.16
Electrocardiogram ECG
Note the waves of the ECG graph correspond to
the spreading depolarization through the heart
tissue. Muscle contraction follows this
Figure 18.17
Electrocardiogram ECG
Figure 18.18
Heart Sounds
Heart sounds the lub dub Lub the sound
produced by the closure of the AV valves Dub
the sound produced by the closure of the
semilunar valves Murmurs abnormal heart
sounds, indicating valve problems
Figure 18.19
Cardiac Cycle
  • Cardiac cycle the events of a single heart beat
  • Systole heart contraction Diastole heart
  • Ventricular filling blood flows through the
    atria into the ventricles. The AV valves are
    open, and the semilunar valves are closed. Then,
    the atria contract forcing the remaining blood
    into the ventricles
  • Isovolumetric contraction ventricles contract,
    forcing the AV valves closed. The volume in the
    ventricles is now the end diastolic volume (EDV)

Figure 18.20
Cardiac Cycle
3. Ventricular ejection ventricular pressure
forces the semilunar valves open and the blood
enters the great vessels 4. Isovolumetric
relaxation ventricles relax, and the blood
within them is the end systolic volume (ESV). The
semilunar valves close and the atria begin to
fill. 5. Ventricular filling atrial pressure
forces the AV valves open which restarts the cycle
Figure 18.20
Cardiac Output
Cardiac Output (CO) the amount of blood pumped
by each ventricle in one minute CO heart rate x
stroke volume Stroke volume (SV) EDV - ESV
Practice Question If a persons EDV is 125mL and
their ESV is 50mL, what is their CO if their
heart rate is 80 beats/min? Answer SV 125mL
50 mL SV 75mL CO
75mL x 80 beats/min CO 6000mL/min 6.0L/min
Figure 18.21
Fetal Heart Structures
Foramen ovale a hole in the interatrial septum
allowing blood to pass from the right atrium to
the left atrium. Its remnant is the fossa ovalis
in adults Ductus arteriosus a passage from the
pulmonary trunk to the aorta. Its remnant is the
ligamentum arteriosum in adults Both structures
allow the fetal blood to bypass the pulmonary
Figure 18.24