Download Heart

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REVIEW: cardiovascular system
o Components:
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Heart
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Blood vessels
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Lymphatic vessels
o Circulation:
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Pulmonary circulation:
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De-O2 blood in heart  pulmonary aa  lungs
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O2 blood from lungs  pulmonary vv  heart
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Systemic circulation:
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O2 blood from  arteries  other tissues
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Nutrient XΔ occurs in capillaries
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De-O2 blood from tissues  veins  heart
o Tunics/layers (can have up to 3)
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General:
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Number of tunics, cellular & extracellular compenents varies w/ size & fxn of diff’t bv’s
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Heart wall layers (discussed later) are analogous with vessel tunics
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Layers:
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Tunica Intima - innermost layer of bv wall
o Endothelium = simple squamous
o Subendothelial layer
o Internal elastic lamina
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Tunica Media – middle layer of bv wall
o Predominate element is variable, but is either:
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Circumferentially arranged smooth muscle
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Elastic lamellae
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Tunica Adventitia – outermost CT layer of bv wall
o Longitudinally arranged:
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Collagen
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Elastic fibers
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Smooth muscle cells
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Fibroblasts
PERICARDIUM & HEART
o General: Heart is located in middle mediastinum & is surrounded by pericardial sac
o Pericardium
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Three layers of pericardial sac
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(1) External Fibrous layer: DCT
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Serous pericardium (layers continues via “reflection”):
o (2) Parietal layer:
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LCT
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Layer of squamous epithelium (mesothelium)
o (3) Visceral layer
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LCT
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Layer of squamous epithelium (mesothelium) = epicardium
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Pericardial cavity
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Space b/w the parietal & visceral pericardium
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Contains: pericardial fluid
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Fxn: allows the heart to beat without restriction
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Pericarditis (infection in pericardial cavity) restricts heart from beating properly
o Chambers of the heart
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Four chambers = RA & LA and RV & LV
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Path of blood flow:
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De-O2 blood from tissues  IVC/SVC  RA (tricuspid valve)  RV  (pulmonary semilunar
valve)  pulmonary artery  lungs  gas XΔ in alveoli  O2 blood
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O2 blood from lungs  pulmonary veins  LA  (bicuspid valve)  LV  (aortic semilunar
valve)  aorta  atrial tree  systemic circulation (tissues)  capillary beds  gas XΔ  De-O2
blood
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Separations:
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Atria = interatrial septum (mostly cardiac muscle cells)
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Ventricles = interventricular septum (thick)
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AV compartments = cardiac skeleton & valves
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CARDIAC SKELETON
o General Features
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iDCT
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Central supporting structure of the heart
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Supports valves
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Cardiac muscle fibers attach
o Components
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Annuli Fibrosi
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Surrounds/stabilizes ea. of the 4 cardiac valves
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Valve cusps arise from this CT
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Trigona Fibrosi (right & left fibrous trigones)
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Triangular “islands” of CT
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Location: superior to AV valves; sides of aoric valve
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Strengthen the annuli fibrosi
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Rt trigona contains AV bundle
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Septum Membranaceum (membranous part of the interventricular septum)
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Extension of cardiac skeleton (┴ annuli fibrosi) into interventricular septum
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Associated w/ a segment of the AV bundle
o Functions
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Separates atrial musculature from the ventricular musculature
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Fxn’s as origin (pnts of insertion) of cardiac muscle
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Localizes & stabilizes valves
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Limits the diameter of valves
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Prevents spread of electrical impulses (except via the conducting system)
HEART WALL
o Epicardium – external layer of heart wall
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Analogous to tunica adventitia of bv’s
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aka visceral reflection layer
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Consists of:
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Mesothelium
o Simple squamous epithelium
o With associated BL
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Subepicardial CT
o Fat storage of heart (a lot)
o Collagen fibers
o Elastic fibers
o Coronary arteries (supply heart)
o Caridac veins (supply heart)
o Nerves (supply heart)
o Myocardium – middle layer of the heart wall (analogous to tunica media)
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Cardiac muscle cells (myocytes, cardiomyocytes)
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One (usually) or two nuclei
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Packed with myofibrils & lg mitochondria
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Intercalated discs
o Connection b/w cardiac muscle cells
o Connections or Communications:
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Fascia adherens – binds actin thin filaments of two cardiac mm cells
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Desmosomes – connect 2 cardiac mm cells via desmin/vimentin intermediate
filaments with desmoplakin/plakoglobin anchors
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Gap jxns – provide for ionic communication & coupling (impulse “passed”)
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Myocardial thickness differences
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Atrial myocardium <<< ventricular myocardium
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LV myocardium = 3X thickness of RV myocardium
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o
Cardiac muscle cells differ b/w atriums & ventricles
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Atrial (relative to ventricular myocardial cells):
o Smaller
o Less elaborate T-tubule system
o More gap jxns
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Atrial myocardial cells
o Contain e- dense granules that contain atrial atriuretic factor (ANF)
o ANF (“stretch” is biggest stimulator of ANF release)
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aka atrial natriuretic polypeptide or atriopeptin
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Produced, stored, secreted by atrial myocardial cells
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Secreted into surrounding capillaries
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Receptors found in adrenal cortex, kidney, & vascular smooth mm
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Stimulates:
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Kidney excretion of Na+ in urine (water follows; ↓ blood volume)
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Regulation of fluid balance
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Regulation of electrolyte balance (Na+ levels)
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Regulation of BP (↓ in atrial BP)
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Arrangement of muscle cells (fibers):
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Ventricular Wall
o Trabeculae Carnae – complex spiral & helical pattern
o Papillary Muscle – Ventricular wall projections into lumen
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Atrial Wall
o Pectinate musculature
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aka musculi pectini
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Innermost mm fiber bundles in lattice arrangement (gives ridged appearance)
Endocardium – internal layer of the heart wall
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Analogous to tunica intima of bv’s
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Ventricular <<< Atrial
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Lines:
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Cardiac valves
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Papillary muscles
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Inner walls of atria
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Inner walls of ventricles
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Consists of:
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Endothelium with associated BL (vascular endothelium makes contact w/ blood)
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Subendothelial (subendocardial) CT
o Collagen fibers
o Elastic fibers
o Smooth muscle cells
o Small blood vessels
o Nerves
o Components of impulse conduction system
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IMPULSE CONDUCTION SYSTEM
o Characteristics
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Specialized cardiac mm fiber
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Initiate & conduct electrochemical impulses 
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Coordinated contraction & relaxation of the heart
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Control of contractions
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Heart able to contract w/o any CNS stimulation
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CNS modulates heart rate
o SS stimulation = ↑ heart rate
o PS stimulation = ↓ heart rate
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Impulse pathway:
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SA node (pacemaker) initiates impulse  atrial mm (p wave)  AV node (PQ interval)  Bundle
of His  left & right bundle branches  purkinje fibers  cardiac ventricular muscle (apex) 
spiral/upwrd contraction (QRS wave)
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Electrocardiogram – conduction of electrical impulse thru the heart  voltage trace recorded as EKG/ECG:
PQ interval
P wave
Q R S
P wave = atrial contraction
PQ interaval = AV node (“delayed”)
QRS wave = ventricular contraction
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Sinoatrial (SA) Node
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Location:
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Wall of RA close to orifice of the SVC
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Often surrounds a branch of the coronary artery
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SA nodal cells
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Modified cardiac muscle cells
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Histology
o Smaller than typical cardiac mm cells
o Exhibit paler staining appearance
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Myofibrils – fewer (in #’s) & less organized than normal cardiac mm cells
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Not joined by intercalated discs
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AKA Pacemaker
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Initiates impulse
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Spreads along tracts of modified cardiac muscle fibers to AV node
Atrioventricular (AV) Node (slowest – “delayed”)
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RA floor just above tricuspid valve
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Similar in appearance to SA nodal cells
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Appear as a mass of small, pale-staining cells isolated by CT
Bundle of HIS (AV bundle) & left & right bundle branches
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Runs RA  traversing right fibrous trigone  RV  along septum membranaceum margin 
interventricular septum & divides into rt & lft branches  terminate in subendocardial layer as purkinje
fibers
Purkinje fibers (fast)
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Location: subendocardial CT of ventricular endocardium
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Transmit impulses to cardiac muscle cells of apex of the heart
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Characteristics (of purkinje fibers):
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Relative to normal cardiac muscle cells:
o 2 – 3 times larger
o Nuclei more rounded
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Lg amt of glycogen
o Appear pale-staining
o Appear vaculated
o Fxn: resistant to ischemia (important when conducting electrical impulse
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Contain few myofibrils
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Lack T tubule system
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Cells connected via desmosomes & gap jxns (rather than intercalated discs)
VALVES OF HEART
o Four Valves – cusps come off of annuli fibrosi
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Left AV (mitral or bicuspid) valve = 2 cusps
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Right AV (tricuspid) valve = 3 cusps
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Pulmonary semilunar valve = 3 cusps
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Aortic semilunar valve = 3 cusps
o Structure
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Cardiac valves extend from the cardiac skeleton
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Consist of Fibrosa
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Fibrous iDCT
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Covered by endocardium on free atrial & free venricular surfaces
o Chordae Tendinae
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Fibrous cords
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From free edge of valves to papillary muscles of ventricular wall
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Fxn: prevention valve leaflets from flapping back into the atrium during ventricular contraction